Acceptable flywheel runout for 350 sbc..clutch chatter.. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-13-2008, 05:49 PM
F&J F&J is offline
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Acceptable flywheel runout for 350 sbc..clutch chatter..

66 chevy pickup restored no expense spared.

It gets a few hundred miles per year max.

He had the most expensive trans shop here put in a new 11"clutch kit, resurfaced flywheel, new pilot bushing (he claims they did the bushing). He said it quickly started a slight chatter weeks later but figured it may go away. This shop also redid the muncie, plus put a posi in at the same time.

I now get the job and he already ordered a new 11" kit AND a new flywheel from LMC. The flywheel has tons of balance holes and is made in Mexico.

Before I pulled the old flywheel, I measured the runout to 15 thou on the outer edge of the wear surface. The new one is about 13 thou, and maybe it did not really change because I switched to a bigger dial indicator when I put the new F-wheel on.

Now, I am going to mark the high spot and then index the flywheel 180* to see if the crank is out, in the AM.

I'd like to know what runouts are acceptable on this?? Real world advice from you all, not a book spec that might not mean anything as far as chatter.

The old bushing definately was worn, but not super bad. The old clutch kit looks like it was put on yesterday, and the f-wheel resurface looks the same age..mint.. No choppy spots, no nothing. The disc has not even worn in 100% yet!

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Old 09-13-2008, 06:43 PM
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i dont know about a chevy but iv replaced lots of clutches on semis with cummins and max runout is 6 thou and your talking about a clutch thats 14 1/2 inches and 250 pounds.so if you have 14 thou i whould think it be way to much.you might be able to take the old one to a shop and have it ground.
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Old 09-13-2008, 10:23 PM
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Did you check the bellhousing bore and mounting surface for proper alignment? A BH out of alignment could make a clutch chatter too. Line boring a motor will move the crank up .020 or more, so it only serves to reason that the bellhousing should be re-aligned with the crank. .005" TIR is usually acceptable.

Also...

I'd be wondering if the old flywheel had some heat checks in it that were ground off by the resurfacing, but are now hard spots...that might cause chatter.


Another also.

I'd also be looking at the motor/trans mounts for dissimilar cushions,(like poly motor mounts and a rubber trans mount, or vice-versa), or possibly a loose or busted mount.



I'm also thinking that .015" R.O. is too much.

The flywheels that I've checked were usually within .005" and seemed to not chatter.

A friend of mine just put a whole new setup on his 350 in a 40 chevy and it chattered some out of the box. It was a cheap-o 11" HD clutch, and a hecho-en-mexico flywheel. It apparantly has developed a bent finger on the diaphram, it didn't show up until the car was running and then you can hear an intermittent squeak..The squeak would go away when you pushed in the clutch. Upon looking inside the release bearing arm hole in the BH you can see one finger rubbing on the release bearing. I don't know if it broke a diaphram, or what.
We still need to pull the trans on that one.


Those are just some suggestions, I know you are already very knowledgeable about all this stuff.


Later, mikey
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Old 09-14-2008, 07:35 AM
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Well that's two replies that think there is too much runout.


Quote:
I'd be wondering if the old flywheel had some heat checks in it that were ground off by the resurfacing, but are now hard spots...that might cause chatter.
The 350 was built 15 years ago with a resurfaced stock flywheel, and then it was fine until 4 years ago when it developed minor chatter. That's when he decided to have the shop do a new clutch, resurface again, plus rebuild the trans & rear. Only 1000-2000 miles since. The flywheel surface in good light shows no weird spots, it still has the machining pattern lines, plus the disc & plate look like 100 miles. It all looks new, no kidding.



Quote:
I'd also be looking at the motor/trans mounts for dissimilar cushions,(like poly motor mounts and a rubber trans mount, or vice-versa), or possibly a loose or busted mount.
Ok, The truck was run off the road during a beer related burnout about 3 years ago and bent the frame up front. He was already having chatter before that hit, so when I put a cherry frame under it, I changed from the old side-bellhousing-mounts to the proper tailhousing x-member & mount. That helped, but not 100% cured.



Quote:
Did you check the bellhousing bore and mounting surface for proper alignment? A BH out of alignment could make a clutch chatter too. Line boring a motor will move the crank up .020 or more, so it only serves to reason that the bellhousing should be re-aligned with the crank. .005" TIR is usually acceptable.
No, I did not even think of that I'll measure today. No records available from when the first engine shop did the motor 15 yrs ago.

I will also mark the highest spot on the flywheel and then pull the bolts and spin it 180 degrees to see if the crank is the problem.....If the high spot moves 180 on the flywheel, then that means the crank is off.
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Old 09-14-2008, 07:45 AM
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That's a good thought about misalignment...

All of the parts look like 100 miles except the pilot bushing. He insists they put a new one in at that time.

You know the deal, did they really?

If they really did replace it, it shows way more wear that should be possible in that short 1000/2000 miles over 4 years or so.

I'll stick the indicator on the crank and check the bore on the bell housing to be sure.
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Old 09-14-2008, 07:52 AM
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An excessively worn pilot bushing will definately cause chatter.

If the pilot bushing was wearing really fast,(like the trans shop DID install a new one), that would really indicate to me that checking the bellhousing bore / mounting face is in order.

Lakewood has a PDF file on the procedure, ( you probably know it already but I always like to brush up on stuff like that)
http://go.mrgasket.com/pdf/bellhousi..._procedure.pdf


Hope that fixes it


Later, mikey
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Old 09-14-2008, 08:09 AM
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I will read that.


I was just thinking.... I should find out if the crank is bent first. I will put the indicator on the inside of the bell and run the pointer inside the bore where the bushing is pressed in, and rotate the crank. That will tell if the crank is out.


