86 cyl with 88 pistons

[regg187]

Ok I know it is not recomended for long tod pistons to go in 85-86 cylinders because of possible skirt issues with intake port.

I would like to know has anyone here had this combination and did anything ever happen.

is there any possible improvments to this situation maybe machining a different angle on the bottom of the intake side skirt and then balancing

heres my situation I got A 86 P Turner national cylinder to go on my 88, it came with the 5mm spacer plate that one would need to run a 88 piston in the 86 cylinder. if it is such a disastor why is there a 5mm plate at all. Do I really need to get a thinner plate and run an 86 style piston, or is it more theory than actuallity!

[Honda 250r 001]

Need to know what rod your using first! you can use 88 cylinder with 86 piston on short rod without spacer, but if your running long rod then you need the spacer plate.

[regg187]

OH sorry 88 crank with 86 cyl! if I use 88 piston I need 5mm spacer which I have. if I use 86 piston what size spacer do I need?

[atv fan 28]

Some good info in these vids.

http://www.youtube.com/watch?v=l3kYLJajA2o


http://www.youtube.com/watch?v=ydCQkJsO_cU

[deathman53]

you can use the 88 piston/ w/ nothing else, as others said NOT recommended. Or 86 piston w/ 5mm spacer plate. Depending on the size of the bore, you can use a yz piston w/ 3mm spacer plate.

[regg187]

Ok deathman Thank YOU! that answers my question, but how about the rest have you run the not recomended setup or know someone first hand that has? do they live or gernade when they get a little wear?

[deathman53]

I personally don't know anybody who used the 88 piston in 85/86 cylinder. I use 86 piston and 5mm spacer in long rod crank. My friend had some that used a yz piston and 3mm plate, never had any complaints about it.

[derby]

I have never used the combo like that. But I am guessing that you could have some problems with the 86 rounded intake and the 87-89 piston which does not have a half moon cut on the intake side. I wonder what the possibility that the piston skirt would stick in the intake port when the piston approaches bdc.

[fearlessfred]

im wandering if the ring locaters on the piston would even allow u to run the 88 piston in the 86 jug

[C-LEIGH RACING]

All years of 250R cylinders, that boost port tunnel is shaped the same, same width if not widened by someone & ring pin locators are the same on all year pistons, so probably not a problem with the ring ends comming out into the port.

Only problem I can see, is if that P/T race cylinder has been ported in the area of the intake & the oval part of the intake has been widened a great amount.

If it has, then you'll probably have support issue on the intake side of the piston.

You could round off the bottom of the intake area, make it round like instead of flat & then bevel the sleeve so as to not catch the piston skirt.

I think you could use the 88 piston in the 85/86 cylinders, but will need the intake area modified, not widened, just the floor area & bevel the sleeve.

I've used the 87/88/89 full skirt style 72mm big bore pistons, in the Pro-x big bore cylinders before that has the oval intake just like the old 85/86 TRX250R cylinders, no problems using them in those cylinders.

Another thing you might want to think about, you'll need to set it up tight, little tighter than normal piston to cylinder clearance. Dont want that piston doing any rocking up & down the bore & probably will need to check clearance sooner that normal.
Neil

[fearlessfred]

Originally posted by C-LEIGH RACING
All years of 250R cylinders, that boost port tunnel is shaped the same, same width if not widened by someone & ring pin locators are the same on all year pistons, so probably not a problem with the ring ends comming out into the port.

Only problem I can see, is if that P/T race cylinder has been ported in the area of the intake & the oval part of the intake has been widened a great amount.

If it has, then you'll probably have support issue on the intake side of the piston.

You could round off the bottom of the intake area, make it round like instead of flat & then bevel the sleeve so as to not catch the piston skirt.

I think you could use the 88 piston in the 85/86 cylinders, but will need the intake area modified, not widened, just the floor area & bevel the sleeve.

I've used the 87/88/89 full skirt style 72mm big bore pistons, in the Pro-x big bore cylinders before that has the oval intake just like the old 85/86 TRX250R cylinders, no problems using them in those cylinders.

Another thing you might want to think about, you'll need to set it up tight, little tighter than normal piston to cylinder clearance. Dont want that piston doing any rocking up & down the bore & probably will need to check clearance sooner that normal.
Neil thanks for the info on the ring locater . i did not know because i have never compared the two together. iwas doing all these modds in the late 80s. i made my own spacer plate out of a sheet of brass plate.the 265 cylinder was a runnin son of a gun and i did not want to give it up when i bought my first 88.REG 127 is there a reason that u want to do this combo,because i dont see any gains to be had.this is only my opinion and not said to be insulting.however it would be interesting to know if anybody out there has ran this combo.

A few years ago I used an 88 piston in an 85/86 cylinder. It was setup with a Wossner Piston at 68MM. The Wossner’s require a tight piston to sleeve clearance, around .0024” or .06MM just like Neil suggested.

Never had any issues with the Wossner 88 piston in the 85/86 cylinder; used it for two seasons and it ran like it was on fire.

I think the trick here is to bevel all the edges, piston & sleeve on the intake side and make sure your ring ends are well captured and not exposed into the intake windows.

You should be fine…

Carlos.

[regg187]

Originally posted by C-LEIGH RACING
All years of 250R cylinders, that boost port tunnel is shaped the same, same width if not widened by someone & ring pin locators are the same on all year pistons, so probably not a problem with the ring ends comming out into the port.

Only problem I can see, is if that P/T race cylinder has been ported in the area of the intake & the oval part of the intake has been widened a great amount.

If it has, then you'll probably have support issue on the intake side of the piston.

You could round off the bottom of the intake area, make it round like instead of flat & then bevel the sleeve so as to not catch the piston skirt.

I think you could use the 88 piston in the 85/86 cylinders, but will need the intake area modified, not widened, just the floor area & bevel the sleeve.

I've used the 87/88/89 full skirt style 72mm big bore pistons, in the Pro-x big bore cylinders before that has the oval intake just like the old 85/86 TRX250R cylinders, no problems using them in those cylinders.

Another thing you might want to think about, you'll need to set it up tight, little tighter than normal piston to cylinder clearance. Dont want that piston doing any rocking up & down the bore & probably will need to check clearance sooner that normal.
Neil

As always C-Leigh is correct, from what I can see, the PT cylinder is widend in the intake area which seems to be very wide and I could see a full skirted piston with some wear on it either causing excesive wear or potetially catastrophic destruction. the port edges are very beveled where it is widest. and at the very bottom .
I went ahead and picked up 85-86 piston, because of that widened intake!!

thank you everyone for your answers!