RM400 BORE SIZE

[burty400]

Does anyone have any info on how big you can bore a rm 400 n/t cylinder.I read that someone used a maico 490 piston i am not sure if this would leave  enough metal on the bore for when it gets hot it may seize.Has anyone used any larger pistons other than the maico 440 or kx500 and what power differrence did it make.

[oldfart]

Big K, may be able to help you out here.

[LWC82PE]

as they say no substitute for cc's but not always true

[JC]

RM400s ran 80mm bore I'm fairly sure. ... Yes, just checked Wiseco cat, same 80mm for C/N/T.

490 Maico ran 86.5mm, KX500 86mm. Far too big for std barrell surely.

440 Maico ran 82mm piston & same 18mm gudgeon dia as RM. That may well work (if deck ht & skirt length comparable)

[bigk]

We regularly use Maico 440 pistons in RM400's with excellent results at 82mm which puts the bike close to 430cc. I believe there is enough in the cylinder wall to go to 84mm using a 2.0mm O/S Maico 440 piston, but that's as far as you'll get and even then the liner is getting thin. I haven't had to go that far yet, but no doubt will one day. I actually hated the last RM400 we did at 82mm, with a derestricted standard pipe. The bike was fun for about 5 minutes with a brutal aggressive hit, but after that it just became tiring and hard to ride. Apparantly a DG pipe & muffler combo goes a long way to smooth the power or so I'm told.
Cheers,
K

[lukeb1961]

the PE400 had the 85mm bore - I think that is where you got the kx500 reference from, yeah?