Diagnosing scored cylinders: any rules of thumb?

[GN SBS]

Hi folks,

A friend and I pulled the pistons out of my motor yesterday afternoon and upon inspection of the cylinders noticed some scoring.

In each case the scoring ran vertically and tended to be centered in the cylinder on the walls not next to the adjacent cylinder (description make sense?). It was not deep enough to feel or catch a fingernail in. Any rules of thumb on this?

Also, the part numbers on my pistons differed from those posted on gntype.org: 25531260 http://www.gnttype.org/techarea/pictureguides/pistonguide/38turbopiston.html

I've mislaid the paper on which I wrote the number, but they were labeled hepolite as above and the number was close. Any thoughts?

thanks,
Scott

 

[steve hughes]

Was this a erbuilt engine? Could have been caused by alot of things. Engine not clean on assembly, overheated, detonation, overly rich washing oil off cylinder walls, pisons or rings not fitted correctly, to much timing, bad air filter letting dirt in the engine, turbo shrapnel. Hard to tell without seeing it. Do the rings still fit on the pistons tight? What do the top of the pistons look like? What do the plugs look like? Where you racing it at the time? Info???

 

[Quick6'n'-K.C.]

straight up and down lines not next to the next piston, but closer to the lifter valley and outside of block?

sounds like piston skirt wear-


ive seen it in everyone ive pulled apart, are the cross hatches still there from the last hone?

 

[GN SBS]

Originally posted by Quick6'n'-K.C.
straight up and down lines not next to the next piston, but closer to the lifter valley and outside of block?

Yes, that's it. Again, they're not deep enough to feel with a fingernail. Can see some crosshatching.

Tops of pistons have deposits, tan and flaky on 2 of them; rest have carbon deposits.

The engine has not, to my knowledge, been rebuilt, but I'm not the original owner. Head gaskets were stock, pistons look stock, rear main seal has been replaced, but that's about it in terms of changes.

Something caused wear in cam and crank bearings and after taking things apart found excessive endplay (and damage to compressor wheel) in the turbo. I don't know which caused which.

Just looking for feedback on what to do giving this type of scoring. Re-ring and go or other options?

Scott

 

[J Banning]

Probably from piston skirt wear. This would show on both sides of the cylinder opposite from the wrist pins and would be lower down in the cylinder.

 

[Quick6'n'-K.C.]

if you feel confident reringing the engine, then yes that is what i would do-
matter of fact thats what i did this spring on a 156K untouched motor-

slight hone for 8 seconds with trans fluid on each cyl, clean and clean and clean the bores out with soap and water, then oil on a rag- you wont believe how much metal comes out on the rag-

i used napa full circle rings, and clevite bearings-

sounds like the bearings are just worn,, was it down to the copper on all?
do all the rod caps face away from each other? as in do the angles of the top of the rod caps face away from each other?

hope this helps some
BW

 

[GN SBS]

Originally posted by Quick6'n'-K.C.
was it down to the copper on all?
BW

In general no, but there were fairly deep gouges in a few places on both crank and cam bearings.


Thanks for the responses to all!

Scott

 

[GN SBS]

Piston part numbers found

The piston part numbers are as follows:

25531068 (Hepolite 21917)

Any information on these? I've started a new thread on the piston IDs-- please reply here: http://www.turbobuick.com/forums/showthread.php?threadid=95103&referrerid=1129

Scott