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Plastigauge, torque specs, mock-up questions
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65calvw
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PostPosted: Thu Nov 21, 2019 10:15 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

How does Plastigauge know it's being used in a Volkswagen Type 1? Or a Ford or a snowblower?
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slalombuggy
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PostPosted: Thu Nov 21, 2019 10:29 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Glenn wrote:
It looks like you have it backwards and the tangs are actually down.

The rod closer to the flywheel is #3 and the numbers are on the tang side.

Image may have been reduced in size. Click image to view fullscreen.


The rods are symmetrical so it really doesnt matter where the tangs are. I always install the rods the same on a crank but up or down makes no difference.

Plastigauge doesn't know what it's being used on. I've used it lots, it's better than nothing

brad
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Last edited by slalombuggy on Thu Nov 21, 2019 10:34 am; edited 1 time in total
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Glenn Premium Member
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PostPosted: Thu Nov 21, 2019 10:33 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

CBs instructions say tangs down.
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PostPosted: Thu Nov 21, 2019 10:36 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Glenn wrote:
CBs instructions say tangs down.


OK, Must be new, none of my CB rod sets ever came with instructions only a final torque spec.

brad
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PostPosted: Thu Nov 21, 2019 11:16 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

It says torque 15,20,25,29 with tangs down.
Didnít mention anything about threadlocker though so I didnít use it.
Did I use plastigauge?? No I didnít want to be an idiot.😄
I put them on, lathered them up with assembly lube, torqued to spec, held them up and let them drop- no extra play and no pinching. They dropped slowly on their own weight so Iím thinking they are good.
I used this picture as a reference...

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PostPosted: Thu Nov 21, 2019 11:48 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

I wouldnt use anything from JBugs as a reference lol
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PostPosted: Thu Nov 21, 2019 12:11 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Quote:
How does Plastigauge know it's being used in a Volkswagen Type 1? Or a Ford or a snowblower?


The point is, in a VW, if the rods are hanging off the crank, they are normally free to move around, which would distort the plastigauge and give a false reading. So if the rod is fixed, from moving around, then you get a more accurate reading
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PostPosted: Thu Nov 21, 2019 12:16 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

65calvw wrote:
How does Plastigauge know it's being used in a Volkswagen Type 1? Or a Ford or a snowblower?


On most other engines, you torque the rods while they are attached to pistons in bores.

With a VW, you torque the rods while they are free to rotate on the crank journal. ANY rotation of the rod on the crank journal smears the plasti-gauge, rendering the reading/measurement null and void, or worse, fooling the engine builder into thinking the clearance is too tight.

Experience is a wonderful thing

Having gone through this experience once upon a time, at the end of the day, I felt as through there was a village somewhere, missing it's idiot...

and I found him, staring back at me in the mirror Embarassed Laughing
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67 Sunroof
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PostPosted: Thu Nov 21, 2019 12:33 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Hey as silly as my questions are I feel itís best to ask rather than slap it together without any experience. I feel comfortable asking for the most part because the samba can be a wealth of information and thereís some fart smellers around here.
I mean smart fellers....haha
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PostPosted: Thu Nov 21, 2019 12:43 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

The only stupid question is the one you don't ask.
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PostPosted: Thu Nov 21, 2019 1:46 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

67 Sunroof wrote:
Hey as silly as my questions are I feel itís best to ask rather than slap it together without any experience. I feel comfortable asking for the most part because the samba can be a wealth of information and thereís some fart smellers around here.
I mean smart fellers....haha


I appreciated you asking. I had no clue the about using or not using plastigauge. So with some saying its dumb to use it, what else are we supposed to use if we don't have expensive/calibrated calipers? Trust the bearings and crank measurements from the machinist and the parts stores? Or just put it together and spin it, and if it spins fine without a bunch of slop, it's good?
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67 Sunroof
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PostPosted: Thu Nov 21, 2019 1:47 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

slalombuggy wrote:
Glenn wrote:
It looks like you have it backwards and the tangs are actually down.

The rod closer to the flywheel is #3 and the numbers are on the tang side.

Image may have been reduced in size. Click image to view fullscreen.


The rods are symmetrical so it really doesnt matter where the tangs are. I always install the rods the same on a crank but up or down makes no difference.

Plastigauge doesn't know what it's being used on. I've used it lots, it's better than nothing

brad


You say the numbers are on the tang? I donít think mine are. The numbers are on the other side of the tang?!
So if the crank is laying facing away from me on the workbench (pulley closest to me and flywheel furthest away)
First rod is #2 facing right
Second is #4 facing left
Third is #1 facing right
Fourth is #3 facing left

So I shouldnít be seeing any numbers looking down on it from my workbench if the tangs are facing down.
Right??
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67 Sunroof
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PostPosted: Thu Nov 21, 2019 1:52 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Actually thinking about it at work. You were probably right from the start as I have the rods facing the wrong direction in my first pic in the vice.
Ugh...
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PostPosted: Thu Nov 21, 2019 1:55 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Nobody has to resort to plastigague anymore. For $55, you can get a set of micrometers and a set of snap gauges from Harbor Freight.
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M. Notary
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PostPosted: Thu Nov 21, 2019 2:22 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

TomSimon wrote:
65calvw wrote:
How does Plastigauge know it's being used in a Volkswagen Type 1? Or a Ford or a snowblower?


