Need Help on YFZ trouble cranking

Yamaha

My buddy called me up a couple days ago to tell me the local Yamaha dealer had screwed him on a service deal. It was so bad that the service manager got canned and my buddy got his YFZ with a torn down top end and box full of parts on bolts.

It started like every other horror story, he lent the bike to his friends and they messed it up. They took it directly to the service department so he never got to see what the problem was. Pretty dumb on their part, I know. They claimed it would not crank at all.

The service department at Yamaha said the crank was broken. When the bike finally made it to my garage, the cylinder head and cylinder were off the bike as well as the stator and starter, starter clutch and basically everything off the stator side. The crank spun very well in my opinion. Had little to no end play in any direction. I'm thinking the Yamaha shop service manager was planning on taking my buddy for a ride on this repair. I started looking elsewhere and noticed a link on the timing chain was seized up. Was able to break it free with some pliers but told my buddy it would be best if he just went ahead and got a new one. Today we started putting it back together. I oiled the cylinder before slipping it back onto the cylinder. Turned the crank at the stator end and it turned fine.

Threw the head on as well and torqued it down. Lined up the cams and the crank just like in the service manual. Threw on the caps after I cleaned them, and lubed them. I checked valve lash and they were all fine. Threw the rest of the bike on and went to fire it up.

The bike started and ran for like 10 seconds then stopped. I tried to start it back up and and it cranked but then abruptly stopped cranking. I thought the battery may be low so I threw the charger on it and went to crank it again and it would crank for like a second then abruptly stopped again to the point where it seemed like the motor was seized up. I removed the timing plug and used a ratchet to spin the motor and it would spin fine for like 4 or five full turn then tighten up a bit which I figured was compression. I would go to crank it again and it again started for like 5 second but then stop again and the cranking problem would start again. Rather that keep that up I called it a night and told my buddy to bring it back Sunday.

Anyone got any ideas or suggestions? I never got to see what the original problem was so its hard for me to pinpoint where the original problem was or whether the seized up timing chain link could have damaged something else I may have missed.

Fred

EDIT Bike is an 05 YFZ450

Is it safe to assume you reset the timing chain tensioner?

It started like every other horror story, he lent the bike to his friends and they messed it up. They claimed it would not crank at all.

The service department at Yamaha said the crank was broken. When the bike finally made it to my garage, the cylinder head and cylinder were off the bike as well as the stator and starter, starter clutch and basically everything off the stator side. The crank spun very well in my opinion. Had little to no end play in any direction. I'm thinking the Yamaha shop service manager was planning on taking my buddy for a ride on this repair. I started looking elsewhere and noticed a link on the timing chain was seized up. Was able to break it free with some pliers but told my buddy it would be best if he just went ahead and got a new one. Today we started putting it back together. Turned the crank at the stator end and it turned fine.

The bike started and ran for like 10 seconds then stopped. I tried to start it back up and and it cranked but then abruptly stopped cranking. I thought the battery may be low so I threw the charger on it and went to crank it again and it would crank for like a second then abruptly stopped again to the point where it seemed like the motor was seized up. I removed the timing plug and used a ratchet to spin the motor and it would spin fine for like 4 or five full turn then tighten up a bit which I figured was compression. I would go to crank it again and it again started for like 5 second but then stop again and the cranking problem would start again.

A broken crank does not seem all that far fetched! Its definitely a possibility. The crank pin could have a diagonal fracture from one crank half to the other. The fractured crank pin would be held together by the large end of the connecting rod. When the motor is not running under its own power everything might seem as if it is "OK" but when the motor is cranked or started the crank halves could become out of phase and create a binding action in the large end of the connecting rod. That would make it seem like it were seizing.

I would pull off the clutch side cover and see if you can rotate the crank halves in opposite directions.

Maybe the the service manager was right???

Well, thats my two cents worth!!...just a thought....

....heres another thought......If(big IF)this is the case I would not try cranking/starting the bike until I verified that the crank is not broken. I only say this because if the connecting rod were to become larger(on the big end)from the binding action the stroke could be changed slightly possibly sending the piston into the valves or pulling the piston skirts down into the crank weights.

Is it safe to assume you reset the timing chain tensioner?

yes sir. Had to borrow a tiny flat blade screw driver from my neighbor.

A broken crank does not seem all that far fetched! Its definitely a possibility. The crank pin could have a diagonal fracture from one crank half to the other. The fractured crank pin would be held together by the large end of the connecting rod. When the motor is not running under its own power everything might seem as if it is "OK" but when the motor is cranked or started the crank halves could become out of phase and create a binding action in the large end of the connecting rod. That would make it seem like it were seizing.

I would pull off the clutch side cover and see if you can rotate the crank halves in opposite directions.

Maybe the the service manager was right???

Well, thats my two cents worth!!...just a thought....

....heres another thought......If(big IF)this is the case I would not try cranking/starting the bike until I verified that the crank is not broken. I only say this because if the connecting rod were to become larger(on the big end)from the binding action the stroke could be changed slightly possibly sending the piston into the valves or pulling the piston skirts down into the crank weights.

Never considered that. Would splitting the cases be the only way to check this?

Well, tore the motor back down again checking stuff to pinpoint the exact cause of the bind in the motor and determined it was the rod bearing going out. When the guy first brought me the bike it spun fine with no binds but now it binds. This could have been the original problem but I'm wondering why it did not bind the first time he brought it to me. Having him order a new hot rods crank.

Well, tore the motor back down again checking stuff to pinpoint the exact cause of the bind in the motor and determined it was the rod bearing going out. When the guy first brought me the bike it spun fine with no binds but now it binds. This could have been the original problem but I'm wondering why it did not bind the first time he brought it to me. Having him order a new hot rods crank.

Hmm....looks like someone(not You)owes the service manager an apology and a Job!

Let us know the final diagnosis...preferably with pics!!:bonk:

Well, if you consider stealing parts, lying to customers, and having drugs delivered to you while at work acceptable, then yes he should get his job back. LOL

Well, if you consider stealing parts, lying to customers, and having drugs delivered to you while at work acceptable, then yes he should get his job back. LOL

.....You know what "Dude"??....you never mentioned any of that before....I guess you are "Devious".........:bonk:

.....You know what "Dude"??....you never mentioned any of that before....I guess you are "Devious".........:bonk:

That is true I never did mention that. I'm just really pissed at myself for not catching that before I put it back together. :bonk:

I swear I turned that crank 20-30 times whe it was apart and the bearing seemed fine. :bonk:

least u figured it out

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