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Busstom
Samba Member
Joined: November 23, 2014
Posts: 3854
Location: San Jose, CA
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 Posted: Sat Mar 24, 2018 8:29 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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Sorry, just saw your latest post. Using the depth function on your caliper really isn't adequate, the slightest little rock of your hand will change your numbers. Please see if you can find a depth micrometer, it really is the appropriate way, especially given all the anomalies you seem to be encountering.
And I don't know about depth mics, but Harbor Freight sells a cheap dial indicator that will suffice for locating actual TDC. You could be mis-eyeballing a couple thou there too.
Oh, and lightly torquing your cylinders with spacers will work just fine as you're currently doing. |
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sat Mar 24, 2018 8:54 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| Busstom wrote: |
Sorry, just saw your latest post. Using the depth function on your caliper really isn't adequate, the slightest little rock of your hand will change your numbers. Please see if you can find a depth micrometer, it really is the appropriate way, especially given all the anomalies you seem to be encountering.
And I don't know about depth mics, but Harbor Freight sells a cheap dial indicator that will suffice for locating actual TDC. You could be mis-eyeballing a couple thou there too.
Oh, and lightly torquing your cylinders with spacers will work just fine as you're currently doing. |
You beat me to it. The caliper is not the tool to use for this and can easily be 100% of the problem.
The last set of measurements looks decent. I hate using the term good enough....because correct means in spec. Anything else is not gooe enough unless you are building a sweep the floor beater for a POS type 1 engine .....which is fully replaceable down to the crank and block.....with a planned lifespan of 50-70k miles. Disposible in other words.
Really you need to borrow or buy a depth micrometer. Even a cheap Grizzly brand at $50 is fine for this.
Actually....a bolted down straight edge and good feeler gauges will work just fine for this particular task.
Hyperbolic drama queen?.....I hope you are not speaking to me.... 
Why?
Because from his previous measurements.....knowing the quality of the pistons he is using....if what he was saying is actually true.....that the case decks are clean and cylinders are in fact level......then his numbers indicate that something is bent or machined crooked....period.
If you are building a beater....go for it....slap it together.
But...... IF.....something is actially bent or machined/honed crooked to get numbers like that measured between 3 and 9 on the pistons.....the rings in the average POS type 1 engine will outlast this engine. And that would be a sad waste of good parts.
But....though the last set of measurements look relatively normal and usable......now that you tell us they are being done with a slide caliper......they are also a risk.
You cannot eyeball TDC. You can check most of this with a dial indicator.... .even a cheap harbor freight one.
Look at the pictures of those last tools that Steve posted. You need a simple straight, flat bar that you can affix across the cylinder top. Bring the piston up and use that bar just like your straight edge ....bringing the piston up until you get the tightest gap. Measure the gap between the bar and piston with a feeler gauge.
Chances are you are pretty close or just fine. But you need to know that for sure. Ray |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sat Mar 24, 2018 10:56 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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there should be no significant variation regardless which rod and piston combination are used together. VW built these on assembly lines.
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RalphWiggam
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Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Sun Mar 25, 2018 5:24 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| raygreenwood wrote: |
| Busstom wrote: |
Sorry, just saw your latest post. Using the depth function on your caliper really isn't adequate, the slightest little rock of your hand will change your numbers. Please see if you can find a depth micrometer, it really is the appropriate way, especially given all the anomalies you seem to be encountering.
And I don't know about depth mics, but Harbor Freight sells a cheap dial indicator that will suffice for locating actual TDC. You could be mis-eyeballing a couple thou there too.
Oh, and lightly torquing your cylinders with spacers will work just fine as you're currently doing. |
You beat me to it. The caliper is not the tool to use for this and can easily be 100% of the problem.
The last set of measurements looks decent. I hate using the term good enough....because correct means in spec. Anything else is not gooe enough unless you are building a sweep the floor beater for a POS type 1 engine .....which is fully replaceable down to the crank and block.....with a planned lifespan of 50-70k miles. Disposible in other words.
Really you need to borrow or buy a depth micrometer. Even a cheap Grizzly brand at $50 is fine for this.
Actually....a bolted down straight edge and good feeler gauges will work just fine for this particular task.
Hyperbolic drama queen?.....I hope you are not speaking to me....
Why?
Because from his previous measurements.....knowing the quality of the pistons he is using....if what he was saying is actually true.....that the case decks are clean and cylinders are in fact level......then his numbers indicate that something is bent or machined crooked....period.
