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What piston?

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Posted by: JEEP FARM

Hey guys,

I am going to rebuild my top end on my 2002 CR250R. I bought it used this past fall. I am wanting to replace the parts so that I know it's fresh and I don't really want to take buddies word that it's good to go.

So my question is, what pistions is everyone using. I am a rookie and just want to keep it stock. I don't race and will not be boring anything out.

Thanks, Jay


Posted by: ellandoh

i used the vertex double ring last time, ill just say i m going back to either pro-x or wiseco. 03 cr250


Posted by: crashnburn

Wiseco pro lite, no complaints. Don't have to worry about A, B, or C piston size.


Posted by: MX Junkie

Quote:
Originally Posted by JEEP FARM
Hey guys.... I am a rookie and just want to keep it stock. I don't race...


If your not concerned about gaining a little extra performance (with the pro-lite that is), stick with the stock piston, they are a little cheaper than the Wiseco and are very reliable. With the pro-lite you will gain a little more overrev (lighter piston) but you need to make sure you warm up the engine properly before you "punch it" reason being the pro-lite has a greater piston/cylinder clearence (engine siezure may occur if not brought to proper operating temp).


Posted by: Peer Lovell

I would go with an o.e.m. piston. The Wiseco "one size fits all" won't always give you the best performance.
Go with the size stamped on the side of your cylinder for your particular bike.
If you don't know where to look for it let me know.
I've been riding Hondas for 15 years and never had a failure with OEM pistons. Be sure to also use new Honda rings, circlips and top end bearing.


Posted by: John Cena

Slap an oem piston in there and get out riding.


Posted by: JEEP FARM

Right on guys thanks, OEM it is! I do know stock is the most reliable, that's for sure!


Posted by: JEEP FARM

Hey Peer Lovell,

So I have stamped on the side of my cylinder (Piston Stoke 72.0mm). Is this telling the size of piston I should be looking for?

Thanks, Jay


Posted by: ellandoh

Quote:
Originally Posted by JEEP FARM
Hey Peer Lovell,

So I have stamped on the side of my cylinder (Piston Stoke 72.0mm). Is this telling the size of piston I should be looking for?

Thanks, Jay


i believe its on the front left side of the base and it will be stamped with an "A" "B" "C" or "D" they are slight variations in tolerance from the factory


Posted by: Peer Lovell

Yup, yer looking for the"A,B,C or D" stamp on the side of the cylinder.
When ordering your piston just give them the year, make and size and specify the stamp number.
Be sure to order new rings with exactly the same size stamp.


Posted by: JEEP FARM

Thanks guys,

Ok Peer Lovell, what do yo mean by "exactly the same size stamp" sorry (ROOKIE) lol!

Ok on the side of the cylinder I have stamped "A". When I called Machine racing to order my chit for the rebuild. I was told that they take measurements for each year and pic the best stock piston for that bike. They gave me a piston with "B" on it.

So do I go with an "A" (which I think I should do) or go with the one they gave me?

I am also going to be posting some pics of what the piston looks like. I would like to see if it looks normal or not, just so I know!

Thanks, Jay


Posted by: JEEP FARM

Ok here are some pics I just took so could you guys tell me what you see!

I just want to know if everything looks like it should?

Thanks, Jay


Posted by: MX Junkie

Running a little rich, got lots of blow-by. Other than that looks normal.


Posted by: JEEP FARM

Thanks MX Junkie for the reply!

The guy I bought the bike from, told me to only ever run it with 50:1 mix. Then I read the manual and it said to run it with 32:1. So I ran one tank of gas at 32:1 and it smoked like a mother @%&!er and ran like chit!

Do you think one tank of rich gas would do that?

Thanks, Jay


Posted by: Peer Lovell

Jay, that's a totally bizzare response you got from Machine Racing.
To suggest that you use a "B" size, when the cylinder was already measured at the factory for an "A" size just doesn't make sense. Machine Racing is usually excellent.
I would call them back and get this clarified. You want the "A" size piston for your year of bike.
All pistons are available so I don't know what the deal is. Perhaps you got a rookie on the phone.
Shots of your piston look good. I agree slightly rich but lots of blow by. Needs new rings for sure.


Posted by: Peer Lovell

Whether you use 32:1 or 50:1 should have absolutely no impact on smoking.
How long did you ride it? If you just started it up in your garage for a few moments then a lot of smoke is pretty normal.


Posted by: JEEP FARM

Hey Peer Lovell,

Ya I know I thought it was weird also. So I called Machine today and to talk to John (the owner). I asked him about needing a "A" piston for my bike instead of the "B" I recieved from them, (because I didn't know better, yet!).

