'85 Tri-Z crank issues...

[Bigyellow]

I have an '85 Tri-Z that I bought for a rebuild a few days ago. Got it for a steal, but there is one problem: the crank bearings are bad from little flakes of metal in the crankcase that I noticed when I split it. I also noticed
that there is grind marks on the bottom of the big end of the connecting rod and crankcase. I also noticed what appears to be heat stress marks on the crank halves near the connecting rod pin. I'd like a second opinion before I lay down money to buy another crank from someone who would know...

Thanks for any helpful info in advance

[barnett468]

Hello



I have an '85 Tri-Z that I bought for a rebuild a few days ago. Got it for a steal, but there is one problem: the crank bearings are bad from little flakes of metal in the crankcase that I noticed when I split it.

Just curious, are they steel or aluminum, you can tell with a magnet?

Is there a piston in it and if so is it good?




I also noticed that there is grind marks on the bottom of the big end of the connecting rod and crankcase.

Do you mean marks from a grinder or just minor scrapes? When a piston breaks, some of the pieces that fall into the crankcase occasionally get lodged between the rod and case as the engine is either still rotating or when the rider keeps kicking it over in hope against hope that the piston will magically glue itself back together and the engine will run again, lol.




I also noticed what appears to be heat stress marks on the crank halves near the connecting rod pin.

If you mean blue color but no stress cracks than it’s most likely ok, that’s typically caused by a rod seizing. Just have the pin hole miked when it’s apart. I have rebuilt many previously seized cranks and they have been run in the Pro class and never had an unusual problem.




I'd like a second opinion before I lay down money to buy another crank from someone who would know...

Just buy a complete rod assy after you have it checked out, don’t rebuild it with just a pin and bearing.

[barnett468]

If you have photos you can put them on flickr etc and simply post a link to them here in a post.

[Bigyellow]

They were little flakes of steel from the big end of the rod I'm guessing...could the rod have gotten hot enough to where the rod started to spall and flake? What really baffled me was the scars in the crankcase, normally those are caused by a blown rod. Curious, what causes rod seizure?

As for a rod kit, the Hot Rods kit sounds suitable.

The piston had some light scarring marks, but it is ok. It was freshly bored .010" over and ran for a little bit before the motor quit on the previous owner.

Thanks for answering my question by the way, I appreciate it

[barnett468]

Hello



They were little flakes of steel from the big end of the rod I'm guessing...could the rod have gotten hot enough to where the rod started to spall and flake?

Anything can happen. What does the rod say on the side?




What really baffled me was the scars in the crankcase, normally those are caused by a blown rod.

It’s 26 years old, might have broken 2 or 3 pistons or a rod in there by now.




Curious, what causes rod seizure?

Same things that cause piston seizure, cheap oil, mixed too lean, lean jetting, rebuilt with not enough clearance, cheap aftermarket parts etc.




As for a rod kit, the Hot Rods kit sounds suitable.

I know the name but know nothing about them. I would buy US made parts only and OEM whenever possible when it comes to critical parts like this.


OEM ROD AND OTHER PARTS FOR SALE

http://www.cmsnl.com/yamaha-ytz250n-1985_model9122/partslist/A-06.html#results

.


The piston had some light scarring marks, but it is ok. It was freshly bored .010" over and ran for a little bit before the motor quit on the previous owner.

Sand them lightly with 800 wet just to remove any protruding edges. Do not remove the scratches.




Thanks for answering my question by the way, I appreciate it

Sure no problem, hope it helps. Others may have some info for you also.