3.5mm Oil ring in 78 SC should have been a 4.0mm?

[psjoe]

not debating Mahle / KS Alusil.

What if this ring set:
930-103-986-00-M42
Piston Ring Set, sold per each cylinder, (95mm-1.5 X 1.75 X 3.5mm), 911 3.0 (1980-83), 911 3.2 (1984-89)

Was installed in a 1978 3.0 that calls for this ring set:
930-103-963-00-M42
Piston Ring Set, sold per each cylinder, (95mm-1.5 X 1.75 X 4.0mm), 911 3.0 (1978-79)

any problems with the 3.5mm oil ring v.s the 4.0 that should have been used for a 1978SC?
per goetze
for 3.0L for up to July 1980 (4.0mm oil ring)
for 3.0/3.2L August 1980 onwards (3.5mm oil ring)


Related post:
Oily plugs from overfilling engine with oil?

Thanks in advance - Joe

[john walker's workshop]

a 3.5 in a 4 slot wouldn't really be too good, now would it?

[psjoe]

John-

Nope, I would think not.

Could it cause the oily plugs I noted in the linked post?

If the engine had run 30K miles this way can a re-ring with the correct rings help? Or does this engine need a new P/C set as well?

Thanks - Joe

[YTNUKLR]

Originally posted by psjoe
John-

Could it cause the oily plugs I noted in the linked post?

If the engine had run 30K miles this way can a re-ring with the correct rings help? Or does this engine need a new P/C set as well?

Thanks - Joe

They are "oil control rings" that means they keep oil out of the combustion chamber...but probably not so well with .023" ring land clearance.

Maybe changing the rings will help. You'll need to take it apart and see, I bet after 30k miles the ring lands will be hammered well out of spec, meaning at least new pistons. Oil consumption at 5-600 miles means you need to do something internal to the motor, bottom line. What kind of shop did this rebuild? Didn't read the whole other thread, how did you come to find out about the rings being likely the wrong ones?

[psjoe]

yntuklr-

I just noted the part number on the engine rebuild invoice. It's 930-103-986-00 indicating the 3.5mm oil control ring.

The rebuild was done by a reputable shop. 30K miles ago but back in 1992. So the invoice is all we have to go by.

I pasted the invoice in the linked thread that's over in the Tech forum.

Thanks - Joe

[psjoe]

Thanks for all of the replies. Seller won't move on his price so i am moving on with the search.

-Joe