850 engine,,,,????

[Guest]

hi guys ,,,what bigger kits can i easily put on an 850 ,,,, ,,regards oldgrumpy

[Dogma]

What? Like a big bore kit? Probably easier to swap in a 1000G or 1100G engine.

[tkent02]

What he said, and use the 850 engine as a big bore kit on a 750.

[bwringer]

Yep. Just get the engine, carbs, airbox, and driveshaft from an 1100G or 1000G.


With that said... if you're unhappy with the amount of power from the 850, I might suggest you manfully grab the twistgrip and spin the thing. The 850 is a very entertaining engine, but you have to keep it spinning between 6,000 rpm and redline to get real thrust.

There's no replacement for displacement, of course, but a properly prepared and ridden 850 won't fall behind a 1000G or 1100G at all.

[zl9]

Nobody ever answered this. How big can you go with the 850 hardware?

[7981GS]

Back in the day, you could buy either a 870 kit or a 920 kit for them.
They are now incredibly scarce.
Wiseco will make you 70mm or larger pistons with the same 16 mm rod pin size but, you must buy the kit. ($6-700 IIRC)

Eric

[kdo58]

some one on here had custom pistons with higher compression, wilder cams, he was happy with it, you will have to search to find the write up on it.

[7981GS]

some one on here had custom pistons with higher compression, wilder cams, he was happy with it, you will have to search to find the write up on it.

I did all of that back in 1980 myself.

Eric

[kdo58]

http://www.thegsresources.com/_forum/showthread.php?t=104446&highlight=gs850+custom

http://www.thegsresources.com/_forum/showthread.php?t=119089

[49er]

JE 894 Update

I thought an update was now appropriate on this issue.

I did my JE 894 cc rebuild at 77000 kms. The bike has now just klicked over 100000 kms. It still runs great and out performs much higher capacity machines on a regular basis.

When I did my dyno testing, the bike was down on compression on the #3 cylinder. This was due to my clumsy hands at assembly resulting in a damaged oil scraper ring which gouged a groove on the cylinder wall. That pot was reading 160 psi when all the others were at 180-190. the Dyno Operator was concerned at the amount of smoke being generated during each run. I assured him the the engine wasn't about to blow.

I have since fixed the oil control rings on #3 and improved the carb tuning since the dyno sessions. Also, I have found that I can run 91 octane up to 28 deg C and gain further torque than that achieved while using 98 during the dyno sessions. When temps reach 30 deg+ I use 95 and accept the reduction in mid range torque to safe guard against detonation.

My current BB 850 is getting close to completion. I will dyno it and then re-dyno the 894 cc version to find out what improvements I have achieved since it's first dyno session.

These engines do respond well to going well over square! The comparison between the 2 engines should be interesting.

[7981GS]

Looking forward to the comparison.

Eric