If you are building a beater....go for it....slap it together.
But...... IF.....something is actially bent or machined/honed crooked to get numbers like that measured between 3 and 9 on the pistons.....the rings in the average POS type 1 engine will outlast this engine. And that would be a sad waste of good parts.
But....though the last set of measurements look relatively normal and usable......now that you tell us they are being done with a slide caliper......they are also a risk.
You cannot eyeball TDC. You can check most of this with a dial indicator.... .even a cheap harbor freight one.
Look at the pictures of those last tools that Steve posted. You need a simple straight, flat bar that you can affix across the cylinder top. Bring the piston up and use that bar just like your straight edge ....bringing the piston up until you get the tightest gap. Measure the gap between the bar and piston with a feeler gauge.
Chances are you are pretty close or just fine. But you need to know that for sure. Ray |
I did do some checking with a feeler gauge. It seemed to be about as accurate as the caliper. I agree that neither of them are perfect.
Here is my main issue....when the piston is installed in the cylinder with no rings it can rock back and forth slightly due to the big end/crank side gap. When the piston rocks, it changes the measurements slightly. My problem is that I don't know what position the piston will operate in the cylinder. It is impossible to float it in the middle to take measurements.
In fact during operation, the .004" end play on the crank AND the rod big end/crank side clearance will shift the axes of the wrist pin slightly and change deck height like I am seeing. One could calculate exactly how much the wrist pin axes can change but I haven't had my coffee yet.
Even though I'm pretty confident in my last set of measurements, I think it might be a good idea to take my rods to a different machine shop on Monday and have them checked for straightness. |
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Wildthings
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Joined: March 13, 2005
Posts: 50353
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| Posted: Sun Mar 25, 2018 7:25 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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The crankshaft end play should not effect the deck height at all as there should be enough back and forth movement between the small end of the rod and the piston to allow for this.
Take two of your rods and slip a wrist pin through their small ends and take a picture for us of how they mate together, rotate one of the rods and take another picture. For a single pair of rods you should be able to assemble them together four different ways, so we need to see four different picture of how they fit.
A-B-C-D
A-B-D-C
B-A-C-D
B-A-D-C
I am thinking that for some very odd reason you have a none standard set of rods and the solution to your problem is just a set of normal everyday Type 4 rods. |
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sun Mar 25, 2018 8:49 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| Wildthings wrote: |
The crankshaft end play should not effect the deck height at all as there should be enough back and forth movement between the small end of the rod and the piston to allow for this.
Take two of your rods and slip a wrist pin through their small ends and take a picture for us of how they mate together, rotate one of the rods and take another picture. For a single pair of rods you should be able to assemble them together four different ways, so we need to see four different picture of how they fit.
A-B-C-D
A-B-D-C
B-A-C-D
B-A-D-C
I am thinking that for some very odd reason you have a none standard set of rods and the solution to your problem is just a set of normal everyday Type 4 rods. |
Oh!......damn.
Good reminder!
Ralphwiggam.......What is the wrist pin diameter on your pistons?
Is it 23mm or 24mm? Or do you have a mix by chance? Not that I think that is the issue.......
BUT.....lets go back to your teardown......you have one connecting rod.....that is a 022 prefix number.
That rod is not JUST a 1.8L rod. It was originally used....before the 1.8L even existed......in the early European 1.7L with carbs........and that engine used 23mm piston pins and many of the rods had a 1mm smaller bushing bore. Which means its very easy to get the bushings scrrwed up and make the center to center length of the rods incorrect...when trying insert 24mm pins.
And....I have.....just in the last few months seen this exact issue. I received a full set of 022 rods that have the smaller bushing bore.....to go into the 1.8L I am building. All sorts of problems ensued .....pin fit....rod length variation...because the machine shop that worked on them.....sanded the OD and crammed 24mm bushings into a 23-ish mm bore....then had to hone them so thin they distorted.
Worth checking. You have one odd rod in the set. Ray |
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RalphWiggam
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Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Sun Mar 25, 2018 9:20 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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All of the wrist pins are 24mm on the dot. I took another set of measurements this morning with the cylinders torqued down pretty tight with spacers and TDC measured for each piston with my dial indicator. Here is what I have now...
This looks way better to me. Still getting some variance front to back, but across the board the numbers are extremely close. For piece of mind I've decided to take the rods to another machine shop on Monday and have them checked. I would rather do it now than always wonder about it.
