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Globedog12
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Joined: April 11, 2024
Posts: 168
Location: Atlanta, GA
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 Posted: Wed May 21, 2025 6:39 pm Post subject: Deck height difference |
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2.0 type4 shooting for stock 7.3 comp ratio.
70cc combustion chamber
Cyl 1 .041
Cyl 2 .042
Cyl 3 .044
Cyl 4 .049
I’m pretty happy with 1-3 but a little concerned about the .008 difference between 1 and 4. I put the number 4 cylinder and piston on 1 and measured .041. I can play around with pistons to see if the measurements change. I’ve seen mentioned .005 variance between cylinders as a max. Not sure what my question is other than what now if anything?
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1976 VW Type 2 Original fuel injection |
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SGKent 
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Joined: October 30, 2007
Posts: 42046
Location: at the beach
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| Posted: Wed May 21, 2025 11:33 pm Post subject: Re: Deck height difference |
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well it depends where you want to go with it. Was the case and crankshaft running Ok before you rebuilt it? The difference could be the case deck, or the crankshaft / rod throw. If the engine was running Ok before rebuilding it - meaning there was no sign of it shaking itself to death, damaged crankshaft or main bearings, I'd run it and see what happens. Did you Vee block the crankshaft to see if it ran true on the mains? You could lay a straight edge as best you can across the case halves at the cylinder decks and see if they are straight. You could also have a rod that is a little shorter than the others between the big and small end. Finding 2L parts is not all that easy anymore and even if you figure out where it is, you may find it a challenge to change. When JR left building engines he told me it was because it was getting to be too much of a challenge finding good core parts to work with. I considered building a backup short block just for giggles, and gave up because it was too much work trying to find a set of good rods, and a 2L crankshaft that wasn't damaged. There are some new ones out there but that does not guarantee they met factory specs when they were sold as parts, and the price is way too prohibitive.
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Wildthings
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Joined: March 13, 2005
Posts: 52085
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| Posted: Thu May 22, 2025 4:33 am Post subject: Re: Deck height difference |
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| What is the condition of the deck where the pistons sit? |
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orwell84
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Joined: May 14, 2007
Posts: 2755
Location: Plattsburgh, New York
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| Posted: Thu May 22, 2025 6:29 am Post subject: Re: Deck height difference |
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Some variation in deck height is normal, but I can’t really say how much is too much. Here is a list of possibilities that come to mind:
Crank out of true
Sagging case deck between the cylinder spigots
Rod length
Case bored off centerline at the factory
I would be most concerned about the difference between cylinders sitting next to each other because of the possibility of a poor seal with the head.
I find deck height fiddly to measure. I made a jig that so that the cylinders are bolted down evenly and measure parallel to the piston pin and on both sides of the piston. It’s easy to get variations due to error in measurement….at least when I do it. I would do my best to rule that out, then check the case deck for flat. |
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Globedog12
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Joined: April 11, 2024
Posts: 168
Location: Atlanta, GA
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| Posted: Thu May 22, 2025 3:06 pm Post subject: Re: Deck height difference |
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The deck looks good with a straight edge. Also the top of cylinders 3 and 4 look good with straight edge. Maybe short connecting rod? If the crank was out of true I’d think I’d see that in at least number 2 also? I’m pretty confident with how I had the cylinders bolted down and my measurements. I didn’t think there was too much vibration prior to me pulling it apart. Originally i pulled it because I had a bad leak at the cylinder head on number 1. To SGKents point I guess I’d rather give it a go and have it turn to shit in six month then spend the next year chasing down parts. Just wanted to see others opinions. I’ll let you all know how it goes 
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1976 VW Type 2 Original fuel injection |
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SGKent
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Joined: October 30, 2007
Posts: 42046
Location: at the beach
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| Posted: Thu May 22, 2025 4:06 pm Post subject: Re: Deck height difference |
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| Globedog12 wrote: |
| The deck looks good with a straight edge. Also the top of cylinders 3 and 4 look good with straight edge. Maybe short connecting rod? If the crank was out of true I’d think I’d see that in at least number 2 also? I’m pretty confident with how I had the cylinders bolted down and my measurements. I didn’t think there was too much vibration prior to me pulling it apart. Originally i pulled it because I had a bad leak at the cylinder head on number 1. To SGKents point I guess I’d rather give it a go and have it turn to shit in six month then spend the next year chasing down parts. Just wanted to see others opinions. I’ll let you all know how it goes |
someone in it's history may have clipped the rod side of the rod a lot more when resizing it than the cap. Normally the cap and the rod side both get an even clip before resizing it. If the rod side was clipped too much, then the rod would be shorter. Look carefully at it to be sure it does not show signs of ever having been seized in its life. You may see it on the side thrust surfaces, or it will have a lot more thrust clearance than the other rods. Doesn't mean you can't run it if it was done right, just might explain it. But if you don't like what you see, you should be able to find a single good 2L rod you can have resized. You did have all of them done for this rebuild, right? They elongate with use.
