Valve Damage

The cams have to be timed with the crank pulley.
Steve

 

If the spark plug has hit the piston; to me, that sounds worse than just a bent valve. It suggests that the spark plug is too long; or the piston has come up higher than it should; or even maybe if a bent valve has smashed the piston crown.

As Birdie says, both cam pulley timing marks and the crank pulley marks should all be aligned at the same time.

 

i would suspect the head of the valve has broken off. It will have bounced about and smashed the spark plug and will now be weged in the top of the piston. when the puston goes up the wedged valve stops it going all the way and locks the engine.
it happened to me on my 916sp engine.
i had my head repaired at an engineering workshop in Northallerton. he also sourced me some Forged Valves which were far cheaper than Ducatis 2 piece friction welded stuff

 

Don't worry about re-timing belts on assembly, there are plenty of people on here who will talk you through the procedure, best get the head off as you say and see how bad the bad news is. Hopefully it's the horizontal cylinder? which means you might be able to fix the whole thing in situ

 

In your original post you say you got it as a non runner. So I assume you have no idea how fast it was going when it went bang
I was lucky in one respect as I was pulling out of a junction when mine went and it stopped dead.
You need a new head or repair. Repair will cost you about £400
You need a new barrel and piston and it's quite possible that the rod is bent. The exhaust valve could be bent as well
You also need the cases splitting to clean out all the swarf from the busted valve and piston.

 

I tend to agree, you're either in for a major engine strip to fully ascess the damage or else source a secondhand running engine that you can preferably hear going before you buy (not that easy).

Really depends on how good you are with the spanners and how much you really like the bike I guess.

If all else fails, then break it for spares and you'll probably get most of your money back if you have the time and inclination?

 

I had a belt go at 90 and only bent 1 valve.
S/h valves are rare as rh pooh.

 

My experience dropped inlet on after market Daytona Cams, vertical cylinder cam not good? valve head bounces around smashes head, sparkplug ends jammed in piston crown?
valve timing jumped after cam locked?
hope works out well

 

Go a new 954cc big bore kit and a set of keihiens, then its starting to go?
Daytona cams my road engine in Patersons ducati's drag frame ran high 10sec, fix it better?

 

That's an awful lot of money to spend out on a 750, especially if the OP has a engine strip and other OEM expensive bits to find - besides, don't forget the 750 engine isn't just 150cc smaller than the 900 (just thought I would mention that bit).

IIRC the 750 big bore kit can only go to about 825cc.

 

Stein Dinse do valves. A full engine strip and rebuild could be costly if it's damaged inside. Bearing etc can be costly.