What Caused This?

He's right that it's pretty hard to know for sure until the engine's out and the covers are off the belts.

If a cam sprocket bolt broke it would have the same result as simply coming loose. This is highly unlikely but I wouldn't rule it out until you look at it. Assuming the bolt was tight at the beginning I wouldn't bet on any of the others as likely but the only way to know is to just look at it.

If the bolt was left loose and the sprocket "walked" out far enough (1/4" or so) for the dowel pin to become dislodged, it will be pretty obvious. Try to be there when the engine comes out and take a picture.

 

A broken pin definitely isnt their fault. Broken bolt due to overtorquing maybe, but unlikely??? Broken valve hard to know which happened first. Bad luck, probably. I think the guy is being generous after 4 years and 4k miles offering to investigate without obligation.

 

Bruce, I think he meant that the previous major was 4 years and 4k miles ago (not the more recent major in question here).

 

Bruce...red herring...Those figures are for the PREVIOUS Major. IIRC this problem happened less than 600 miles from the most recent Major.

Edit...Ahh Jeff beat me to it

Jeff CHANGE YOUR POST COUNT...Quick

 

LOL! I didn't notice that was my 666th post... Uh oh...

 

$25k is silly money for an engine rebuild, much less tear-down. When I blew my 348 motor (cam belt sprocket gear got jammed by external debris), it cost me $6k from start to finish to pull the motor, get the heads machined by a shop, replace the broken internal bits, and reinstall.

At some price point you'll want to go to a hand-fabbing race car shop where they will get you running again for much less than $25k, even if they have to hand-make certain unobtanium Ferrari bits. Or buy a running motor from someone who has spare motors in the 355 Challenge race series. Or buy a running motor from a reputable shop.


OK, granted, I live in a low-cost region of the world where race-car shops are common...so perhaps I am insensitive to the different costs of business in other areas, but a $25k repair for a ~~ $60k car is steep!

 

If the bolt is loose, it was left loose. No other explanation.




There is no wiggle room here.

 

I HIGHLY recommend you be present at tear down....Maybe bring along a buddy (your attorney) also.

 

I don't know, to me it seems hard to imagine these tiny little valves jamming a cam enough to shear the dowel pin. But as others said it is important to get pictures of parts as they rest when the engine is taken apart to help solve what happened first. If you want a hand in fracture analysis I can help out

 

Just observe, take pictures, bring a friend if you want but there's no reason to play "tough" the guy is hopefully going to fix it.

As Rifledriver said, if the bolt (it's a big bolt not a nut) is loose and things moved, "oops" he screwed up. If everything's still tight, it's another story.

Sounds like it only affected one head, probably a couple valves. If you let him fix it it will cost him mostly labor and a few parts. If you take it to the dealer, big $$$ and the other guy isn't gonna pay that. No reason you should either.

The bolt is part 15 the dowel pin is part 12.
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Im with Brian on this one. Properly torqued that bolt does not come loose and I have yet to see one fail.

Only variation I have seen is upon assembly the machined flat in the washer was not lined up with the dowel pin head. It took near a thousand miles but in time the bolt worked loose as the pin head seated into the washer. That condition is perfectly obvious with whitness marks on the underside of the washer.

 

Witness Marks = marks that are used to line things up the same way they were originally. A factory example might be position marks on a chevy cam gear. In Daves case...the witness marks (painted) were on the UNDERSIDE of the washer proving it was touched and installed differantly.

 

No. A witness mark is what will be left by the pin being clamped on the wrong position of the washer.

No one is going to put paint marks on the underside of the washer. The bolt is torqed to 100NM as I recall. At that clamping force a mark will be left if the washer is out of position. In any event it will be visable to the naked eye when the belt covers are removed if the washer is out of position and there will be a significant oil leak as well.

 

I stand corrected..they can ALSO be marks made during the normal assembly of an item such as gauling made on a washer by the application of torque.

 

Just curiosity, when you say thermo you mean thermostat?

 

That might be the best plan. I still think the original guy should be in the loop for a couple of reasons but you want to be sure of what happened.


Take some really good close up photos of what we have been talking about.

 

I think even with witness mark this will be hard to prove because no one knows what the pin and washer looked like before it was removed. I've seen some pretty sloppy machanics and I can easily see how a guy could bang the bolt in with a air gun with washer unseated. Then take it off and reposition the now scratched washer and pin and retorque it. It does seem quite possible someone just screwed up however.

 

Have you guys thought of this: if the guy is a real hack he may not have caused the bolt to come loose because you can easily do the nail polish thing and change the belt and charge for timing by degree wheel and never have to take the cam sproket off. Who's to know. 90% of owners could not feel the difference. I know this is being done in the real world by many every day. There are even threads here with pictures dedicated to it with cam lock tools etc.