yamaha 1200r engine failure

[Angus R]

Hello,
I have a 2002 yamaha 1200 with the power valve engine. It stopped running and after a partial teardown i found aluminum chips on top of #1 piston. With the head off it seems to turn over fine. The top of #1 piston has been hot and has melted a little on the front edge. I'm not familiar with these engines and am at a loss to figure out what happened. Any ideas on the cause of this and where these chips came from? Any help would be greatly appreciated.
Thanks,
Angus

 

[Silvertip]

Re: yamaha 1200r engine failure

Lean carburetion, detonation and ignition timing burns down engines. That is probably what made it necessary to rebuild the engine in the first place. Rebuild the engine and be sure to thoroughly clean and rebuild the carbs before placing the engine back in service.

 

[Angus R]

Re: yamaha 1200r engine failure

Thanks Silvertip for the reply.The top end of this engine was just rebuilt, however, when i pulled the head i found two very loose headbolts. The cylinder has a couple of very minor scratches. Can i replace this piston and rings, clean the carbs and put it back together? How about an oil block-off and go with pre-mix, good idea or not? Thanks so much for the help..
Angus

 

[seaboo]

Re: yamaha 1200r engine failure

I've done repairs via replacing 1 piston/rings, but in all honesty you are right there and you will be further ahead if you did a complete top end rebuild. To me it sounds like #1 was running on the lean side (carb cleaning/adjusting should fix that though).

Just a sillly little reminder, If you convert it to premix you may want to place a pre-mix only sticker near the gas fill. If you loan your ski or ride with friends, sooner or later they will try to dump some gas in it (either to be nice or just to empty the last bit from their jug). They WON'T remember you run a mix unless you give them a reminder!!! (been there, done that).

 

[Angus R]

Re: yamaha 1200r engine failure

Thanks Seaboo for the reply. I think you are right, i'll do a complete top end overhaul. Not having pulled this engine down anymore i'm still puzzled as to where thesr aluminum chips came from, any ideas?

 

[Jeff Walkowiak]

Re: yamaha 1200r engine failure

did you inspect the oil lines to see if that line fell off? and did you check the power valve to see if it snagged a ring? they make pv clips for those,, also the diaphragm or internal filter in the carb could be the culprit, or someone never surfaced the head and the gasket leaked.. really hard to tell without seeing the piston and the spark plug.

 

[Angus R]

Re: yamaha 1200r engine failure

I bought this ski from a guy that had just had the top end re-built at a Yamaha dealer. The original problem was the oil line on #3 fell off. Now as i said earlier it's the #1 cylinder that's bad. When i pulled the head there were two loose headbolts(on the right side under the exhaust). I'm sure the carbs have not been cleaned or re-built either. According to the bill he got, they replaced the power valves, but at this point i'm not too sure. The dealership that did this work went out of business a week after he got it back, so no recourse there. He also told me that it only ran for about 45 mins. before stopping.

 

[bkwapisz]

Re: yamaha 1200r engine failure

Sounds like if you put a little more $$$ into it, do a proper rebuild and convert to a premix you'll have a heck of a nice little ride there. When buying used stuff I'm never confident until I've completely taken it apart and then put it back together correctly. You just never know what the last guy did until something like this happens.

And 2 loose headbolts is totally not acceptable. I'd suspect shoddy rebuild work.

 

[Jeff Walkowiak]

Re: yamaha 1200r engine failure

you will need to do the top end and the carbs, add clips to the power valves and go to premix,, check with www.sbtontheweb.com for a top end kit and carb kits etc

 

[Angus R]

Re: yamaha 1200r engine failure

Thanks Jeff,
I plan to re-build the top end, have the head surfaced and re-buid and clean the carbs. Is there anything else i need to do? How about contaimination in the crankcase from this latest problem? Can i clean that out enough to be sure i don't have another problem? Thanks, Angus

 

[Jeff Walkowiak]

Re: yamaha 1200r engine failure

if you pull the engine you can clean the crank case out pretty easily,, if not you should be able to get it clean it will just be more difficult,, and you should check for play in the connecting rods, any free-play in those and you could end up having more trouble if you don't replace the crank,, you probably need to check the reed valves also

 

[Angus R]

Re: yamaha 1200r engine failure

Thanks for the information, you guys are great! I'm going to finish tearing this down this weekend and i'll let you know what i find. Thanks again..
Angus

 

[Angus R]

Re: yamaha 1200r engine failure

What brand of reeds do you recommend? Where is the best place to buy them?

