Combat motor

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Hello everyone, hope you all had a Merry Xmas and wish you all a Happy new year

I have a 1972 Roadster with a combat motor which has done 7,400 miles, and has never ( to my knowledge) been pulled down. I have heard that this motor is a bit fragile, due to oil problems. I haven't had any problems yet, but i do not rev past 6,000 and never cruise at greater than 4,000 RPM (115 KPH ). Is there anything i can do to prolong the life of the motor ??. Any advice would be appreciated

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Allan
 

L.A.B.

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The most worthwhile modification you could do would be to fit the FAG NJ306E C3 main bearings, if they haven't already been fitted?

And maybe do the sump & breather modification while the cases are apart?: http://www.oldbritts.com/n_c_case.html
 

Ron L

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Your call. If you ride it as you say, keeping the revs down and maintain it with valve adjustments and oil changes, you probably can get quite a few miles in before problems arise.

However, when main bearings fail, they can take the crankcase and crank with them. I am never comfortable not knowing what is inside my motor. For peace of mind, I would take the motor down. Since you don't know how the previous owner (or owners) treated it, it could be a time bomb or it could be in excellent condition. Splitting the cases to replace the rod bearings and examine/replace the main bearings will also let you fix the oiling problem.
 
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A qualified engine builder could have you all sorted for a reinstall with two days labor plus parts. If nothing has gone bad so far. Compare that to the cost of braking something big. 4000 RPM is the absolute minimum IMO all the bad stuff has occurrences below this. Do some reading on dynamic compression ratios, hard loads are down low you are doing the motor no good doing a 3000 RPM long ride. My minimum RPM is 4250 for a cruse mode. Still returns 59 MPG US gallons. Third gear work for 60 MPH on my bike.
 
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