821-30 Rebuild/Bent Push Rod

[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]

Thanks for the comment it is a logical explanation, but that's what strange, there is no indication of valve to piston contact.

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?

[BDA]

Are you saying that when you turn it by hand, you don't bend the push rod until it's turned several revolutions? I have no explanation for that, but I would still check the following areas: More lash = less valve lift. and duration,  I think it might be worth putting some clay or other tell tale material or marker in the valve pockets of the pistons and make absolutely sure your valve isn't hitting your piston. Have you checked that your deck height is the same on all four cylinders? Next, I might also ensure that all your valves are the same length. Since you said they were shortened, it would be unfortunate if they weren't shortened properly. If an answer is still not found it is Less likely is that your push rods aren't the same length (is there any reason to suspect that your cam followers are not the same effective height?) and even less likely is that your rocker ratio is now off because of the replacement rockers you have but it might be worth double checking them. Probably the least likely is that you have a cam lobe that is too high.

[Fred]

I think the discussion on piston to valve clearance makes a lot of sense. Let me get that measured and we can go from there. And, yes I think some bonehead did not trim the valves correctly, which is one reason why I want to do a tolerance stack build-up on No.2 Valve system. The engine was running when the push rod bent, and again no valve or piston damage can be seen. So one area we are looking at is spring coil binding if the tolerances are off.
Thanks again to all for the suggestions.

[jbcollier]

Don't just increase the valve clearances to suit.  You need more space than that at high rpm: at least 1 mm but I would be happier with 1.5 mm.  Also, increasing the valve clearance changes the cam position on the lifter where it starts moving the valve.  A cam has opening and closing ramps to "ease" the valve open and shut.  Increasing the clearance moves the cam/lifter initial contact point off these ramps and can lead to severe stress/wear.

[GavinT]

Fred,
I'm not sure where you're going with the valve trimming thing. Were the valves too long?

Anyway, let's suppose the valve is 1mm to long (or 1mm too short).
Given you can adjust the lash to spec, then there's no reason to suspect valve length as the cause of the breakages/bending.
NB: The valves need to be the correct length but for other reasons.

Another question . .
In your initial post you said:

. . Springs have been check for binding no issue, even went back to original springs and still an issue.

Do you now think it is an issue?

How do you propose to measure the valve to piston clearance with the head on?

I think you're going to need to remove the head no matter what the cause.
What do Renault USA in Springfield have to say?

[Fred]

Thank for the help guys just fired up last night. This was a joint build I took the disassembled engine from my NC home up to Renault USA in Springfield Oh for the build. I had rebuilt the 45 DCOE Weber and Lumenition Distributor, had the cam reground by Crane Cams in Daytona Beach before they closed, and the pistons and sleeves reworked.
Looks like the boys in Springfield did have a valve clearance issue as you guys suggested which is now corrected by a thicker head gasket (the head was shaved somewhere in its life).
I developed a lot of data on valve springs/replacement if anybody is interested. We are using early MGB outer springs and the original inner springs.

Here is a run.

https://www.youtube.com/watch?v=gw5pMiL4AMA&feature=youtu.be

Thanks
Fred

[jbcollier]

Very nice!

[skippopotamus]

Fred, that is exciting!
I'm in the throws of an 821-30 rebuild for my car so I'm really happy for you.

[BDA]

Congratulations, Fred!  I'm glad you finally got it all sorted!

[dakazman]

Congratulations Fred,  Glad to hear what this block of metal should sound like.
Cant wait for the first drive video.

Dakazman

[Certified Lotus]

Gotta love it when you can listen to the engine rev. 125HP? That’s great!