The Stovebolt Site Forums The Shop Area Engine Shop Duble head gasket

Here's a crazy question. Has anyone ever used two head gaskets on a head? Would it seal? My 235 head may have been milled too much. I'm looking at all options.

Sorry about the typo. Thats double head gaskets.

I have seen two gaskets used to reduce compression.

The engines were so low on compression when new, I can't imagine it having to much! You can safely run 9.5 on todays mid to high octane fuels. Joe

It might alter the torque specs but I'm not sure of that. As noted above the only difference should be lower compression.

Have you tried looking for shorter pushrods, or does this have nothing to do with your broken rocker issue?

Baldy,
Yes, I have tried shorter pushrods. I actually shortened mine 1/8". I still broke a rocker. I also bought the next shorter pushrod for a 216 but it was about 1" too short.All this together makes us think that the head may be milled too much.

1/8" shorter pushrods. can a head be milled over 1/8 and still have a sealing surface? what about your cam?

I would be interested in seeing a shortened pushrod that did justice to either end...how would it be done?

Stuart

I'm amazed it's breaking rocker arms instead of bending pushrods.

GEC52,

Would you mind explaining (again?) the history of your engine? Some people might not know what you have posted before.

Did the engine run OK prior to your problems?

Was the engine rebuilt and then the problems occurred?

Did you replace some parts and then the problems occurred?

Tim

As far as the need for a shorter or longer pushrod.The only adavantage would be to correct the rocker geometery .The geometry could cause a breakage issue.An easy way to check if you need a different length is to remove the rocker arm .Remove the oil film from the top of the valve stem and the contact area of the rocker.Use a permanent black marker and paint the top of the stem .Reinstall the rocker and adjust the valve .Turn the engine
360 degrees and remove the rocker.Look at the top of the valve stem and see if the contact is in the middle of the stem.If the contact area is away from the rocker stud you need a shorter pushrod,if it is closer to the stud you need a longer pushrod.As far as milling the head .125 it is possible but that is crap load to mill.Normal milling will remove .004-.005 at a time from the deck surface .Have you measured a head for thickness that has not been milled ? It would not be advisable to double up a gasket it wont seal.You may be able to find a manufacture that makes a copper shim to use with your gasket .Have you checked the valve stem height? Good luck

Maybe you have just got a hold of some bad rockers! Are the valves hitting the pston causing the rocker to break? Are they bottoming out on the guide? If it was just worked on, thats where I would be looking.... Joe

Boy I wouldn't do that. It would be almost impossible to get multiple head gaskets to seal. If you did want to do that, I'd recommend solid copper head gaskets and plenty of that copper gasket seal spray.

I ran my 235 with 60 thousandths shaved off the head to bring compression up to 9.25:1. (I cc'd my head to verify compression). I had absolutely no problem with clearance at all.

You should be fine.
My head, by the way, will be for sale in the spring when I pull my blown engine to drop a 350 in it. In case anyone wants decent compression in their 235.

mayby your valve springs wont compress any farther so its braking the rocker arm or the springs may be to strong i think your rockers are being over stressed some way

Just a little help...GEC52 will chime in on Tuesday or Wed...

He has had issues with rockers breaking...he has replaced several on different cylinders. He gets about 20 miles on them and them one breaks. Joe H is on the mark for what GEC figures is doing it...the head has been milled too many times... the intake (?) valve is flat and makes impact with a piston..not enough to wreck the piston, just enough to destroy the rocker.. GEC was thinking of trying two head gaskets to get a little more clearance between valve and piston....

further thought is that it takes the engine being warm and everything expanding just a little before the impact occurs...

Click on his profile and search previous posts...he has a couple of threads going on his problems...

His truck is looking VERY sharp..he just needs to get the rocker issue solved to get on the road....

I have a 58 235 he is looking at installing, but he would like to stay with his 216...

Just little more info on his problem to keep the answers coming until he gets back....

oh k, no amount of shorter or longer push rods will change the lift of the cam. i have heard of using 2 head gaskets, i think it would depend on the type of gasket, to work. possible a shim between two gaskets.
changing the pivot on the rockers is a thought, but i don't know what other rockers could swap.

