HD happy time

Discussion in 'Performance Mods' started by unraw, Dec 4, 2008.

  1. unraw

    unraw Member

    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.
     

  2. unraw

    unraw Member

    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.
     
    Last edited: Dec 4, 2008
  3. mountain80

    mountain80 Member

    If you are have it apart then goto the stihl dealership and order a needle bearing for the top of the rod out of an 028. Havent put mine in yet but i shaved 0.050 thou off the head and trued the crank with better crank bearings. I run 5500 rpm all the time and have 2800 kms and it still goes strong fwiw. Do a compression test and see what the compression is.
     
  4. unraw

    unraw Member

    What crank bearings did you use? I will try to find a needle bearing like that. Was there a specific year for that chainsaw that that bearing comes out of? Did you bring the crank away to get it trued or did you do it your self?
     
  5. mountain80

    mountain80 Member

    No specific year just tell em the number and they will know. Cost me 12 bucks and good for 13,000 rpm. If I remember correctly the bearings are 6202 but you will find out for sure when you pull it apart. As far as the bearing name I believe it was NSK but it doesn't really matter the bearing is common just go to a bearing supply place and they will sell a decent bearing. I trued the crank myself(ex motorcycle mechanic turned machinist) as best as possible, the two crank halves still wobble slightly but that is do to the pin bores in the crank halves not being perfectly perpendicular but the bosses run good on their axis. The bearing on one side of the crank had 0.005 thou play on the crankshaft so I ended up using high temp bearing locker.
     
  6. Gru Bee expansion chamber dimensions

    I would like to build an expansion chamber for my 70cc. Gru Bee. Do any of you have a set of dimensions for one including header length/diam. and stinger also? That is what a bored mind does to one. KW:thinking:
     
  7. unraw

    unraw Member

    I will have to pull my bearings out of there and bring them to a bearing supply place to get other ones. I've heard of increasing you compression by sanding down your head with a piece of sandpaper on a sheet of glass. Has anyone done it this way? Can you give me a detailed description of how you did it? I don't have any milling tools or anything and our local machine shop charges around $75 and hour so that would not be very cheap.
     
  8. mountain80

    mountain80 Member

    I lapped 12 thou off the head to get rid of the small spigot on my head. I also made a thinner head gasket out of copper sheet, heated it cherry red after to sofften it and bolted it on. I took 0.05 thou off in total. Make sure you have adequate piston to head and piston to sparkplug clearance. I had to slightly grind a small bevel on the outside of the chamber for safety and it also produces what is called a squishband which forces the air fuel mixture in a concentrated package which helps with the burn and can produce more torque as a result.
     
  9. unraw

    unraw Member

    the thinner head gasket idea sounds like a good idea. Where did you buy the copper sheeting? Are there different thicknesses? What thickness did you use. (if there are different thickenesses)
     
  10. mountain80

    mountain80 Member

    I bought at the metasl supermarket which cateres to small volumes and hobbyists. Ended up getting it free as it was a small piece. Yes there are different thicknesses, I ended up using 0.019 thou but it was supposed to be 0.032thou. The stock headgasket was 0.057 thou so that is 0.038 thou less right there and the remainer was removed off the head. I must say it has alot more torque and revs well.
     
  11. unraw

    unraw Member

    so if I did just the thinner head gasket and used 0.019 thou copper sheeting, would this improve my compression enough that it would make a difference?
     
  12. mountain80

    mountain80 Member

    It would depend on how thick the stock head gasket is to start with. I bought a gasket kit when I souped up my engine and the head gasket in that kit was only 0.028 thou vs the 0.057 that was originally in my engine. Measure it with a micrometer or caliper and go from there. If you don't have these tools find someone who does.
     
    Last edited: Dec 11, 2008
  13. unraw

    unraw Member

    ya I dont have these tools. I missed driving my MB soo much that I did a wierd thing. I put it back together completly stock, and drove it. Its fun to drive in snow. I will continue this project maby in the spring because this is my winter bike. In spring I will drive my other one and then I can Soup this one up.
     
  14. unraw

    unraw Member

    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. Should I heat it up before I put it on or will it seal 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?

    Old Bearing

    New Bearing
     
    Last edited: Mar 2, 2009
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