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cylinder base gasket blown - why???

Just had a trip to Germany and Nürburging. Noticed that engine was leaking oil, but was not able to do anything until I got back home.
Engine was never over revved.

Was under the engine today, and it looks like the cylinder base gasket on cylinder #4 is pooped out.
I'm really not sure, but looks like the gasket on this cylinder is more out than on the other cylnders, and the leak looks like coming from this place.

Not any leak when engine is not running, but when running it leaks too much for me to like driving it.

I had a misfire due to coil problem earlier, could this have caused too much pressure in the engine to blow this gasket?

Any suggestions why this has happened?
Engine is newly rebuilt, new head studs and torqued according to spec.

Seems like I have to take out the engine again to verify and fix
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
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Old 05-29-2010, 02:57 PM
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They will do that if the cylinder has been detonating.
Old 05-29-2010, 04:07 PM
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It doesn't make sense for detonation on just one cylinder and the base gasket, aka cylinder shim, is extremely difficult to blow out or move for that matter. Check for broken cylinder head stud on that cylinder.
Old 05-29-2010, 07:07 PM
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I had a cylinder base gasket leak (#5 in my case, IIRC) develop 20,000 miles after rebuild. The shims used were very thin, and just the one gasket got chewed up and part of it was crinkled up and sticking out of the base by 10-15mm.

I just noticed the oil spoor in the regular parking spot - wasn't like I drove the car hard and it was leaking after. Cylinder head studs (from Supertec) were all fine.

Shop found nothing apparently wrong - although they did point out trace indications of detonation on a couple of pistons, but no way of telling precisely when that happened.

They decided the shims were too thin, increased the thickness to .5mm or 1mm (I forget) so they'd behave like a real copper gasket.

No problems since.
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Old 05-29-2010, 10:19 PM
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The base gasket I used came from the complete gasket kit bought here.
Is there any recommendation to use copper instead?
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 05-30-2010, 03:33 AM
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The car runs strong and has no indication of detonation.

The engine run hot on the track, but never entered the red line, and due to this I only had one lap before cooling the engine.
BTW not sure if this happened on the track, because I had the oil leak before going on the track
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 05-30-2010, 03:36 AM
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Guess the only way to know is to lower the engine and verify :-(
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 05-30-2010, 03:37 AM
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Quote:
Originally Posted by totle View Post
The base gasket I used came from the complete gasket kit bought here.
Is there any recommendation to use copper instead?
Ok, I'm confused.

What type of material is sticking out of the base of the cylinder? Could you take picture of the base where the gasket material sticks out?

Could it be the engine has C2 cylinders and is not using any base gaskets and what you are seeing are the viton o-rings that go into the spigot bores?
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Old 05-30-2010, 06:02 AM
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Quote:
Originally Posted by spuggy View Post
I had a cylinder base gasket leak (#5 in my case, IIRC) develop 20,000 miles after rebuild. The shims used were very thin, and just the one gasket got chewed up and part of it was crinkled up and sticking out of the base by 10-15mm.

I just noticed the oil spoor in the regular parking spot - wasn't like I drove the car hard and it was leaking after. Cylinder head studs (from Supertec) were all fine.

Shop found nothing apparently wrong - although they did point out trace indications of detonation on a couple of pistons, but no way of telling precisely when that happened.

They decided the shims were too thin, increased the thickness to .5mm or 1mm (I forget) so they'd behave like a real copper gasket.

No problems since.
Wow - that completely screws up the deck height (squish) if nothing else was done. But if you're running ok, then....ok.
Old 05-30-2010, 06:57 AM
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Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by totle View Post
The base gasket I used came from the complete gasket kit bought here.
Is there any recommendation to use copper instead?
Most likely, it was copper. It is commonly called a cylinder shim because you primarily use it to set the deck height - piston to top of cylinder. For a forced induction air cooled motor, its pretty important. I use .25mm copper shims with no problems. And yes, they create a gasket between the cylinder and case, but there is very little pressure generated there. With proper head stud torque, the seal should be good. If they do develop a leak, don't sweat it unless you're super anal. If you are, then dropping the motor for a top end rebuild is in your cards...
Old 05-30-2010, 07:03 AM
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I used KW Copper Coat on my gaskets at installation. I don't know if helps seal and hold them in place, but I figured it couldn't hurt.
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Old 05-30-2010, 07:30 AM
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Wow - that completely screws up the deck height (squish) if nothing else was done.
Yup. But I'm happy with the work this guy's shop does:



They didn't build the motor, another (respected) independent had. They agreed it was in spec and said "should have been fine - never seen one fail like that before".
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Old 05-30-2010, 10:30 AM
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Quote:
Originally Posted by DonE View Post
. With proper head stud torque, the seal should be good. If they do develop a leak, don't sweat it unless you're super anal. If you are, then dropping the motor for a top end rebuild is in your cards...
Not that I'm too anal, but the leak is too much to drive with for my taste.

I cleaned the engine and started the engine for a minute, and it started to drip right away.



This is the gasket that I have been using. Looks like they are sort of teflon on, but might be copper underneath.

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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 05-30-2010, 12:36 PM
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That sucks... It would bother me enough to fix it.
Old 05-30-2010, 01:22 PM
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Quote:
Originally Posted by spuggy View Post
Yup. But I'm happy with the work this guy's shop does:


They didn't build the motor, another (respected) independent had. They agreed it was in spec and said "should have been fine - never seen one fail like that before".
I love it when shops use specs more as guidelines....
Old 05-30-2010, 01:25 PM
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the gaskets are all copper the black ones are teflon coated copper
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Old 05-30-2010, 06:02 PM
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Do you have a clear look at the base gasket and are you sure the oil is coming from there and not something above the motor?

How old is the build?

It seems a low probability that if the motor was assembles correctly and there was no damage to the surfaces that there would later be an issue with the base gasket. (Did some of the 3.6 motors have this issue?)

Also, how much boost are you running?

Might check your blow by at the oil cap (BMW has a pressure tester I think but you might just look to see there is suction w the cap off) and do a leak down to see if you might have something going on that might pressurize the crank case?

It should be under vacuum because of the dry stump design I believe.
Old 05-31-2010, 04:44 PM
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Base gasket

Hi There, Im a new member to this forum and love to read and learn from the wealth of knowledge here. I often read the questions and answers to different problems. This particular problem prompted me to join. I have my own shop here down under and have been specialising in euro cars for 20 years. I have had 3 911s, modified,rebuilt and restored them. I rebuilt my 930 engine here at the shop and did all the usual performance up grades and proud to say she makes 447bhp at the tyres. I have had personal experience with your problem. It seems to be a very,very rare problem indeed. What seems to happen is the case threads wear/stretch,thus causing the stud to move and this allows the gasket to move. Once the gasket slips out the resulting movement between the barrel and head can quickly destroy your cyl head and barrel. This problem sounds like the magnesium case issue however at 30 plus years of age some alluminium cases can suffer from this aswell. It may only be one case thread but i used time serts in all of mine. Many people will strip your engine and inspect it and report no problems found, leaving you unsure about how long untill it does it again. Unfortunatly this task requires splitting the case and have a top quality machine shop install them for you.
Old 06-11-2010, 05:31 PM
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Good info...
Thanks
Old 06-11-2010, 05:46 PM
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Quote:
Originally Posted by Andy930 View Post
Hi There, Im a new member to this forum and love to read and learn from the wealth of knowledge here. I often read the questions and answers to different problems. This particular problem prompted me to join. I have my own shop here down under and have been specialising in euro cars for 20 years. I have had 3 911s, modified,rebuilt and restored them. I rebuilt my 930 engine here at the shop and did all the usual performance up grades and proud to say she makes 447bhp at the tyres. I have had personal experience with your problem. It seems to be a very,very rare problem indeed. What seems to happen is the case threads wear/stretch,thus causing the stud to move and this allows the gasket to move. Once the gasket slips out the resulting movement between the barrel and head can quickly destroy your cyl head and barrel. This problem sounds like the magnesium case issue however at 30 plus years of age some alluminium cases can suffer from this aswell. It may only be one case thread but i used time serts in all of mine. Many people will strip your engine and inspect it and report no problems found, leaving you unsure about how long untill it does it again. Unfortunatly this task requires splitting the case and have a top quality machine shop install them for you.
Hey Andy, where in Oz are you?
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Old 06-11-2010, 11:07 PM
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