He then told me that you could use a A in a B cylinder or vise versa. That it didn't matter, and that they do it everyday! So I said ok well as long as your telling me I can use a "B" piston into a "A" cylinder. OK.

About the smoke!

It didn't smoke with the 50:1 I used with the first owned tank. Then when I thought it would be a good idea to use 32:1 it smoked right away and the intire time I rode the bike!

I have the piston to so I thought I might aswell just use it also eh?

Thanks guys, Jay


Posted by: killerdwarf717

I have a B cylinder on my bike with an A piston, it tightens up the clearances. I think, using a B piston with an A cylinder will loosen clearances. The only way you can make sure this combo will work, is to break out your manual, and check to see (by measuring) if your clearances are within spec. also dont forget to check your ring end gap while your at it!


Posted by: john stu

Quote:
Originally Posted by JEEP FARM
Right on guys thanks, OEM it is! I do know stock is the most reliable, that's for sure!



humm ive had three stock pistons fail over the years (been riding seince 1989) but never a wiseco (and as soon as its time to replace i have always used wiseco after those few problems i had) and eric gorr stated in his book that in a few models the stock piston is prone to failures(one is the 97cr250 something about the ring locating pin comming lose and there were other bikes but i cant remember) if it was me i would use wiseco but i have not herd of "ANY" problems with stock on the 2002 cr250 except for excessive piston noise (slap) but on that bike with the stock piston i havent herd of any failures so use what ever you want but i think on that year and newer the wiseco is susposed to have less piston slap not sure why but i herd the engine noise is quiter (im not talking exhaust)just be sure to warm the engine up at low rpms close to idle until the engine is very warm and you'll be all set


Posted by: JEEP FARM

Ok I have taken a look at the two pistons the "A" and "B" piston. They both seem to be exactly the same in size. I know it's only by eye but it must be pretty close if the owner of a major bike shop like Machine is telling me that they do it all the time and it's ok.

You know?


Posted by: killerdwarf717

MEASURE!!!! you can't see the difference between the two, because it will only be a couple thousands of an inch difference. The only way to be sure (which you are not, or you wouldnt have started this thread) is to break out your service manual (you do have one?) and MEASURE!!! 2 thousands of an inch too large or too tight WILL be the difference of your engine blowing up! Do you actually think MRC just puts pistons in engines without measuring clearances? I doubt it, they wouldnt be in business too long. I suggest you get somebody who KNOWS what they are doing to help you out. But then again, it's your bike!!! Good luck.


Posted by: MX Junkie

The difference between an 'A' and a 'B' is a lot less than a thou of an inch. Go ahead and trust John.


Posted by: JEEP FARM

Ok thanks MX Junkie,

I was going to do it tonight and get it over with but changed my mind and thought I just better get a "A" piston if that is what it says I need on the cylinder. I wish I would have recieved your reply sooner, lol!

I would have been done by now!

Any tricks for getting the piston and the rings in the cylinder on the install?

Thanks, Jay


Posted by: MX Junkie

Just patience. Make sure the rings are in the right place, don't twist the cylinder on the install and pay attention to the head gasket.


Posted by: killerdwarf717

And don't forget to coat the cyl., and rings with 2stroke oil, preferably with the oil you run, but not synthetic. Check your ring end gaps first!!! before assy.


Posted by: JEEP FARM

I use Honda synthetic oil, why do you say not to coat the cylinder with it?

Thanks,


Posted by: MX Junkie

You should use a petroleum based oil for break in to help seat the rings properly (this helps prolong ring life).


Posted by: JEEP FARM

Oooops!

I used the Honda synthetic oil tonight when I finally got around to putting it back together.

It ended up being alot easier than I thought it would be. These bikes are so nice to work on. It's actually fun, tinkering around!

Anyway thanks to all for your help, untill next time!

Jay


Posted by: John Cena

Quote:
Originally Posted by JEEP FARM
Oooops!
These bikes are so nice to work on. It's actually fun, tinkering around!

Jay


Yea it sure is fun! It's a great thing to do when you get bored. There's always something to mess with.


Posted by: JEEP FARM

Ya that's for sure, especially when it's in the basement about 5 steps from the couch, lol!

It's alot easier and cleaner working on the bike than it is this!


Posted by: i_955

A lot less expensive too.

I told you the top end was easier than you thought, once it was done.

I took the Liberty wheelin twice.
First time, scratched the paint, second time dented the door and more scratches.
It now has all season radials and sits in the Cute-Ute catagory, my life partner insists


Posted by: JEEP FARM

Ya sometimes it's to much fun to worry about sheet metal.

You were right about it being easy, but only untill I broke a head bolt in the cylinder last night torquing the bolts down! Bummer!

Thanks, Jay



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