kr250 crankdampers

gandalf · Post by **gandalf** » Sun Feb 08, 2009 9:34 am

Ive just aquired a kr and its got wear in the splines that locate the crank dampers /drive gears. Anyone know how fussy the fit is? Im a bit concerned because the motor has been taken out to 64m.m. bore and it will have lots more torque, alternatively does anyone have a set of standard barrels and pistons for sale or swap?

ScottaKR · Post by **ScottaKR** » Wed Feb 11, 2009 11:00 am

Hi gandalf,

Welcome to the forum mate.
I've never heard of a KR wearing out the crank damper splines.

Is it the splines on the crank or the dampers that are worn? How much actual wear is there?
Whether it's crank splines or dampers, I think you'll find it easier (and better in the long run) to replace the worn parts rather than taking a step backwards in the power stakes just to prolong the inevitable.
The thing that really has me curious, is the 64mm over-bore!

I don't have any good standard barrells spare, unless you want to repair/re-plate some. Direct replacement pistons arn't available as far as anyone has been able to find so far either.

Do you have any idea what pistons have been used in it, as I've been looking into using RG150 pistons for a 61mm (300cc) build for my next engine, but the extra 25cc is very tempting. The deciding factor for me would be a) ease of sourcing pistons, b) performance/reliability, and c) amount of mods required (least amount of machineing to fit).
I'm assuming that it would be running an 'O' ringed head.
Would it be possible for you to take some measurements of the port heights as well as the gudgeon pin height for comparisson?
Also, post up some pics of the bike when you can too.

Cheers, Scott.

gandalf · Post by **gandalf** » Wed Feb 11, 2009 9:01 pm

Both the crank dampers and the crank are worn. Ive just got another engine and that shows the start of the same problem. by mixing and matching Ive got the ply down to a minimum. I dont know how many ks either of the engines have done though. the bike is in a thousand pieces at the moment . Ive just built a sand blaster and bought a big can of kawasaki green ready to staert on it. Im missing a couple of parts if anyone has them. Indicator bulb holders and tail light bulb holder. Im thinking about changing the bars to clip ons as all the ines i have have cracks in them. Does anyone know of a type thats a good fit?. someone tell me how to get a picture one here please?[/img]

KwakOn · Post by **KwakOn** » Thu Feb 12, 2009 12:06 am

open a tag, using Img button - [img]

then put the URL (web address of the image - which you will have uploaded to Webspace e.g. Photobucket.com)

[img]http://i472.photobucket.com/....etc...._0211003.jpg

then close tag using same button (Img*) - [/img]

[img]http://i472.photobucket.com/....etc...._0211003.jpg[/img]

it usually puts the tags at the end of your text (also you can type in the tags).

Upload to Webspace e.g. Photobucket.com

go to site, join/register, find upload (from your PC) button, find files on your PC, clicky click.
when uploaded you should see tags (direct or [IMG]) to copy and paste into your post. as you wil guess if you use the [IMG] tags then you wont have to insert the tags.

hope this helps

gandalf · Post by **gandalf** » Thu Feb 12, 2009 10:23 am

well its coming together. I painted the tank and the frame today, They look like new. Ive used two pack paint that goes as hard as and doesnt chip so just a bit of care putting the engine back in when its back together and all will be well, Any one here in NZ know of a competent man for refurbishing seats , When we lived in the UK we had a trimmer that worked for Aston Martin who did it for beer money and you couldnt tell them from new and I want this one as good. Anyone see the idiot on trade me trying to sell a miror while giving the impression he is selling a KR. His sort need their balls chewing off bigtime

ScottaKR · Post by **ScottaKR** » Thu Feb 12, 2009 12:28 pm

Good to hear it's coming along well.
Just remember to leave the barrells and head off until the bottom-end is bolted into the frame, as it just wont fit otherwise and youll scratch the hell outta your frame trying to get it in.
The trade me ad has been going for ages, and is a pretty standard wrecking ad (see it all the time on ebay as well).

As for the crank damper issue, if the play is minimal (after swaping bits around) I'd be tempted to bolt it together and run it while searching for a better bottom-end to rebuild.
I'm still very curious as to what pistons have been used if you have any idea what they are or if there are any identifying marks. [-o<

gandalf · Post by **gandalf** » Thu Feb 12, 2009 9:01 pm

Im still struggling with the photo thing. You obvuiosly have an email address if you give me that I will send some pics to you, Ive seen mension of yamIT175 andRGB pistons as a posibility. These have been designed to be in a cylinder with the carb exhausting into the cylinder as the pistons have large ports on one side cut into the skirt, I suppose this also implies reed valves ?

gandalf · Post by **gandalf** » Thu Feb 12, 2009 9:24 pm

Did I say RGB I meaned 350 yam pistons

ScottaKR · Post by **ScottaKR** » Fri Feb 13, 2009 1:11 pm

Here's gandalfs over-bored barrell.

and here's the piston that had been living in said barrell.

Hmmmmm..... 325cc Tandem Twin..... me likey very much!

any idea what particular pistons they used there gandalf?

gandalf · Post by **gandalf** » Fri Feb 13, 2009 9:25 pm

I wouldreally like to know what they are Ther is a marking 25 on the top of the piston does that denote a plus 2.5 mm bore?. there has been various suggestions but if theres anyone out there in the know please tell us. Has no one found a replacement for standard pistons or anything close?

ScottaKR · Post by **ScottaKR** » Sat Feb 14, 2009 12:19 am

So far the closest to standard is apparently a 2mm o/s KMX125 piston, but no-one has tried it out yet (that I know of), and they arnt available on this patch of dirt.

Still need to find some more piston cataloges that show all the specs, as the ones I have only cover a limited amount of bikes. I'd really like to find one for Pro-X pistons, but havn't found one yet.

gandalf · Post by **gandalf** » Sat Feb 14, 2009 5:35 am

Ive sent pictures of the piston to a mate in the UK who says he knows a piston guru so we may know in a few days . Whats about thats near standard? I haver a spare pair of barrels ( one buggered) so I thought I might set to and make a pair of liners for something easy to get you hands on. Any suggestions?

gandalf · Post by **gandalf** » Sat Feb 14, 2009 9:38 am

I just found an outfit called campbell enterprises in the US that make forged pistons to order. Does anyone think it might be work getting together and getting a batch made?

ScottaKR · Post by **ScottaKR** » Sat Feb 14, 2009 10:55 am

do you know what his minimum order would be (cant really expect high demand on these) and what the unit cost would be for each piston?
If we were to get a batch of pistons made I'd think it perhaps better to get cast ones made, as the extra expense of forgies wouldn't be worthwhile for most people I'd expect.
Also, this still leaves us out in the cold if we decide to build another engine a few years down the track or one of them nips up in the bore unless you want to buy 3 sets straight of the bat (I know I can't afford that

). Hence many people have sought out an alternative piston from something that is still catered for in the aftermarket, even it it requires some extra machining (like the over-sized slugs in your beastie).

Sorry if I'm coming accross all doom and gloom on the idea, but I just think it would be better to find something that is still available of the shelf.
That said, if you could get some made up cheap enough, I'd be interested.