R90/6 Jugs on an R75/6

[bprigge]

Hi Guys,
Does anybody know if '76 R90/6 cylinders will bolt up to '76 R75/6 heads
and crank case? There's a pair of R90/6 cylinders on ebay this week.
Sure could use a little extra torque going up those mountain sides with my
fully loaded R75.

thanks, Bruce

[flash412]

I have put R100 jugs on an R80 bottom end without any problems at all.
While I have never personally done it with your two specific engines. The crankcase, crank, rods, cam and pushrods are all the same between the two.

IIRC the R75 has smaller valves than the R90. But what that means is that you'll have a lot more torque and you can probably run the carburetors from the R75 without much tuning effort.

If you have any doubts, take a good hard look at the parts fiche for both.

[James.A]

There is an E.O. change in 1975 regarding the cylinder barrel spigots and the fly-cut holes that they fit in. Generally speaking, the model year build out occurs in september of any given year. The change correlates to the switching from flat cylinder base gaskests to O-rings. , the later E.O. being O-rings. You should be O.K. if they are both 1976 assemblies. How much do you trust the seller?

[bprigge]

Thanks for the replies WOODNSTEEL and FLASH412,

The seller has a 99.8% positive rating out of 450 transactions so I trust
him/her. Don't really know who it is. If the jugs are not what's described I
would think the seller probably doesn't know it. Nobody has placed a bid yet
so maybe everybody knows something about the seller that I don't????

Do you think the vibration factor would go up much at cruise RPM? I run between 4000 and 4800 rpm when traveling.

Also, the seller says the jugs have some broken fins. Can those be repaired
by a good welder/fabricator? I weld myself but have never tackled aluminum.

Bruce