If the crank IS out, then I can't see how I can indicate (off the crank) to see if the bell hole is misaligned.


Man, I was already thinking how to make offset dowel pins for the bell on my old lathe with a 4 jaw
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Old 09-14-2008, 08:15 AM
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Good site, I'll get some measuring done this morning. Thanks
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Old 09-14-2008, 09:23 AM
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Any flywheel surfaced on an actual flywheel surfacing machine will be within .001 of actual runout.
There could have been debris between the flywheel and machine mount that would cause runout.= machinist error.
Some people machine flywheels on large belt sanders, some on "table rocks", and some on brake disc lathes. Be sure to get yours surfaced on an actual flywheel turning machine..... obviously with a good machinist doing the work.

Second.... The nose of the transmission shaft itself could be worn enough that it flops around in the new pilot bushing.

Third..... align honing mains usually changes the crank centerline about .002 per each aligning operation.= raising the crank towards the camshaft.

Fourth... Linkage adjustment could be changing as the engine torques over. I changed one car from AC condenser, engine, trans, shaft, and diff with totally different components.... and the new clutch still chattered... mechanical clutch linkage problem.

Fifth.... Be careful installing the PP. It can be warped slightly by not sequencially torquing the mounting bolts= causing a twist in the housing.

Sixth.... Be careful of the alignment when installing the transmission shaft into the disc. The disc center itself is more easily bent than most people think and it causes the disc to wobble slightly.

I NEVER install ANY rebuilt clutch component. I don't want to do the job a second time.

Also make note of the other things already mentioned.

Last edited by ScoTFrenzel; 09-14-2008 at 09:35 AM.
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Old 09-14-2008, 11:11 AM
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The crank is what's wrong


I indicated & marked the "high spot", then moved the flywheel 180* different on the crank. Now, the high spot mark now shows as a low spot. I am measuring on the f-wheel face out 6" from the crank C/L.

So then I indicated the bore of where the bushing rides. A little under 2 thou out, and "it's" high & low spot corresponds with what would happen to the outer edge of the flwheel (if you follow what I am trying to say)

Now what? I don't have any time to pull the motor and or wait for a shop (or me) to swap a crank. I need to patch it somehow. The only thing, I wish I buzzed the engine higher when I drove it in the shop to see if it vibrated at 3-4k. I know it was OK at lower rpms, or I would have noticed.

Any ideas?


I am guessing a 3 thou or less correction on the crank flange?
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Old 09-15-2008, 08:01 AM
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Ideas....
With the trans out already it would be a short job to pull the crank with the motor still in the truck...I did it once before, and it worked out fine. Shove the pistons up in the bores, the rings won't turn in the bore even if the piston turns. You need alot of short peices of rubber tube to keep the rod bolts from marring the crank when you pull it and then put it back in, but with the pistons pushed up, it's not hard to get everything lined up again.


Then throw that crank in the lathe and face off the flange.

I don't think shimming the flywheel is a good idea, if somehow you could face the flange while it was in the motor, that would work, but building a grinding setup to do that successfully would take eternity...(there is a machine that can turn disc brake rotors on the spindles, why not a crank?...no machine exists for crankshafts though, and I'm sure there isn't much call for one). Bridge across the bellhousing mounting bolts with some linear slides and rails, and make a plate to bolt to the linear slider blocks that would hold an arbor with an adjustable grinding wheel....


The crankshaft endplay would be the killer in that setup though, unless you made a thrust bearing holding bridge for the front of the block that would hold the crank in it's rearmost position while you were resurfacing the flange.


How did the crank get bent at the flange? Did someone drop it on the flywheel at some point in the past?



Here is a really strange idea, that would work with your job requirements...put the flywheel on a big rotary table on a mill, face down, shimmed up from the table the amount of indicated runout at the high spot. Shim it so that you don't flex the flywheel. ( I usually put an indicator on a part that I'm clamping weird like that, at the clamped area to make sure it is not warped after clamping it down, ) then flycut around the mounting surface where it meets the crank so it runs true to the table.


Mount the flywheel back on the crank and it would probably run true.

Just a thought.

I'm sure alot of folks would say that was a crazy idea, and would never work....(I always accept that as a challenge to prove them wrong )


Unique problems require unique solutions....

Later, mikey
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Old 09-15-2008, 09:09 AM
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Quote:
Originally Posted by F&J
I will read that.





If the crank IS out, then I can't see how I can indicate (off the crank) to see if the bell hole is misaligned.


Man, I was already thinking how to make offset dowel pins for the bell on my old lathe with a 4 jaw

I just saw that post...

When you are checking bellhousing bore alignment the indicator runs in relation of the crank spinning in it's bearings, not the surface of the flange. You could mount an indicator to a flange that went through the apocalypse, and as long as the crank was not wobbling in the block, and your indicator mount was not flexing, you'd get an accurate reading of parallelism and concentricity..


You are measuring the alignment of the bellhousing bore with a crankshaft's axis of rotation, not the bore to the flange.


Later, mikey
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Old 04-07-2012, 05:52 PM
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I'm running into a similar problem. The crank flange appears to have some runout. Not sure how much but it's resulting in about .0045" at the flywheel. I was wondering what the final solution was for this case.

I'm thinking of making a tapered shim between the flywheel and crank to reduce the runout. (maybe .005 on one side and .004 on the other side, which would be magnified at the flywheel surface)

This is in response to long standing clutch chatter through different clutches, flywheels, pilot bearings. I've checked the usual suspects - including checking bellhousing concentricity w/ crank shaft.
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Old 04-08-2012, 11:08 AM
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You cant check runout with the flywheel mounted to the engine unless you crank thrust is zero.
Take the flywheel to a machine shop with a flywheel grinder and have it checked.
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