I am picking up a 87 txr250r Thursday that needs a new cylinder. What years are interchangeable? Are the cr250r interchangeable too? What about cylinder heads?

 

The 87 I believe is a long rod crank, which requires the 87-89 cylinder. You could use an 85-86 cylinder, but you would need the short rod crank to go along with it. Like I said in another post though, Ebay has several of all different years for less than $100(stock). I don't think the CR250 cylinders are interchangeable, but don't quote me on that. I have no clue about the heads.

 

I think 86 and up CR Cylinders had PV so they wouldn't work.

 

Some places do use the cr cylinder just use a block off plate for the pv. Finding a cylinder from a trx shouldn't be a problem tho.

 

I picked up an 88 model cylinder today for 57 shipped and it had the head with it. It is supposed to be on it's first overbore. I hope that is true. Now I just need to get me a piston and have the cylinder bored.

 

All 85-89 TRX and ATC cylinders are interchangable. Just use the correct piston for the rod you have. 87's should have a long rod, so use a 87-89 piston. If it is a short rod, use the 85-86 style piston. Use a spacer plate when using the 85-86 piston with a 87-89 crank.

The early style 85-86 have a non-bridged intake (piston chatter when ported), and the 87's seem to be the slowest when fully ported. The 88-89 are easily the most desirable. I currently have a play ported 86 and an 87 alky drag cylinder on an 86 short rod bottom end.

There are some CR cylinders that will work, but few offer any real performance gains when ported. The powervalve cylinders will not operate correctly because the valve is driven off components not on the TRX. Most CR cylinders used on TRX's have the powervalve's welded open for more top-end.

 

Nicname is right, you can use 85-89 cylinders with the right piston/crank combo. The 85/86 cylinders don't have the reliability of the newer ones. My preference is the 88-89 cylinder, longrod crank, 86 piston w/spacer plate.

 

Why the long rod with the spacer and 86 model piston? What is the advantage?

 

The spacer plate increases crankcase volume, which can spread out the power, or move the powerband hit to a different RPM range. I prefer the bridged intake cylinders, short rods, and 86 style piston to keep the hit of the powerband and the quicker revving. An early cylinder can have good reliability; I have over a hundred hours on my 86 cylinder with no top end work. Just don't get too wild with the porting, and use a good pre-mix oil and ratio. 927 at 40:1 works great for me.

 

The 86 cylinders wear hard on the intake side due to the large intake port w/no bridges, advantage 87-89. The 86 pistons were prone to cracking on the intake side as well, mostly due to the 86 cylinders. But the 86 piston is still a good choice in an 87-89 cylinder, plus it gets you more bores upto .140 over. I'm leaving the rod issue alone.