It's a Mystery... (Valve damage)

[mikepellegrini]

My son Trav and I just bought another car - an 88 944 Celebration Edition.

The previous owner had parked it about 7 years ago after the timing belt slipped. The car ran, but badly and he didn't want to deal with it, so there the car sat until last weekend.

Because the car actually still ran, the PO believed it was just one valve involved.

We wanted to know which cylinder before we dove in, so after making sure it was properly timed we did a compression test (yeah, we turned it over a few times by hand before we did anything, just to check. And yeah. even after 7 years, the belts looked ok).

The results: 180, 210, 150, and 190! Trav repeated the test a couple times more just to be sure, and the results came out about the same each time.

Because this was inconclusive, we decided to do a leakdown test. Only No. 2 would hold pressure - the other three cylinders intake valves would not close (we had the intake manifold off, so it was easy to tell).

The mystery? How on earth could the compression have been so good if the intake valves wouldn't close?

We pulled the head and found all 4 valves had contacted the pistons (although like I said, No. 2 apparently isn't damaged).



The damage on the pistons is very slight - just a shiny area on the edge of the cut-out.


We have another head with four good intake valves and we're gonna install the new valves tomorrow.

But I'd still like to understand what happened and why the compression was so good even when the intake valves wouldn't fully close.

Anyone have any ideas?

More pictures: 88 Porsche 944 Celebration Edition

[John_AZ]

I like the DME with the snake skin.

I have a lot of shedded skin around the house outside.

Congratulations on the find and a "ton" of work.

John

[mikepellegrini]

Thanks! It is shaping up to be a neat project.

We hope to get the engine mechanical stuff sorted out shortly (knock on wood). At 140K miles, we're hoping most of the other major mechanical systems are good.

We've got a new set of grey leather seats to install. The old plaid seats we're gonna store against the chance we can find a source for some fabric and have them recovered. It really does look nice - or would if they weren't all torn up.

The windshield is pretty well toast - that'll have to be replaced soon.

The paint we'll deal with in the summer.

When we get it done, Trav's gonna use it as his daily driver.

Then onto the next project - putting the new engine in Trav's 951 (the old one needs rings). Donor engine from the car we parted out last month.

[wild man]

Originally Posted by mikepellegrini

But I'd still like to understand what happened and why the compression was so good even when the intake valves wouldn't fully close.

Anyone have any ideas?

Of course! Those are things that I never seem to run out of.

The answer is simple - with the amount of time that the cylinder is under pressure when cranking for compression testing, not all of the compressed air can escape through the available gap, thereby producing SOME amount of compression.

With the valves replaced, compression should be much better, and be much better matched, across the cylinders.

[mikepellegrini]

Yeah, I just woulkdn't a thought the compression would be so good. The numbers were decent.

But we'll see shortly. I installed four new intake valves. Trav's gonna put it together tomorrow.

[89-944NA]

Correct me if I'm wrong guys, but isn't the 944S a 16v car? Pictures are of 8v engine.

Source for your fabric: www.werk924.com

[romad]

As stated the cranking compression test is flawed, the leak down tester is the only device were you can isolate compression problems. You would have know what the problem was as soon as you put air to it....the intake would have sounded like a large kazoo.

[mikepellegrini]

Yeah, the results from the leakdown test were pretty dramatic.

The badge: According to what I read, the 88 Celebration Edition 944 had no badge at all. Apparently some PO didn't like that and for some reason, put the 944S badge on. Dumb...

[wild man]

I don't think there could have been very much gap though. I think you're pretty lucky, and they barely hit - could have been much worse. You might want to check into WHY hey hit. Maybe shaved head (double shaved?) and not used oversize head gasket? Slight over-rev? How noisy are the lifters?

[mikepellegrini]

The valves were damaged when the belt slipped. The PO was re-tensioning the belt at the time and missed the fact that the timing had changed.

Trav spent all day reassembing the motor and we finally got it finsihed just a bit ago.

It fired right up - after seven years! The lifters were noisy for a few minutes but they quieted down pretty fast. We've got a lot still left to do, but it's shaping up to be a great car.

Lots of oil on the manifold.

[mikepellegrini]

We finished the car last night and Trav drove it home today.

We had kind of a scare, though.

We'd started the car for the second time, intending to let it get hot so we could change the oil (we'd put in some el-cheapo oil to use just to start it and run for the first 1/2 hour). It started running like crap, then died!

We were frantic! The timing had jumped; something bad had happend.

We tried to start it, and it sounded weird, like it had no compression. It just kept getting worse and worse, and he we had visions of having to tear it all apart and start over. Gah!

Trav pulled each plug, looking to see if maybe the plugs had fouled or something - but nothing. The plugs looked great.

Next we set it OT to see maybe if the timing had jumped. Nope, it was perfectly in time.

Jokingly, I suggested maybe we should pull open the air cleaner to see if maybe there was a rat's nest or something in it (the car had set seven years).

Trav just shook his head, no way, it's gotta be something else.

I kept after him, so finally he opened the air box.

Here's what we found:



Yup, it was a rat's nest. This what was left of the air filter. You can see where the rat chewed a hole in the filter - he came in the cold air intake. It was living in the bottom of the air box. There was all sorts of disgusting stuff in there - rat crap, and all. It looked like the sort of insulation they blow into attics (plus the crap).

We pulled off the J-boot - there was a big glop of the stuff hung up on the throttle plate.

No actual rats were found, I'm glad to report!

I vacuumed it all out and cleaned it up, and then we tried to start it. It took maybe 5 minutes, but we finally got the car to run. After another 5 minutes of running badly, it evened out and now sounds great again. There was actually some debris that came out the tail pipe!

The moral of the story, I guess, is that if you're starting a car that's set for seven years, always check the air box for rats...

[pigeon]

When I finally removed the airbox cover on my "sat for a long time" 951 about 300 miles after I bought it I found the same thing - mouse nest on the top of the air filter. The K&N in there prevented any chew-through though.

[Rasta Monsta]

Nice job Mike.

[mikepellegrini]

Thanks.

Trav did maybe 80-90% of the work so he deserves the most credit.

[trivgar]

Now I just gotta get it running correctly. Has weak spark and won't start reliably unless it's hooked up to the charger. Then once it warms up it starts misfiring and stumbling until it dies. Haha. I love old cars.