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Late Model CRF Cylinder on Older XR 100 Question

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Hello all

 

Ive got an 86 xr100 with a worn out cylinder.  I have a nice later model in spec cylinder and piston w/rings from an 08 or so crf100.  I know the new cylinder is a bit longer than the old cylinder but can i use it with new style gaskets?  I bolted it on but I can't get the cam gear on the cam with the timing chain on it, it is just a tiny bit short.  The timing chains are the same for the years according to part numbers.  Whats the secret to using the new cylinder?

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Considering you dont have to specify what year big bore kit when ordering, i would think theyre all the same. Did you back off the cam chain tensioner?

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You would think, but they are not.  The later model cylinders are  just a bit longer (like 1 mm) and apparently used thinner gaskets to achieve the same overall length.  I do have the tensioners backed off.  I was just slapping this thing together and having trouble getting the cam chain on but all the cam chains seem to be the same so I must have something else going on. 

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Stroke hasn't changed on this engine since inception.

 

The only change in the top end of this engine over the years is the appearance / disappearance of the valve seal on the exhaust valve.

 

The lower adjuster is your enemy.  Hook the spring, push the rod down, apply tension to the locking screw then install the cylinder, head, cam chain, upper adjuster.

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Stroke hasn't changed on this engine since inception.

 

The only change in the top end of this engine over the years is the appearance / disappearance of the valve seal on the exhaust valve.

 

The lower adjuster is your enemy.  Hook the spring, push the rod down, apply tension to the locking screw then install the cylinder, head, cam chain, upper adjuster.

So is there any truth to the longer cylinder as stated?

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I figured it out!  Overall,  Each cylinder, with the correct gasket, is the same length, BUT,

 

YES, the newer cylinders are about 1mm taller than the old ones.

 

The old cylinders are slightly shorter and use a thicker head gasket. 

 

The newer head gasket is just a thin metal gasket, the old gaskets  are the old style thick material ones with just a metal ring around the cylinder sealing area. 

 

I was trying to use a newer (taller) cylinder and the older (thicker) gasket which made the timing chain too short, probably would have significantly lowered compression too had I been able to get it together.  I broke out the mic to verify all this.  Got the later model cylinder with the thin gasket and went together fine. 

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