loss of compression

ex-28

ex-28

New Member
Have an 8cc zoom zit on my seccond seaSon. Alll running fine , today we were driving out to go fishing and all of a sudden I heard a hissing sound thought I blew a tire but they were ok , now I cAn only go about 35 km and it takes forever to get there , any hill and I toatallly slow down , if I have clutch disengaged. It revs up and sunds great and fine ,but soon as I release clutch its fighting to go , any ideas ? I checked the gaskets they All look good and I have no air leaks as I have gasket sealer on all points.. I was thinking maybe I blew a ring but can't check it till I get home later tonight I don't think carb it plugged as it idles and revs perfect but I do have to keep it reved up a bit to keep it running
 
Ya were about an hour away from home. And fishing so onnce I get home will také off head and check it , thanks for the input I appreciate it
 
Based on your description of a "hissing sound", I vote for a blown cylinder head or base gasket too.
I too am interested in what you find after teardown.
 
welp got another 15 min ride out of it then the same ticking noise and engine slowed down to a hault , nephew towed me home with his zoom bike and took the head off , sure enough rings blew and scraped up the walls pretty bad ,


thankfully i have a spare head body piston ad rings after i replace top end of engine should i run more oil for a re break in period ?
 
took the head and piston out , i took out the 2 clips that hold the shaft pin through the piston , but i couldnt get the pin out so i had to tap it out with a hammer , when i got it out theres a berring in the middle of the cam shaft that the pin goes through , but only 1/2 of it was here , i guesing other 1/2 is in bottom of motor now so i will have to take motor off and flush it outr well with gas.

has anyone ever heard of the berring on the top of the cam shaft breaking and working its way up the piston and the walls ???

wondering if my bottom end is ok now , i can freely move the cam shaft up and down with no resistance and everthing feels smooth , i just can see how that berring on the cam shaft would break or if somthing else in my bottom end did , but i dont think so.

any ideas what i should do ? flush out bottom end and good to go with new head body piston and rings.
 
That is called a connecting rod, not a cam shaft. The bearing that failed on you is the wrist pin bearing, also known as the small end bearing, piston pin bearing, or gudgeon pin bearing. All the same parts, just different names for them.
Unfortunately the teeny rollers in the stock bearings are known to be soft and fail easily.
I am sad to say that is what you are dealing with now.
You may be able to get away with holding the engine up-side-down and rinsing it out well with kerosene, but I wholeheartedly recommend splitting the cases and doing a very thorough inspection of every last nook and cranny. Also unfortunately when this happens metal debris is known to work it's way into the crank pin bearing, also known as the big end bearing. It is on the other end of the connecting rod, in between the flywheels.
The only way to inspect this bearing is to press apart the flywheels to gain access to it.
Alot of folks get lucky and this bearing actually survives a wrist pin bearing failure, but I lean towards the side of caution and warn that not all are this lucky.

I leave the choice to you.
Take a calculated chance that the crank pin bearing is ok and simply replace the top end after rinsing out the crankcases (or better yet, splitting them and inspecting them), or a replacement engine is in order.
It is much cheaper to buy a whole new replacement engine than it is to buy all the parts needed to rebuild a whole engine.
Either way, I wish you the best of fortune!
 
Last edited:
GearNut said:
That is called a connecting rod, not a cam shaft. The bearing that failed on you is the wrist pin bearing, also known as the small end bearing, piston pin bearing, or gudgeon pin bearing. All the same parts, just different names for them.
Unfortunately the teeny rollers in the stock bearings are known to be soft and fail easily.
I am sad to say that is what you are dealing with now.
You may be able to get away with holding the engine up-side-down and rinsing it out well with kerosene, but I wholeheartedly recommend splitting the cases and doing a very thorough inspection of every last nook and cranny. Also unfortunately when this happens metal debris is known to work it's way into the crank pin bearing, also known as the big end bearing. It is on the other end of the connecting rod, in between the flywheels.
The only way to inspect this bearing is to press apart the flywheels to gain access to it.
Alot of folks get lucky and this bearing actually survives a wrist pin bearing failure, but I lean towards the side of caution and warn that not all are this lucky.

I leave the choice to you.
Take a calculated chance that the crank pin bearing is ok and simply replace the top end after rinsing out the crankcases (or better yet, splitting them and inspecting them), or a replacement engine is in order.
It is much cheaper to buy a whole new replacement engine than it is to buy all the parts needed to rebuild a whole engine.
Either way, I wish you the best of fortune!
Click to expand...


thank you for all the info on this i really appreciate i , i was going to flush it out and hope the wrist pin berring is ok , i do have another piston berring in my other motor that blew the rings here that i could use as i know splitting the engine is alot of work and i dont have new gaskets to replace them in there . going to unmout the engine from the bike today and see where i am at

thanks again
Mike
 
quick question , theres no oil in the bottom crankcase is there ? , thats just oil in there from my gas/oil mixture ?

just wondering if i can use gas to flush out the bottom end of engine is all
 
You are correct. There should only be a little bit of residual oil in the bottom end, left over from the fuel mixture.
I always recommend using kerosene as it makes for a good solvent that is not nearly as volatile as gasoline, and will not harm the rubber seals like mineral spirits, paint thinner, or MEK. I simply cannot recommend using gasoline as I feel it is too dangerous, but it would work.
 
GearNut said:
You are correct. There should only be a little bit of residual oil in the bottom end, left over from the fuel mixture.
I always recommend using kerosene as it makes for a good solvent that is not nearly as volatile as gasoline, and will not harm the rubber seals like mineral spirits, paint thinner, or MEK. I simply cannot recommend using gasoline as I feel it is too dangerous, but it would work.
Click to expand...

I'll second that. When putting it back together add a few cc of oil to the crank case. Oil what you can get to.
 
welp all back together and running smooth ! thanks for info and help all , on a side note this thing is slow now :( i was averaging 50km beforee now its at about 30-35 , would having 2 gaskets on exhaust affect that? i accidently put 2 on oops :)

or does it need to go through 2 tanks agian for break in , which is what i a guessing then it should speed up again
 
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