I just did the test wild things suggested and it turns out the 022 rod that I have has the largest big end discrepancy when the small end is locked to the other rods. Flip it one way and there is a bigger gap between the large ends than when flipped the other way.
What might be the case is that whenever my dad swapped that 022 in there, his machine shop bored out the small end like Ray suggested. They probably bored it slightly off and my machine shop just replicated it when they put a new bushing in. Hopefully when I tell the machine shop this, they can straighten the bore and rebush it. Or should I start over with a new unknown to me rod with other potential issues? |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sun Mar 25, 2018 11:11 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| RalphWiggam wrote: |
| raygreenwood wrote: |
| Busstom wrote: |
Sorry, just saw your latest post. Using the depth function on your caliper really isn't adequate, the slightest little rock of your hand will change your numbers. Please see if you can find a depth micrometer, it really is the appropriate way, especially given all the anomalies you seem to be encountering.
And I don't know about depth mics, but Harbor Freight sells a cheap dial indicator that will suffice for locating actual TDC. You could be mis-eyeballing a couple thou there too.
Oh, and lightly torquing your cylinders with spacers will work just fine as you're currently doing. |
You beat me to it. The caliper is not the tool to use for this and can easily be 100% of the problem.
The last set of measurements looks decent. I hate using the term good enough....because correct means in spec. Anything else is not gooe enough unless you are building a sweep the floor beater for a POS type 1 engine .....which is fully replaceable down to the crank and block.....with a planned lifespan of 50-70k miles. Disposible in other words.
Really you need to borrow or buy a depth micrometer. Even a cheap Grizzly brand at $50 is fine for this.
Actually....a bolted down straight edge and good feeler gauges will work just fine for this particular task.
Hyperbolic drama queen?.....I hope you are not speaking to me....
Why?
Because from his previous measurements.....knowing the quality of the pistons he is using....if what he was saying is actually true.....that the case decks are clean and cylinders are in fact level......then his numbers indicate that something is bent or machined crooked....period.
If you are building a beater....go for it....slap it together.
But...... IF.....something is actially bent or machined/honed crooked to get numbers like that measured between 3 and 9 on the pistons.....the rings in the average POS type 1 engine will outlast this engine. And that would be a sad waste of good parts.
But....though the last set of measurements look relatively normal and usable......now that you tell us they are being done with a slide caliper......they are also a risk.
You cannot eyeball TDC. You can check most of this with a dial indicator.... .even a cheap harbor freight one.
Look at the pictures of those last tools that Steve posted. You need a simple straight, flat bar that you can affix across the cylinder top. Bring the piston up and use that bar just like your straight edge ....bringing the piston up until you get the tightest gap. Measure the gap between the bar and piston with a feeler gauge.
Chances are you are pretty close or just fine. But you need to know that for sure. Ray |
I did do some checking with a feeler gauge. It seemed to be about as accurate as the caliper. I agree that neither of them are perfect.
Here is my main issue....when the piston is installed in the cylinder with no rings it can rock back and forth slightly due to the big end/crank side gap. When the piston rocks, it changes the measurements slightly. My problem is that I don't know what position the piston will operate in the cylinder. It is impossible to float it in the middle to take measurements.
In fact during operation, the .004" end play on the crank AND the rod big end/crank side clearance will shift the axes of the wrist pin slightly and change deck height like I am seeing. One could calculate exactly how much the wrist pin axes can change but I haven't had my coffee yet.
Even though I'm pretty confident in my last set of measurements, I think it might be a good idea to take my rods to a different machine shop on Monday and have them checked for straightness. |
There should only be .0025" roughly clearance at the rod big end bearing to crankshaft with the bearings in. If you haven't plasti-gauged it you should. When you measure directly over the wrist pin hole there should be very little rock unless the rod clearance is too great or the wrist pin is loose. You don't put a lot of pressure on the piston when you take your measurements - maybe feels like how you would hold something or rest your hand. If they are taken 90 degrees to the wrist pins there will be a lot of rock.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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RalphWiggam
Samba Member
Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Sun Mar 25, 2018 3:09 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sun Mar 25, 2018 3:24 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| RalphWiggam wrote: |
I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
what is the gear number you have now? meaning - / + not part number. Also do you feel wear on the steel gear, a step down where the cam teeth rode? That isn't highly common. I've used new ones and measured no difference with the old ones.
