TheSamba.com :: View topic - What is the allowable variance for a flywheel?

Thu Nov 20, 2008 8:27 pm

I am working on my engine and noticed there is some variance with my flywheel as it rotates. I have already checked the end play and I have right at .003" (the .004" doesn't quite fit but the .003" slides easily) so I know my end play is within tolerance. But as I rotate the flywheel around I notice there is a high side and a low side. The difference between the two is about .006". In other words if I put the flywheel at the high side and check the end play with the end play tool it is at .003" (I pull the flywheel back as far as I can with two large screwdrivers, set the end play tool the use a rubber mallet to push the flywheel back in and the difference is about .003"). But when I rotate the flywheel around to the low side the gap now measures about .009" (giving me a difference of about .006"). Is this common, or within acceptable limits? Or is it in need of being resurfaced or something (like having your breaks turned). I really don't want to proceed until I figure this out-no point in putting in an engine with a defective part. Incase it is relevant I have a 69mm counterbalanced crank with the 4140 lightened 8 pin flywheel attached.

Thu Nov 20, 2008 8:58 pm

Check to be sure the O-ring did not get pinched between the flywheel and crank during installation, also check for any and I mean any signs of burrs at the crankshaft and flywheel mating surfaces.
.003" lateral run out is not uncommon, but you do want to achieve as close to zero as possible. Should not cost you much to have a machine shop true up the flywheel for you, and money well spent.
What you really want to check for is vertical run out (up and down) that is what will shake things up, I assume you had the rotating assembly balanced?

Thu Nov 20, 2008 9:54 pm

The o-ring is seated in the flywheel properly and the mating surfaces of the crank and flywheel are smooth (they are both brand new and purchased from the same supplier). The engine is a stockish 1600 with only a mild cam and 1.25 rockers so I have not thought it necessary to go to the expense of having everything balanced (I was told with mine it was unnecessary). Every part of the engine is a new part from the case on down so there is nothing that should be worn. The flywheel does not move up and down or side to side it just seems- for lack of a better term- warped. When you rotate it there is a high side and a low side. If I need to have it machined to true can any machine shop do this or do I need to find some specialty VW shop, and what do I ask them to do to it?

Thu Nov 20, 2008 10:06 pm

They need to index the flywheel from the crank to the flywheel mating surface when it's put into the surfacing machine, then surface the flywheel.
One more thing, you should be taking your measurements from the pressure plate mounting surface of the flywheel, not the outer most face where the starter teeth are.

Thu Nov 20, 2008 10:12 pm

So are you saying that I have to disassemble the engine to get this done, to take the crank out with the flywheel? My dad and I have had this thing fully disassembled 5 times now and I don't think he could take the news that we would have to disassemble it again. I have been taking my measurements from the outer edge so when I go back to dad's to work on it I will take my dial micrometer and measure from the inside surface where the pressure plate mounts and see if there is any difference in measurement.

Thu Nov 20, 2008 10:21 pm

mac-vw wrote: The o-ring is seated in the flywheel properly and the mating surfaces of the crank and flywheel are smooth (they are both brand new and purchased from the same supplier). The engine is a stockish 1600 with only a mild cam and 1.25 rockers so I have not thought it necessary to go to the expense of having everything balanced (I was told with mine it was unnecessary). Every part of the engine is a new part from the case on down so there is nothing that should be worn. The flywheel does not move up and down or side to side it just seems- for lack of a better term- warped. When you rotate it there is a high side and a low side. If I need to have it machined to true can any machine shop do this or do I need to find some specialty VW shop, and what do I ask them to do to it?

Seening that I send many NEW parts back because they are not acceptable and can not even be balanced. as in Mahle forged pistons that differ from up to 7 grams. and rods that differ up to 8 grams.

And New heads that require a 3 angle valve job out of the box before I will sell them. I just hope you bought from a supplier that Checked all of these things before you ponied up for them.

As for your difference in the end play Take SRP1's advice

Thu Nov 20, 2008 10:29 pm

I understand about new parts sometimes being defective and that is a very valid point. I guess what I am asking is, is this flywheel defective because of the .006" variance that I measure on it. And if so what is my solution? Am I better off trying to return it for another or is it better to try to fix this one. I understand the part about getting the flywheel machined back to true (like you would do with your break rotors). But is this something that needs to be done with the flywheel attached to the engine, or can it be done by just taking the flywheel off and taking that to the machine shop?

