[sirwaldizmo]

I didn't know what happened but i heard a faint pop coming from under and i felt a slight loss of power. I continued to twist the throttle but bike didn't accelerate. Finally i made it to the side of the freeway and visually inspected the bike with the fairings off. Didn't notice anything suspicious... so i attempted to start the bike again. The engine started but would not idle. It'll stay on if i kept twisting the throttle but did not sound healthy at all. It was then i realized i'd be down for a while . Towed the bike home and she sat for a couple of months until i finally had the courage to tear her apart to find the lower timing belt snapped.

Open'ed up the valve covers to inspect the rockers/valves but really have no idea what i'm looking for. Any pointers to how to inspect the motor for more damage w/o tearing off the heads?

 

[paulmm600]

sounds like it's fine to me, if a valve had hit the piston you would have known about it. pull the spark plug and check for marks, drain the oil and check for bits. i aways thought they were a interference motor but if you didn't hear a bang followed by alot of noise as the piston went up and down maybe not.

i'd just replace the oil and belts and do a compression check.

this is the first time i've ever heard of a belt actually breaking, how old were they? how many miles, are they the original belts with white lettering or newer kevlar with red lettering? has the bike been stored outside in the cold?

keep us posted on what you find, photos would be nice.

 

[Matt_P]

You can check your oil screen for metal chunks. You can also try taking the velocity stacks off and peering down the intake side of the cylinder. That said, if you're going to make a no bullshit assessement and find out exactly what it is you're facing then you need to pull the head off.

My suggestion: your valvetrain is toast, and if a valve dropped in to the cylinder then you've got even more problems. It will be a pain in the ass to rebuild. Just replace the motor with a used one off ebay. This way you'll save yourself a lot of time and money.

You can always sell the broken motor later

 

[Matt_P]

sounds like it's fine to me, if a valve had hit the piston you would have known about it. pull the spark plug and check for marks, drain the oil and check for bits. i aways thought they were a interference motor but if you didn't hear a bang followed by alot of noise as the piston went up and down maybe not.

i'd just replace the oil and belts and do a compression check.

this is the first time i've ever heard of a belt actually breaking, how old were they? how many miles, are they the original belts with white lettering or newer kevlar with red lettering? has the bike been stored outside in the cold?

keep us posted on what you find, photos would be nice.

Its an interference motor. If his belt broke then the piston smacked some valves.

 

[tonered]

You can also peek at the exhaust valves by pulling the headers.

Please definitely post an update on the belt details, i.e. age, mileage, and method used to check tension.

I've heard of a few busted belts. It maybe hard to find with the search function, but they were posted here.

Good luck.

 

[Crarrs]

You might have gotten lucky and the belt broke while the cams were on the compression stroke. The fact that the engine still turns over and somewhat runs is a good sign.

The timing chain on my ZX7 broke while I was on the highway; pistons on the 1 and 4 cylinders hit the exhaust and intake valves, respectively. The motor was locked solid. I was lucky my clutch slipped and fried for the 3 seconds it took me to figure out what happened. Otherwise, that thing would've spit me off onto my head before I even knew something had gone wrong.

 

[Matt_P]

You can also peek at the exhaust valves by pulling the headers.

That'll be kinda hard, since he'd have to get his head under the bike for the horizontal cylinder (assuming he doesn't have a lift).

OP: in case you weren't fortunate enough to have the belt break while the valves were closed (pretty unlikely at operating speeds) then take a look at these alternatives:

916 motor with 8k for a thousand bucks:
http://cgi.ebay.com/ebaymotors/DUCA...6331170QQptZMotorcyclesQ5fPartsQ5fAccessories

Pretty decent 996 motor with 8k (with 6k service). You'll need a wire harness and some other crap IIRC.
http://cgi.ebay.com/ebaymotors/Duca...cyclesQ5fPartsQ5fAccessories#ebayphotohosting

And in case your piston isn't too damaged here's a set of 748 heads (IIRC a direct swap on the 916)
http://cgi.ebay.com/ebaymotors/Duca...4966937QQptZMotorcyclesQ5fPartsQ5fAccessories

 

[paulmm600]

yeh i thought so, but no noise is a good sign, might just be bent valves, try turning the cam by hand. you could also try a leak down test on the inlet.