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Last edited by SGKent on Sun Mar 25, 2018 3:27 pm; edited 1 time in total |
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sun Mar 25, 2018 3:26 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| RalphWiggam wrote: |
I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
Yep....I mentioned that in another thread just last week. There are some small differences in the steel crank gears just like any other gear. If you have a few...and I recommend buying a spare to keep as a spare...because they are not made by ANYONE....you can swap around and see the difference.
But really...while having bang on factory spec for the cam gear backlash is ideal...its not a big deal at all.
Its not going to have any noticeable effect on how the engine runs (maybe a little if you ran D-jet)....its not going to make any noise....and its damn sure not going to ruin the crank gear.
What it will cause is slightly more wear over a long period of time...to the aluminum cam gear.
So....eventually every cam gear wears some. You may start out with 0.00 to .001968"...which is the factory spec...but at 150-175k miles....it will probably be .0025".....and your engine was probably running fine with that..right?
So you may experience excessive cam gear wear by say 100-125K miles....and for the price...thats not going to kill you if you cannot fix it.
This coming week I am fitting crank gear to the 1.8 I am working on. I have several. I may try a few and see how it changes the cam backlash. If I find one that does tighten it up....I will measure a few spots and see if I can put together what one can look for to find a crank gear that results in tighter lash...other than having to install it. Ray |
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RalphWiggam
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Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Sun Mar 25, 2018 3:27 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| SGKent wrote: |
| RalphWiggam wrote: |
I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
what is the gear number you have now? meaning - / + not part number. |
It's from the type 4 store. They only sell this one gear. No options. Should I buy a scat gear and a Webcam gear to test? Seems like an expensive test. |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sun Mar 25, 2018 3:28 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| RalphWiggam wrote: |
| SGKent wrote: |
| RalphWiggam wrote: |
I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
what is the gear number you have now? meaning - / + not part number. |
It's from the type 4 store. They only sell this one gear. No options. Should I buy a scat gear and a Webcam gear to test? Seems like an expensive test. |
what was the number on the old gear that came out? No one knows what those replacement gears are. Some say zero, others say -3. My experience with one was miserable, so was Colin's experience.
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RalphWiggam
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Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Sun Mar 25, 2018 4:51 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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| SGKent wrote: |
| RalphWiggam wrote: |
| SGKent wrote: |
| RalphWiggam wrote: |
I think I've got this deck height issue figured out.
Now, what do I do about .004 gear lash for the cam? I've put some feeler's out for some + original gears but I doubt anything original will be in proper shape to run. Gowesty article said something about swapping the crank gear. I can't find those sold anywhere. Has anybody run the flat cut gear set? I assume they would be really loud and probably not last as long? |
what is the gear number you have now? meaning - / + not part number. |
It's from the type 4 store. They only sell this one gear. No options. Should I buy a scat gear and a Webcam gear to test? Seems like an expensive test. |
what was the number on the old gear that came out? No one knows what those replacement gears are. Some say zero, others say -3. My experience with one was miserable, so was Colin's experience. |
I can't find a number on the one I took out. It has a mofoco stamp on it so it is not original. I assume it is generic like all the new ones. I guess my 2 options would be to run it with .004 or try and find some non existent '+' crank gears and randomly try them..?... |
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sun Mar 25, 2018 4:53 pm Post subject: Re: Sealing rings at top/bottom of cylinders |
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I have had nothing but good experiences with the aftermarket cast aluminum gears from both Webcam and the type 4 store.....which are the same.
I say good....meaning they were round/concentric and flat and the machining quality was excellent. That being said.....they appeared to be a range from -1 to 0 to +1 from what I have seen.
But as you mention....others have had less then stellar concentricty on some gears. You have to mic it all around.
Another option is to have one anodized. Just mask the center hole where the cam goes in. This would easily bring all dimensions up evenly by .0005" to .0015". Just tell them what you need. A good anodizing shop....not just some shop that does wheels and parts for looks....can dial coating thickness up and down by a handful of microns at a time.
By that same token....later this year....probably mid summer as other projects get out of the way (unless it turns out that I need a better gear fit on the 1.8L build).....I will be electroless nickel plating a few of my spare crank gears. That will bring their size up in all dimensions by anywhere from .0005" (which equals total growth of .001") or upwards to total growth of .002".....and it will make the surface about 20% harder and about 50% smoother.
The only thing to be careful of when anodizing or nickel plating of either one of these gears....is to measure the available gear valley tolerance available with a small rod gauge. You do not want to make it to where the gear running on it bottoms out.
