wrist pin bearing

[brianjlinke]

i have a 70cc drr and just blew up my second motor. wrist pin bearing both times, quad was running great and fast right up until bearing came apart. i have a motoforce crank with 12x16mm bearing i have noticed other cranks take a 12x17mm. anybody else have problems with the smaller motoforce wrist pin bearings

[selbygirl]

when you put it together are you lubing all your parts i put one together at the track dry and it only lasted an hour now when i put motors together i use tons of 2 stroke on the parts good luck tommy

[brianjlinke]

i looked at my calender and counted up the races i got 5 races first motor 4 the second. there has to be something that is causing this crank? bearing? oil? yes i am oiling during assembly the motors ran great and showed no sighs of blowing up, 170compression the night before

[chuck 8A]

We had a similar issue a couple months back where we blew two motors in a row at the gncc nat's. When you take it apart are the little needle bearings cut in half??? Also are you running the coil/cdi box combo (yellow one). chuck..

[D&DDAD]

why ask about that coil cdi think thats whats doing it

[chuck 8A]

Yes.... Possibly. My issue was that I bought this combo thinking that it would be nice to get rid of an additional box and a little wiring. Not only that, it was adjustable. I installed it and the motor had a small skip on wot only. Ran it in a few localls and won the races. I first thought it could be jetting or the adjustment dial for advancing the timing so I was all over the board with it. I had two wrist bearings come apart back to back much like this guy. Completely trashing two cylinders and one crank:grr: Turns out I needed a different style stator to go along with it. I was so disgusted by this point and I removed it all together. The needle bearings both time look like you have taken a hacksaw and cut them down the middle perfectly. chuck..

[fomospede]

this yellow box is it the one sold at gforce? iff so weve used ours for tons of hours with no problems at all ! how far are you advacing it ??

[chuck 8A]

Yes it is the one from g-force, Gary was the one to help me with solving my problem. He said that I would need like the apex style or maybe slot my drr stator to make it work. I decided I could not afford any more motors and went back to stock. I tried it in various settings didnt seem to make a difference. Where is your setting and have you got a different stator or slotted one? chuckl.

[D&DDAD]

ok I running 08 apex have had trouble with it thanks

[BradLoomis]

Check the rod end for ( oval'ing ) where the needle bearing goes.

Check for knicks and gouges from the other needle bearing destruction.

Also, when the needle bearing is in it's place in the piston, there should be no more than 1/8" space between the needle bearing and the side of the piston. If there is more than this, the needle bearing will shift to one side and crack the needle rollers in half because they are not supported in the rod across the entire web. We had this problem and Gary got us the correct width bearing for the piston's we were running.

[fomospede]

now here is the real deal, this totally makes sense ,i would like gary to reply and give us his input on this! i will pm him and see what happens
as for how i set the cdi box . i advanced it fully then backed it off till the throttle response was a little slugish then moved it forward just a bit and have not touched it sense
Originally posted by BradLoomis
Check the rod end for ( oval'ing ) where the needle bearing goes.

Check for knicks and gouges from the other needle bearing destruction.

Also, when the needle bearing is in it's place in the piston, there should be no more than 1/8" space between the needle bearing and the side of the piston. If there is more than this, the needle bearing will shift to one side and crack the needle rollers in half because they are not supported in the rod across the entire web. We had this problem and Gary got us the correct width bearing for the piston's we were running.

[brianjlinke]

brad you are correct i had to much side to side movement. my crank is one manufacture and piston was a diff one and the wrist pin bear comes with crank 13mm wide and the piston calls for a 15. i guess ordering parts myself and a less exspensive crank didnt pay off , just bought my third top end .

[mydirtkids]

Gary and Les have saved me tons of time, money and sanity! Lucky to have them around:D Thanks guys

[BradLoomis]

brianjlinke,

Glad you got it fixed and didn't cost you alot more problems down the road.

Now get that kid back out there racing and smiling!