 

[Angus R]

Re: yamaha 1200r engine failure

I pulled the cylinders off and removed the pistons on this today. The piston skirt on #1 is broken off on the exhaust side. The bottom edge of the sleeve has about a 3/16" piece broken out of it as well. When taking off #1 piston i found that the shim that goes on each side of the rod bearing was only on one side of the rod. As far as play in the rods there does'nt seem to be any on the crank. Any ideas as to what caused this? Thanks, Angus

 

[seaboo]

Re: yamaha 1200r engine failure

I bought this ski from a guy that had just had the top end re-built at a Yamaha dealer...---...... The dealership that did this work went out of business a week after he got it back, so no recourse there. He also told me that it only ran for about 45 mins. before stopping.

Sounds to me like someone screwed up on the original rebuild, forgot to put (or lost) a shim and it just took it 45 min. to pop the skirt and lock up. Just a guess, of course.

 

[Angus R]

Re: yamaha 1200r engine failure

Could that missing shim actually cause this engine to break the piston and lock up? I'm still not understanding just how it took a piece out of the sleeve either. Any ideas on that? Thanks, Angus

 

[seaboo]

Re: yamaha 1200r engine failure

In my line of thinking a missing shim would make for a vibration or shimmy in the part.. I can see how it could get the skirt sliding into the bore on the "upstroke". Clearances are CLOSE, a little off kilter can do massive damage. If it ran hot (oil starved) on that piston I could also see how it got the skirt. Does your piston pin have a bearing in it? If so is it good?

My Kawasaki (for no apparent reason other than ALOT of compression) took out a rod bearing, piston pin bearing and a piston (skirt chipped, and detonation marks on the top). I cleaned it up, rebuilt it, and it is doing fine.

Personally I wouldn't worry too much about the why, if you don't see anything obvious, the bore is straight, crank is good, and everything looks good (chalk it up to Murphy's law), rebuild it and enjoy it.

 

[Angus R]

Re: yamaha 1200r engine failure

The rod does have a bearing in it and it looks fine. There does'nt seem to be any play in the crank bearings that i can detect. I'm mostly concerned now as to why it took a small piece out of the bottom of the sleeve?

 

[kend301]

Re: yamaha 1200r engine failure

Your failure was most likely due to pre ignition rocking the piston , A lean fuel mix is probable the root cause but also look at 3 main things :
1. The cylinder was honed and the piston was too loose and rocked until the skirt broke
2. The piston rings were to big and never gapped allowing the piston once again to rock n the bore
3. Bad / stuck ring allowing the compression to be low and uneven again allowing the piston to rock and break

Of course there is always the possiability that it had a bad piston that just broke , I have seen that in many race engines .

As far as the "chip " in the sleve , Measure from the bottom piston groove to the end of the piston skirt and the measure the distance from the end of the ring polishing inside the cylinder to the top of the chip . If it is really only 3/16 you should be fine IF IT IS SMALL . You also need to look at what percentage of the bore the chip covers , If it is over 20% put a new sleve in it . Posting Pics would help alot if you could !!

 

[Angus R]

Re: yamaha 1200r engine failure

I measured this cylinder and piston. They are 80mm at the top of the cylinder and 79.33 piston. This seems loose to me. Also, when they did this"rebuild" they used SBT pistons which i've heard several people say are junk?? This chip is 3/16" in height and 3/4" in width right in the center of the sleeve at the bottom on the exhaust side. I'm going to replace the sleeve i think, just to be on the safe side.