low compression and smoke
#1
Rennlist Member
Thread Starter
low compression and smoke
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.
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.
#3
Rennlist Member
Thread Starter
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.
#4
Nordschleife Master
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.
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.
#6
Rennlist Member
Thread Starter
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.
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.
#7
Nordschleife Master
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.
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.
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#8
Rennlist
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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.
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.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
#9
Rennlist Member
Thread Starter
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.
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.
I appreciate all of the comments
#11
Rennlist Member
Thread Starter
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.
#12
Rennlist Member
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.
#14
Rennlist Member
Thread Starter
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.
Bill assures me we are all good on the valves and bearings.