Possible 300cc conversion

ScottaKR · Post by **ScottaKR** » Mon Oct 13, 2008 9:28 am

Sheik Yerbouti wrote:Who wants to take the plunge and buy one to check it for fit?

Well, I've just put a bid on one, so if I can get it cheap enough we'll have something to measure up.

ScottaKR · Post by **ScottaKR** » Sun Oct 19, 2008 8:51 am

missed out on the piston in the end as I was re-sitting for my bike L's (so couldn't watch the auction till the end) and was beaten by a last minute bidder.

Oh well, I'll keep looking I guess. At least I got my L's again

. Just have to remember to sit for my P's before the permit expires this time.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Sun Oct 19, 2008 10:19 am

He he yeah I just snuck in by a few days when I did mine.

pity about the ninja bidder, how much did it go for?

ScottaKR · Post by **ScottaKR** » Mon Oct 20, 2008 8:04 am

Sheik Yerbouti wrote:He he yeah I just snuck in by a few days when I did mine.

pity about the ninja bidder, how much did it go for?

Went for $72

(I'd also forgoten to up my autobid

)
There's one on there with $120 buy it now, but I will wait for another cheapy to show up since I'm not in any sort of rush and it's only for comparison atm.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Tue Nov 04, 2008 10:14 am

ok I've been mucking about drawing a model of my "new" kr250 barrel.
Kr250RR maybe.....
Currently the bore is 56mm as per standard, but if we can get some reasonably priced pistons at 61mm as we've been trying it could be a KR300RR

Obviously no water jacket drawn in yet, but plenty of room for that. Not sure where Im gonna route the water yet anyway.

ScottaKR · Post by **ScottaKR** » Tue Nov 04, 2008 12:24 pm

Looking promising there Shiek.

Have you designed these useing standard or KR1/KR1S port timming?
Are you planning on making these in 2 pieces? (just looking at the 2 different colors)

Trying my luck on another RG150 piston atm, so fingers crossed on that. [-o<
The other thing you could look at if keeping it a 250, is tweaking the design to suit a more common piston. That's part of the reason I've been looking into the RG150 piston, as it's at least available unlike the standard KR250 pistons. Turns out Prox make RG150 pistons, but it dosn't seem they sell them in the Australian market.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Tue Nov 04, 2008 10:39 pm

At the moment just standard KR250 timing, but its easy enough to change now that the model is there.

Its in 2 peices (green bit is the liner, red bit is the outside), cause otherwise its too hard to machine inside the transfer ports.

I was thinking about pistons for 250cc, but it seems that most of the later 250 twins have a smaller bore/longer stroke. As do 125 motocross bikes.

By the way, what is the gudgeon pin size for the standard KR250, it seems thats the only thing thats really critical at the moment.....

ScottaKR · Post by **ScottaKR** » Wed Nov 05, 2008 7:41 am

Gudgeon pin diameter is 16mm (just measured it again to make sure) which I'm pretty sure is the same as the KR1. Unfortunately, the KR1 has a higher piston pin, so has never been a viable replacement in a standard KR250 barrell. That would be easy to overcome with your "new" barrells of course, but the KR1 pistons arn't all that easy to get over here either.

It may be worthwhile haveing another look through the catalogue (and finding some other catalogues as well) since the piston pin height is no longer a major issue.
As for the 2 piece design, are you planning on an alloy or steel liner?
I know a plated alloy liner would be lighter and offer better heat transfer properties, but a steel one would offer cheaper manufacture (no plateing) and the ability to use o/s pistons on subsequent rebuilds.
I'm not sure about any thermal expansion rate issuses, and there may be a few other factors I've missed here, but thought it was worth mentioning.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Wed Nov 05, 2008 10:35 am

I was thinking of aluminium for the liner. But of course plating is still a problem, ( will probably cost a bomb ). Alternatively I could use cast iron, (better than steel) but as you said, it tends to get loose as the engine gets hot, and heat transfer to the water jacket is not as good.

