Sounds like its time for a rebuild

Motorbike Wanabe

Motorbike Wanabe

Member
I've got about 1500 miles on my Grubee 66cc and it's starting to sound like it's got a bad case of loose knuckles. There's a rapping noise coming from within that I'm quite sure is a loose rod (either top or bottom) and I'm thinking of rebuilding it before I have to replace it. I looked and so long as the crankshaft isn't all boogered up, I should be able to get everything for about $45. That's new rings, rod, etc. The question that I have is, Gas Bike.net, where I bought the engine, only shows one piston, rod, ect for the 66cc engine. Are these engines that uniform in those main components that they will fit my Grubee engine?

The engine still runs great and has good power but, when it starts to wind out, you can hear the size of the marbles get considerably larger.
 
Very possible. I'll know more once I get it broken open. Now, the next question that I'm asking is, if it is only a wristpin, how much deeper should I go? If I'm going to order the parts, should I get all of them and do it all? I mean, how much could it actually cost $50?
 
I would take the cylinder off and check to see which bearing is loose. You should be able to tell at that stage if it is just the wrist pin or the bearing on the crank pin, or both. Then replace the ones that are loose.

Not that it qualifies my opinion or anything, but I work part time as an aircraft mechanic (licensed and everything). If it were my BIKE I would do what I said above, if it were someones airplane, I would recommend a complete overhaul of the engine. Of course, airplanes (usually) don't use little chinese 2-strokes either. ;)
 
Tim,

True, it's not as much of an issue as would be in a plane. Now, my question to you would be, have you done this before? I've thrown around how much to tear down the engine. I understand that if you find a bearing bad, then you've probably found the issue but, the rest of the parts have the same amount of time and wear on them, they just don't show it as much as the part found faulty. How much of a difference does that make? I don't know but I may find out. Still looking at options and parts. Mainly, would all 66cc parts interchange? like the bearings and stuff?

Thanks for any info!
 
TBO in HT language =

T = seconds spent in construction

B = Belts of the hammer

O = operations per second per T*B

Therefore TBO = 60 motors/hour

Total Belts /Hour
 
I actually have not needed to do this on a bike engine yet.

Here is my theory though- sense there is no oil being pumped to the bearings, you rely on the oil in the gas mix to lubricate everything, which we all know. That oil may not always get to everywhere that it needs to and so you end up with some parts more worn than others.
 
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