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821-30 Rebuild/Bent Push Rod

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Fred:
Help I am into a full rebuild on my 821-30 the engine was originally built in 1969. The rebuild includes a re-profiled cam done by Crane Cams in Daytona before the closed up shop. 45 DCOE rebuilt, Headers, and the distributor has been modified with an optical switch. Looks like the head has been saved and the valves stems cut during a previous owners rebuild.

The main work started last May working with Renault USA in Springfield Oh. Had issues with the head bolts, fixed. Valve springs turned out to be way under spec at 200 Deg F, replaced with early !964-1967 MGB duel springs. Two rocker arms were damage, one was cracked, found a lightly used full set from Precision-Marine from 1965-1969 Mercury Marine 80HP inline 4 Renault engine, exact fit work great.

How the issue, in setting up the engine the number two cylinder intake valve is bending push rods at the proper lash setting from the Cam Data sheet .010. The issue is not immediate but after a number of Revolutions. If the lash is set to .014 no issues. Springs have been check for binding no issue, even went back to original springs and still an issue.

Anybody got an idea what is up? Maybe just a tolerance build-up that valve, spring and retainer combination?

Thanks
Fred
 

GavinT:
G'day Fred,

Are the valves hitting the pistons?

That's what I'd be checking, particularly in light of your saying the head has been shaved.
Bending pushrods and breaking rockers could easily be from that same cause.

In normal service rockers and pushrods don't seem to be a problem.

That would be my 2 cents worth.

jbcollier:
+1 on Gavin's suggestion Re-profiled cam = greater lift and perhaps more duration.  Shaved head = less piston/head clearance.  Clay the pistons and see how much clearance you actually have.  Measure your head to see if it is below the minimum thickness.

Fred:
G'day
Thanks for the comment it is a logical explanation, but that's what strange, there is no indication of valve to piston contact.
Just seems like opening the lash by .004 it works but make the standard Valve Lash noise. It seem to me that if it is not piston valve contact it is some kind of a tolerance build up on that valve,springs,retainer and keeper. Next will be measuring the other three intake valve combinations.
But we'll take a real hard look at the number two piston.
Ta
Fred

GavinT:

--- Quote from: Fred on Saturday,December 16, 2017, 07:34:29 AM ---Thanks for the comment it is a logical explanation, but that's what strange, there is no indication of valve to piston contact.
--- End quote ---

Fred,
Was the piston to valve clearance checked when the engine was dry assembled? (I'm presuming it was dry assembled)

I'd suggest if a .004" lash difference produces the breakages or pushrod bending you're experiencing and only in #2 cylinder, then it's quite possible #2 piston is a little higher than the others.
That is to say, #1, 3 and 4 may be only a poofteenth (engineering term) away from hitting their valves.

On the road, if you sink the welly in, they may all hit. Valve trains are designed with sufficient clearance to accommodate this.

What leads you to believe there's a tolerance stack happening on #2 cylinder and not the others?

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