A couple years ago I rebuilt my son's LT80. In the process I rebuilt the crankshaft with a new rod. I had the crank true within .001" in all directions. In the process of the rebuild I took .030" off the head. That was too much and the piston contacted the head. I replaced the head with a stock one and he rode it for two years. The piston pin and rod bearing wollered out in the piston. I took it apart and split the case to clean out the junk. While out, I put the crankshaft in my truing fixture and it is off by .012". Now I'm scared that if I true it back and run it that it will not stay true. Could the initial piston contact with the head knock the crank that far out of whack?

Thanks
Lynn

 

Lynn, I think most are bent during the assembly of the cases. I get everything to slide together freely. I know alot of ppl get it 1/2 way in and it sticks then they use the bolts to draw the cases together. IMO, not good.
IMO, something is different. My readers and I have prolly shaved 100 heads .030 and non of them hit.
This might be why I recommend a new crank instead of fitting a new rod. I can't imagine what would be different on the new rod, but whatever.
I'd be happy to explain how I do it.

"The piston pin and rod bearing wollered out in the piston" 20 years and I've never seen this happen.

 

Hello I am new to the atv world and yhis site. I recently purchased a 1988 lt80 for my son. It was a project for us and we are rebuilding the entire thing. I have purchased a new crankshaft and bearing kit as the old one was shot. I have split the case and removed the old crankshaft and bearings. Im having a hard time pin pointing how it should be assembled. I have read I need a tool to pull the crankshaft back into the case and I have heard of a heating,freezing and sanding method. Any advice would be greatly appreciated. Thanks in advance!

 

I guess you have read my opinion.
I get everything to go together without any binding. That's the key to a straight crankshaft after installation.
You've taken on quite a project.

 

Yes it is quite the project! I did read your comment and understand that everything must go and smoothly without cattywampus pressure. Could you possibly explain to me how you press bearings on and press crankshaft back into crankcase? Thanks I really appreciate your reply.

 

I will PM you.
Not right now tho.
Long day.

 

Awesome! I could definitely use advice. I have done some research and can't seem to find a straight answer. I have heard I need a pull tool, sanding, heat and freezing.
I'm just not sure and don't want to tear anything up. Thanks and look forward to hearing from you.

 

That's because there is always more than one way to skin a cat!!


Crank tool - this works by pulling your crank into an already seated crank bearing in the case...it pulls on one end of the crank and pushes on the same case...in theory there is no way to end up with a crooked crank as all the forces are on the same side of the crank pin. However you need to seat the crank bearings in the cases...


Seating the bearings:
1) Use a press (machine shop does this)
2) Make a press - I've used a socket, plate steel and a bolt/nut to make a mini press...add in an air gun and some heat (it doesn't hurt) and it will pull the bearing into the case - the equal forces at each end will keep the case from getting damaged
3) Hot & Cold - throw your bearings into the freezer overnight...next day heat up the cases (or the bearing seating area with a torch)...drop the very cold bearings into the very hot cases...they should drop right in or require a love tap from a rubber mallet.


No crank tool - Hot & Cold again...this time throw your crank into the freezer overnight...heat up the cases (or bearing area), quickly install the very cold crank into the very hot bearings (don't forget the yamabond or other case sealant)


Jack's method - sanding the bearing riding surface on the crank is a novel idea, just don't know how to accomplish with decent results not having a lathe...

 

I know I say sand but it's really a good clean-up. The crank is very hard thus actually sanding it down isn't going to happen quickly.

 

Yeah...I was curious about the "sanding"...thx for the clarification. I guess it doesn't matter how...but rather the end result.


All I know was this it was a PITA to split the cases...sure hope it goes back together a bit smoother...


I was, however, very impressed with the condition of the internals...well built little critters!!!