Cr250R Porting

[dues201]

So I picked up a new street supermoto project, and shes in need of a top end.

I'm looking for a local shop to mill the head and do some porting. Any suggestions on a place around town that has a good rep with 2 strokes?

[Sortarican]

The CR is still a 2-stroke right? Not sure there's enough room in the head to truely port it.
Polish the ports and look into aftermarket intake manifold and expansion chambers for increased power.
(Sorry if this makes no sense, last CR I owned was in 1977 and they've probably changed a bit.)

[dues201]

it is still a 2 smoke, I'm not looking to port the head, but mill for less squash. Cyl porting also.

[Sortarican]

it is still a 2 smoke, I'm not looking to port the head, but mill for less squash. Cyl porting also.

What part of town are you in?

Any machine shop should be able to mill the head and bore the cylinder on a 2-stroke for dirt cheap.
Haven't used anyone in town for bikes, but have used G&S Auto Parts & Machine Shop in Littleton for automotive machining work.

Up north I know a lot of people use Acme (in Ft. Collins I think).

[dues201]

I'm in thornton, I was hoping for a shop that has some experience with 2 strokes, but I may just stick with the milling the head for now depending on whos local. Just dont want to send stuff out.

[Bueller]

You are going to street supermoto a 250 2 stroke?
Good luck on that one. Find a good machine shop you'll need one :lol:
I wouldn't try it on less than a 500 and don't plan on much but screwing around in town.

[Sortarican]

Anyone remember the name of the shop on Hampden frontage road around Federal?
Thunder/Mountain/Eagle/something or other?
When I was doing the RD cafe project that guy was referred by several people as being a 2-stroke expert.


Good luck on that one. Find a good machine shop you'll need one :lol:.

Don't listen to Bueller, just cause he IS a Tard he thinks that makes him an expert ON tards.
The CR is fine bike! And a 250 2/stroke is equal to your POS KTM 450 or whatever it is for output.
(Oh wait, you shelled your motor didn't you? So basically a boat anchor has more power than your KTM now.)

J/K, Man.
Bueller really does knows his motards and is a good source if you want to pick his brain.
Just outta curiousity Dave, why do you thing the CR isn't a good choice?

[irdave]

Two-smokes are/can be a little peaky... Maybe a little testy... I've got a plate for my KX250- haven't ridden it around on the street much yet, don't know that I will.

And FWIW, a 2-stroke 250 is plenty fast as it is... Faster than the 4 stroke 400 I'm riding around on (and no, not the heavy, slow drz400sm...)

[Bueller]

For that very reason, a 525cc 4 stroke with a 6 speed gear box and I've gone thru 1 motor @ 5500 miles. Expect way less out of a motor that will not deal well with stop and go traffic in the heat and turning 10K+ rpm to get anything out of it. There is a reason everyone races 4 strokes. Don't get me wrong I love 2 strokes but in the same breath I would never turn my YZ450F into a street tard either, it would eat itself in less than 1K mi.on the street.

[Aracheon]

On that note Dave (and Dave), what WOULD you recommend for a streetable tard?

[Bueller]

If you want to ride forever without worry a DRZ400SM, but for power and good streetability, Yami WR450, KTM 450-525 EXC, Honduh CRF450X, KLX450R

[MattTLS]

it is still a 2 smoke, I'm not looking to port the head, but mill for less squash. Cyl porting also.

You should know that milling the head does not affect the squish at all -- you'll simply increase the compression ratio. To change the squish you'd either have to mill the cylinder (top is easier, but the nikasil coating can be chipped and is relatively expensive to replate -- bottom is more difficult but less chance of damage), use thinner base and/or head gaskets, or your most expensive option is to use a custom length rod or custom wristpin-to-crown height piston. I'd go the gasket route if it would work to attain the desired squish. But of course make sure that you measure everything accurately or you could have some big problems.

As for porting, removing material isn't always the way to go. And there are definitely arguments against polishing as well. If it were me, I'd match up intake, expansion chamber shape, and piston shape to best meet your requirements.

[kosh]

Do NOT have a machine shop port your cyclinder
Do NOT have anyone shave off the head to improve compression use a thinner gasket and ensure you have the proper tolerances from head to piston

If you want to port and polish your cylinder it needs to be sent to a professional that has flow testing ability or your will ruin the cyclinder.
Also since you want porting done might as well have a new sleeve inserted sleeve inserted.

There is alot to do with the dirtbikes power if you want to know anything im pretty good in this area

^^^^ refer to above post as well

[dues201]

You are going to street supermoto a 250 2 stroke?
Good luck on that one. Find a good machine shop you'll need one :lol:
I wouldn't try it on less than a 500 and don't plan on much but screwing around in town.


Im not new the striped down supermoto on the street, I run my 450smr almost daily all over. The 250R is just for screwing around the neighborhood, you cant beat a 2 stroke for pure hell raising

I was thinking about doing a 500, but my old 250R had plenty of pep in the fields, should be the same thing on the street I would think.

[dues201]

Do NOT have a machine shop port your cyclinder
Do NOT have anyone shave off the head to improve compression use a thinner gasket and ensure you have the proper tolerances from head to piston

If you want to port and polish your cylinder it needs to be sent to a professional that has flow testing ability or your will ruin the cyclinder.
Also since you want porting done might as well have a new sleeve inserted sleeve inserted.

There is alot to do with the dirtbikes power if you want to know anything im pretty good in this area

^^^^ refer to above post as well

this is what I was expecting to hear, and what Ill most likely end up doing

[jplracing]

For years one of the top dirt bike motor and suspension guys around town was bruce sass who works at vickery.

I would assume they would do the work on a honda..but would probably want to call just to make sure

Joe

[Jayock]

Depending on your piston age, it may need replacing soon. If so, a perfomance piston can be purchased for little over an OEM piston, and will modify your squish. When I looked into doing this with my CR250R, I was advised that it couldn't be changed too much without the need to run race gas.

[kosh]

You really dont need to run race fuels unless your running a compression over 13.5 to 1. I use a JE 13.5 in my crf250 and pump 91 works fine i get 0 detonation.

[FZRguy]

Does your CR250 have a power valve? I think you are wasting your money on porting a 2-stroke with a power valve. Spend your $ on a Wiseco piston kit, FMF exhaust, V-Force reed valve and get the carb jetting right.

[Jayock]

You really dont need to run race fuels unless your running a compression over 13.5 to 1. I use a JE 13.5 in my crf250 and pump 91 works fine i get 0 detonation.

But you dont have squish to worry about in that 4-stroke.

[dues201]

Does your CR250 have a power valve? I think you are wasting your money on porting a 2-stroke with a power valve. Spend your $ on a Wiseco piston kit, FMF exhaust, V-Force reed valve and get the carb jetting right.



it does have a power valve and an FMF exhaust and sliencer (needs repacking) I am going to do the Reeds, not sure on V-Force yet(Ive always prefered boysen) as well as a torque spacer. As far as piston I am trying to find one of the lighter Wiseco single ring, but no luck yet.

It seems this build is going to take a little longer than I would have liked, the ktm is starting to feel more and more sick each day and I have a feeling its going to be pricy to rebuild her.

anyone have a timming chain breaker for KTM, their kinda pricy..

[kosh]

See if you can get em directly from wiseco check the site out. I use www.motosport.com (http://www.motosport.com) for most of my parts, but have had to contact manufacturers like ferrea before.

Even with the power valve porting will benefit the hp output.
It all depends again on what your looking for top end increase will decrease your bottom end.