Need Help Diagnosing Engine Knock


IHC in the early to mid-fifties.

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Golden Jubilee
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Post Tue Apr 20, 2021 5:36 pm

Re: Need Help Diagnosing Engine Knock

The rocker stands on the SD's and BD's (and BG's) are bolted down with the cylinder head bolts. An entire row of head bolts would have to be loosened to raise the rocker arm shaft. Might be able to do it, but I can see it causing me more problems than I might solve. Skill level comes into play. :lol:

Golden Jubilee
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Post Tue Apr 20, 2021 6:41 pm

Re: Need Help Diagnosing Engine Knock

I'll have to take your word for it, I don't have anything in terms of manuals that cover the small OHV six. Having said that, I haven't seen that in other engines. 1st it would require really long bolts, to pass thru both the rocker stand and the head into the block. 2nd the longer the bolt the more area to stretch, it is just poor engineering.
The other sixes IHC designed used separate bolts to hold the head down and the rocker stands on.
When some were dealing with broken head bolts in 855 Cummins, they would replace the bolt even after the head gasket leaked combustion gases and not change the head gasket. Just torqued it back down.
Unless the two parts held together and sealed by the gaskets are moved relative to eachother, the seal will not be broken.
Many headgaskets used to have to be re-torqued, with the bolts loosened and then brought back to the torque after the engine had been in service for a while.
I did find a breakdown of the small 6 and it does look like you are correct, but that wouldn't stop me from removing' the rocker shaft without head gasket replacement.
Sorry to have ever doubted you!
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Golden Jubilee
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Post Tue Apr 20, 2021 8:38 pm

Re: Need Help Diagnosing Engine Knock

You won't doubt me half as much as I do.

Rusty Driver
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Post Tue Apr 20, 2021 9:00 pm

Re: Need Help Diagnosing Engine Knock

cornbinder89 wrote:The bearing in question has 80K miles on it, so will not look new. Little specks of dirt and a scratch or two will not cause a knock. If it was worn into the copper plate or thru the copper then it would be of concern.
An engine doesn't have to be "blueprinted" to run well for a long time.
Chevy survived a long time on dipper tubes and splash oiling.


Sorry I disagreed with your bearing opinion. Didn't mean to cause a rant. I'll be watching from the side lines now.

BTW Paul, what is the clearance of your bearing measured with plastigage with a good crank throw? Either condemn it or accept it and move on from there.

Dennis
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Golden Jubilee
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Post Tue Apr 20, 2021 9:33 pm

Re: Need Help Diagnosing Engine Knock

I'll confess that I didn't measure with plastigauge this time. When I rebuilt the engine the journals were all turned and I did carefully measure them at that time. This little teardown I really only wanted to find the cause of the knock, and mostly to eliminate the rod as a cause of it. So when the bearing surface was still intact, I just reinstalled it.
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Golden Jubilee
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Post Wed Apr 21, 2021 6:20 am

Re: Need Help Diagnosing Engine Knock

My vote is piston slap , wouldn't you be able to see a wear pattern with the piston all the way up ?
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Golden Jubilee
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Post Wed Apr 21, 2021 6:47 am

Re: Need Help Diagnosing Engine Knock

I wasn't able to see a wear pattern, but then I'm laying on my back in a dark garage with the engine still in the pickup and the crank and rods attached, so the view is really restricted. Counterweights on that crankshaft are huge when it comes to trying to see around them. This noise is a more distinct hammering than I would expect for piston slap, but my experience there is based on youtube and google, so I certainly can't rule it out as a possibility.

I'm still thinking that my best chance of finding out the cause of the noise is to go from what I know stops it. A feeler gauge, smaller than the valve gap, inserted on the valve, stops it. I'm fairly certain it isn't unloading the cylinder, as it's smaller than the gap. Compression and leak down testing seems to rule out a broken valve, one stuck open, etc. I have no idea whether cam wear is an issue. Just not something I can look at and say, "that's bad" or "that's good". I posted some pics of the cam, and if anyone has an opinion from those, I'd appreciate hearing it. That would leave rocker arm, push rod, and lifter. I don't find any play in the rocker arm on the shaft. Unless I'm mis-thinking it, I figure the next step should be to take the side cover off and get a view of the push rods and top of the lifter and bore. And then maybe swallow hard and unbolt cylinder head bolts to raise the rocker shaft enough to get the push rod and lifter out.

Golden Jubilee
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Post Wed Apr 21, 2021 10:40 am

Re: Need Help Diagnosing Engine Knock

If you set the valve lash using the dial indicator method, you take any wear in the parts out of the equation. If the tip of the rocker is worn, such that the gap is not even, the feeler gauge will say one thing and the actual clearance is another.
Kind of like setting points with a dwell meter vs, with a feeler gauge, one is an approximation, the other measures the exact thing you are trying to set.
I'd start there.
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Golden Jubilee
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Post Wed Apr 21, 2021 11:04 am

Re: Need Help Diagnosing Engine Knock

I do need to be more precise in my valve lash setting, and doing it with a dial indicator is a good tip. But the noise I'm dealing with isn't ticking from too much gap, it's a banging. If I adjust the lifter so that at top dead center I have just a few thousandths of clearance, but am certain it isn't holding the valve open, the banging goes away, even starting cold so there isn't a change in gap due to engine warming.

Golden Jubilee
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Post Wed Apr 21, 2021 11:06 am

Re: Need Help Diagnosing Engine Knock

Paul sent me a short video running, and slipped his feeler gauge in between, and the noise stops, it's weird.
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