Engine: compression

[brooker]

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

[TWChamp]

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.

[70Avanti2]

I see two choices

1st full rebuild

2nd pull head and piston. Inspect for condition.

[brooker]

its a 62 hawk v8 all cylenders have a compression of 140-150 except 1 and now its about 50 ,

[StudeRich]

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.

[TWChamp]

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.

[Jeffry Cassel]

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!

[Bud]

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

[brooker]

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 ,,

[brooker]

the valves in this pic is same as all the others

[PackardV8]

i

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

[brooker]

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 ,

[brooker]

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

[Bud]

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

[Studebakercenteroforegon]

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.