Tri Z and 250R big bore....there is HOPE!!!

[Darius1502]

I have another question: I was reading about a big bore kit for the Fourtrax 250R that uses a KX 500 piston. The company is LRD. I was wondering if most 2 stoke pistons are pretty similar (other than displacement). Shapewise is a piston from a honda two stroke 250 fairly similar to the shape of say an KTM 380 piston or KX 500. Also could the piston be used interchangable provided the cylinder had enough bore size?

I was wondering if the old YZ 400 piston could work in sleeved up overbored Tri Z? Assuming you have enough room to bore it out that wide, do you think the piston would work.

You could also use an old RM 370 piston, I suppose.

What do you think?

[Trikeaholic]

I DO NOT KNOW FOR FACT, but this sounds reasonable. I posed the same basic question to my engine boring shop. He says that its true, they are all basically the same EXCEPT the ring stop tabs in the piston ring grooves must be the same as the original piston, so the rings wont rotate catch in a port. Made perfect sense to me. Also, I have seen some 2 stroke pistons with transfer ports right in the skirt. The pins in the ring grooves must be dead nuts on the wall of the cylinder, and not the port openings or there will be problems. Sound reasonable?? the trick is finding a piston with the same pin location. mabey bearing size too.

[x.system]

My 250R paul turner motors use a yz 250 piston.

[YTZ250#1]

My R ran the yz piston also,But you also have a spacer plate in it.Besides the ring pins and rist pin bearing you will have to make sure the skirts are not to long.If they are you will have major problems.Also the ports in the piston should be in the right locaction,if they don't line up with the ports in the jug then the port timing will be off.It will run like crap if they are of by much at all.That is the reason for the spacer plate on the R,it lets the piston skirts clear the block,it lines the ports up,and increeses cc size of the cylinder.I think the yz piston is taller from the rist pin to the top and increeses the stroke.I would make sure all of theese things will line up and clear every thing before you just throw any old piston in it.You could end up with a major repair bill if the piston hits the head or the block,or if the ports don't allow enough fuel in to lubricate the top end.Just my 02 I hope it helps out a little.

[Darius1502]

Great information guys.

The real trouble is with experimentation. It could get awful costly to try out all these different pistons.

Oh...well...back to the drawing board!

I wonder if some of the YZ pistons from the big bore YZ kits around would be close enough. There are alot of 300 kits sold for the YZ. Again you would have to just really study the pistons.

[YTZ250#1]

I think the 83-87 yz piston is the same as the Tri Z,Maybe a big bore sleeve and piston for that would fit the Z cylinder.It might be worth looking in to.