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Help Understanding End Play?
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luftgekuehlt
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PostPosted: Sat May 08, 2021 11:50 am    Post subject: Help Understanding End Play? Reply with quote

Hi -

I am just getting started with VW. I have a 1970 with an oil leak at the engine/bell housing junction. I have been trying to read as much as I can before moving forward.

I am not sure I understand end play, so here's another newbie question:

From what I have been reading here, measured end play shows the state of the crankshaft bearings.

Is it right that excessive end play is not to be corrected with the shims since this does not fix the underlying problem with worn bearing seats?

If this is true, what is the recommended wear tolerance limit? At what measurement is it necessary to rebuild with new bearings?

Thanks,

Chris
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TinCanFab
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PostPosted: Sat May 08, 2021 12:39 pm    Post subject: Re: Help Understanding End Play? Reply with quote

Yes, there is a wear limit spec, but in your case, I would not mess with the end play, just check to make sure it is not a HUGE amount. These things will still run when you are able to grab the pulley and move it back and forth a 1/4". If it's barely moving back and forth, then just move on to fixing your leaks. Just push and pull, an engine that is totally worn out will flop around with no strength required.
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ashman40
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PostPosted: Sat May 08, 2021 1:33 pm    Post subject: Re: Help Understanding End Play? Reply with quote

The crankshaft end play is the measure of movement between the crank and the main bearing (specifically the #1 thrust bearing). Here is a pic of the #1 bearing at the front of the case (closest to the flywheel). It is the only flanged main bearing with a thrust surface. This means the bearing wraps around the saddle in the case and does not move fore/aft at all. When the crank moves fore/after this bearing flange limits the movement. The crank spaces off the outer flanges of this one main bearing.
Image may have been reduced in size. Click image to view fullscreen.

To the left of the bearing is one of the crank throws. When this contacts the bearing flange it limits how far the crank moves to the front of the case. To the right is the flywheel. There are normally three shims between the bearing and the flywheel. By adjusting the thickness of these three shims you control how much "gap" there is between the crank and the bearing. This gap is the end play. Stock setting for this gap is 0.004" with a tolerance of +/- 0.002", so up to 0.006" max. Most people would have a difficult time visually seeing with their eyes something move only 0.006". This is why feeler gauges or dial gauges are used to measure the movement.

The problem... while a new engine only has play between the crank and the bearing flange, a well worn engine may also have movement between the bearing and the case saddle it is resting on. This adds to the measured end play (flywheel to case movement).
For example, let's says your old worn engine has a measured 0.010" of end play (flywheel moves this much relevant to the case). You remove the flywheel and replace one of the three shims with a new one that is 0.004" thicker to tighten up the excess play. You now get a reading of 0.006" of end play so are happy you are within spec once more. Unfortunately that 0.006" end play is all movement between the bearing and the case saddle which has worn. The 0.004" you removed was the gap between the crank and the bearing. Your actual crank to bearing end plan has now been reduced to zero! After a few miles of driving down the road your #1 bearing over heats and seizes to the crank. The bearing spins in the case saddle destroying the engine.

If you remove the flywheel and apply pressure to the #1 bearing in the case. Alternate pushing from the flywheel side and the fan belt pulley side and see if the bearing moves in the case. If you can measure movement, the bearing or case is bad. To fix the case will need to sent to a machine shop and an undersized thrust bearing will need to be installed to take up the gap between the case and the bearing.
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Busstom
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PostPosted: Sat May 08, 2021 2:15 pm    Post subject: Re: Help Understanding End Play? Reply with quote

TinCanFab wrote:
These things will still run when you are able to grab the pulley and move it back and forth a 1/4".


Just two points to add context for you kids, and future generations who may read this:
1) a 1/4" is about the thickness of a yellow #2 pencil, and;
2) if it runs with a 1/4" of end play, it won't be for long, because a) the excessive side-loading on the connecting rods will have broken or seized something in very short order, and b) because with much more than about 1/8" of end play, the flywheel seal will no longer be sealing, at which time the oil, under pressure from the oil pump, will be pouring all over the ground and the engine will run itself dry in even shorter order, again, causing seizure of the engine. Wink
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Eric&Barb
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PostPosted: Sat May 08, 2021 2:44 pm    Post subject: Re: Help Understanding End Play? Reply with quote

Also with the end play being a bit over the tolerance, the crankshaft and flywheel act like a battering ram on the #1 bearing every time one pushes the clutch pedal. That will keep bashing that bearing more and more as long as one ignores the problem.

Most folks can not notice .006" or a bit more end play by feel, so using proper tools to check it now and then is a must.

Additionally when you go to start the engine, do not push on the clutch pedal. Better to slip the VW into neutral and then start the engine without pushing on the clutch. That way the #1 bearing is not under 200+ Lbs. of pressure without much of any oil in between the flywheel, shims, crankshaft and the rear of bearing.

Only time it makes sense to push on the clutch pedal when starting an engine is if the weather is way below freezing and the gear oil in the transaxle so thick with the cold that the engine will not start easily.
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Zundfolge1432 Premium Member
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PostPosted: Sat May 08, 2021 7:06 pm    Post subject: Re: Help Understanding End Play? Reply with quote

Sounds like a good argument for using a modern synthetic gear oil rather than the what was common in the 60s and 70s. Welcome to the 20th century 😀
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calvinater
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PostPosted: Sun May 09, 2021 4:27 am    Post subject: Re: Help Understanding End Play? Reply with quote

Make that the 21st century.
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finster
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PostPosted: Sun May 09, 2021 6:47 am    Post subject: Re: Help Understanding End Play? Reply with quote

Busstom wrote:
TinCanFab wrote:
These things will still run when you are able to grab the pulley and move it back and forth a 1/4".


Just two points to add context for you kids, and future generations who may read this:
1) a 1/4" is about the thickness of a yellow #2 pencil,


I thought a banana was the unit of scale for kids on the 'net... Laughing

end play also caused variable ignition timing on my cabrio as the distributor is driven off the crankshaft
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Busstom
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PostPosted: Mon May 10, 2021 11:22 am    Post subject: Re: Help Understanding End Play? Reply with quote

finster wrote:
I thought a banana was the unit of scale for kids on the 'net... Laughing


Ha! Probably, pretty sure I'm out of touch Smile
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Zundfolge1432 Premium Member
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PostPosted: Mon May 10, 2021 3:09 pm    Post subject: Re: Help Understanding End Play? Reply with quote

calvinater wrote:
Make that the 21st century.


It’s called irony in my book or a sad attempt at humor. 😀
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