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Old 10-01-2013, 10:33 AM
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Do GM bellhousings need to be centered to the crank?

I own a 1960 Corvette since 1983. It has a small journal 327 with a scattershield (Lakewood I believe) and Muncie M21. In 1983 when I purchased the car I replaced the clutch and pressure plate. The auto store where I purchased the pressure plate matched it to a Ford Bronco. The clutch is Chevy.

The flywheel is worn and requires replacement, so on the weekend my younger brother Rick, 56 years old and a mechanic for 35+ years assisted and we removed the transmission.

I've been told on another forum that the scattershield needs to be centered to the crank as it appears the flywheel wore unevenly. I mentioned this to brother and he said in the 35+ years he has worked as a mechanic he has never had to do this and has never had any problems. He said this must be something that needs to be done to scattershields only...

So the question is do GM bellhousings have to be centered to the crank? I ask as I am contemplating of tossing the scattershield in favour of a GM two piece (open bottom) bellhousing ....
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Old 10-01-2013, 10:34 AM
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A few more photos....
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Old 10-01-2013, 11:24 AM
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Quote:
Originally Posted by KENMO View Post
So the question is do GM bellhousings have to be centered to the crank?
I never saw the need to center a GM bellhousing. Maybe because the bell is cast and tolerances can be tighter.

The Lakewood is a different story. It is hydro-formed from sheet steel and therefore cannot be spot-on every time. Every one I ever installed required mounting a dial indicator on the crank and rotating it through 360 degrees to see where the front bearing retainer hole is off, relative to the crank centerline, then using offset dowels to move the housing around and as close as possible to square. You will never get it 100%, unless you have more patience than I do, but it'll be close enough to work.

I cannot stress strongly enough, the importance of using a steel scattershield with a manual transmission. If you had seen the injuries I've seen over the 50-plus years I've spent hanging around drag strips, you'd be a believer also. Don't forget to include an engine plate between the scattershield and the block. Sometimes stuff breaks the back of the block.

Here are the offset dowels.....
http://www.summitracing.com/parts/lak-15940/overview/

And related threads....
Scattershield vs Bellhousing

Scatter Shield & Blanket

clutch scattershield options?

Lakewood Scattershield

scatter sheild

Last edited by techinspector1; 10-01-2013 at 11:47 AM.
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Old 10-01-2013, 11:37 AM
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The answer isn't simple. The company I work and our distributors have a lot of race customers; which require the bellhousing be within .003 - .005" TIR (total indicated runout) for proper high rpm operation of the gearbox.
Think of it this way: When your trans is shifted into 4th gear which is direct drive (4th gear in a 4speed is the input gear); the 3-4 synchronizer needs to "lock on" to the engagement teeth on the back of your input. Muncie synchronizer design dates back to the T85B which is pre WW2. Its hard enough for it to do its job with twice the power and twice the rpm it was designed for. If your bellhousing isn't centered enough, now the synchronizer has to speed/slow down up one gear, disengage itself AND suck the input into alignment to engage itself all the way.

Anything you can do to expedite the process; use the proper oil, at the proper level, use a tight fitting hub and slider in the synchronizer; rings with sharp grooves to cut through the oil film; and good alignment...will not only help it shift fast, but also KEEP IT FROM POPPING OUT OF GEAR, which is one of the leading complaints on a worn gearbox and has nothing to do with the bronze rings.

If your pilot bushing is worn unevenly, or your disc is; I would say that the bellhousing/transmission are far enough out that it SHOULD be aligned. Lakewood/McLeod are both famous for having misalignment; but Ive seen factory aluminum bellhousings out by .018" installed.

So, in short; do they need to be aligned? Only if its more than .009" TIR on a street car and .003 - .005 TIR in a competition car.

Make sure you replace your pilot bushing.
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Old 10-01-2013, 11:41 AM
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Oddly, I cant click "THANKS" on Tech Inspectors post. He is absolutely spot on (as usual).
If you want an easier to install scattershield; the Quicktime brand BH seems to be much more consistent, however you should still sweep it with a dial indicator.
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Old 10-01-2013, 12:38 PM
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How expensive and where does one purchase a dial indicator?
I'm leaning more towards a stock GM bellhousing especially if it doesn't have to be centered to the crank which sounds too tedious for me. And I don't drag race my Corvette. The prior owner did.

