8-1 compression, cam ?

[CDNTX650]

I am tinkering with the idea of it in this motor build as i want a nice cruiser to eat up some miles. I know the cam timing needs to be retarded by 2*, does anyone offer this service? hugh?. the rest is pretty straight forward.

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[nj1639]

XSJohn did mine and I believe that if and when I get another one of these bikes I'll try my hand at it. He was kinda specific on what to do and I believe I could pull it off but it's going to be a while.

 

[CDNTX650]

hmm, too bad for now. Thats the hardest part of it.

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[Punkskalar]

Low compression? You guys are killing me here

I know it works to lessen the vibes, but what other real benefits are you looking for? There will be no specific amount you can retard the cam, as those need to be done on and engine-engine basis...

 

[nj1639]

John scribed a mark on the cam, pressed it apart, moved it, and then pressed it back together. He did say it would sometimes take a coupe of tries.......

 

[yamaman]

Hugh, maybe you should read some of xsjohns posts on the subject before passing judgement. I, like your good self, see motorcycles as a sporting machine. Others however want to just cruise along, I think for those, the 8:1 is a good mod. Pretty sure the cam sprocket retard required has a direct relationship to the head gasket (2 gaskets) thi
ckness, so would be the same on any motor. Also, Yamaha would not have indexed the sprockets one by one, just done to spec. cheers

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[Punkskalar]

Hugh, maybe you should read some of xsjohns posts on the subject before passing judgement. I, like your good self, see motorcycles as a sporting machine. Others however want to just cruise along, I think for those, the 8:1 is a good mod. Pretty sure the cam sprocket retard required has a direct relationship to the head gasket (2 gaskets) thi
ckness, so would be the same on any motor. Also, Yamaha would not have indexed the sprockets one by one, just done to spec. cheers

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No judgement passed, I've done plenty of reading on it. I just like go-fast motors And from what I remember, he was basically stacking head gaskets. I would think a thicker base gasket would be nice. I could easily draw some up and have them custom made from Copper if folks were interested.

And yes, if change the height of the crank/cam relationship (thicker or thinner gaskets, decking heads, etc..) then you will need to redegree the camshaft. There is a good writeup on it here:

http://www.650motorcycles.com/isky.html

http://www.650motorcycles.com/CamTiming.html

Basically, you'll want a dial indicator (cheap one will do, think Harbor Freight) and a method to mount it to the head cover. Degree wheel on the crank, and find out at what degree your cam starts to open the valve, then tear the engine down, add gasket thickness, and press of the cam gear, retarding it just 2-3 degrees at most, and dial it in again. This is a time consuming task, but I do it all the time with our rephased engine builds. You'll be removing the head cover a few times, readjusting the camchain several times, and setting valve last several times in the process... But, any XS650 engine can benefit from having the cam degreed in properly.

 

[CDNTX650]

your killing me....I drove a Ducati 999......but i shouldnt pass judgement on our what out definitions of go fast are..

Thanks for the info people.

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