medipedicman

It has recently been discovered that the M28/11 Euro S engine that is being rebuilt for use in my 79 suffered from low compression on all 8 cylinders and smoked.

The engine used to blow a lot of oil through the intake, according to the previous owner.

The engine has been dis assembled and cleaned. We have a new complete gasket set and water pump so I am all in at this point. The cylinder walls look great, the valves are not bent, the bearings are smooth.

All indications are great but the builder has now suggested piston rings as a safeguard against the new information. Any thoughts would be appreciated.

Hilton

Has the rebuilder measured the exhaust valve guides?

medipedicman

Hilton, I was at a shop with the builder today and another 928 guy that I respect. He asked the same question and my guy (straycat) said the valves were in great shape. Not sure about measurements.

GlenL

Broken piston rings.

The last time I got special rings from Total Seal. These are not "gapless" but are designed for turbo engines.

101896 AP 038250 0585 150 C-33 STEEL TOP
"That top ring is stainless steel with a chrome nitride coating"

$25 a ring. I plan to get a set of these for top rings and use a set of Goetze rings for the 2nd rings and oil control rings for rebuilding a Euro S for track use.

medipedicman

Would that help to explain while all eight had low compression?

Thank you

medipedicman

Thank you Glen. Please forgive my ignorance. Is that two rings per piston?

GlenL

There are three rings. Or they are counted as three. The top two are single rings: Top or "1st" and "2nd." The third ring is the "oil control ring" and is different on different engines and in different ring sets. The groove is much wider and often there are two thin rings separated by a zig-zag spring.

I plan to get the special top ring and then use the 2nd ring and oil control ring from an OEM set of Goetze rings. Cheaper than getting the set from Total Seal as they don't make the right 2nd ring for a 97mm bore.

Talk it over with your builder. I broke rings twice on one Euro S engine. That results in low compression and oil problems like you mention.

GregBBRD

It's pretty simple.

Piston rings, like bearings, are a wear item and should be replaced.

Ignore what the factory manual says about valve guide wear....unless you happen to enjoy buying oil. Most all of these engines will need the guides replaced by 100,000 miles.

medipedicman

Thanks for the explanation.
I appreciate all of the comments

outbackgeorgia

Brian,
Pay attention to Greg's post. Why not just a new set of rings? You don't need anything special, I don't believe.
Stock is good in this case.
Dave

medipedicman

Thanks Dave. I called Bill (straycat) last night and shared Glenn and Greg's advice and information.

Bill suggested new rings when I saw him at lunch Wednesday, that is what started this query. I think I mistook his polite tone and apologetic demeanor as uncertainty. My bad. I called Roger from the shop but he was tied up with another customer. I will try again today.

Bill knows that this 928 hobby of mine is self sufficient. He felt bad asking for more parts which equals more $. My stock pile of parts to sell is getting pretty skinny but I am sure that I can dig something of value out to pay for the rings.

Dave928S

^^ This.

Not worth the risk of not renewing rings.

... and in addition to Gregs comment re guides. The guides are relatively short, and valve rock in the guide bore becomes pronounced early. The factory spec on guide wear limit is excessive ... when they reach that point they're stuffed, and get worse quickly.

karl ruiter

+1. Guides, and rings. And rod bearings.

medipedicman

Thanks Karl, Dave and Greg. Pistons rings are on order. May have come in today, probably tomorrow.

Bill assures me we are all good on the valves and bearings.

Imo000

Did you actually measure the leakdown and compression on this engine or you just took the PO's diagnosis?