Hi there everyone...

last year, I had to replace the barrels and pistons in my 1988 930 due to detonation. To make a long story short, I got everything back together and unfortunately, the old girl leaked like mad. Diagnosis, the barrels were leaking at the bottom.

Point of concern is that I replaced the Mahle barrels with a set of Perfect Bore cylinders and I just noticed that the bottoms have a groove and are not perfectly flat like the Mahle's. Is there some type of special gasket that is required for the Perfect Bore barrels?

I'm in the process of reassembly and it looks as though I might encounter the same problem if I use the standard OEM barrel gaskets.

Please advise as to what options I have available to cure this problem.

Thanks in advance for any advice and/or direction that anyone can offer.

Best Regards,

Todd

 

I have the same problem. There are different gaskets/shims available plus Curil T are essential.
You could try draining the oil and get as much sealant up there as possible, but that rarely works.

 

Hi,

Thanks for the response. I'm having difficulty finding the proper gaskets. My engine is out of the car and disassembled, so I want to address the gasket issue while the motor is out of the car....Do you know where I can possible obtain the proper gaskets or shims?

Thanks again for responding...

Best Regards,

Todd

 

Check with your supplier of piston barrels if they use the viton o-rings found in the C2 Turbo engine. This may be your problem.

__________________
Dave
'85 930 Factory Special Wishes Slant - B&B Headers/Muffler, Werke I Cams, Kokeln IC, Electromotive Crankfire Twin-Plugged,
Tial Wastegate(1.0Bar), K27-7006 turbocharger(Werke I), Euro fuel distrib, 8:41 R&P

 

The base gaskets are included in the gasket kit. But you may want to order another set since they come in 2 different thicknesses.

 

Hey Dave,

Thanks for the suggestion. I was thinking along the same lines but was unsure of whether or not a rubber o-ring would hold up to the heat. I'll check into it....

Best Regards,

Todd

 

This is the barrel that I'm having the problem with finding some type of sealing gasket for. I have no clue what to do at this point. Can't proceed with putting her back together until I'm absolutely sure of what I need to fix this issue...

 

Well, finally came up with a solution. Going to have the barrels shaved and fitted with aluminum adapters....

Best Regards,

Todd

 

Update, actually went with Daves idea of using the viton o-rings. Just about to put the engine tranny back into the car. It's been awhile, so I'm keeping my fingers crossed...

Thanks again Dave for the suggestion.

Best Regards,

Todd

 

Although I can't speak to the issue at hand, it does appear that the barrels are machined to accept an o'ring. Viton is good stuff....I use Viton crankshaft oil seals on all of my air cooled 2 stroke dirt bikes. They see extreme duty riding full-tilt-boogie in the desert. Viton is good chit Maynard.

 

Hey Mark, thanks for chiming in. Appreciate the feedback...I'm sure she'll be fine.

Best Regards,

Todd

 

Oh the humanity. Finally got the strip the engine to fix the base gasket leak at #4 only to discover, base gasket leaks only slightly from the top of #1 and 3. The base gaskets shifted up and were blowing oil on top of the crankcase. To add insult to injury #1 and #4 only had broken top rings and stuck oil rings. I know the timing was set improperly for awhile after the last rebuild. Could all this be due to detonation? Are my pistons reusable with changed oil ring gaps?

 

Hey Rob, sounds like my situation as well. After pulling the barrels, I noticed that there were several pistons where the rings had been damaged and it appears that it was caused by detonation. I remember playing with the dial of death (Again) and boosting over the max limit for my engine of 1 bar...So I replaced the rings and installed the o-rings and low and behold, there are no more leaks and the engine ran fine up until a few weeks ago. Plenty of power. I was happy as could be.

Now, I have what appears to be a knocking sound coming from the engine. I was going to work one morning and when I was exiting the freeway, I noticed what sounded like a tapping sound, like a loose rocker arm. Initially, under acceleration, it would stop and then you would here it when you let off the accelerator; however, by the time I got the car back home, it was doing it consistently, whether or not if I was accelerating or not...

I took a stethoscope to see if I could pin point the source of the knock; and it appeared as though the knock was more resonant towards the front of the engine closer to the driver side. So I pulled the valve covers but all looks well.

I've now got to pull the passenger side covers to see if anything is loose...

I really hope I don't have to pull the motor out again.....

 

Looks like you are few steps ahead of me. My prayers are with you. Please share what you discover.
My recap: 2 years ago rebuild due to oil leaks and smoke. The apprentice set the timing wrong. I drove the car for about 6 months thinking it was a fuel problem. I suppose that's when the detonation and subsequent damage to the top rings occurred and contributed to the blowing out of the base gaskets. Interestingly the right side #4 blew down and on the left side #1 blew up.
After installing a 965 intercooler last month, on a test drive I pegged the boost gauge, causing the blue smoke on deceleration. I think that's when I compressed the oil ring lands. Strange that only #1&4 were affected.
My shop recommends I set it back to original, but I can afford new P&C now. Last week I took #1&4 pistons to work where I filed and sandpapered the lands to make sure the oil rings move freely.
EBS racing confirmed I have old Mahle Motorsport 98mm pistons due to their strange 1.5, 1.2, 3.0mm ring setup. I ordered custom made rings. On the weekend I carefully cleaned all the pistons and cylinders using dishwashing liquid and a kitchen cleaner.
I hope to re-assemble the engine this weekend. I didn't bother to separate the heads from the cam carrier so it shouldn't take much time.
Ill be sure to use as much Curil T as possible.
Wish me luck.

 

Hey Rob,

Sure thing...Good luck.

I'm going to attempt to pull the passenger side covers sometime today or either tomorrow to inspect for any loose rockers. If nothing there, then I'm going to try and do a partial drop so that I can pull the timing chain covers to see it there's anything going on there.

Will keep you posted.

Best Regards,

Todd