CMB RS91H ENGINE

[Piston1]

I am thinking about buying a couple of these engines. Does anybody has any performance feedback. Input from Naviga, IMPBA, NAMBA, Australia, etc., etc. is highly appreciated.

JOSE

 

[Piston1]

I am presently building a new "Roadrunner Twin Extreme". Yesterday I recieved a pair of new 91HRs. Here's some information. Motors are ABC type. All ports are substantially bigger than the 91RS ports. The top of the exhaust port is flat (horizontal), not arc'ed like the RS91s. Transfer ports are "T" shaped vertical similar to MAC motors but not exactly the same shape. Cylinder/crankcase port matching is good. Carb draw bar is big and appears to be strong / conmensurate with the size of the carb that it is intended to hold. The head button volume is substantially bigger than the 91RS volume and it has a flat squish band. The head button has a volume of approximately .89cc and it has a tub shape.

I found only one flaw. It appears that during assembly a small piece of debris got caught between the front plate and the drum plug insert flange. This condition was causing a slight misalignment of the plug to drum that was allowing the parts (plug/drum) to alightly rub against each other. Adequate alignment was restored after cleanup.

 

[Speed Jr.]

Thank you, great information! Where did you get them from if you dont mind me asking?

Larry

 

[Don Ferrette]

I am presently building a new "Roadrunner Twin Extreme". Yesterday I recieved a pair of new 91HRs. Here's some information. Motors are ABC type. All ports are substantially bigger than the 91RS ports. The top of the exhaust port is flat (horizontal), not arc'ed like the RS91s. Transfer ports are "T" shaped vertical similar to MAC motors but not exactly the same shape. Cylinder/crankcase port matching is good. Carb draw bar is big and appears to be strong / conmensurate with the size of the carb that it is intended to hold. The head button volume is substantially bigger than the 91RS volume and it has a flat squish band. The head button has a volume of approximately .89cc and it has a tub shape.

I found only one flaw. It appears that during assembly a small piece of debris got caught between the front plate and the drum plug insert flange. This condition was causing a slight misalignment of the plug to drum that was allowing the parts (plug/drum) to alightly rub against each other. Adequate alignment was restored after cleanup.

Hey Jose-

What are you going to use for a cowl on your Roadrunner that clears the carbs? :blink:

 

[Piston1]

I bought them through Bob Kernodle but they came straight from Tidewater.

I have one of Ralph's prototype carbon fiber cowlings, works great without interferences.

 

[BigChuck]

Also the Eagle Cowling works. That what I have for the K-motors.