HD Happy Time Engine

unraw

New Member
Oct 30, 2008
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Grunthal, Manitoba, Canada
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. :)
 

unraw

New Member
Oct 30, 2008
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Grunthal, Manitoba, Canada
Re: HD Happy Time

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.
 

jasonh

New Member
Jun 23, 2008
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Re: HD Happy Time

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

Technocyclist

Motorized Bicycle Senior Technologist
Jul 7, 2008
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Asia
Re: HD Happy Time

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.
 

unraw

New Member
Oct 30, 2008
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Grunthal, Manitoba, Canada
Re: HD Happy Time

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.
 

jasonh

New Member
Jun 23, 2008
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Re: HD Happy Time

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

jasonh

New Member
Jun 23, 2008
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Re: HD Happy Time

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

ran49

New Member
Mar 5, 2008
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So.In.
Re: HD Happy Time

I can tell you seperating the crank is a PITA.After exhalsting all the means in my home shop(heat,cold,6 ton press)I gave up and took it to a machine shop.It took their largest press and sounded like a gunshot when it finally gave.($20.00).All this to find the bearing is a real oddball.Never could find one.Bear in mind reassembly will be more difficult as the two halves need to be perfectly indexed.Never got that far.Ron
 

ran49

New Member
Mar 5, 2008
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So.In.
Re: HD Happy Time

"Just buy a new crank+rod assembly"
I ended up just buying a new motor.Now I have alot of spare parts but no lower bearing upgrade which was the my original objective.
I have read where a upper bearing from a Stihl 028 fits the wrist pin on these motors.Ron
 

jasonh

New Member
Jun 23, 2008
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Re: HD Happy Time

don't know if you have to, but if done correctly it definitely won't hurt, and will most likely help.
 

unraw

New Member
Oct 30, 2008
71
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Grunthal, Manitoba, Canada
Re: HD Happy Time

I got a PM back from ChrisHill and he said that he uses INA bearings. They can be found at Canadian Bearings. Mabe I can find a Canadian bearings near my house.
 

ChrisHill

Manufacturer/Dealer
Re: HD Happy Time

Yes, the bearings I put into my engines are INA. You will want to make sure that you bring your originals in when you go to see those guys so they can get you an exact replacement...depending on what you're after, it could be "special order only" and a little on the pricy side.
Good luck.
 

unraw

New Member
Oct 30, 2008
71
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0
Grunthal, Manitoba, Canada
Re: HD Happy Time

The needle bearing was starting to sound loose when the engine was running so I took it apart and ported it. I found some copper sheeting .010 thou thick and made a head gasket. Do I have to heat it up so it seals or can I just use it how it is?
I got a needle bearing from my shtil dealer and it is not as wide as the one that was in there. Should I use spacers on each side or should I not worry about it?

New Bearing

Old Bearing

brnot
 
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