This thread has been going on for some time now. I actually thought Glenn had the problems figured out.

Lots of ideas being tossed around, and who knows why this is happening. I will say this...If a valve were to hit a piston with enough interference to cause a rocker arm to break, the valve would bend, and stay bent. This would be obvious and have permanent after effects.

Cutting pushrods and installing two head gaskets will further cloud the issue. This isn't a common ailment for these engines and there is a reasonable answer somewhere.

Stuart

Did he have any seat/guide work done on the head? If he had seats installed, did the shop check the valve stem height before and after seat install? I've seen head work fail because valve stem height was not checked. Also if new guides were installed, is the guide height the same as the previous guides. How about valve springs, were they replaced, and are they possibly different than original, and bottoming out? Just a few ideas off the top of my head. Take it for what it's worth.

Wow! I sure got responces from you guys. For just a brief review. I have broken 10-12 intake rocker arms on my 51, 235. This is a car engine. It has hydralic lifters. The engine sat for 25 years in the truck before I got it. I got the truck thru a third party. The guy I got it from is dead now and the other two owners I don't know.I went thru the engine checking the bearings,compression and general condition. It turned out to be in pretty good shape and runs great. I had the head looked at by a guy who is also gone now. He pressure checked it, reseated the valves and milled the head just enough to clean and true the surface. How many times or how much it had been milled in the past I don't know. I pulled the head to check if the valve had hit the piston. There were no marks on either the piston or valve. I measured the cam lift and it came out to be as per Chevy specs. So, the lift isn't too high. If the head were milled too much the stock pushrods in effect could get too long since the rocker assembly would be closer to the block. The pushrod has a very big foot on it . I ground 1/8" off the foot and smoothed it out. After about 30 miles another rocker broke and one cracked. I'm pulling the head again to check the piston and valve. Does anyone know how you would check to see if the head is too short? There is no specific intake rocker that breaks. All but #1 has broken. If the height checks out I'll check the guides and valve height. If the head is too short I'll replace the engine. Also it just stopped oiling the rocker shaft so now I have to fix that. That is probably a crank shaft pull to get at the oil passages.

I can't believe there's no mark on the piston or valve if they are making contact. If it hits hard enough to break a rocker, there should be some evidence of contact. I would bring a piston up to TDC and compress a valve until it contacts the piston or binds against the valve spring. Measure this valve deflection with a dial indicator. I would suspect the wrong valve springs (coil bind) or cheap rockers. If a piston hits a valve, I would think a pushrod would bend first.
Scott

Glenn,

The plugged passage is usually a pretty easy 'in place' fix. If your rig has hydraulic lifters then I think a tube runs from the rear cam journal up to the center oiler. This small tube and its related fittings plug quite easily.

The pushrods would never actually be 'too long', but the geometry would be thrown off where pushrod meets rocker and rocker meets valve stem.

This would probably be minor and not cause problems. Although I don't know for sure, I think the head would have to have seen full out drag race service to have been milled too much.

A automotive machine shop would remove the least amount of material necessary to clean up a head. The 'clay in the combustion chamber' trick is the last word in determining clearance issue inside the engine.

It would be interesting to put a rocker arm in a vise and see exactly how much abuse it took before it broke. This is a very intriguing problem, and I hope you figure it out and share the results with us.

Stuart

Gec52,
Do a site search there is a tech tip on how to measure a 235 head for being overmilled http://www.stovebolt.com/techtips/milledheads.htm this article is what you need .Good Luck

Stuart,
I have pulled the oil line that runs from the rear cam connector in the pushrod compartment to the oiler. It was open. I don't get any oil to the tube. So, I has to be from the oil galley to the rear cam bearing. This passage has to be drilled straight since you can't drill around a corner. The passage from the rear cam to the pushrod compartment seemed to be open. Once I get the oil galley plate and spring off I should be able to find the passage (I hope). Anyone know where I can get new oil galley gaskets besides Chevs of the 40s?

Glenn,

You indicate you pulled the tube and it was clear, but how about the fittings the tube attaches to. These have a much reduced ID and I have seen them plug...tube is clear, fitting in block is plugged. Just a thought.

