VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Broken intake rocker arms

I have a 51, 235 in my 52. 1/2ton. I just finished a frame off. The engine sat for 20-25 years before I did a frame off. I did not rebuild the engine. I did go thru it inspecting and cleaning the oil passages. cleaning and replacing some of the hyr lifters and all of the pushrods. It runs like a top with no smoke or knocking. Compression is between 100 and 105. Vacume steady at 19. I'm real lucky. Exept for one thing. I keep breaking intake rocker arms. All have broken except for #1. #6 broke twice.I usually get 20-40 miles before another goes. There seems to be plenty of oil to the rocker shafts. This as you know is a low pressure oil system. I've been told to remove the new valve guide seals. Any ideas? No exhaust rockers have broken. I have MMO in the oil and gas.
Glenn,

sounds like the lifters might not be compressing under load and pushing too hard on the rockers or more likely the valves might be sticking in the guides. Some thing is not moving correctly in the valve train. Are the push rods bending on the broken arms? Are the rockers breaking on the push rod or valve side? Might be best to remove the head and have a machinist inspect for problems.

videoranger,
Lifter theory makes sense. But, what would cause the lifters not to compress? Also it seems funny that only the intake lifters would do that.The arms are breaking in different places. Some on the valve side, one in the middle and some on the lifter side. The push rods have not bent. The engine doesn't have any signs leading up to the breaking. No popping, backfiring or other signs. It just all of a sudden loses alittle power and the pushrod starts to rattle. This thing runs ok on 5 cylinders. If the valves were sticking enough to break an arm you would think they would stay frozen in the guide. Not the case. You right though. Something isn't moving. Pulling the head is probably the best idea though. Thx.
Glenn,

If the lifters were pumping up you would have a miss and a very rough idle.
You have deposits on the valve stems or the guides are too tight.Squirt some MMo directly on the top of the guide (thru the valve spring) and pour some (a pint) thru the carburetor) with the engine running.If this dosen't help the guides will need to be honed out another .001" or .002".

Chevgene,
She runs smooth at idle. I've got MMO in the gas and oil. I'LL run a pint thru the carb. The valve guides have new o ring seals but, I may be able to stretch them enough to get some MMO in there. Any idea why only the intakes? Thx.
Glenn,

It breaks the intake rocker arms because the intake valves strike the tops of the pistons when the valves stick.The exhaust valves are recessed into the head and can not hit the pistons.Can also bend the push rods.

The stock seal used on the valves was the small O ring that fit between the valve cap and valve stem....don't mess with these.It an external shedder or umbreala type seal was used it will be difficult to lube the guides from "the out side" - with the stock set up you can get at the stem thru the spring.

If you suspect the lifters just back off the adjustment until they click and turn down just 1/2 turn.

Adding MMO to the gas is OK but not enough if your having a sticking problem....also the guides tend to get tighter as the engine heats up.

The problem may also be related to poor cooling through the head due to rust blocking the internal coolant passages. As the engine warms up the softer metal valve guides could be expanding enough to grab the valve stems. This could explain why the valves don't appear to be stuck when the engine has cooled. This seems much more likely than lifter issues. I still would advise removing the head and having it hot tanked and rebuilt to avoid further problems. Sometimes the easy fixes are like putting a bandaid on a broken leg.

there is a long string about this on www.stovebolt.com , with many ideas about what the cause. valve springs binding, are they right side up? keepers hitting the guides? wrong parts? and on and on. we want to be posted as what the outcome, thanks.