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Thread: compression

  1. #1
    Commander Member brooker's Avatar
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    compression

    Hi everyone , situation is acquired car checked all compression all was good 140-150 range had sump off even seen fresh hone marks unfortunately i never could contact previous owner, to ask about car , so i am assuming since hone marks in bore was still visible the motor had not been long reconditioned, now one pot has lost compression , after wet test in bore compression built and held , so i am assuming its definitely a broken piston ring,,Now would it be better to replace all rings or taking in to account may have just been a bad ring and only replace the effected piston rings any advice and experience would be appreciated ,, Ray

  2. #2
    President Member TWChamp's Avatar
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    I don't recall the story. What year and engine, and what is the problem?
    Sounds like you had low compression on one cylinder.
    If so then do a leak down test while the pan is off and see if you hear air getting past the piston with low compression.
    Looking at the hone marks from the bottom most likely isn't showing the part of the cylinders where the rings rub.

  3. #3
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    I see two choices

    1st full rebuild

    2nd pull head and piston. Inspect for condition.

  4. #4
    Commander Member brooker's Avatar
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    its a 62 hawk v8 all cylenders have a compression of 140-150 except 1 and now its about 50 ,

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    Golden Hawk Member StudeRich's Avatar
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    In the States you usually cannot find ONE Piston Set of Rings, unless you find a shop that does a lot of Stude's and has a broken Set laying around.

    When you get the Head from the side that has the weak compression off, you will better know whether to do a complete re-ring or just one, by the wear and size of the Bore where the Rings run.
    StudeRich
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    Proud '54 Starliner Owner




  6. #6
    President Member TWChamp's Avatar
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    I would do the leak down check first to determine if it's a bad intake, exhaust, or rings, then pull that head and let us know what you find.

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    It would be very strange to have a broken ring. If so you could see vertical scoring on cyl wall with a scope. A leaky or mal-adjusted valve is possible and cheaper to fix. Might want to adjust valves. If engine worked on by unknown perpetrator could have ground exh valves too thin and you are burning one out. Tell us what you find!

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    I agree with TWChamp, the cylinder in question needs to be pressurized in order to find whether there is a leaking valve or something has failed on the piston. The 194 Chevy Six uses the same rings as a 259-289 Studebaker so you might be able to find a set of rings for one piston. You can also squirt a bit of engine oil into the offending cylinder and then check the compression. If it increases, then you have a problem with the piston, if not, then you have a valve problem such as a burnt exhaust valve or possibly you have exhaust valve seat recession which will decrease the valve lash to the point of holding the valve open. If you have seat recession, the valves can be adjusted, but the only permanent fix is to pull the heads and have hard seats installed in the exhaust valve ports. Bud

  9. #9
    Commander Member brooker's Avatar
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    20180625_072700.jpg20180625_073848.jpg Ok update i did the oil in cyl and it bumped compression to around 100 , without oil squirt in cyl was about 50 the cylinder bore is till covered in hone marks and there is no scouring on bore the vales in pic is the ones that have low compression,, all the pistons have zero movement everything is tight as you would expect,the piston has a 20 marked on the top they are flat so i am presuming they are a standard 20 tho over ,,

  10. #10
    Commander Member brooker's Avatar
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    20180625_072720.jpg20180625_073010.jpg20180625_074038.jpgthe valves in this pic is same as all the others

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    ts a 62 hawk v8 . . . . ,the piston has a 20 marked on the top they are flat
    A bit of clarification please. We Yanks would expect to find a 289" with dished pistons in a '62 GT, but what did South Bend send to Oz? Flat top pistons are usually in the more common 259" and the less often found R1.

    jack vines
    PackardV8

  12. #12
    Commander Member brooker's Avatar
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    i wish i could help you jack , but i hey im just learning about studes, and its always a bit of a hassle finding enough knowledge here ,,engine #P89602 with the 3 rings at the end and like i have said i have no knowledge of whats been done to motor ,

  13. #13
    Commander Member brooker's Avatar
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    i know we live in the land down under jack , but the pistons are still flat , south bend may have said stuff the aussies they can have the rejects ,,,,give them all the flat ones

  14. #14
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    Unless my eyes are deceiving me, it appears that the exhaust valve has a razor thin margin and is quite possibly showing signs of valve seat recession both of which can lead to low compression. Bud

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    Quote Originally Posted by PackardV8 View Post
    i

    A bit of clarification please. We Yanks would expect to find a 289" with dished pistons in a '62 GT, but what did South Bend send to Oz? Flat top pistons are usually in the more common 259" and the less often found R1.

    jack vines
    Maybe it is one of your favorite surprises...a 289” block that someone put a 259” crankshaft and pistons in.
    It would be simple to measure the stroke to find out.

