650cc XR kit for XL 600 RF?


11 replies to this topic
  • aaronjthompson

Posted February 05, 2006 - 09:05 PM

#1

I have just purchased a 650cc piston kit for an XR 600 but intend to use it on my 1985 XL 600 RF - see:

http://cgi.ebay.com/...me=STRK:MEWA:IT

Can I just over bore the cylinder by 3mm or do I need a HRC cylinder as well? i.e. can the cylinder take a 3mm overbore or will there be problems?

Thanks,

Aaron

  • aaronjthompson

Posted February 06, 2006 - 05:43 PM

#2

Can I please have some feed-back guys?

Thanks,

Aaron

  • don87xr600

Posted February 06, 2006 - 05:58 PM

#3

Who is going to bore your cylinder? Take the piston and cylinder to them, they will let you know.

  • Bob East

Posted February 07, 2006 - 12:21 AM

#4

Hi,

3 mm is .118 inch. That's quite a bit of boring. I don't know what the
limits are for one of these cylinders but most engines only allow about .030
overbore. I'd do like one of the other posters suggested, take the piston
and the cylinder to your machinist and see if it is possible.

Rgds,
Bob East

  • skillet

Posted February 08, 2006 - 08:22 AM

#5

Might have some bad news for you. You are about to destroy your motor, I think. All the big bore RFVC motors (XL, XR, GB) Use the same rod even though the stroke is different. The change is made in the deck height of the wrist pin in the piston. The XL600 used a 75mm stroke and the XR600 uses a 80mm stoke. I think if you put that piston in you will send your head towards the sky! But maybe I'm picturing this all wrong.

Model bore stroke
XR600 98mm 80mm
GB500 92mm 75mm
XL600 100mm 75mm
XR650L (NX650) 100mm 82mm
GB400 84mm 72mm

Warren

  • aaronjthompson

Posted February 09, 2006 - 04:38 PM

#6

Thanks,

I'll have to look into this!

Aaron

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  • brichter

Posted February 09, 2006 - 11:58 PM

#7

Might have some bad news for you. You are about to destroy your motor, I think. All the big bore RFVC motors (XL, XR, GB) Use the same rod even though the stroke is different. The change is made in the deck height of the wrist pin in the piston. The XL600 used a 75mm stroke and the XR600 uses a 80mm stoke. I think if you put that piston in you will send your head towards the sky! But maybe I'm picturing this all wrong.

Model bore stroke
XR600 98mm 80mm
GB500 92mm 75mm
XL600 100mm 75mm
XR650L (NX650) 100mm 82mm
GB400 84mm 72mm

Warren



You're picturing it all wrong.
Changing the location of the wrist pin in the piston doesn't change the stroke, although it will change the compression.
Changing the distance from the centerline of the main bearing journal to the centerline of the rod journal is what changes the stroke.

As stated before, .118" is a helluva lot to bore a cylinder, only your machinist knows for sure.

  • pcmartin

Posted February 10, 2006 - 05:06 AM

#8

Sorry brichter you're picturing it all wrong. What he's saying that Honda used the same rod for all the different stroke motors and changed the location of the wrist pin to allow them to do that. By raising the location of the wrist pin in the piston you keep the piston at the same deck height. I have by accident have bored a XL600R to 3.996 inches and there was plenty of meat left in the liner just no pistons to fit my miss bore.

  • brichter

Posted February 10, 2006 - 09:58 AM

#9

Sorry brichter you're picturing it all wrong. What he's saying that Honda used the same rod for all the different stroke motors and changed the location of the wrist pin to allow them to do that. By raising the location of the wrist pin in the piston you keep the piston at the same deck height. I have by accident have bored a XL600R to 3.996 inches and there was plenty of meat left in the liner just no pistons to fit my miss bore.


Nope. I didn't see it wrong. Your description states his point better than his description. :thumbsup:

  • onaXR

Posted February 10, 2006 - 01:12 PM

#10

You're picturing it all wrong.
Changing the location of the wrist pin in the piston doesn't change the stroke, although it will change the compression.
Changing the distance from the centerline of the main bearing journal to the centerline of the rod journal is what changes the stroke.

As stated before, .118" is a helluva lot to bore a cylinder, only your machinist knows for sure.

The location of the wrist pin will change where the top of the piston is in the bore, it will change the compression. BUT it also may stick the top of the piston too high in the bore and blow the head or the valves. A machine shop may be able to fly cut the piston down if need be and the ring land will allow it.

  • pcmartin

Posted February 10, 2006 - 03:13 PM

#11

brichter; ok I'll go along with that.

As far as milling the top of the piston, I've milled the top of mine .025 inch for lower compression since all I could get at the time was 12.5:1. However this also brings up the point of valve clearance. If in fact you do raise the deck height of the piston to a plus number you will also change the relationship of the notches in the pistons to the center of the valves. As well as the valve clearance itself. Someone who remembers their geometry better than I can do the math for us. That's a long winded way of saying the valve notches would also have to be re cut for proper centering and depth.

  • pcmartin

Posted February 10, 2006 - 03:28 PM

#12

crap I just reread the original question! If in fact he has a xr650l piston and a xl600r motor there's no need to bore at all, they are both 100mm bores. But there is no way he's going to mill .2756 inch off the top of the piston to make up for the 7mm difference in stroke!





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