Some T3B - KX Engine Questions

[JohnR.]

I've been doing my homework on building the motor in my T3. Its tired and needs a new piston and rings at the least but I think I want to try to make some nice hp while keeping it a 250. I read this thread (http://www.3wheelerworld.com/showthread.php?61355-84-85-tecate-cylinder-difference-kxt-kx-questions-answered) but since it is focused on 84/85 engines I have some questions for you Tecate experts out there.

From reading the thread I understand that the 83/84 KX cylinder was superior HP wise to the 84/85 T3 cylinder and could be distinguished by its having an exhaust port bridge which the T3 did not in those years. Does the 86/87 T3 cylinder have the bridge or is it similar to the 84/85 T3 cylinder? Basically, if I'm going to go through the trouble of porting and building this thing I want to make sure I start with the best foundation and it sounds like the 83/84 cylinde might be it. However, the piston on the KX was the same all the way up until 1986 so wouldn't stand to reason that assuming the cylinder from an 86 KX250 would bolt on, it might have better ports than the 84 KX250?

I don't know enough about the history of my T3 to know for sure if someone had already swapped the jug out or not. It already has a 38mm Mikuni round slide on it so its possible that there may be more to it than I know. I'll have to dig into it and see what's what after I find out what I'm looking for.

John

[JohnR.]

EDIT:

OK, so I realized that the 84-85 T3 had no power valve system so those year cylinders are not in the cards. I see there are different part numbers for the 1985 and 1986 KX cylinders. I'm going to have to guess that the 86 is a better piece? Is there a significant difference between the power valve equipped KX and T3 cylinders or will a well ported T3 one be every bit as good as a well ported KX one?

[nd4speed]

86 cylinder might bolt on 84/85 trans but there is one major problem- the exhaust port.

The 83/84 KX cylinder was the way to go back in the day but a Sprock big bore would be the way to go today.

[JohnR.]

Yeah, but I have an 86 (see sig) so that's not a concern. I've already got a big bore machine, I want something that I can run against the other 250's. I know I could sneak it into the 250's since the Sprock kit is way sleeper but I'm not the type of person that would bring a gun to a knife fight. I may end up changing my mind and going with a big bore but I'm hoping to get info on getting the most out of a standard bore set up.

John

[Tecate 50]

86-87 kxt and kx are the same across the board. The 85 kxt 250 can utilize the 83-84 kx cylinder. All the pistons are the same that come stock at 70 mills. Not brag because I own both.....but I have yet for any anyone to come close to my non-power valve motor yet with and 86-87 in the 250cc range.

[nd4speed]

I misunderstood your post.

The 1985 KX250 power valves are not the same as 1986 KX250 and Tecates. (I bought a cheap NOS 85 KX cylinder and found that out)

I dont see any difference between 1986 KX250 cylinder and Tecate.

[JohnR.]

OK so I'll have to either get an 86 KX cylinder or work with one of the 86 T3 ones that I have. The 1987 KX one is different, it has a 67.4mm bore like the T4 does. I'll talk to my buddy about doing the port work this weekend. I need to have him look at my spare cylinder to see if the nikasil is OK so I can just pop a new piston in.

John