Greg86andahalf

$2500, shipping and some clean-up

http://www.mailordercentral.com/928i...s.asp?dept=115

bcdavis

Hearing that the belt did not snap, makes me think that sometimes people freak out about things, before knowing for sure, what the situation is. Maybe the water pump froze, the belt overheated, and fried a bit, and the whole thing locked up, and the car died. But it may not have jumped any teeth, and it may not have bent any valves. It may have just been a lot of noise and water leaking, when the pump and belt fragged. But the valves may be fine. Or even if the valves were bent, it may only take a set of new heads, and a new timing belt and water pump, and you are back on the road. I mean sure, it *might* have bent valves, broken pistons, and cracked the block, etc. But maybe the engine is fine. It is always worth it to just crack that sucker open, or at least do a compression test with the new belt on... You still might want to sell the car, but at least you can sell a running car...

Big Dave

4pm Eastern update:

The belt is off. It did not snap. It was reduced to 2/3rds of its original width. The best I can tell is that the tensioner arm bolt bent, allowing the belt to walk toward the edge of the gears and shave itself. I believe the coolant (which mixed with the belt shavings to make one HELL of a mess) leaked from the tensioner arm bolt hole. I'm still not certain yet.

My theory is this: The belt was probably too tight. It bent the bolt a little. I tightened the belt again at the proper time interval, increasing the stress on the bolt, which bent more. When I checked tension again earlier this summer, I tightened again to within specs, again increasing stress on the bolt, making it bend even more in its weakened state. Thursday the belt finally slipped. I don't see any components that seized. The pump still turns freely.

Observations:
1. The passenger side cam gear appeared to be in line with the crank.
2. The driver's side cam gear was off about 45 degrees.
3. With the crank put at the 45 degree mark (belt removed), I can turn each of the cams with a wrench. I don't heard anything grinding, but both of them seem spring-loaded. It's impossible to line up their timing marks exactly since they move to a certain point and then leap forward past the mark.

Questions:

1. With the plugs removed, should the cam gears be spring-loaded? Should I be able to turn them by hand?
2. If valves are bent, would I hear clanging or other noise inside the heads when I turn them?
3. Will my timing be correct again if the crank is at the 45 degree mark, and the notches on the cam gears match the notches behind the gears? I assume that I don't have to worry whether I'm 180 degrees off if all of the notches match up and the crank is at 45 degrees.

My next step is to put on a belt, line up the timing and test compression. Here are some pictures of the activity, complete with 2 of my sons showing that they want to imitate their dad by working on their bikes. You'll also see my high-tech information and entertainment system to pass the time....

PorKen

Ouch!

Time to upgrade to the 87-up water pump with the brace.

Mark

With the exception of a few parts vulchers .....

A bunch of us crossing our fingers for you! So far - things sound MUCH better than in the beginning!!

jserio

Baby steps Dave. Ya know the one foot in front of another thing. We're pushing for ya Dave.

Gregg K

Let's hope for the best.
Heinrich said something that really helped me out in this subject. The 928 is not the only interference engine with a belt. I'll just remain quiet until we hear he rest of the story. I want to get philosophical. Hell, it's a high performance vehicle. That doesn't really help.
Good luck...

Old & New

Hi Dave,

Cam gears should behave as you describe; you probably won't hear any noise when turning them.

You will need to get a belt on and do a compression test to know the extent of the damage.

Good luck & keep us posted.

Bill Ball

Dave:

Everything sounds good so far. Removing the spark plugs reduces the effort since you don't fight compression, but the springs your are feeling are the valve springs. So, that is all normal. Yes, it can be a bit tricky to get the notches to line up - you may have to hold it in place. NOTE: since you are sliding the belt over the cam gears loose, you will see some movement back when you tension it, so I set it with the cam gears advanced a tooth. That usually brings things right in line when I crank up the tension. You are OK 180 degrees off. Whether the one cam being off 45 degrees did damage remains to be determined.

Looks like a nice day to be working on the car, although I'm sure you'd rather be doing something else. Cute kids. Keep plugging away.

I'm a bit surprised that a little overtensioning of the belt can bend that bolt.

Continued good luck,

Bill - checking in from the bottom of the World in Ushuaia, Argentina

Thaddeus

That bolt shouldn't bend from overtensioning of the belt. If it was snugged to the block, the shoulders of the thing where it flares out past the threaded portion would prevent it from bending at that point. HOWEVER: if the bolt was even a little bent going in, the shoulders would not be seated. You'd torque it to the correct value, but there's still be a gap on one side. And eventually, the bolt would rotate or bend, or both, and kablooie.

Any chance the bolt was a wee bit bent when it was installed?

Greg86andahalf

two theories-

I wonder if the bolt was fully seatet when torqued. Maybe it hit some debris on the hole and didn't seat. Since the torque value is low, maybe it was a false seating. IT could bend it not fully seated.

or

I wonder if the bolt worked loose and turned out a rotation or two. If it came loose, it could bend at that point.

Greg

Big Dave

I've got a compression tester and I'm ready to check tomorrow. As I understand it, I'm going to put the tensior back on, thread the belt back on with the crank at the 45 degree BTDC, both cams gears having their notches lined up with the notches on the backing plates. With that done, I plug the compression tester into each spark plug hole, reconnect the battery and turn the starter on for a few seconds (the caps and rotors are not installed). Then I turn off the starter, get out and check the gauge for the reading. It should be 150-180 right? Or....do I have someone else turn the key so I can watch the guage while the starter is spinning? Can I turn the crank by hand instead?

I've never done compression testing, so I need confirmation that I'm doing it right before plowing ahead here. I don't want to cause more damage.

Big Dave

I don't know. I suppose it's possible.

About the cam gears: I'll probably have to hold them in place with a wrench. They just won't stand still with the notches line up. They want to leap forward past that position, it seems about 4-5 teeth past where they would line up.

Greg86andahalf

Dave,
Do you have a fresh bolt to use in place of the bent one?

Big Dave

Nope. I'm thinking it may be wiser to go ahead and order a new one. It'll just postpone my progress while I wait for it to be shipped out Monday and however long UPS takes via ground freight. Is it really necessary if all I'm doing is testing compression? I'm even using an old belt, albeit one that is fully intact.

My head is spinning with all the while-you're-at-it stuff that fixing is going to entail if I do decide to fix. Motor mounts, head gaskets, oil pan gasket, plug wires, vacuum lines, new coolant, oil, oil filter, etc. The engine bay needs a SERIOUS scrubbing due to all the debris. It's truly awful right now.

Can I work on the engine with it out of the car and still on the hoist, or do I need an engine stand, too? The tally sheet of expenses is becoming intimidating.