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Pushrods collapsing?

PostPosted: Fri Jul 22, 2022 6:01 pm
by pappas
My friend has a normally aspirated Aerovee in his Onex. He did not build it. During maintenance, we noticed that 2 of the chrome moly pushrods were collapsing. The pushrod tips look like they are being driven into the pushrods and the tips could be pulled out by hand with almost no resistance. We noticed that those valve adjusters were screwed all the way in but the valve lash was still way too wide. Unadjustable as they are.

I noticed that 3 of the 4 rocker assemblies were sitting on top of 4 shims and the 4th was on 3 shims. I know that is likely to be a build error.
Additionally, a couple of the rocker arm pushrod cups are showing signs that the oil passage holes are becoming elongated.

Does anyone have any insight as to what is causing this? I thought someone here has likely seen this before.

Re: Pushrods collapsing?

PostPosted: Sat Jul 23, 2022 2:16 pm
by Onex107
I take it that this is just on one side? I think too many shims would cause this but also it could be that the push rods where cut too short when they where made. The different amount of shims is strange. Compare the length of the push rods. They should all be the same length even if it's wrong. The cylinder shims also come into play here. Do you know the combustion ratio? You need to know more about this engine.

Re: Pushrods collapsing?

PostPosted: Sat Jul 23, 2022 6:15 pm
by Area 51%
Too many shims would indicate compensating for pushrods that were too long. Deformed pushrods at the ends probably indicate the units were overheated during the installation of the tips. An annealed pushrod is never a good thing.