Need help understandig my two latest engine failures.
12-27-2015, 07:08 PM
#31
And all 968's have piston squirters, none have failures at 40 miles. In fact most of us would like to have a 968 block to work with. There are two oil scrapers with a mesh between them to collect any the first scraper missed and oil diapers back into the crankcase thru little holes on the piston in the oil scraper grove, below the two compression ring groves, and they do there job well if the engine is built right. The squirters don't spray "that" much oil to make the engine want to smoke, or even damage the Pistons. Oil out the tail pipe would be engine damage or valve stem issues. If you notice all engine have a grimy intake manifold up to the throttle body but not wet with oil. That's because of the effect of equalization of air under vacuum between the cylinder and intake manifold, but other engines don't have that much blow bye past the rings into the cumbustion chamber. The reason your intake is wet is because the rings are improperly installed and/or piston clearance and/or wrong rings for pistons and/or pistons rings not gapped correctly and/or wrong Pistons for sleeves and/or valve stem issues. And as pointed out rings usually do break if to tight but I have seen them weld themselves being to tight. However with that much oil with the piston blow bye I could see carbon building up very fast because the compression rings are failing and then the oil scraper rings become compression rings for a second then fail immediately and burn the oil that they have collected, turning the oil to carbon and seizing the rings to the pistons. The builder is completely responsible for your failed engine. Twice! Third time isn't a charm!!! And if your asking us about why so much oil is in the intake because your biulder can't explain it, it's because they don't know how engines work.
But I understand what you are saying (writing).
Last edited by 964-C2; 12-27-2015 at 07:41 PM.
12-27-2015, 08:28 PM
#34
Rennlist Member
And 3% or less leak down I've done one 944 motor but I've done boat loads of high-performance Japanese sport bike engines I've also screwed up a few
12-28-2015, 12:06 AM
#35
Rennlist Member
I agree with most of the people on here it is a clearance issue. Who ordered the pistons and how did they size them? The Darton sleeves are a 104 mm bore, which would be a 4.095-in after market ring. The rings are also ordered as to what material the sleeve is. Did you order rings for the alusil or for steel?
You are definitely getting blow by, what did your oil smell like? Normally with significant blow by you can smell the gas in the oil.
You are definitely getting blow by, what did your oil smell like? Normally with significant blow by you can smell the gas in the oil.
12-28-2015, 05:04 AM
#36
I agree with most of the people on here it is a clearance issue. Who ordered the pistons and how did they size them? The Darton sleeves are a 104 mm bore, which would be a 4.095-in after market ring. The rings are also ordered as to what material the sleeve is. Did you order rings for the alusil or for steel? You are definitely getting blow by, what did your oil smell like? Normally with significant blow by you can smell the gas in the oil.
12-28-2015, 05:07 AM
#37
Thanks for all inputs.
I was really confused with the oil in the intake runners before I posted here, but I understand now that this can come FROM the combustion chamber.
I understand it is very likely that cylinder-piston clearance issues, and / or ring issues are causing my problems.
I was really confused with the oil in the intake runners before I posted here, but I understand now that this can come FROM the combustion chamber.
I understand it is very likely that cylinder-piston clearance issues, and / or ring issues are causing my problems.
12-28-2015, 06:33 AM
#38
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12-28-2015, 05:26 PM
#39
Rennlist Member
If the engine it's still in the car you can check the torque of the crankshaft bolt (210Nm) and try to run the engine without balance shaft belt for a short period of time.
12-28-2015, 06:59 PM
#40
Drifting
12-29-2015, 08:15 AM
#41
Rennlist Member
One thing you def need to change and that is your engine guy. All that experience lead you to 2 rebuilds and giant mess. i hope he is covering all of the rebuilds.
01-03-2016, 10:45 AM
#43
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One more thing to check is the exact piston-squirter used. The 968 ones have a check-valve in them so that they only squirt at higher-RPMs when there's more pressure. Your low oil-pressure at idle may be a sign that you don't have squirters with check-valves.
Any decent builder should have an engine build-sheet where ALL the specs are recorded. Each bore should've been measured at 6 locations and each piston measured in 4 places. The gap of each ring should be on that sheet. Same with every single rod and main crank bearing.
Any decent builder should have an engine build-sheet where ALL the specs are recorded. Each bore should've been measured at 6 locations and each piston measured in 4 places. The gap of each ring should be on that sheet. Same with every single rod and main crank bearing.
01-04-2016, 06:29 AM
#44
Rennlist Member
Who is your engine builder care to share in pm . I would like to get mid sleeves in Norway but like always I will rebuild the engine my self. Something is off for sure. Me as a amateur mechanic have rebuilt 3 or 4 944 engines and never had issues . Different pistons depending on material has different expansion rates so does steel liners. Is it possible that he has used clearance values for alusil liners? I believe if not incorrect that you need bigger clearance's with steel sleeves I know we had with JE pistons than stock
01-04-2016, 06:32 PM
#45
Different pistons depending on material has different expansion rates so does steel liners. Is it possible that he has used clearance values for alusil liners? I believe if not incorrect that you need bigger clearance's with steel sleeves I know we had with JE pistons than stock