Thanks
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Old 10-02-2013, 07:27 AM
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I've had clutch disc failures on a near stock 283.I know a disc failure is not as serious,but aluminum is not the answer.
Curious,do you have seat belts in your 1960 Vette?
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Old 10-02-2013, 07:41 AM
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Yes. I have seat belts. I purchased my Vette in 1983. The prior owner used to drag race the car. The interior was gutted but did have both seats. He used to run a big block and later swapped in an early 327 (small journal).

I don't abuse my Vette so I'm thinking a GM bellhousing would be a better fit for me. Also I like the idea that with some GM bells there is a shield (plate or shroud) which can be removed for flywheel/clutch inspection.
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Old 10-02-2013, 07:59 AM
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QUOTE:
"I don't abuse my Vette so I'm thinking a GM bellhousing would be a better fit for me."

I would reread what Autogear and Tech posted.
no idea how often you inspect the clutch? If it's for wear,then look through the fork slot and use a light. If you need to see the disc surface,either way the trans will need to come out.
I'm sure you can borrow a dial indicator if you dont want to buy a cheap one.
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Old 10-02-2013, 08:07 AM
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Thanks kindly for the replies. If I do swap out the scattershield I am thinking of a bellhousing like this... It's two piece.

This is what was recommended by a poster on the Corvette Forum. It's steel and used on the early Corvettes (C1).

Cheers

Ken
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Old 10-02-2013, 09:32 AM
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Here is my fave bellhousing adjustment video. Its long, but detailed and he explains his reasoning. He also endorses the RobbMC dowel pins which I have used and I agree they're the absolute best. Set em, and install em; no loss of adjustment or adjusters that dont adjust.

He says to use .000 -.005 for your adjustment. Note that TIR most likely doubles a measurement ie -.002" will probably end up being .004" TIR. Another way to look at it... if a shaft in a lathe chuck is a thousandth low on one side, and a thousandth high on the other, then the TIR is two thousandths, since that's the total. So his call out for .000" - .005" would be .000 - .010" TIR. For a street car; .009" or less is more than adequate.

DO NOT buy your dowel pins until you get a repeatable measurement. Invariably you'll buy the wrong ones.

If you are using a cast iron flywheel Id put a blanket over the bellhousing. Most blankets are SFI 4.1 which is fine for an automatic but not for a hardcore clutch explosion (SFI 6?). Gordon Levy used to sell a blanket for integral bellhousing stickshifts however I can't remember its rating. Tech Inspector?

Last edited by AutoGear; 10-02-2013 at 09:50 AM.
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Old 10-02-2013, 09:34 AM
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This is what happens when a cast flywheel lets go. No idea who owns this, or if he survived. It was on speedtalk.com awhile ago
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Old 10-03-2013, 10:49 AM
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Quote:
Originally Posted by KENMO View Post
I own a 1960 Corvette since 1983. It has a small journal 327 with a scattershield (Lakewood I believe) and Muncie M21. In 1983 when I purchased the car I replaced the clutch and pressure plate. The auto store where I purchased the pressure plate matched it to a Ford Bronco. The clutch is Chevy.

The flywheel is worn and requires replacement, so on the weekend my younger brother Rick, 56 years old and a mechanic for 35+ years assisted and we removed the transmission.

I've been told on another forum that the scattershield needs to be centered to the crank as it appears the flywheel wore unevenly. I mentioned this to brother and he said in the 35+ years he has worked as a mechanic he has never had to do this and has never had any problems. He said this must be something that needs to be done to scattershields only...

So the question is do GM bellhousings have to be centered to the crank? I ask as I am contemplating of tossing the scattershield in favour of a GM two piece (open bottom) bellhousing ....
Having to align these "bullet proof" bellhousings is not that uncommon, I keep a supply of offset dowels and thin front end alignment shims for this very purpose as this often has to be done in 3 dimsnional space, not just getting the tran's input shaft centered but getting it straight in plane to the trans as well. Actually having to "tune up" the factory parts for alignment has to be done from time to time. I'd say most people don't experience this as for a production daily driver quite a bit of missalignment will be tolerated with acceptable result and life span; racing is a different story.

Bogie
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Old 10-29-2013, 08:26 PM
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I have heard the stories and seen pictures, and admit the mechanics for the failure exist. I feel the aluminum and factory steel bells that came on the performance OEM 4 speed bigblocks of the 70's are more than capable of handling the power they produced. Not to mention handle a generous amount of clowning and abuse. Not sure about racing, and that level of use. Fine for a dealership or enthusiast level for sure.

What they cant handle is operator error. Trying to get ridiculous miles from a clutch or whatever.
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