Combat motor rebuild questions

maylar · Jul 27, 2012

My buddy is rebuilding his 72 Combat motor after an unfortunate oil related incident.

First question is about removing the nuts on the connecting rod caps. They seem to be 1/4 Whit but we can't get a wrench or socket on them as the caps prevent access. What's the correct tool?

Second question, if the crank journals need turning is that something that any good auto machinist can do, or does he need to find a Norton shop?

Thanks

rvich · Jul 27, 2012

I am thinking my nuts were UNF, 1/2 inch. But this was on a '74. Memory is kinda fuzzy on it tho. As for the grinding, seems I have seen comments here that the problem is the radius. It apparently takes redressing a wheel and a lot of shops won't do it for one crank.

Russ

pete.v · Jul 27, 2012

In my estimation the most critical aspects of the Motor is the crank journals, particularly the radius in the corners. You need knowledgeable expertise and nothing less.

ILLF8ED · Jul 27, 2012

pvisseriii said:
In my estimation the most critical aspects of the Motor is the crank journals, particularly the radius in the corners. You need knowledgeable expertise and nothing less.

The word on making sure the corner radius is correctly machine is if it isn't done correctly the crankshaft can break. Reference the workshop manual for spec or as mentioned take it to an experienced shop.

lcrken · Jul 27, 2012

maylar said:
My buddy is rebuilding his 72 Combat motor after an unfortunate oil related incident.

First question is about removing the nuts on the connecting rod caps. They seem to be 1/4 Whit but we can't get a wrench or socket on them as the caps prevent access. What's the correct tool?

Second question, if the crank journals need turning is that something that any good auto machinist can do, or does he need to find a Norton shop?

Thanks

I use a 1/4 Whit socket (3/8" drive) from an old Japanese made socket set. It is a tight fit to clear the rod cap, but it does fit. The 1/4 W box end wrench in my Britool set also works, but I find the socket more convenient.

Ken

Hobot · Jul 27, 2012

i ground outsides down on both 1/4 W socket and a bent shank end wrench and worked well on half hand full of rod nuts. i go by .0065" stretch not by torque wrench for these but find torque valves given gets bolts in the .006" acceptable stretch range. Do note some rod nut seats needs bottom surround clearance to avoid trapping a silver under nut for fracture prone stress riser.

Combat motor rebuild questions

maylar

rvich

pete.v

ILLF8ED

lcrken

Hobot

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