  16. #16
    Commander Member brooker's Avatar
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    pistons are approx 90.5 mill od stroke of bore is 93 mill

  17. #17
    President Member TWChamp's Avatar
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    93 mm equals 3.66".

  18. #18
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    Quote Originally Posted by brooker View Post
    pistons are approx 90.5 mill od stroke of bore is 93 mill
    Either a 259" or 289" +.020" bore diameter of 3.5825" would be 91mm. A 3.625" 289" stroke would be 92mm.

    jack vines
    PackardV8

  19. #19
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    A 259 stroke would only be 82.5mm so that kind of rules out the transplanted crank. Flat top pistons in a 289 seems a bit racy... The comp rising to 100psi when oil added points at a bad ring. Since you have the heads off the next step would be removing the pan and popping out the piston...

  20. #20
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    And to save yourself some agony, just turn the head upside down and pour some gas in the offending cylinder. It should stay there.

  21. #21
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    My experience with pistons having a broken ring is that the piston groove is beyond repair or worse...

  22. #22
    President Member TWChamp's Avatar
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    Quote Originally Posted by GrumpyOne View Post
    My experience with pistons having a broken ring is that the piston groove is beyond repair or worse...
    I agree with the ring land being bad if the rings are broken. Might be time for all new pistons and rings.

  23. #23
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    Quote Originally Posted by TWChamp View Post
    Might be time for all new pistons and rings.
    You'll be voted off the CASO island for that. Any true believer saves all his old parts. He'd pull a used piston and rings out of the bucket, wipe it with a greasy rag, drop it in and she'll run another hunnerd thousand miles.

    jack vines
    PackardV8

  24. #24
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    Three cheers for Jack!! Sounds interesting: basically you cannot trust anything that was done to this motor. Once again as noted above that exhaust valve looks like you could shave with it.

  25. #25
    Commander Member brooker's Avatar
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    i will remove engine and go over it check everything, a quick question also is it easier to remove trans and engine together and if i do both do i need to remove front cross member or can the transmission be guided out successfully without removing it thanks in advance for your reply's Ray

  26. #26
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    A broken ring sometimes happens on installation. Or mixed up .

  27. #27
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    Brooker: Before you remove engine, pull the head and install and seat a new exhaust valve. You can take a real close look at the cylinder walls for vertical scoring which is the tell for a boken ring. It's a lot easier and safer to remove the cross member.

  28. #28
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    while you're at it, and the head is off, remove the oil pan and pop that piston out and check the rings carefully. (Remember there may be a ridge at the top needing to be removed first).

  29. #29
    President Member Jerry Forrester's Avatar
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    Quote Originally Posted by brooker View Post
    i will remove engine and go over it check everything, a quick question also is it easier to remove trans and engine together and if i do both do i need to remove front cross member or can the transmission be guided out successfully without removing it thanks in advance for your reply's Ray
    I wouldn't remove the engine until I knew what was wrong with it.
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    See all of Buttercup's pictures at https://imgur.com/a/tBjGzTk


  30. #30
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    I'd agree with Jerry, might be able to just change a piston in the car. . And/or the head.

  31. #31
    Speedster Member whitehawk759's Avatar
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    I hear a lot about a broken ring, but I do seem to remember when I was in high school, ages ago, that I was not careful enough aligning, or should I say not aligning, the ring gaps and produced a weak cylinder. It is possible that something as simple as that could be the problem. Just saying!

    BTW Those valve edges do look a mite thin.
    Don Watson
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  32. #32
    Commander Member brooker's Avatar
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    update , bores are slightly glazed gap between ring in bore .030 tho , 3 measurements taken in bore all consistent,

  33. #33
    Commander Member brooker's Avatar
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    20180715_161643.jpg can someone explain the difference between the 2 lifters i am guessing the one with the grove promotes a better oil flow ?

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