You can do electroless nickel at home. But you do have to bake it at 700°F for an hour if you need the extra hardness. Running against an aluminum gear its not really necessary. Ray |
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RalphWiggam
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Joined: February 02, 2018
Posts: 906
Location: SouthEast
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| Posted: Mon Mar 26, 2018 8:26 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| raygreenwood wrote: |
I have had nothing but good experiences with the aftermarket cast aluminum gears from both Webcam and the type 4 store.....which are the same.
I say good....meaning they were round/concentric and flat and the machining quality was excellent. That being said.....they appeared to be a range from -1 to 0 to +1 from what I have seen.
But as you mention....others have had less then stellar concentricty on some gears. You have to mic it all around.
Another option is to have one anodized. Just mask the center hole where the cam goes in. This would easily bring all dimensions up evenly by .0005" to .0015". Just tell them what you need. A good anodizing shop....not just some shop that does wheels and parts for looks....can dial coating thickness up and down by a handful of microns at a time.
By that same token....later this year....probably mid summer as other projects get out of the way (unless it turns out that I need a better gear fit on the 1.8L build).....I will be electroless nickel plating a few of my spare crank gears. That will bring their size up in all dimensions by anywhere from .0005" (which equals total growth of .001") or upwards to total growth of .002".....and it will make the surface about 20% harder and about 50% smoother.
The only thing to be careful of when anodizing or nickel plating of either one of these gears....is to measure the available gear valley tolerance available with a small rod gauge. You do not want to make it to where the gear running on it bottoms out.
You can do electroless nickel at home. But you do have to bake it at 700°F for an hour if you need the extra hardness. Running against an aluminum gear its not really necessary. Ray |
Pardon my math ability for a second, but what thickness am I looking for to take up let say .003 of the gear lash? Half of that (.0015)? .0015 on each face of the cam gear would be .003 total?
I called a large anodizing shop just now and the owner said there is no way to predetermine how much the anodizing will build up. There are several factors which affect the build up including the exact alloy composition of the gear itself (who knows). There is also a pretreat process that depending on how many steps they use, eats away at the surface I have now. It would be a fairly large shot in the dark to be able to just pick one of their many anodizing processes and hope to gain .0015.
Does the cam gear bolt to the cam in only one of the 5 positions correctly? If not, I will try the other 4 positions and see if I get a more concentric measurement. |
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SGKent
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Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Mon Mar 26, 2018 9:14 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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What gear size was in it when you took it apart? Where is that gear now?
Ray - my understanding is that the difference in say a -2 to +2 is the pitch of the gear, not the tooth thickness or gear diameter.
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Wildthings
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Joined: March 13, 2005
Posts: 50353
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| Posted: Mon Mar 26, 2018 9:50 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| Being off .003" in cam timing is probably not going to be noticeable. Maybe it will give you a tiny bit more power (like 0.1%) or maybe it will cost you that much. The valves are open over an arc of 4.5-5" on the timing gear and you are talking about .003". |
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RalphWiggam
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| Posted: Mon Mar 26, 2018 10:55 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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So I just got back from the machine shop and they checked the rods for straightness while I waited.
Turns out according to their machine all 4 of the rods are "twisted".
By this much:
1 - .007
2 - .008
3 - .012
4 - .013
Seems crazy to me that all 4 of them are twisted. He said it was near impossible to machine the small end wrong because the machine is locked to the axis of the big end while it is doing the cutting on the small end. To me, if that were true, it seems like the cut would compensate for any twist in the rod. I didnt see the machine though, so I cant really picture it in my head.
Anyway, I have ordered a new set of rebuilt 1.7L rods from European Motorworks and the guy on the phone assured me that his were "perfect". They should be here Wednesday. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Mon Mar 26, 2018 11:14 am Post subject: Re: Sealing rings at top/bottom of cylinders |
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| SGKent wrote: |
What gear size was in it when you took it apart? Where is that gear now?
Ray - my understanding is that the difference in say a -2 to +2 is the pitch of the gear, not the tooth thickness or gear diameter. |
Not exactly. In general terms...the pitch is the number of teeth for the diameter of the gear...and in that "general" respect all of the timing gears have the same "pitch".
However....with a gear of a known "pitch" or tooth spacing frequency.... its effect on gear lash is or tooth contact is affected by two different numbers/measurements...out of many:
1. Circular pitch : The width of the tooth and the space between them measured on the pitch circle.
And....the pitch circle is measured as a section of the gear diameter that intersects a measurement point called the addendum...which runs from the tip of the gear tooth to the highest contact point of the other gear on the tooth face before it begins disengaging.
