Billet case am6



LewieBike

Active Member
Joined
May 21, 2014
Messages
685
You use the bushings or just a up graded bearing? I've always wondered how well a bushing would work without oil being fed under pressure for lub.
Brass rod upper bushings in a 2 cycle engines are a really bad idea with low oil to fuel premix ratios. This is reason why nearly all small 2 stroke industrial engines use needles and rollers top and bottom. It is because 2 strokes don't have any thrust reversals on the rod bearings so the lubrication film has a chance to renew itself. You would have to run 16:1 to 20:1 mixes for these to last any amount of time.

It's just a bad idea, especialy when used in a really high RPM/performance 2 cycle engine.

Duke Fox of Fox Model Airplane Engines, and one of the 1970's writers for Cycle World explained in detail the reasons why you never find bushings in modern 2 stroke engines any more. And both these articles were written in the 1970's. Needle bearings for the small end of the rod can work reliably for hundreds if not a couple thousand of hours with the fuel-oil mist of a 40:1 fuel ratio in weedeaters and chainsaws.
 
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Ethan

Guest
Would anyone know if u would be able to buy the gt90 and the am6 conversion kit and put that into the gt90 bottom end or is the am6 bottom end designed with different sizes or something
 

ESmalik

Member
Joined
Oct 22, 2019
Messages
54
Would anyone know if u would be able to buy the gt90 and the am6 conversion kit and put that into the gt90 bottom end or is the am6 bottom end designed with different sizes or something
The issue with the gt90 case is that the stud holes need filled and redrilled and there is not nearly enough meat on the transfer port area of the case. The transfers of the am6 cylinder alone are wider than the entire chinagirl case. It can be done with the proper spacer plate setup but it is not a simple conversion my any means. Its not even simple with the billet case
 

ESmalik

Member
Joined
Oct 22, 2019
Messages
54
Brass rod upper bushings in a 2 cycle engines are a really bad idea with low oil to fuel premix ratios. This is reason why nearly all small 2 stroke industrial engines use needles and rollers top and bottom. It is because 2 strokes don't have any thrust reversals on the rod bearings so the lubrication film has a chance to renew itself. You would have to run 16:1 to 20:1 mixes for these to last any amount of time.

It's just a bad idea, especialy when used in a really high RPM/performance 2 cycle engine.

Duke Fox of Fox Model Airplane Engines, and one of the 1970's writers for Cycle World explained in detail the reasons why you never find bushings in modern 2 stroke engines any more. And both these articles were written in the 1970's. Needle bearings for the small end of the rod can work reliably for hundreds if not a couple thousand of hours with the fuel-oil mist of a 40:1 fuel ratio in weedeaters and chainsaws.
We run ampco18 bushings in our am6 motors, its an aluminum bronze. We have thousands of miles, bottom end failures 14k+ rpm and
 
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