R80 heads on R100 jugs & pistons

[gog]

I have acquired a nice set of R100 cylinders and pistons, vapour blasted with new rings and pushrod tubes installed.

I am going to fit them on to my R80RT. My bike is a 1986 and the new jugs are off an '88 so shouldnt have any issues with o-ring and casing differences. I have read that ideally the R80 heads should be machined to accommodate differences in the R100 pistons to optimise squish bands and compression, but I have also heard of people running them stock without any problems. I understand that there may be small areas in the chamber that suffer increased carbon buildup and a slightly less than optimal power output, but Im not overly concerned about this unless I can be reliably told different.

Im considering changing to 2.66 needle jets in the carbs from the standard 2.68 (fuel consumption apparently better?), and possibly swapping to a 135 main jet from the current 145 as seems that may release a few more horses.

I have been putting off pulling the heads for ages due to a potentially pulled cylinder stud (evidence of it being shortened with a hacksaw (top NSF stud) but my grotty, leaky PRTs do need addressed.

Any thoughts appreciated.

 

[Beemerboff]

Standard stock 1000 cc pistons/ barrels stock exhaust, jetting , etc worked OK on my G/S.
With a freer flowing exhaust and inlet system, a Boyer Micropower ignition 40 thou off the head and a little unshielding of the valves it works better than OK.

Getting someone who knows what they are doing to set the piston/ head clearance and and perhaps rework the heads will improve most every airhead, not just those with a barrel swap.
I get 20 km/L with 2.68 / 145, dont think I would get much better if I leaned it out , but it is on the rich side.
And I dont pussy foot around, rarely get any more than 5000 km out of a set of tires .
My riding buddy rides a GSXR750R, the first air /oil cooled type and I can match his speed up our test hill so my bike seems to work better than you would expect, but the low G/S gearing probably helps both the perceived performance, and fuel consumption.

 

[gog]

cheers bb. good to hear that im unlikely to blow the engine up in this config without reworking the head. i appreciate that some head work may benefit, and may well consider it once i have a bit more disposeable cash (2 daughters and a high maintenance OH, wishful thinking perhaps?).

20km/l works out as 56mpg i think, thats pretty damn good. I dont think ive been even close to that on the R80, but i havnt really worked it out. I suspect its around the 40mpg mark though.

 

[ianboydsnr]

My R80Gs has 1000cc barrels and pistons, seems to work ok!

not done that many miles on it, but I can't see it being any problem.

 

[gog]

thanks ian. did you stick with the standard jetting in the carbs?

will be checking the state of my valves when i pull the heads, as suggested by someone on adv. anyone know where i can get the heads looked at if needed? prefer scotland or north england but suppose doing it by post is an option. would be interested also in a rough guide price wise if anyone knows.

 

[Kenny]

Also done it a few times and stayed with the standard jetting etc ( carbs are usually worn anyway )

I can't believe this is almost 20 years ago

 

[gog]

nice one Kenny. what are you doing to that poor pannier though?