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raygreenwood
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Joined: November 24, 2008
Posts: 23004
Location: Oklahoma City
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| Posted: Thu May 22, 2025 5:44 pm Post subject: Re: Deck height difference |
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| SGKent wrote: |
| Globedog12 wrote: |
| The deck looks good with a straight edge. Also the top of cylinders 3 and 4 look good with straight edge. Maybe short connecting rod? If the crank was out of true I’d think I’d see that in at least number 2 also? I’m pretty confident with how I had the cylinders bolted down and my measurements. I didn’t think there was too much vibration prior to me pulling it apart. Originally i pulled it because I had a bad leak at the cylinder head on number 1. To SGKents point I guess I’d rather give it a go and have it turn to shit in six month then spend the next year chasing down parts. Just wanted to see others opinions. I’ll let you all know how it goes |
someone in it's history may have clipped the rod side of the rod a lot more when resizing it than the cap. Normally the cap and the rod side both get an even clip before resizing it. If the rod side was clipped too much, then the rod would be shorter. Look carefully at it to be sure it does not show signs of ever having been seized in its life. You may see it on the side thrust surfaces, or it will have a lot more thrust clearance than the other rods. Doesn't mean you can't run it if it was done right, just might explain it. But if you don't like what you see, you should be able to find a single good 2L rod you can have resized. You did have all of them done for this rebuild, right? They elongate with use. |
Yes!.....I have found this to be the case from sloppy shops. I have also see that when big ends are put together, the distance to the CL of the small end might be off. What you note can cause that....and....also crappy installation of machine in bushings.
Each of the above might change center to center on the rods by say...0.003" each. Both of the above might get you a total of 0.006".... having a rod set where one rod is 0.006" short and the other is 0.006" long can really throw you off.
Usually it always seems to be one damn rod in a set of four when that happens.
The other odd thing. If swapping rods around does not fix it, then it's not the rods.
It may be the one crank journal ground offset slightly. Best to be found with the crank between live centers but if your case has flat decks you can discover this with a depth mic.
What it usually is though....is the crank main bore is offset to one side.
The key to noticing this is that....let's say #2 seems to have 0.010" excessive deck.
Look at the diagonal cylinder to it....#3. If it's deck seems just a few thousandth TIGHTER.....first swap rods between the two. If #3 gets a couple thou looser and the #2 gets a couple thou tighter...but not enough between the two to fix the big difference....well....you found smaller variation between the rods.
But....next, take one case half and with a dial depth gauge in in main saddle....measure the depth of each. It is very common to find cranks from the factory offset by about 0.002" to even 0.005" ....to one side of the case.
But.....it can also be twisted in the other axis. So the rearmost main bore is say offset toward #3 and #4 but the forward end is offset toward #1 and #2.
Ray |
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Wildthings
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Joined: March 13, 2005
Posts: 52085
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| Posted: Thu May 22, 2025 5:51 pm Post subject: Re: Deck height difference |
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| Tencentlife who once had a business building WBXer engines for later Vanagons, found that it was common for the deck height to be different from cylinder to cylinder when using off the shelf parts, so he would shave the heads of the pistons and then re balance the the piston/rod combo to get the weights to match. |
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SGKent
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Joined: October 30, 2007
Posts: 42046
Location: at the beach
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| Posted: Thu May 22, 2025 6:03 pm Post subject: Re: Deck height difference |
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I prefer to have the connecting rods machined properly. In watching different videos, Jim's Machine shop in Gill Colorado does good work, if they will take air cooled stuff. Generally a connecting rod is a connecting rod so they would probably do them.
https://jamsionline.com/?srsltid=AfmBOorbGp6XNDYNX3YKFPrA4dE7NkCHYrEwjnjwklLdqqUeXUUD3n70
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