HD Happy Time

For my winter project i want to totally rebuild my old faithful pk 80cc. It has over 2000kms. I want to replace the crankshaft bearings, wristpin bearings, and piston rings good quality non Chinese stuff. I also want to do some mild porting and compression mods. So, I'm gonna need some help here. Does any one know of any high quality replacements for the rings, crankshaft bearings, wristpin bearings, etc. Suggestions welcome for what else i could do to it to make it more heavy duty/ faster.

I disassembled it and was shocked to find out that it had a needle bearing top end. I had always thought it was a bushing. There is some up and down play in the wrist bearing. The rings look not too bad. The cylinder walls look pretty scratched up. The piston looked like there was some overheating .i'm thinking thats from not using a muffler. To those of you who have changed the rings on your engines, at how many miles / kilometers did you do it at?

I put the cylinder back on without the base gasket to find out if the piston would touch the head. I put the head back on to see if i could notice a difference in compression when i cranked it. The piston didnt touch the head, but it might still when it heats up. Once i cranked it, I found out that it has no compression! (yes the spark plug was in) Is this from the lack of nothing sealing it between the crankcase and the cylinder?

Do you guys think that the crankcase bearings that are in there would handle the compression mods? I'm tempted to just rebuild the top end and do porting and mabe compression mods.

I believe most of the newer HT motors are needle bearing instead of bushed like the older ones.

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You need to balance and have the crankshaft centered. Then all other modifications can follow. It is the crank being unbalanced and off-centered that limits the RPM and causes so much vibration on this engine.

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This perticular engine is pretty good with viberations. I've built 6 happy time motorized bikes and this engine has barley any viberation compared to the rest of them. I think I read somewhere that for the wrist pin bearing you can use a bearing from a o81 stihl chainsaw.

You may want to try contacting Chris Hill. I believe he has sourced his own bearings and such for his motors.

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good idea. Is he a member of these forums? i dont know his website of hand.

I've seen him on here.

His website is here:
Home of the CH bicycle engine, CH80 Bicycle Engine Kits by Chris Hill, Motorized Bicycles, Bike Engine, Bike Motor, Bicycle Motor kit

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http://www.jasonhight.net/videos/mot...etowork-sm.wmv

Just PM'd him. Or at least the person whose user name is ChrisHill.

I wonder how much a machine shop would charge to balance one of these little cranks.

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