Aluminum rod 5A motor

[Mark Annan]

I have some tech questions.  I have an early 5A motor that I'm getting ready to do some work on.  I am hoping to build a 152cc engine out of it.  As I recall the aluminum rod is required to build one.   What type of bearing set up is used on the big end of the aluminum rod engines?  I know the pin end is a bronze bushing, I assume the big end uses a roller bearing and some kind of hardened insert in the rod.  How reliable is this rod setup?  Are the big end bearings replaceable and if so are they available? Does the pin bushing need to be modified?  Any help would be much appreciated.

Mark

 

[Doug Wilford]

Mark;
The big end of the alum rod uses the same bearing as the steel.   The reason we had to use the alum rod for the 152 was because we could ream out to size the wrist pin for the 152 piston, the first pistons were from Yamaha (and don't ask me the year or model,Yamaha, the memory banks crash on that one) and then Wiseco made them.  There is a special tool, (jig) and adjustable reamer to ream the bushing while the engine is complete, except for the head and cyl. of course

 

[Mark Annan]

Do the Wiseco pistons require the aluminum rod (and bushing reaming) or is the pin size the same as the stock Sachs piston?  How much rebalancing is required when installing the 152cc piston?  Is there any additional cylinder machining required, other than boreing it to fit?  One last question.  I know that the radial fin head from a 125cc bike is recomended.  Is the combustion chamber resized to adjust the compression ratio?  I have a later model 5B head that has a much larger combustion chamber that I am planning to use.

Thanks,  Mark

 

[Doug Wilford]

Mark;
The Wiseco piston does required reaming the bushing, besides boring the dylinder you also need to machine off the bottom flange, the head was also machined to compensate for the larger bore and bring the compression back to a useable amount.  I am at a loss on how you could use a 5B head.   I am not aware of any cast iron 5B engines??? Write me at [email protected]