mshobe

Stuff like this makes me say unpleasant things under my breath.

Took my '89 to Chris' German Auto here in Bellevue, WA on Monday, where I've had fairly routine service completed before. This trip called for flush-and-fill on the hydraulic pump and valve adjustment.

When they drained the oil to facilitate the valve work, they found a chunk of piston ring from a single piston in the drainage. A compression/leakdown test revealed 85% loss on cyl #5, so clearly it's shot.

I had a top-end rebuild done in Chicago, in early 2009 to address sadly ignored head warp issues inherent to these early '89s, and the car has run flawlessly since then. I didn't really notice the loss of power, but I also don't drive this car very often.

I don't have any more info at this point, but what's the minimal service possible, and what's the worst case scenario? Anywhere from replacement of #5 cyl and piston, up to a re-do of the full top-end? I need more info from the shop, but how would the Rennlist 964 brain trust recommend I approach this? Car isn't safely drivable, according to them.

scped

I guess there are 2 paths to follow:

1) least expensive / greatest risk:
With the recent top end rebuild, you might get away with a top end disassembly and repair / replacement of just the damaged cylinder

2) most expensive / least risk:
Not knowing where all the metal shards may have gone, you may want a full engine teardown, inspection of all places oil travels, and replacement of any worn or damaged parts.

based on mileage (e.g. it has 200k miles) one may be a more reasonable approach.

My $0,02

Indycam

How does part of a ring get out of the groove it was in ?

Makmov

break the ring land.

mshobe

Exactly what they told me - the land was broken.

The car only has ~68K miles, about 8K since that top-end, and about 2K since last oil change. I'd sure like to lean toward focusing on that single cylinder if at all possible.

Arrowhead

I agree with Indycam. Lets say its the top ring or the second from top ring. If it is either one it would have to break through its own ring gland and every one below it. Something else!!!!!! or it is an oil ring and even then it would have to bypas the piston/skirt. I have seen many broken piston rings and for the most part they stay there and do their damage to the cylinder wall. Correct me if I am wrong

Makmov

For the most part a broken ring with stay in the land, but all kinds of things can happen when a broken part is flailing around inside an engine.

It could get down the oil ring land and go inside the open grove and not have to drop down past the skirt.

I have seen bits of broken valve springs that looked a lot like ring material.

No telling for sure until its broken down to the damage.

Unfortunately, a Mahle P&C set is a set they are matched size and balanced so 1st you wont be able to find just one, secondly, if you do you are not going to want to do it becuase it will never be right. If that is indeed what is wrong with the motor you are looking at a whole set of pistons and cylinders... basically a complete rebuild and not just a patch job.

FeralComprehension

Have you seen the part? I wonder if what you think is piston ring could be a piece of valve spring?

mshobe

I haven't seen the part yet - all of my communication with the shop, so far, has been by phone. Hoping to get over there later this week, but it's poor timing with work and spare time is at a minimum right now. I will ask about the valve spring possibilities, maybe see if they can give me a pic to post here.

mshobe

Just spoke with the shop. Groove cut in the part found is for sure from the second piston ring; chunk is big enough "to get a part number off of," as they say. So no doubt about the ring. Question now remains whether damage is confined to #5, and the lead tech (Chris, the owner) hasn't had a chance to look yet.

Thanks for the advice/perspective. Trying to, erm, remain calm, as I hold small hope this doesn't require a second full tear-down in the 5 years I've owned the car.

race911

Sorry to hear of your problem. And yes as I read down I would have suspected there would be confirmation that a ring can work its way past a broken land and into the sump. How many have I seen on 930s with boost *****, back when I had my shop? Not to mention my own Euro 3.2 that I got caught out with running up at Seattle one time way back when. Drove it all the way home not really suspecting anything......

Of course the engine is coming apart to the P/C set. How thorough you want to go from there I'd say depends on your relationship with the shop. He's got to balance his professional reputation and ability to honestly compensate himself against your budget. Always a challenge, and always easier to crank out brake jobs, clutches, and service work.

I know I do have one broken set of 5 964 P/Cs that came off of a ~80K track rat RSA sitting around. Odds of it being the same weight group are pretty slim though. And yes you can machine things to make it work. Again, I'd refer you back to your guy.

Indycam

I bought a used set of 89 barrels and cylinders off of ebay .
I've never done anything with them , I got them just in case ...
If you need some let me know .
I'd like to see the piston that the ring came off of . I'd like to see how the part of the ring got out of the groove . If the piston isn't a total mess , I might guess that the ring was busted when the motor was put together and fell into the case before the piston made it into the barrel .
The side gap between the piston and barrel is very small , much smaller that a ring . For a chunk of ring to go from the groove to the bottom of the case ...

Makmov

It is always possible to break a ring putting the engine together... but then that is the engine builder's fault becasue you just know when it happens and it sucks, but it happens. I have broke some rings assembling motors but never had a broke piece fall off into the case.

User 040621

Question for the experts: If all parts of the ring can be accounted for during the P/C teardown, would that make a difference on how much deeper to go?

bobaines

Some good news for you, with Cris you have one of the best motor builders in the country.
As far as what you decide to do, it needs a total rebuild. How long do you plan on keeping the car? Future value will be determined by the path you choose. If you do not want to spend the cost of a rebuild you may do better by selling as is and let the new owner build it the way he wants it. With these cars anything less than a proper rebuild with the needed parts will diminish the value.
My guess is that Cris can give you good guidance.