 

[tonered]

That'll be kinda hard, since he'd have to get his head under the bike for the horizontal cylinder (assuming he doesn't have a lift).

Yup. That is exactly what I was suggesting. Don't you lay on your back or on a creeper to change oil? Same method. lol. Quite a bit easier than pulling heads to do a quick eval.

The vert cylinder is harder, IMO, but an inspection mirror could be handy.

Have a good one.

 

[ZDM]

This cam belt replacement interval seems to be a real unknown. I had mine replaced at 6400 and my tech said they were in great condition but he suggested that because the bike at the time was 5 years old to change them anyway.
I just took the horizontal cylinder cam belt cover off and the belts looked really good. I have a ducted cover so some dirt gets in there, but the teeth were in excellent condition, no fraying, no nothing. I believe FBF replaced them w/ kevlar ones in 8/2007. A few members here have gone well over the reccomended service interval w/ regard to changing belts. I can't see why, unless you race it or bang it off the rev limiter, these belts can't last 7-8000 miles.
By the look of my service manual they are easy to replace. It's just getting the tension correct. That said anybody know what the "allen key" method/trick is? or any other inexpensive method to tension the belts?
Please update us as you go!

 

[tye1138]

Yea, ya gotta pop the head off and start examining things. There is very little chance things are fine. Most likely, you'll need to rebuild the head.

When my cam belt broke, I was doing around the same speed, higher RPM and it destroyed the head, yet the cam's still rotated OK. It wasn't until I got it apart, I noticed the valves were bent, the valve guides had been destroyed, the cam bearings were gonzo and I destroyed 2 rockers. I should have just bought another head, but 748R heads arn't a dime a dozen, so I had a friend re-build it and he did a good job, but its expensive.

 

[Photon]

What do you have to lose by pulling the heads? It's not that big of a deal, and aren't you curious to see exactly what's happened in there?

 

[KiwiEd]

As posted earlier they are an interferance head. The valves will have touched the pistons and bent. As Tye said, the valve guides are usually damaged as well, and, depending on how long it ran after it happened, the rockers could be damaged. Attempting to start it again after it happened is/was a bad move. The piston should be ok.

The repair does not necessarily need to be expensive if you can do some of the work yourself.
Remove the head, dissassemble, purchase new guides and valves (FBF valves are not to badly priced), take head to engine specialist who will heat it up in an oven, pop the damaged guides out and insert new ones, then he will recut the valves and seats.
Reassemble. :abduct:

 

[IF 6 WAS 996]

Had my belt snap on my 92 851 do not run it till you pull the head.

 

[sirwaldizmo]

Thanks for all the responses guys... I don't know what i'm thinking. It seem pretty darn obvious i need to remove the head. Just hoping on a slight chance that my valves and pistons are still good. The oil has been drained and nothing out of ordinary was found. I removed the oil cooler took some pics from down under... (bike was on front and rear stands btw...)

Exhaust port

From the top

The belt had white lettering

I tried to turn the cams by hand and the upper cam seems to have seized. I could spin the lower one about a 1/4 of a turn. Could it be possible that the upper cam was the culprit causing the belt to shread apart?

I'll post more pics after i get the head off.

 

[safetyfish]

You would have known if the valve did this to the piston.

If I was you I would take the head off and have a good look around on the inside.

SF

 

[amullo]

Sounds like your gonna need to pull the heads..

And it COULD be worse!

 

[paulmm600]

any idea how old they were and how many miles?
funny though the belt looks fine apart from the broken part, i've seen them frayed quite badly and still holding up, but they may have been the new kevlar belts.

are they nice and soft or hard like an old fan belt?

 

[paulmm600]

meant to ask you guys

amullo that had to hurt, any ideas on the cause?

safetyfish did you drop a belt too?

 

[safetyfish]

The bike dropped a valve, which destroyed the one barrel completely.

SF