Low end knock?

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mike2u
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Re: Low end knock?

Post by mike2u » Sat May 13, 2017 7:50 am

All plugs are the same and correct for the engine. A tired engine I believe. But I'm still stumped on why the back to plugs remain cold.


motto
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Re: Low end knock?

Post by motto » Wed May 24, 2017 3:16 pm

Almost two weeks since the previous post. Surely some progress has been made in identifying the problem/s?

David

mike2u
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Re: Low end knock?

Post by mike2u » Sat May 27, 2017 7:53 am

Sadly not much. I removed the head and am going to take a closer look at the valves. The walls all seemed in good condition, no excessive wear or scoring. Head gasket also seemed good.

motto
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Re: Low end knock?

Post by motto » Sat May 27, 2017 2:49 pm

What you found with the head off is what I would expect - no apparent problem. The compression check indicated that.
Have you had a good look at the valve springs? Particularly the inlet on #6 cylinder. Broken sections can wind into each other and look ok at a glance as they appear little different to a compressed spring. Another (slim) possibility is a valve fractured through the peg slot or a broken or displaced peg which would have the same effect as a broken spring.
If all is mechanically ok the only remaining possibility is spark which is easy to check.

David

mike2u
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Re: Low end knock?

Post by mike2u » Sun May 28, 2017 10:35 pm

The engine had a good strong blur spark on all cylinders. I did however find that the distributor was off, ahead of where it should have been. I feel confident that this would explain the miss on the read cylinders, but while i have the head off. I would like to figure out the confession. The valves appear pretty burnt at a closer glance, and I'm going to delegate this one out to an expert for a second opionon on where to go from here.

I appreciate all the help, will update as work progreses.

motto
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Re: Low end knock?

Post by motto » Sun May 28, 2017 11:25 pm

mike2u wrote:I appreciate all the help, will update as work progreses.
Please do, this one has me intrigued.

David

mike2u
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Re: Low end knock?

Post by mike2u » Sat Jul 22, 2017 8:36 am

Update. I pulled the head off as mentioned, and the carbon buildup under the valves was substantial, but that was the only thing that stood out. Cleaned it all back up and going to fire it back up and see what happens. Somehow I don't think this will fix it though. Worst case scenario, are there any good reliable engine rebuilder in Minnesota that anyone could recommend?

mike2u
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Re: Low end knock?

Post by mike2u » Mon Jul 24, 2017 3:27 pm

For anyone still reading this. I did finally manage to figure out my issue. The brake booster was leaking slightly, and that vacuum line sits right at the rear of the manifold. The air leak down at the booster was causing the air to be sucked into the rear of the manifold, and that was leaning out the 2 rear cylinders...

I am having a problem getting the manifold gasket to seal. I cleaned the surfaces real well, but it just leaks exhaust. I suppose I will probably have to get the manifold machined smooth. Not sure if there are any other tricks to getting it to seal. I really don't want to go through another gasket.

motto
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Re: Low end knock?

Post by motto » Mon Jul 24, 2017 5:20 pm

Hi Mike
Yes, still following the story and glad that you have finally got it sorted. Artificer was very close to having the answer some time back. Accurate vacuum gauge behaviour analysis would have most likely identified the problem immediately. Trouble shooting is much more difficult when you are not on site.
If you want to stop manifold gaskets from failing you had better get the manifold machined flat

David

smithtw
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Re: Low end knock?

Post by smithtw » Tue Jul 25, 2017 6:05 am

Really, I never could get the knock out of my JXD. Decided take it out and send it to rebuilder again. Only had less than a hundred miles on it. No one in years could find that knock.

mike2u
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Re: Low end knock?

Post by mike2u » Tue Jul 25, 2017 9:03 am

Just out of curiosity l, what does one of these Hercules cost to do a full rebuild. Just ballpark

smithtw
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Re: Low end knock?

Post by smithtw » Wed Jul 26, 2017 6:35 am

Don't remember, its was several years ago. The person I'm sending it to said it won't be that much because he just has to find what's wrong and to find and fix what's knocking. I'd expect a new rebuild to be a couple thousand though.


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