3pg Rebuild Help

The Hurling Buffalo

Just found out my 1990 3pg 244cc Robin needs to be rebuilt as the piston is chewed up a just lil around the top edge like something got in the cylinder at some point. The strange thing is that the cylinder walls don't seem to be though. There is a very slight lip to the wall at the top but nothing uncommon as far as my engine repairing experience. The guy I got it from said it had been rebuilt and I am wondering if the guy just re ringed the piston after something happened and slapped it back together. It's been running for 2 years with no issues but then again we dont give it hell or anything but what do you guys think? And is there a good DIY for rebuilding this engine? I wish I could post a picture but I can't figure it out.

BGW

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The Hurling Buffalo

Also since i am rebuilding it I gotta ask..... Can I go bigger lol!

The Hurling Buffalo

Also my crank bearings all seem tight with no vertical slack when picked up on the shaft. As long as the bottom end is solid is it safe to just replace the piston and jug or just the piston? Or is a whole rebuild mandatory?

The Hurling Buffalo

If I have the machine shop bore the cylinder up .50mm for the larger piston will I need to have it sleeved or anything?

Sean5545

The machine shop I went to said they could do .50 without any hassle. Unless your badly gouged I would go to .25 over first and get yourself another rebuild out of the head. Going to .50 won't give you any noticeable power increase. As for doing the lower end also that's completely up to you, if your opinion is its good and you want to leave it then just do the top end. When I did mine I did everything together but I also was leaking all over the lower case.

Sean5545

I know I mentioned it in another post...you can buy the whole top end kit including the new head for about 75 bucks more then it will cost you for a new piston gaskets and bore job, again the decision is all on you. Don't forget to run your first tank mixed to the spec break in ratio, I know a 2PG is 52:1 with injector installed and 40:1 without injector installed....not sure if the 3PG is the same

rvkersh

I had ordered an after market kit for a 3pg. It was manufactured in India. When I tried to assemble the reed cage I had to do some grinding to get it to fit. After the engine was back together, it had 1/2 the power it had prior. Pulled it back apart and did some measuring, found the ports were poorly sized and not in the same location from the deck surface as the stock cylinder. Last time I will chance an after market kit, not saying all are bad, but not always the same quality as stock. Ordered a new stock piston .25 over, bored the stock cylinder, did some port work and cut .035" off the head. Been running 50:1 oil mix. It has been running flawlessly for the last 6 years. Mine pulls an 800LB lawn roller, a lawn trailer, and has many miles of road running at full throttle. Read an article several years back that stated they ran them lean with oil to get them to warm up quicker for golf. But if the vehicle was to run for sustained full throttle operation or heavily loaded such as a work vehicle to use a richer oil mixture to prevent piston scuffing and premature ring failure. I know what the operator and service manual says for a golf vehicle, so let the beating begin.

The Hurling Buffalo

I don't want to just throw the extra $75 away if I can bore and rebuild the head.

The Hurling Buffalo

I went ahead and ordered the piston and ring set as well as the gaskets and crank seals. What I really need to know now is how much slack does the machinist need to allow for the new piston?

Sean5545

I've always handed them the new piston with the rings on it and the head and said "make it fit". They measured and did the rest...