Thu Nov 20, 2008 10:30 pm

mac-vw wrote: I understand about new parts sometimes being defective and that is a very valid point. I guess what I am asking is, is this flywheel defective because of the .006" variance that I measure on it. And if so what is my solution? Am I better off trying to return it for another or is it better to try to fix this one. I understand the part about getting the flywheel machined back to true (like you would do with your break rotors). But is this something that needs to be done with the flywheel attached to the engine, or can it be done by just taking the flywheel off and taking that to the machine shop?

It is best to take the crank and the flywheel to the machine shop and have them checked.

I would never accept that much run out

Fri Nov 21, 2008 12:35 am

I would rather you said every part from the case on down was re-machined original German.
Yes take it back apart and have it balanced, while your there have the crank and flywheel checked out regarding your run out issue, sound like what you have is no good.
One more thing .003" is dangerously tight for end play, I would shoot for .005" it's within spec and leaves a little room for error, the last thing you want to have happen is the crank locks up on the rear main and you do it all over again.

Fri Nov 21, 2008 11:23 am

.003-.005 is spec for end play. I always shoot for .004. .003 is definately scary close.

Fri Nov 21, 2008 10:52 pm

The minimum end play specified by VW is 0.07 mm = 0.0027", so 0.003" is definitely fine.

I've run 0.002" end play on one motor and didn't have any problems, but I'm not recommending that to anyone :wink:

Sun Nov 23, 2008 1:13 am

I have done some research and it seems, according to the repair manuals that I have, that the acceptable lateral runout is no more than .012". The lateral runout that I am measuring at the flywheel on the outer edge where the teeth are is .006". This is half of the acceptable amount. I will also take another measurement on the inner flywheel surface where the pressure plate bolts on to see if there is any difference.
So I guess what I am getting at is, what is the tolerance for lateral runout if it is not the .012"? And does it change if you are using a counterbalanced crank and lightened 4140 flywheel?
Sorry to keep asking but I want to be sure I understand what I am doing here.

Sun Nov 23, 2008 10:38 pm

Just checkin if anyone had a comment about my last post on this subject-

I have done some research and it seems, according to the repair manuals that I have, that the acceptable lateral runout is no more than .012". The lateral runout that I am measuring at the flywheel on the outer edge where the teeth are is .006". This is half of the acceptable amount. I will also take another measurement on the inner flywheel surface where the pressure plate bolts on to see if there is any difference.
So I guess what I am getting at is, what is the tolerance for lateral runout if it is not the .012"? And does it change if you are using a counterbalanced crank and lightened 4140 flywheel?
Sorry to keep asking but I want to be sure I understand what I am doing here.

Sun Nov 23, 2008 10:56 pm

You want your lateral run out to be as close to zero as reasonably possible, but is not as critical as vertical run out.
The spec of .012" sounds like a lot IMO, you say you have .006" and are concerned.
Like I said prior, take it apart and have the rotating assembly balanced, while your at it have the machine shop true up the flywheel a little, your there anyway might as well get things in line as best as possible.
If you are not going to have the engine balanced then run it, the engine running off balance will have a greater negative affect than .006" of lateral run out on the flywheel so nothing to worry about.

Mon Nov 24, 2008 11:02 pm

So I got to the engine today and here is what I found. I removed the flywheel and the o-ring is in place. I checked the mating surfaces on the crank and flywheel and they are free of any burrs. Then when I put the flywheel back on I put my dial micrometer to the inner machined surface of the flywheel where the pressure plate attaches and this time I only got lateral runout of no more than .002". I took measurements on about a dozzen different places and it was less than that in some places but nowhere was it more than .002". This leads me to believe that it should be good to go. If anyone thinks I am wrong please let me know.

Mon Nov 24, 2008 11:18 pm

mac-vw wrote: So I got to the engine today and here is what I found. I removed the flywheel and the o-ring is in place. I checked the mating surfaces on the crank and flywheel and they are free of any burrs. Then when I put the flywheel back on I put my dial micrometer to the inner machined surface of the flywheel where the pressure plate attaches and this time I only got lateral runout of no more than .002". I took measurements on about a dozzen different places and it was less than that in some places but nowhere was it more than .002". This leads me to believe that it should be good to go. If anyone thinks I am wrong please let me know.

That's very good, run it.