On most other engines, you torque the rods while they are attached to pistons in bores.

With a VW, you torque the rods while they are free to rotate on the crank journal. ANY rotation of the rod on the crank journal smears the plasti-gauge, rendering the reading/measurement null and void, or worse, fooling the engine builder into thinking the clearance is too tight.

Experience is a wonderful thing

Having gone through this experience once upon a time, at the end of the day, I felt as through there was a village somewhere, missing it's idiot...

and I found him, staring back at me in the mirror Embarassed Laughing


THE Tom Simon... old Cal Look days...
Plastigauge always seemed inconsistent. Bore gauge and calipers.
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PostPosted: Thu Nov 21, 2019 2:32 pm    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

I like to do plastigauge sometimes after doing the measurements with mics and a bore gauge.

Fun to see what they all say,
And more information is better.

Kind of a 'sanity check'..

I always do a couple of plastigauge checks on the center main; where this is best used.

A good test to see how well the plastigauge works if you take time to set it up to hold things still and work as well as you can.

After doing 'both' several times,
you can have the plastigauge work well enough.

I'd use it in a pinch if I had to..

And,
yeah,
i'm geeky like that,
I'll admit. Embarassed
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PostPosted: Fri Nov 22, 2019 7:24 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

jpaull wrote:
Nobody has to resort to plastigague anymore. For $55, you can get a set of micrometers and a set of snap gauges from Harbor Freight.


snap gauges are just ok... it takes a while to get real accurate/consistent readings down in the .0005" range, they also smear the soft top layer of bearing material.

What you really want is a decent quality (subjective, I haven't used Harbor freight but they might be plenty good enough) 2"-3" micrometer and an automotive quality Chinese dial bore gauge, plenty good enough for engine building. A dial bore gauge uses light spring pressure, and doesn't rub off the top layer of bearing material like a snap gauge does, and a lot more consistent that a snap gauge. $200 and a little practice, and you're good.

https://www.summitracing.com/parts/sum-900041?seid...-wEALw_wcB

You measure the journal with the 2-3 mic, then use the same mic as a 'standard' to zero the dial bore gauge that you've set up (to measure whatever rod journal size you are dealing with). Since you care more about the clearance, not so much the absolute measurement, a guy doesn't need "Dead-on balls accurate" Starrett or Mititoyo quality measuring tools for this job.

Measure the OD of the crank journal, the ID of the rod and bearing that's torqued together, the difference is your clearance. As an example I like .0021-.0028, from experience that's enough clearance for clean oil to flow and cool the rod bearing and crank journal, not so much that the oil runs out and the pump can't keep up. There's more to it than that, but that's a good start.

If a guy buys a 3"-4" mic, and the right dial bore gauge with enough range to measure 2" up to 4", and you are set up for measuring piston to bore clearances as well.

Another way to do this is to take your crank and rods, rod bearings to a competent engine machinist. Not an assembler, a machinist, who has a rod honing machine (and knows how to use it, good stones, etc). Number the rods and the journals, tell him what to torque your rods to, and what clearance you are looking for, and have him 'hand fit' each rod to each rod journal (most assemblers don't have the courage to stop an engine build if one of the rods clearance is tight, say only .0019" they just convince themselves it must be good enough, and move on). An automotive machinist can open up the tight rod by removing the bearing, retorquing the cap back on the rod, and honing out .0005" of material on only the tight rod, giving you .00024" clearance in the above scenario, and you're golden. In fact, race engine builders do this all of the time.

I hope that's helpful.
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PostPosted: Fri Nov 22, 2019 10:09 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Applause
Tom just wrote a prefect description on the correct way to be building an engine. Plasti-gauge is rather caveman. If you are assembling in your gravel driveway on a milk crate, without a torque wrench...It might get you close.

A set of 2"-6" dial bore gauges are cheap these days. Same with a set of 1"-4" micrometers. Both of these things should be near the top of "must have" tools for engine building. Real true accurately measured oil clearances are much better than a guess and a hope.

Brian
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PostPosted: Fri Nov 22, 2019 10:31 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

Please don't anyone buy that bore gauge that Tom linked to from SUMMIT. I have that exact one, and the spring pressure is too much for bearings. Its perfect for cast iron cylinder bores though. My guess is that a different brand would have a lighter spring for the tension, and could be used for rod bearings. If that spring pressure is adjustable, or if someone else has that summit model and had success, speak up. For the sake of others, I would love if mine is the only one, but just in case, I wouldn't rush out and order that model for the purpose of rod bearings or any other soft bearings.

Snap gauges can mess up bearings too as Tom mentioned, but if your careful they work just fine.

Tom is correct, dial bore gauge is THE way to go. Just get one that has a light spring pressure or can be adjusted so the pressure is not so heavy.
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PostPosted: Fri Nov 22, 2019 11:26 am    Post subject: Re: Plastigauge, torque specs, mock-up questions Reply with quote

I have a china bore gauge set from Ebay bought years ago. It will put a mark on the bearing coating, but it won"t scratch it. Cant feel it with a finger nail, and it will polish right off.

Wonder if you could pull yours apart and snip a coil off the spring?

Brian
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