Pit Bike Rebuild

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I got a old PW 80 a couple years ago for the right price, free.
It needs a rebuild. The whole top end is toast as well as the the big end rod bearings. I can grab the rod and move it moves about 3/4" side to side.

So, I price parts and say its too expensive to fix and it sits. I just recently found some deals on ebay. New crank, main bearings, seals, and gasket kit for less than $100. Then, new top end including cylinder, pistone rings, gaskets, wrist pin, bearing , clips, gaskets, for $100.

I've been into a few 2 strokes before. No big deal. I tear the thing apart, throw the bearings in the freezer, heat up the cases a touch, bearing are in like flynn.

Next up, install the crank. It was a TIGHT fit. I pulled it into the case with my homemade tool. I've had it for about 15 years works great. Basically a piece of thick aluminum with multiple holes. The crank goes in the center hole, put some shims on it, put the crank nut on the crank and tighten away and it pulls itself into the bearing. I don't need no stinking press or machine shop!

After that, the trans goes in. Pretty simple with this thing and only 3 gears. Then the other case half. That went real well too. Just slapped em all together. Lined up the trans shafts. A tap with the dead blow, a LIGHT tap. The it all pulled together with the case bolts. Cases assembled in no time!!

I go to spin the crank and its tight as HELL. Doesn't want to go past TDC if moving it by hand. I can typically grab the con rod and pull it up and the crank will spin all the way around freely on a fresh rebuild. Not this thing though. It tough as nails to turn by hand. I put a nut and wrench on the crank to spin it. It feel smooth but not free? Never had this before.

I checked to see if there is any veritcal or horizontal runout of the crank fly which may indicate an inproper rebuild on the crank when the crankpin is pressed in. I didn't notice anything over a .001" difference in either direction.

Anyone ever have this experience? It turns nice and smooth. NO grinding. It just seems to take WAY more effort than it should.

One more question. There was no case gasket in the kit. I had some permatex ultra black high temp RTV silicone. Put a very thin layer on one case half and then assembled. Anyone have input on this? Hopefully it holds. It seems like it would be fine. There was no gasket there when I tore it apart. Just a real thin layer of yamabond.

Sorry for the lengthy post, I'm bored tonight... Hope to get this bitch running soon.

Got the CR500 working good. I filed the shit out of the clutch basket and it cured my disengagement issues. I can't remember the last time it worked so smooth! Getting ready for the mem day weekend riding trip with the family and hope to have all this old junk working by then.

 

[MikeTD3]

Not sure on the tightness of the crank assembly...perhaps the fact that the crank was a tight fit to begin with is an issue.

I either use Yamabond or Loctite 515 for crankcases, but black ATV sealant may work.

 

[06VMAXIMUS]

I rebuilt my sons Yamaha Blaster engine, and bought a new aftermarket crank assembly off e-bay. The new one was so tight I stopped and put a set of Micrometers on it, found it was .0015 larger than the OEM crank. Chinese garbage. Had to polish it for an hour and a half to get it the correct diameter.

 

[RaWarrior]

The alt and gear covers on my Max are sealed with ultra black sealant. Never so much as a weep of oil, more than I can say for the OEM gasket, which I could never get to quite seal right. Always weeped oil, slowly covering everything behind it in rust-proofing. Can't have a Max imitating a Harley, can we?

Anyway, I'd check the crank diameter. If a kit was only $100 off ebay, chances are it's a chinese reproduction, and like vmaximus said, probably not quite the right size. At least it's too big instead of too small.

Can you start the motor, or is the crank too tight to let it run? If it will run, I'd say just run the shit out of it for a bit and the crank will kind of figure itself out after a few minutes of running. If it's too tight to start, then you really have no choice but to polish or turn it down.

 

[[email protected]]

Well, I decided to say f-it and try to run the bike as is. I put it all together the other night.

This bike was picked up for free. My brother in law was going to fix it for a friend of the family but gave up. He said it was too far gone. It was sitting outside for 2 years or so with the engine torn apart and in boxes.

After putting it all together I took it outside and kicked her over. No signs of life initially. The third kick sounded like something. The fourth kick and it fired right up :eusa_dance:

It would only run with the choke on and had a hanging idle/increasing idle issue. I rode if for a few minutes and pulled the plug. Looked real lean. I've removed the oil injection system and am running premix fuel and installed a clamp on air filter since the stock airbox was MIA.

I raised the needle and played around with the A/F screw a bit yesterday and it is now running really good down low. The top end feels a bit sluggish though so I'm thinking it may need a main jet change, or I'm just too damn heavy for the little thing.

All in all I'm glad I did the work. Hopefully it stays together for awhile.

 

[gamorg02]

Well, I decided to say f-it and try to run the bike as is. I put it all together the other night.

This bike was picked up for free. My brother in law was going to fix it for a friend of the family but gave up. He said it was too far gone. It was sitting outside for 2 years or so with the engine torn apart and in boxes.

After putting it all together I took it outside and kicked her over. No signs of life initially. The third kick sounded like something. The fourth kick and it fired right up :eusa_dance:

It would only run with the choke on and had a hanging idle/increasing idle issue. I rode if for a few minutes and pulled the plug. Looked real lean. I've removed the oil injection system and am running premix fuel and installed a clamp on air filter since the stock airbox was MIA.

I raised the needle and played around with the A/F screw a bit yesterday and it is now running really good down low. The top end feels a bit sluggish though so I'm thinking it may need a main jet change, or I'm just too damn heavy for the little thing.

All in all I'm glad I did the work. Hopefully it stays together for awhile.

any pics?