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Old 03-06-2021, 08:43 AM   #1
Jakno
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Default 59A low compression #4 cyl

Purchased a Project 33 PU several years ago complete with 59 engine. Have decided to get going on completing the truck. Started with checking the engine for issues. Compression check shows all cyl except # 4 to be 80 to 95 lbs. # 4 cyl is 34-40 lbs .All these cylinders are original parts except, #4 cyl intake and exhaust valves have been replaced. The low compression in #4 does not appear to be a valve problem although I am going to replace them with VanPelt valves.
The cylinder walls are what you would expect in this original engine and all 8 cylinders are consistent. I also have new head gaskets.

Would you share your thoughts on anything you might try before I have to tear down the engine. ..... Thanks
Attached Images
File Type: jpg 33 PU.jpg (126.4 KB, 39 views)
File Type: jpg 59A #4 cyl.jpg (116.6 KB, 65 views)
File Type: jpg 59A Right Side.jpg (115.0 KB, 58 views)
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Old 03-06-2021, 08:53 AM   #2
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Default Re: 59A low compression #4 cyl

You could replace the head and do a leak down test to find problem.
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Old 03-06-2021, 09:10 AM   #3
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Default Re: 59A low compression #4 cyl

Since you've come this far, why waste a set of head gaskets on it - when you really don't know the issue. If it was mine, I'd take it all the way down - being careful to label where all the parts go (pistons, bearings, etc) - and check it out in detail. Depending on what you find - maybe you get away with new rings a cylinder hone and a valve job. If you're trying to do it on the cheap, then you might get away with some basic/simple stuff - all depending on amount of wear and condition of everything.

Me - I'm never that lucky and I'm too particular anyway - I always end up with a full rebuild! LOL
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Old 03-06-2021, 09:41 AM   #4
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Default Re: 59A low compression #4 cyl

In pic #2, is that a burn mark at 11:00 on the exhaust valve?...... Mark
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Old 03-06-2021, 09:42 AM   #5
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Default Re: 59A low compression #4 cyl

Donít shoot me, but now is the time to tear this motor down and have it hot tanked and magnifluxed. You may have a crack in the valve chamber that you canít see with the naked eye.most small cracks can be fixed. Good luck.
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Old 03-06-2021, 10:45 AM   #6
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Default Re: 59A low compression #4 cyl

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Thanks for your help and advice which is all good. I agree a full rebuild is what it will need eventually. My problem is I currently have one in the shop being rebuilt for my 35 PU and I'd like to use this engine shot term. FlatFord8, I'm quite certain that the mark at 11 o'clock is not a burn mark.
Question - If I had a stuck piston ring on cylinder 4, could that cause low compression and has anyone ever been able to free it with out pulling the piston. ?
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Old 03-06-2021, 11:07 AM   #7
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Default Re: 59A low compression #4 cyl

I can completely understand the desire to not end up with two flatheads in the machine shop at the same time. I think for the time being, you should clean up the surfaces and re-install the head with a new gasket. Then, as "marko39" suggests, do a leak down test to find out where the problem is. Depending on what you find, I would button it back up and fire it up. You didn't say how long it had been sitting, but things can get gummed up over time. If the engine doesn't make any funny noises and has good oil pressure, using it may just loosen up anything that may be sticking. Proceed step by step, and there is a pretty good chance that you will end up with a good runner. (Don't forget the MMO and maybe some SeaFoam.)
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Old 03-06-2021, 11:17 AM   #8
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Default Re: 59A low compression #4 cyl

Mr. Tubman, thanks for your response and idea's. Your advice is what I'd hoping to try as a Hail Mary fix. The engine has been out of service for at least 10 years maybe longer.

Would you mind sharing on how to go about a "Leak Down test ". I'll try a Forum Search as well.
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Old 03-06-2021, 01:27 PM   #9
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Default Re: 59A low compression #4 cyl

Google might be quicker. Spray some penetrant around that piston for a few days and maybe it’ll free the ring....... Mark
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Old 03-06-2021, 01:31 PM   #10
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Default Re: 59A low compression #4 cyl

https://www.mobil.com/en/lubricants/...-leakdown-test I found this in my stash of info...... Mark
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Old 03-06-2021, 01:32 PM   #11
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Default Re: 59A low compression #4 cyl

Quote:
Originally Posted by Jakno View Post
Purchased a Project 33 PU several years ago complete with 59 engine. Have decided to get going on completing the truck. Started with checking the engine for issues. Compression check shows all cyl except # 4 to be 80 to 95 lbs. # 4 cyl is 34-40 lbs .All these cylinders are original parts except, #4 cyl intake and exhaust valves have been replaced. The low compression in #4 does not appear to be a valve problem although I am going to replace them with VanPelt valves.
The cylinder walls are what you would expect in this original engine and all 8 cylinders are consistent. I also have new head gaskets.

Would you share your thoughts on anything you might try before I have to tear down the engine. ..... Thanks
Can you take a pic without the gasket on ?
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Old 03-06-2021, 02:28 PM   #12
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Default Re: 59A low compression #4 cyl

Question: Was the compression testing performed wet or dry (oil in the cylinder for wet)? A wet test should tell you if it is a ring issue.
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Old 03-06-2021, 02:46 PM   #13
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Default Re: 59A low compression #4 cyl

Thanks for the help everyone. I have removed the head and going to put the penetrant in the cylinder for a couple of days. I'll give it a short turn now and then. Flatford 8 ,Thanks for info on the leak down test. I'll give that a try after the penetrant.
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Old 03-06-2021, 04:04 PM   #14
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Default Re: 59A low compression #4 cyl

A sticky valve (taking too long to close) could cause your problem too.
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Old 03-06-2021, 05:13 PM   #15
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Default Re: 59A low compression #4 cyl

Thanks Mr Newland. A sticky valve might explain why I get different readings each time I do a compression test Ex.. readings of 20 PSI, 35 and 40 PSI
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