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Old 03-16-2024, 01:36 AM
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Default Cold set valve clearance for inital start up

I will be assisting in starting an L78 for the first time since the mid 80's tomorrow. We want to go over the valve clearances first, just to be certain they are acceptable for start up. How much clearance should we add to the hot spec to be close once warm ?
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Old 03-16-2024, 04:14 AM
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You may get 10 answers from 10 different people.

For cold start, I always added .002 to the hot lash spec on a small block. Amazing how often they ended up being spot on hot.

How much longer are the pushrods on the BB? I would think you would be safe at .003.
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Old 03-16-2024, 11:34 AM
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Thanks Lynn, that was my thinking too. Minimum .002, max .004. Been 51 years since I had a solid lifter cam and did this.

A guy in the Chevelle Club has this and we are descending on his home/shop today as a club tech/work/learning session and should be interesting. About half of the members, including the owner, weren't born yet when this engine was made.
Then there's us "seasoned veterans" that still have point files, feeler gauges and dwell meters...
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Old 03-16-2024, 10:18 PM
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Well how did Dereks car run? I should have joined just for this event
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Old 03-17-2024, 01:13 AM
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Originally Posted by dustinm View Post
Well how did Dereks car run? I should have joined just for this event
You didn't have to join, just show up...shoulda said something...

It doesn't. Turns out the PO had been in it and changed the cam to a hydraulic of unknown specs. We could get it to fire, but not start. Sounds just like a jumped timing chain to me. I kept feeding more advance in and it would "run" on the starter, but stall as soon as the key was let up.

#1 exhaust valve had a lot of play in the rocker and we thought it might have a flat lobe. I turned the nut down to remove the play to see if it would open the valve better and the valve stuck full down and the piston hit it. The spark plug was rusty when we removed it and that wasn't a good sign either.

At that point we knew we needed to remove the head, so a few of us jumped on it and had the head off in about 30 minutes only to find..... the valve head was broken off and the cylinder wall is severely broken, presumably from water in there in the past and freezing. The valve had been stuck open a long time as the seat is very rusted as well as the remaining valve stem and the whole exhaust runner.

He has several big blocks to pick from to replace it. It is a 138 car with date correct 12 bolt 3.55 posi and Muncie trans, built 3 days apart. The trans build date does not have an A or B after to determine which one it is. I don't recall if the '69 M22 would have the larger output like a TH400, but this one does not, so presuming it's an M20 or 21 with the gear ratio.
He likes the car and says he plans to keep it, but money talks with Derek.
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1970 Chevelle SS
1966 Chevelle SS
1967 Camaro ss/rs
1938 Business coupe, street rod
2000 FXSTS, original owner, 13k miles
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Old 03-22-2024, 09:46 PM
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1969 m22’s have the small output shaft & 10 spline input shafts , the 1970 Muncie’s were changed to the fine spline input shaft & larger 400 turbo style output shafts I believe…
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Old 03-23-2024, 04:08 PM
L72Chevelle L72Chevelle is offline
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Quote:
Originally Posted by ban617 View Post
1969 m22’s have the small output shaft & 10 spline input shafts , the 1970 Muncie’s were changed to the fine spline input shaft & larger 400 turbo style output shafts I believe…
Only the 70 LS6/LS5 M22 had the larger input/ output. In 71 they all changed to 26/32.

Last edited by L72Chevelle; 03-24-2024 at 04:03 AM. Reason: Added LS5
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Old 03-23-2024, 04:59 PM
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Quote:
Originally Posted by L72Chevelle View Post
Only the 70 LS6 M22 had the larger input/ output. In 71 they all changed to 26/32.
LS5 also....
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