Looking at a catalogue, Yamaha RD350/400 etc etc all have 16mm pin and 64mm bore, that would make a KR322RR.

These are pretty popular bikes, should be able to get a hold of bits

StrokerBoy · Post by **StrokerBoy** » Wed Nov 05, 2008 11:18 am

I don't have anything technical to add here, I'm not much of an engineer.

But I'm enjoying reading about it. Put me down for a 66mm (346cc) kit. With powervalves. [-o<

Piston choice should be governed by future availability to some extent. But I guess whether to plate the bore or not is just as significant.

No point having a KR300R-SP if we're all fighting over the same 3 new pistons like now.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Wed Nov 05, 2008 12:02 pm

Put me down for a 66mm (346cc) kit. With powervalves.

LOL going back to the 350cc grand prix class days eh?

Powervalves are another kettle of fish altogether. Every manufacturer has a slightly different way of doing it, so which way is best?
Developing and tuning the beast is also much harder, and I don't have any friends with engine dynos

.
Maybe an exact copy of KIPS would be appropriate, being a Kawasaki but I don't have a KR1-s barrel here to copy.

Piston choice should be governed by future availability to some extent. But I guess whether to plate the bore or not is just as significant.

I can see it now "GIMME Gimme Gimme thats MY piston!!"

True, we still need to explore plating. I think I read somewhere once that some early Yamaha TZ's had hard chromed bores? (corrrect me here if I'm barking up the wrong tree) Before nicasil was invented that is.
If regular hard chroming works, then it will work out pretty cheep and easy.

StrokerBoy · Post by **StrokerBoy** » Wed Nov 05, 2008 12:31 pm

Sheik Yerbouti wrote:Powervalves are another kettle of fish altogether. Every manufacturer has a slightly different way of doing it, so which way is best?
Developing and tuning the beast is also much harder, and I don't have any friends with engine dynos .
Maybe an exact copy of KIPS would be appropriate, being a Kawasaki but I don't have a KR1-s barrel here to copy.

Don't copy the KVSS setup off the KR250 'S'. It's pretty crude, and would need special heads making as well as barrels.

YPVS bits would probably be the easiest to source. I was about to say that they're still being made new, but just checked and found out the Banshee doesn't have powervalves.

ScottaKR · Post by **ScottaKR** » Wed Nov 05, 2008 12:52 pm

Yeah, 346cc's would be nice, and powervalves would just be the iceing on the cake

. The main problem (after designing and machineing the barrell that is) would be sortin out a powervalve controller for it.
I'd lean towards the KIPS setup for it, but that will still require a custom head.
Maybe easier to just keep it relatively basic and forget about the powervalves for the time being.

Also not sure how much extra power the gearbox etc can cope with (a tuned 300 may even be too much for all we know).

Not sure about the RD pistons as, if I'm not mistaken, they have holes in the skirts due to being designed for a piston-port engine (feel free to corect me here) which may cause an issue.
Need to find me some more piston catalogues.

ScottaKR · Post by **ScottaKR** » Sat Nov 08, 2008 6:37 am

Well happy today!

Just won an auction for an RG150 .25mm o/s piston kit for $65.
Not sure what postage (from NZ) will be yet, but hopefully wont be too much. [-o<
Also had a good chat to the guy at a local bike shop this morning, and he's going to have a talk to his suppliers about standard KR250 pistons as well as KMX125 .2mm o/s. If he cant find them, he's going to get me to fill out a required dimensions sheet that he'll give to his suppliers to find ANY possible matches. He also said that his engineer can (and has many times) relocate ring pegs so they wont snag on ports when fitted to a different engine than they were designed for.

$\:D/$

A pretty good day all up I think.

JanBros · Post by **JanBros** » Sat Nov 08, 2008 10:35 am

Wössner has some oversize KMX125 pistons, but not in 0.2mm

http://www.woessner-kolben.de/english/indexenglish.html