snapped timing belt

[nicksacco]

As others have mentioned, the engine may not be toasted. Verification is necessary.
Before you move to step where you are removing the engine, verify that the engine isn't damaged by putting in a new belt and hand rotating the engine (without the spark plugs).
If you can't, then chances are a valve is broken and jamming a piston - or worse. Damaged pistons will require engine removal.
I've seen a broken valve in a single cylinder dirtbike and valves can embed themselves in both pistons and heads!

If you can rotate the engine, then do a compression test on the cylinders. If one or more are very low or no compression, pull the offending head.
Someone also suggested a borescope to look down and visually look for damage to the piston (Even if the compression is good).
I wouldn't jump to pulling an engine right away is all I'm suggesting.

 

[ST1100Y]

... your valves are more than likely toast as the pistons would continue to move up and down and the valves would be out of position.

Best case: valves snapped shut before TDC reached (slim chances though...) or only "slight" impact, valves bend only marginally...
Realistic POV: valve seats damaged, piston crown damaged, piston knocked sideways, rings & honing, impact on connection rod, bend, damaged bearings, possible crank bearings...
Major worst case: fractured valve plate, chips smacked around created definite havoc in combustion chamber, crown cracked, rods bend, bearings...

Remote diagnosis not doable...
Compression test, visual inspection, disassembly & measurement on (all!) parts required...
Possible that only one cylinder head is impaired, rebuild (or replacement) possible... but I'd still check all crowns, rods, big end and crank bearings...

 

[Uncle Phil]

In my case of my engine 'grenading' at 70 mph with a loud pop, I was more concerned about what happened 'elsewhere' in the engine more so than the valves. IMHO, if you have another 'known' good engine handy, it is much quicker to swap than fuss with putting on a new timing belt and pulling the heads and then trying to figure out what happened in the lower end. Cost wise you are just out the cost of the engine - not all the various parts, timing belt, gaskets, etc. with the necessary headwork. To do a thorough inspection of the bottom end, you would have to pull the engine anyway (see Mr. Millyard's video). There are very few electric connections and bolts to the engine itself - the nastiest part is the exhaust system. And that's a good time to swap over to the Delkevic stainless steel exhaust anyway! But, it's not my monkey and it's not my circus.

 

[Upt' North]

In my case of my engine 'grenading' at 70 mph with a loud pop, I was more concerned about what happened 'elsewhere' in the engine more so than the valves. IMHO, if you have another 'known' good engine handy, it is much quicker to swap than fuss with putting on a new timing belt and pulling the heads and then trying to figure out what happened in the lower end. Cost wise you are just out the cost of the engine - not all the various parts, timing belt, gaskets, etc. with the necessary headwork. To do a thorough inspection of the bottom end, you would have to pull the engine anyway (see Mr. Millyard's video). There are very few electric connections and bolts to the engine itself - the nastiest part is the exhaust system. And that's a good time to swap over to the Delkevic stainless steel exhaust anyway! But, it's not my monkey and it's not my circus.

What have I told ya about spanking ya monkey at the circus .
Now stop clowning about.
If Joe finds out it'll be the high wire for you.

 

[GGely]

Careful, Upt North, or you’ll be next in the cannon!

 

[Andrew Shadow]

I didn't suggest a compression test in my first response because that can be risky until you have an idea of the damage. There are endless variables including the engine design its self but, if the engine RPM was low and depending on where in the cycle the engine was when the belt let go, valves can be bent without any other significant engine damage. Cranking the engine over with the starter to do a compression test can cause more damage and turn a salvageable situation in to a scrap heap. Pulling the valve covers first, or at least rotating the engine by hand, to get an idea of the damage first isn't a bad idea.

 

[Uncle Phil]

Least rotating the engine by hand, to get an idea of the damage first isn't a bad idea.

Not trying to be smart aleck, but how would you rotate the engine by hand on a ST1100?
Just curious.
Also, when I pulled the 'valve covers' there was not much to see to get a 'view' of the valves.

 

[kiltman]

If you haven’t done so already I would be tempted to pull off the inspection cover for the timing belt. Remove the lower fairing,then remove the inspection cover. That way you can confirm if the belt is broken, or shredded. If that’s the case, meaning the belt is damaged or broken, there’s a strong possibility of damage, it would be cheaper and easier in the long run to buy a post 96 bike or motor, which has been mentioned already.

 

[ST1100Y]

... how would you rotate the engine by hand on a ST1100?

Crank sided t/belt pulley; 17mm socket with ratchet on the bolt...
But I'd use screw-in adapters in the plug holes, crank (or remove) the cams and attach my compressor to see if the (closed) valves on that cylinder vent into intake or exhaust...

 

[v8-7]

how would you rotate the engine by hand on a ST1100?
Just curious.

put it in gear, remove the spark plugs and rotate the rear wheel ?

 

[Jethro]

5th gear

 

[Uncle Phil]

Good answers - I was just curious if the was a way without having to remove a bunch of stuff.
I think ST1100Y probably has the best approach.
It sort of boils down to

a) Do I have access to a 'trusted' engine at a reasonable cost and
b) Just how much 'mechanicing' do I want to 'invest' in the project.

For me it was easy - no trust in the original engine due to the high speed 'failure' and I already had a low mileage 'trusted' engine.
It was very little 'parts' expense and a lot less time spent to do the swap than a post-mortem trying to figure out what was bad and good with the old one.
I just wished now I had pulled off the tranny before I tossed the old engine in the scrap bin.

 

[GGely]

And I thought you were perfect, Uncle Phil… Disappointing.

 

[Al st1100]

How bout just pulling the cams and trying a compression tester.

belts normally don't snap. something caused it to snap. Water pump bearing, tensioner bearing or an idler bearing loose/seized causing belt damage. Camshafts seized in the head. you don't need to pull the cams to do a leak down test but you will need to turn the cams.

 

[Larry Fine]

It would be helpful if the OP would answer us about the mileage on the belt when it broke.

 

[Uncle Phil]

And I thought you were perfect, Uncle Phil… Disappointing.

Not perfect, just Forgiven!

 

[Al Gully]

It would be helpful if the OP would answer us about the mileage on the belt when it broke.

I think he‘s so busy wrenching, he forgot about us.

 

[Andrew Shadow]

Not trying to be smart aleck, but how would you rotate the engine by hand on a ST1100?
Just curious.
Also, when I pulled the 'valve covers' there was not much to see to get a 'view' of the valves.

The same way that you do it when you are checking/adjusting the valves.

 

[diferg]

@GGely I never thought Uncle Phill was "PERFECT", just "BIONIC". I think that perfect will have to wait for the next Upgrade.

 

[Sadlsor]

It would be helpful if the OP would answer us about the mileage on the belt when it broke.

Yeah, well, as I check, the original poster has only the one post across this forum, the one that started and turned over the brain trust here. (I'm not including myself in this regard.)
With all your optimism(-s), you could have sent him down the dark crevasse into depression (not compression) and despair (not repair). He could have just decided to take a walk on I-95 in the dead of night.
Let's hope not; I'd like to know the mileage answer, too.