Mating up a 700xx cylinder

[tayyo789]

Bought a cylinder for 30 bucks. I'm going to try and put it on my xr650r bottom end. From my research, it should be pretty close, and I can still use the xr head if I want to. I want to do this to get some extra cc's without resleeving. Hopefully it will work out. I'll take some pictures when I get some progress done.

[Langbolt]

Great!

Are you gonna switch to EFI too ???

Too bad the Electric start wouldn't mate up too!!

What was HONDA thinking.....they should have designed the cases so all the XR650R oweners could update to ELECTRIC start

Keep us posted!

:devil:

[tayyo789]

I'm keeping the carb and kickstart. Just looking for some extra cc's. Should be interesting. One thing I know for sure is that I need to space it a little. Running 2 base gaskets just isn't enough to make up for the difference in height

[700xxmaniac]

the xr head bolts stright to the xx head... u gona use the stock xx piston

[tayyo789]

The heads are a direct bolt on, but the xx cylinder is about 1/8th inch shorter. Other than that its looking like it will fit. I'm keeping my xr head on it right now, because I have an exhaust and intake that fits, and for the extra 1mm valves.

[tayyo789]

Ok, so I came home for the weekend, and got a little more progress. I'm going to use the xx cylinder for the sole purpose of having a 105mm bore. Stock is 102.5, so I have to get a kit, but thats not really a problem. I have another xr cylinder that I'll eventually turn into a 102, so I'll have that option down the road. I just need to build an "aluminum gasket" of sorts to space the jug upwards a little bit. Hopefully I can get it done by christmas, since I have to take the motor out anyways to fix my oil check valve, and move my oil tank

[NED441SUZ]

You need to put the stock cylinder back on and measure how far the stock piston comes from the top. Then have a spacer made for the XX setup that gives you the same. To thin and you may have a valve clearance issue. To much and you will lose compression.

[tayyo789]

already got the measurements. I've got a guy with a mill who's working on one, and I hear I can get Cometic to make one with their gasket templates

[tayyo789]

Problem number 2: This one's a little tougher.

The water port coming out of the cases is obviously for the xr, and apparently when Honda made the xx, they decided to move it inward (toward the piston) about 3/8". So, the xx jug's water port doesn't reach out far enough to cover the xr's on the cases.

Possible solutions being to try and make up for some of the difference by making the hole in the spacer angled, to compensate some, however it wouldn't be nearly enough, OR weld on the xx port, and then grind and shape and drill until it is far enough out to work. Right now those are my only ideas to make this thing work, with the second one being a lot better than the first.

[tayyo789]

and of course as I was typing that I immediately thought of a third solution, where I cut the port off the xx cylinder, and cut one off of one of my xr cylinders, and weld the xr one onto the xx??

[jcs003]

pics would help clearify your issue. but from your description a custom machined port welded in might be the compromising solution. we will have better input from a pic or two im sure.

[tayyo789]

Here's some pictures of what I mean. I hope they help

This is the port on the cases:
<a href="http://www.flickr.com/photos/53199945@N08/5249680303/" title="154356_177278222300011_100000535031068_543570_4416 969_n by taylorramsay1, on Flickr"><img src="http://farm6.static.flickr.com/5129/5249680303_1d904e60c5.jpg" width="500" height="375" alt="154356_177278222300011_100000535031068_543570_4416 969_n" /></a>

When the xx cylinder is on:
<a href="http://www.flickr.com/photos/53199945@N08/5250282720/" title="67804_177278652299968_100000535031068_543573_70983 54_n by taylorramsay1, on Flickr"><img src="http://farm6.static.flickr.com/5168/5250282720_5d220c3d7c.jpg" width="500" height="375" alt="67804_177278652299968_100000535031068_543573_70983 54_n" /></a>

Closer look:
<a href="http://www.flickr.com/photos/53199945@N08/5249680273/" title="66839_177278455633321_100000535031068_543572_36403 61_n by taylorramsay1, on Flickr"><img src="http://farm6.static.flickr.com/5090/5249680273_b5d9e542bb.jpg" width="500" height="375" alt="66839_177278455633321_100000535031068_543572_36403 61_n" /></a>

[jcs003]

i now understand. i do believe a custom port will do what you need it to. assuming you have a good welder. build the weld up and have a good port man match it. its not a two stroke scenario, but those are the guys with the touch. just my opinion.

[tayyo789]

Sorry guys, but this project is being postponed...for now anyways.
I still have all the stuff for it, but we're just going to bore out an xr cylinder to 680 to start with. Everything fits on it, so we figured we would use it until we need the extra power again. In the meantime, we might make a bit of progress, but its not a priority yet.

[rustyATV]

Originally posted by tayyo789
The heads are a direct bolt on, but the xx cylinder is about 1/8th inch shorter. Other than that its looking like it will fit. I'm keeping my xr head on it right now, because I have an exhaust and intake that fits, and for the extra 1mm valves.


Originally posted by tayyo789
I just need to build an "aluminum gasket" of sorts to space the jug upwards a little bit. Hopefully I can get it done by christmas, since I have to take the motor out anyways to fix my oil check valve, and move my oil tank

I was wondering about doing this as well, but more to reduce the height of the engine than to increase displacement. I had read that the 700XX motor was an inch shorter than the XR's, which I thought I had read was done in the cylinder and using a much shorter stroke.

To that end, I was hoping the XX cylinder, head, connecting rod and piston cold be swapped onto the XR bottom end, but you're saying the XX cylinder is only 1/8th inch shorter.

Do you know where they got the rest of the height out of the XX motor? Is the head shorter?

[tayyo789]

I don't have a xx head, so I'm not sure. It could be in the bottom end as well. To put the xx cylinder on, and use an xx piston, you would need to use a custom connecting rod unless you put the xx crank in. The wristpins are different sizes so you couldn't just swap them back and forth.

[mx Eli]

^^^ going of this idea I wonder if anybody makes a xr big bore piston that would fit into the xx cylinder so you wouldnt have to switch cranks or rods

Im not sure if anyone makes a piston that size but its worth looking around

[tayyo789]

They are not produced for anything over a 102mm.
CP pistons will make me some, but I need to buy a minimum of 4.
JE will make them, with a minimum of 2.
I'm also getting a 4mil stroker built by CrankWorks, so we are going to see what we can do as far as a rod goes to make the piston selection easier.
I found out today that CylinderWorks is making an aftermarket cylinder for the xx that is a 105mm, so that is probably the route I am going to go. I will still have to fix the water port on it, but it will be a more capable cylinder than the one I already have, plus it won't need to be bored, reinforced, and plated.

[700xxmaniac]

Originally posted by rustyATV
I was wondering about doing this as well, but more to reduce the height of the engine than to increase displacement. I had read that the 700XX motor was an inch shorter than the XR's, which I thought I had read was done in the cylinder and using a much shorter stroke.

To that end, I was hoping the XX cylinder, head, connecting rod and piston cold be swapped onto the XR bottom end, but you're saying the XX cylinder is only 1/8th inch shorter.

Do you know where they got the rest of the height out of the XX motor? Is the head shorter?

they shorten the con rod but has same stroke.
yes the xx head is shorter