600 into 650???

Started by gizzzy, Sep 20 2009 06:57 AM
8 replies to this topic

  • gizzzy

Posted 20 September 2009 - 06:57 AM

#1


Can anyone tell me if it is possible to fit a 650 cylinder and piston onto my 1997 XR600r. As anyone carried out this modification before and if so what if any changes do I have to do. Can I use the 600's cylinder head? Should I rejet the orginal carb? or fit a XR650'l carb. I have heard that fitting a NX650 carb makes a lot of difference to performance. The bike has a stage1 fast cam FMF high flow headers, and a Leovince exhaust.

Any help is greatly appreciated,
Andy.

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  • HeadTrauma

Posted 21 September 2009 - 12:30 AM

#2

As far as 650s go, only the 650L cylinder can be used on a 600. The 650L piston can be used too, but it will drop the compression substantially. Using a 650L cylinder and a 100mm XR600 piston will get you 628cc. Boring and/or sleeving the XR600 jug to 100mm will do the same thing.

Regarding carburetors, the stock 600 Keihin is better than the carb that came on the NX650 or XR650L, so keep it. You may or may not have to rejet.

  • gizzzy

Posted 21 September 2009 - 10:43 AM

#3

HeadTrauma said:

As far as 650s go, only the 650L cylinder can be used on a 600. The 650L piston can be used too, but it will drop the compression substantially. Using a 650L cylinder and a 100mm XR600 piston will get you 628cc. Boring and/or sleeving the XR600 jug to 100mm will do the same thing.

Regarding carburetors, the stock 600 Keihin is better than the carb that came on the NX650 or XR650L, so keep it. You may or may not have to rejet.
Thanks for the quick reply. Yes the Jug I have is off of a 650l. I have just bought off ebay a JE piston 102mm. And am in the process of having the sleeve bored to suit. I belive this will give the bike a compression ration of 10.5:1
Will I have to use cometic gaskits for the base and the head?

  • HeadTrauma

Posted 21 September 2009 - 11:03 AM

#4

I thought you were talking about using a stock 650L piston. Using one in a 600 will lower the compression.....Installing a JE 650L piston into an XR600 will raise the compression over the rated number and may cause piston-to-head clearance issues. It might be fixable by doubling the base gasket, but I have not personally tried it.

You can use whatever gaskets you want as long as the head and head cover gaskets are the metal shim type.

  • uranys

Posted 21 September 2009 - 11:48 AM

#5

gizzzy,

If your piston is for a 650L your setup sounds similar to mine.

When I put it together, the piston was slightly above the deck at TDC, and although I didn't check it, I'm pretty sure it would have hit. I made two base gaskets out of material that was thicker than stock to raise the cylinder which resulted in the piston a little below the deck.

I've put 2k+ miles on it without any issues.

Your other option is to use a thicker head gasket. I had Lani at copper gaskets unlimited make me one and it looks good, and it was comparable in price to the OEM Honda gasket. I plan on installing it with the stock base gasket this winter when I replace my rod.

  • gizzzy

Posted 26 September 2009 - 08:52 AM

#6

Thanks for the input. I have been intouch with Lani and he is making me a copper head gasket. 1.06mm thick with a 102mm bore. I will also double up on the base gasket. Hopefully that will be enough to prevent the piston from impacting the valves.

  • zipper600

Posted 26 September 2009 - 09:08 AM

#7

Cometic gaskets....my only experience is a no..no.....

  • HeadTrauma

Posted 26 September 2009 - 03:26 PM

#8

gizzzy said:

Hopefully that will be enough to prevent the piston from impacting the valves.

I would be more concerned with piston-to-head clearance, which should probably be at least around 1.0mm given the architecture of the engine. I would say a clay or solder test is in order for both the valve pockets and piston quench area.

  • gizzzy

Posted 12 January 2011 - 12:23 PM

#9

Hi everyone. The conversion is now done and the bike is running well. I had the cylinder head ported and gas flowed while it was off. Well it would of been rude not to. Still running the stock carb and jetting at the moment, how ever I have purchased a Klhein flatslide pumper carb which I shall fit and set up in the spring. The kit is from the USA Sudco performance, hopefully with all the other engine mods we shall see an increase in power.

Other mods I have done are Talon hubs, Excel rims, 320mm disc brake conversion. I also intend changing the stock forks for some Showa USD units which came off a Xr400. Going to be a lot of fun this summer!

Thanks to all for all of your advice:thumbsup:
Now looking to do a similar conversion to a XBr500 turning it into a Cafe Racer



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