Straight cog type spur gears usually have an angle change at this line for tooth contact pressure relief. Helical gears may or may not have one because the teeth actually do not fully disengage....but there is still a pitch circle line or measurement.
And this feature is the part we would be adding to or correcting by making it "grow" in all directions by anodizing.
In very short lingo.....you can consider the "pitch circle"...as the maximum engagement depth of a set of gear teeth.
2. Diametral pitch: The number of teeth of a gear per inch of its pitch diameter.
That part is the one that cannot be changed.
What it means is ...lets say we have 36 teeth on all VW gears. Lets say the # "0" gear is supposed to 7.00" in diameter. So the diametral pitch is 1 tooth for every 0.1944444444".
So a #+2 gear may actually be 7.02" in diameter....with the same tooth spacing....so the diametral pitch is 0.195".
The reason why this +/- type of system that VW used works to correct gear lash....is because if you increase the diameter of the "wheel/gear"....yet the machine cutting tool is actually cutting the same sized "valley"...which is will be....then all surfaces have to grow outward...to fit that new larger wheel/gear blank size.
The cutting tooling is set up on the OUTSIDE diameter of the gear blank.
So...in cutting the exact same tooth size and shape.....all surfaces grow outward to make the new diameter....including the "flanks" of the gear tooth where the crank gear teeth contact.
Anodizing...does "almost" the exact same thing. All of the surfaces of the gear tooth grow larger...so the gap between the teeth of the two gears closes up...and lash is reduced. Tooth angle remains the same...basic pitch does not change.
Its like this....sorry for the really crude sketch 
The black gear with one tooth ...is the crank gear. Call this the "0" gear.
The gap between tooth and tooth flank in the red circle is what is responsible for your excessive "lash".
When you grow the gear blank larger in diameter...say for a #2 gear...and the gear hobbing machine is set to make the same tooth shape and depth...based upon a now larger outside diameter.....all surfaces of the gear teeth grow/move outward...yet your crank gear does not move away from the cam gear to keep tolerances the same....so the gap between gear teeth that creates "lash"....shrinks....like in the sketch above.
Now...in reality....as the diameter of the gear blank increases....in reality the pitch of the gears...REALLY is changing. But moving very small amounts makes no substantive change to timing...because you still have the same number of teeth.
If you make the gear blank large enough....and you still want to keep the same 36 teeth per diameter.....then the SIZE of that tooth must greatly increase...to the point where it no longer even fits the teeth of the crank gear.
So in reality the very small changes they make to each gear size....have no measurable effect on gear pitch (for either the way the engine runs or timing) for our purposes. They are just enough larger or smaller to affect lash.
Ralphwiggan:
While what the anodizer told you is "functionally" correct....it is also...not quite true.
I would ask what this anodizing house really works on. Just because they are large does not mean they are very technically advanced.
A shop that just does architectural railings and wheels for instance....may not have that many controls or do precision work.
A few things:
1. No...the pre-treatment does NOT take a significant amount of material off the surface. If it does...they have very crude processes.
The pre-treatment is a caustic cleaning step and also etches the surface. We are talking MICRONS here...not even 10ths of a mil. They use sodium hydroxide or similar. A few even use an acid pre-etch.
2. You are not just looking for "anodizing"...you are looking for a "class II" at bare minimum which is a fairly standard sulfuric acid anodizing process.....and can make coatings from about 1.5 microns to a maximum of 25 microns......
....or a "class III" at best...called a "hard coat" anodizing. This can produce coating thicknesses between 25 microns and 150 microns (.001 to .0059").
Since yes....without knowing the alloy...they cannot guarantee the exact coating thickness....even if you hit 12 microns in the middle with a class II....that means that the gap between teeth grows by 24 microns combined. That is right at .001". That would easily take you to .003" lash.
If you can get a class III hard coat....of say....20-23 microns...that is .00157" to .0018" lash reduction. That is close to .002".
So just getting it hard anodized should get you close enough that it just does not matter much.
By the way....Web cam is checking into the alloy for me. An anodizing shop that does a lot of precision industrial parts....should have no big issue taking a stab at the alloy. Just getting it into the right family and then seeing what kind of voltage it absorbs and how it reacts in the pre-treatment and bath should get them close enough.
It does not have to be "aerospace" accurate.
Ray |
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