Stuart

Stuart,
The fitting and passageway from that side were clear. I ran a piece of wire down it and didn't get any gunk. The most probable passage then would be from the galley side. Wouldn't you think? I did pull the galley cover and turned the engine. I got good oil to the galley.So, I assertain that it must be the galley side passage.

Glenn,

I put in a link that outlines the oil passages in your engine. There is lots of stuff going on, and I don't know if it is as straightforward as it seems.

http://chevy.tocmp.com/1949_53shop/06engine/6_008.HTM

Stuart

#%@!*, sounds like only a hot tank will work. Is that what you think too?

Glenn,

Glenn,

I'm not sure! It seems to me that the line for the rockers is on the tail end of a large galley for the lifters. I haven't heard of the larger internal passages plugging before. If you could backtrack until you found pressure, then, using a air gun to help you, go forward until you found a blockage, you might have a chance.

Between a can of Brake-Kleen and a rubber tipped air nozzle, you should be able to 'strike oil' somewhere.

The fact that you have a car engine with hydraulic lifters, keep breaking rocker arms and aren't able to get oil to your center oiler seems too coincidental to me...it's all in the same general area.

I did see a note in the service manual that cautions about the gaskets on the oil distribution valve. There are two gaskets and they must be installed in a specific order. Keep us posted.

Stuart

Stuart,
I agree that the two problems seem to run hand in hand. However in my quest to find the rocker problem I did check to see that the rockers were getting oiled. They were and the lifters were filling. The rockers kept on breaking however. Lack of oil to this last broken rocker could be a factor since it is just now that the rockers stopped getting oil. But once again only intakes break.

GEC52 you may find that the rocker arms stop breaking when you get your oiling problem fixed.
I had a small block once that kept putting pushrod through the rockers and sumtimes would pull the stud from the head. it turned out to be a lubriction problem.

Stuart you beat me too it

Glenn,

I'm not sure where I was leading on my post. If the rocker were to seize to the shaft and break the rocker arm, it would be 'permanent and stationary'...you wouldn't have to hunt for the problem. I drove a 235 from San Diego to Arcata, which is almost 900 miles, with nary a drop of oil to the top end. It made noise and ran weird, but it never broke anything.

I was thinking more in terms of lifters going flat or instantly pumping up and affecting the rockers. This thinking is marginal too! The ONLY thing the intakes have in common is they are much lower (higher?) in the combustion chamber than the exhaust...nearer the piston!

The two pregnant questions are, why don't the fragile pushrods bend first, and if it is a valve/piston contact issue, why doesn't the valve bend, or the internals show evidence of contact.

The oiling system is large and feeds not only the cam bearings and lifter galley, but also the mains. These things won't run without lube. I think the passage is plugged just inside where the fitting screws in. Keep looking and let us know.

Stuart

Oh I'LL keep lookin.

I don't know my parts whern't seized together didn't even look to be gulled that bad. That is why it was so hard to trouble shoot.

1956-1965 we had lots of old 215 and 235's. the rockers would be sludged and running dry clacking like mad from no oil. Don't remember ever having a broken rocker. Are all the parts right for the engine?

as a side note, There was an aftermarket stud and oil-line kit that brought oil from the side of the block to the hold-down stud on the rocker shaft.

There is one item that hasn't been addressed yet, the clearance between the bottom of the valve spring retainer, and the top of the valve guide. It's a fairly simple process to roll the engine over by hand until an intake valve is at its full-open position, then try to force the valve open further by prying on the rocker arm. If the retainer is hitting the top of a valve guide, it should be difficult or impossible to move the valve further open. Also, check the valve springs for a "stack solid" condition, where the coils bind against each other before the cam is through lifting. A straightened paper clip wire should fit easily between the spring coils with the cam at full lift. An over-milled head could cause the retainers to hit the valve guides even if the springs don't stack solid. If the valve isn't hitting the piston, just have your machinist shorten the top of the guides a little. We do it on racing smallblock V-8's with high-lift cams all the time, without serious consequences.
Jerry