650cc XR kit for XL 600 RF?

Can I please have some feed-back guys?

Thanks,

Aaron

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

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

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

Thanks,

I'll have to look into this!

Aaron

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.

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.

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:

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.

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.

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!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now