86 crank to 4 mill stroker

[nashport_native]

Im replacing my crank in my 86 with a 87-89 4 mill stroker since i ride in the woods, to give me more bottom.

my question is this, if I have to shim the cylinder up .19 for the longer rod, can I just move the cylinder up another .16? (4mm divided by 25.4) I am a machinist by trade, so I could make a .35 thick spacer plate pretty easy.

also, what piston would I run?

thanks,
mike

[Honda 250r 001]

what i would do is instead of moving the cylinder up 4 mm or what ever the normal spacer is, i would move it up about 6mm, that way you dont have to mill the head and you can adjust your compression that way too by using thicker and thinner base gaskets, use a 86 piston with the spacer.

[C-LEIGH RACING]

Lets throw a kink in the logic.
Spacing the cylinder up, not the proper way to do it, you always want the ports at the bottom of the stroke.

But, sometimes spacing is the only way it can be done.

What your are about to start to do, is something you realy need to know what your doing for it to come out right in the end or else you'll end up with an engine slower than a stock engine build.
Neil

[Honda 250r 001]

ya man im thinkin about screwin my stroker and goin back to the short rod, this is just too complicated for me. And how much hp do you gain with this? and where is it at? (bottom-mid-top?) I have not done anything to the cylinder but i have milled the head 2 mm and i am getting beat by piped 450's and it pisses me off.

[86 Quad R]

Originally posted by Honda 250r 001
ya man im thinkin about screwin my stroker and goin back to the short rod, this is just too complicated for me. And how much hp do you gain with this? and where is it at? (bottom-mid-top?) I have not done anything to the cylinder but i have milled the head 2 mm and i am getting beat by piped 450's and it pisses me off.

are you saying that the cylinder isnt ported for the added fo-mil stroke? :confused:

[Langbolt]

Hey guys....listen to Neil...he knows what he's talking about.

Strokers are a mathemetitions nightmare!

You need to get your port timing just right or it will run like crap!

Like Neil said you want your transfer port floors flush with the piston at B.D.C.

You want to make sure you're getting 30 degrees of blow down, which is your exhaust port timing minus your transfer port timing then divide by 2.

eg. (185deg. exhaust - 125deg transfers) / 2 = 30 deg blowdown.

If none of this is makin' any sense you need to pick up a copy of the 2-Stroke Tuners Handbook.

You're best to start with a STOCK cylinder.....if you're using a ported cylinder for the stock stroke then chances are the cylinder is already no good for the 4mm Stroke increase.

Measure your Exhaust port from the top of the cylinder to the roof of the port and do the same for the Transfers and post the numbers and I'll do some calculations to show you exactly what I mean. (Use a digital vernier in mm's please)



:devil:

[nashport_native]

yes, I am running a stone stock cylinder, only mod to it is a .02 overbore from stock. i ordered the .25 spacer from esr, and i will use base gaskets to shim my cylinder which ever way it needs to go.

the port timing could be off, but it will still run better than the way i got the bike (.02 over cylinder, std size cast piston)

[Buttermilk]

If you are gonna run a 4 mm stroke, then by all means port that cylinder (have someone do it that understands porting, and by that I mean how to set one up for the stroke and what numbers to port to.....).

That added stroke on a stock unported cylinder won't be enough to run with the 4 strokes.

If you run a 4mm stroke (76 mm total) with the 130.3 mm rod and run the '86 style piston, and combine all that with a 0.200 (5.08mm) spacer plate and two 0.020" thick gaskets on an undecked cylinder, that 'should' get you zero deck height.

I ran a plate on my 265 with a 4 mill longrod and set the port "floors" to BDC and raised to port roofs to where I wanted the timing and made good power on an OEM jug (dyno charts are in the dyno section).

It's all in how the motor is setup as a package.

[nashport_native]

so I need to take my plate into work and mill .05 off the thickness of it.

I dont know of any people around ohio that still do port work.

most of my racing is in tight xc stuff, i ride the bike more "off the pipe" than on, I wanted the stroker just to give me a little more bottom.

heck, the way it was befor, was way better than the bike it replaced in the woods (88 lt250r)

[machwon]

Nashport_native, I sent you a pm on port work. You can work with the parts you have, but I'd also recommend you have the head set up as well.

[1promodfan]

Originally posted by nashport_native
yes, I am running a stone stock cylinder, only mod to it is a .02 overbore from stock. i ordered the .25 spacer from esr, and i will use base gaskets to shim my cylinder which ever way it needs to go.

the port timing could be off, but it will still run better than the way i got the bike (.02 over cylinder, std size cast piston)

Hey man, listen.....it WILL NOT run better if you run a 4mil crank without getting it ported for it.

If you just stick in a 4mil crank and don't get it the ports raised for it........you'll prob. get beat by some 400ex's!!! In other words it'll run like CRAP!!!!

[Honda 250r 001]

YES IT WILL

i did this. Im getting beat by DEAD stock 450r's. and i have pretty much everything you can have except a big bore. (which is on thje way). if your not going to do it right. dont do it at all!

[Langbolt]

Mike,

I'm running a 3mm stroker in my R and it works GREAT!

I'll spank any 400ex or stock 450r.

Ya just gotta do the math!

Do me a favour and measure your current port heights.

Then I can give you a bunch of options to suit the kind of power you want.

Then I will let you know what thickness spacer plate to run.

You will have to machine your cylinder head too.

Are you planning on using a head gasket ? or O-rings ?

This is how I've set mine up.....the negative deck height is because my piston comes above the top of the cylinder by 1mm & the zero head gasket thickness is becasue I don't use one...I O-ringed my cylinder.

:devil:

[nashport_native]

langbolt, i will try and get the numbers for you tomorow, my bike is in my dads shop, and i dont have time durning the week to go there and get what you need.

man I should have just bought a stock stroke crank and been done with it....

[Buttermilk]

Once you get the 4 mill crank in and get the cylinder setup correctly, you will be glad you have a 4 mill crank.

I think they are worth some HP over a stock stroke, when both are setup correctly.

There are several people who can port that cylinder for you at a very reasonable cost (one is even a member here....C-Leigh Racing) who know what they are doing.

[kiesta00]

Go with the 4mm if you have to replace the crank. I've got a 4mm motor and its nice...I don't really have anything to compare it with since all of my 250r buddies have 4mm's too haha. You'll be happy you got it once it's all said and done.