KR-1S.co.uk Forum

Getting negative content on this subject regarding still running the B PISTONS IN A KR1 and I find it hard to believe that EVERY ONE THAT OWNS AND RIDES ONE IS USING KR1s pistons(NLA) or replacement Mitaka or if you have deep pockets WOSSNER.

IF YOU ARE RUNNING B PISTONS STILL PLEASE JUST REPLY A “ME” TO THIS POST SO WE CAN GET AN IDEA HOW MANY ARE USING.
COL

it was not meant as negative comment, it was just some sort of warning

Wiseco also offer pistons for the KR-1 and KR-1S according to their most recent catalogue.

Are you referring to the B stamped on the piston crown? If so, it doesn't mean much to be fair, If you're talking about the later kr1s pistons (13001-1372) there's nothing wrong with them, what was the part number of the NOS rings? (Later rings are 13008-1146)
The pistons that fail have holes in the side of them, just behind gudgeon pin hole, later pistons (with enclosed ring pegs) have no hole, both say ART on the inside.

Thanks for the reply and the info much appreciated
Col

No part number for the nos kr1 rings from IMD PISTONS but my invoice says KMX125 so it looks like the same
rings were fitted to the kmx125 single also nla now.
Col

As far as I am aware, the A, B or C on the piston is used to match the cylinder diameter with the cylinders that were also stamped A, B or C by the factory.
Please correct me if I am wrong

Hey scoobie—I’m not the oracle on kr1 or s I’m sure someone on here is but I’m very surprised that there is such a lack of info regarding the engines and what was fitted to solve piston pin problems and an Awful lot of “dunno’s out there where you ask straightforward questions such as “if as you say sir that the b pistons were fitted to the kr1 and the kr1s then why do I get told all the time that the s piston rings(which completely shroud the ring pin in the groove and stop the previous barrel damage when coming loose) won’t fit the kr1–.
Getting lots of don’t fit these unless you want mega financial damage to your engine,just go and buy WOSSNER—yea £260 pair..
Also been looking at kr1 and S when they are parked up but never seen any barrel stamping apart from B if any.

So come on you other members there’s 1530 odd out there of you so how’s
Bout some input on this subject or just a bit of meaningful debate
Col

NOSHER wrote: ↑Wed Jul 14, 2021 8:33 pm Hey scoobie—I’m not the oracle on kr1 or s I’m sure someone on here is but I’m very surprised that there is such a lack of info regarding the engines and what was fitted to solve piston pin problems and an Awful lot of “dunno’s out there where you ask straightforward questions such as “if as you say sir that the b pistons were fitted to the kr1 and the kr1s then why do I get told all the time that the s piston rings(which completely shroud the ring pin in the groove and stop the previous barrel damage when coming loose) won’t fit the kr1–.

the KR1 (which is the KR250 B) has different piston's to the KR-1S (which is the KR250 C or D. They also have different rings. you can swap piston's between the two, but you can't swap the rings. it's as simple as that.

Some interesting stuff on this thread about pistons, mitakas are mentioned as being good, but this was some years ago.

viewtopic.php?f=1&t=10280&p=77084&hilit ... 372#p77084

What pistons are using then? I thought you bought some mitakas?

The mark on the barrels is above the exhaust flange.

Wow that’s a great read fella but it just seems to muddy the pool a little bit more doesn’t it.

Ok yes I bought a pair of Mitaka pistons 55.96mm because when I measured the end gap of the rings that were on my original pistons they were vast—-0.5mm ! But then I had second thoughts looking at the score mark in one bore which was above the exhaust port and strangely not in line with either of the ring pegs(all still in situ) so I sourced through I MD PISTONS the nos std kr1 ring set figuring if I was gonna have a disaster borewise during running in parts wise I was losing the cost of the ring set and not the £126 Mitaka piston set and of course the circa £500 to Nicasil the bores again.
Col

Somewhat, yes, but good info.
0.5mm end gap is okay according to the manual, although following that is a risk with the early pistons.
I've got a decent set of used genuine later pistons with NOS rings, which I could do a deal on, or I'd personally go forged for peace of mind, and save any potential headaches.

Nice offer fella but I think for now I’ll stick with the slugs I took out— it was running (static) ok on both cylinders before the crank seals cried enough and sprayed the garden fence with gearbox oil.!!!! And the crank rebuild and mitaka’s set me back £540 plus £35 for a gasket set but that’s another story watch for my next post— so if your working and have an income it’s no biggy but if you are 77 and squeezing the state pension these hundreds here and there need more than a second thought.Service limit is .60 and mine are close to .55 hence the nos ring purchase.

No worries, hope all goes well

ME

I'll never ever buy Woessner's again.

viewtopic.php?t=4648&highlight=one+seen+kind+damage