healey1968

Hey guys, thought you all might enjoy seeing a few photos from a broken timing belt on an '83 944. This is out of a car we run in the 24 Hours of LeMons

Back story: We picked up this car off craigslist for a couple hundred bucks with a known busted timing belt about a year ago. The guys story was 'I heard some clanking while idling down the road and pulled right into a gas station'. That turned out to be a load of horse $hit

We realized this engine wasn't going to look pretty inside and had a suspicion it had been rebuilt by monkeys so we swapped in a spare engine we found. Race was a few weeks ago and the car ran great. Last weekend I finally got a chance to pull apart the original '83 engine to see what the damage was.

First I took off the cambox. I think the previous 'mechanic' figured out expensive a real gasket kit was and found a tube of orange RTV instead. This stuff was everywhere!



You can probably see that the left most valve spring retainer is popped out of place. I'm not sure how this happened. 2 springs were like this. Oh yeah, 3 of the retaining nuts inside the cambox were missing too....

No, off with the head!



Ok, I figured this was coming. I knew the exhaust valve on cylinder #1 was bent pretty bad by looking through the exhuast port, but dang. Then I tried rotating the engine and couldn't help noticing that the piston wasn't moving.



Ah. That's why.

Wonder where the rest of the piston is?



There.

One more shot of everything on the floor.



So - yeah - change that timing belt.

Dougs951S

......speechless. Insane carnage.

V996

Holy ****

Fara

Man, that engine really went nom nom nom on it's internal components.

Nothing a good long block transplant can't solve though

Van

Holy RTV!!

For what it's worth, I don't think the timing belt breaking was the cause of the damage. I've seen a lot of broken timing belts, and I've never seen that - only bent valves.

I think the piston broke apart first - which left the top half of the piston in the way of the valves. Once the valves started hitting the piston from above and the lower half of the piston and connecting rod was hitting it from below, that caused the timing belt to snap.

V2Rocket

holy cow..


"well, there's your problem"

time to bore and sleeve it, its the only option

re:gasket, i find it funny when reading other forums when pushrod v8 guys say how expensive a master gasket kit is (every seal on the entire engine), in the $150 range...that rtv is a nightmare.

Voith

Wow total destruction. At what rpm did it broke?

I had a roller failure once and it bent valves but it didn't even leave marks on pistons.. It happened while cruising in 5th gear though..

StoogeMoe

Ha ha. Yeah, just idling down the road!

Maybe after a 4-3 upshift at full revs.

mytrplseven

Just plain ugleee

Van

I was thinking more about this. What do the spark plugs look like? And/or the the #1 cylinder's exhaust port? I bet they'll point to a lean condition. Certainly, the lack of carbon on the top of the #1 piston seems to support that theory.

I bet it was a bad injector - that caused the cylinder to be lean, and to heat up much more. The heat caused pre-detonation, and that broke off the piston's ring lands, which then got stuck between the piston and the head, which caused the connecting rod to bust the piston apart when it stopped moving. Now the piston was stuck at the top of its stroke, and the valves hit it, causing such a jar it broke the timing belt.

healey1968

Interesting insight Van, I was just going to ask what you thought the condition was.

I know we have the #1 and #2 spark plugs laying around somewhere, but they were long gone when I pulled the engine apart this weekend. #3 and #4 were both black. Dirty, but not excessively. Not grey like I would expect from a lean condition - if anything indicating running rich.

The exhaust headers are currently running on our race car and just finished a 700 mile endurance race, so they'll be useless for forensics. So is the fuel rail and injectors (we reused them). You've got me a bit worried about that setup now!

The piston in the #1 cylinder, although basically floating, moved just fine. I pulled it out with a pair of pliers in one of the cracks. Not sure if that goes along with a super over heating condition.

Finally, any idea why the valve spring retainers were popped out on 2 of the springs (picture 1 left hand side). Is this a by product of a broken timing belt or did somebody do a terrible rebuild of the engine at one point?

Van

I've never seen a valve keeper jump like that. I'm going to guess, due to the amateurish use of RTV sealant, that the keepers weren't installed properly before. I bet if you look at the corresponding lifter, you'll see there is damage there when the plunger has depressed and the valve keeper had a collision - probably very repeatedly.

I don't really know enough about metallurgy and predetonation, but my hunch is that the heat weakens the metal of the piston, and makes that chamber temp higher. This can cause predetonation as the piston is still moving upward, and the explosion of the air and fuel puts tremendous force on the the rings and lands as the combustion drives the piston down but the connecting rod is still driving the piston up. This "fight" is the knock or ping we hear when an engine is predetonating.

Eventually something has to give - I've seen broken ring lands before, which then, of course, tear up the cylinder walls. I don't think a piston usually seizes, though. The connecting rod has the force to just keep it moving, or to break the piston apart.

Hydro lock is another thing. Water or something (like from a blown head gasket) gets in the cylinder and provides an immovable object the piston can't get past, and it usually bends a rod.