Will I get away with JBWeld, or should I solder this back together?

[bigiain]

I'm glad I didn't just buy a pair of heads before I opened this up...

This was the result of ~17,000km & 10 month old belts, running on 297,000km 12 year old idler/tensioners...

big

[Punx Clever]

and the piston said:

'OMNOMNOMNOMNOMNOM VALVES!"

[Raux]

'should buff right out?

[herm]

definitely the JBweld...

[Ddan]

At least you have a good start on cleaning the carbon off the piston

[MongoReturns]

Whoa! Is that the old 750?

[Speeddog]

A bit past the JB weld, I reckon.

I've got some cylinders (I'm pretty sure they'll fit) if you need 'em, they'd go along well with the 'care package' I'm remiss in sending you.

[bigiain]

Thanks Speeddog, but just out of shot to the right in those pictures is a 10,280km old '99 900 motor. If I get most of 300,000km out of that one too, I'll be very happy.

big

[Ohm3d]

how did that happen?

[ducpainter]

how did that happen?

That's kind of like asking what the centenarian died of.

That motor had 300000 km on it.

[bigiain]

That's kind of like asking what the centenarian died of.

That motor had 300000 km on it.

Yep.

The immediate cause was a cambelt failed, and the inlet valve stayed open as the piston came up and the piston busted the valve head off.

The belt was within it's scheduled service limit - it'd been on there for ~17,000km and just under 12 months, so it was getting towards the suggested 20,000km replacement, but wasn't there yet. The reason the cambelt failed (I think) was that one of the original ~300,000km old idler pulley bearing failed.  That's at least a little bit my fault - the last few belt changes I've looked at them and wondered when they'd need replacing (like you do for most moving parts on high mileage motors), but spin them with my fingers and decided "they seem OK still, I'll check them again next time" - this time I didn't quite get away with it... (And, in retrospect, just "feeling OK" is probably not a good test technique. There's obvious signs of distress/wear on the back ot the failed cambelt, but only one of the idler pulley _feels_ bad, and even that one only occasionally - it sort of crunches a bit sometimes when you turn it. I'm guessing it gets worse when it warms up, from the marks on the belt it certainly looks as though the pulley has seized right up while the motor was running...

I don't know if there's a suggested replacement schedule for the idler pulley/bearings, but for the record perhaps 100,000 or 150,000km might be a sensible service life... That's what I'll be doing in the future, perhaps replace the bearings every 5 or 7 belt changes...

big

[Duck-Stew]

I've seen catastrophic failures @ 11K miles...  The rule ought to be that if you hear a funny squeak/chirp and it gets louder w/the belt covers removed...  Then look hard @ replacing them.

[koko64]

You must hold the mileage/kilometrrage record for sure. 

[Latinbalar]

Wow, most cars never see 186,000 miles.  I would say you got your money's worth on that one. Even if you go out and buy new heads and pistons.