LckyTylr

I have started rebuilding my top end in my 2000 CR250, as I have noticed that it's been down on power the last few rides, and I haven't done it since I have owned it (3 seasons). Soooo, as usual, everything came apart with no issues, and I spent 3 hours cleaning every nook and cranny. Took my cylinder in to get honed, and after paying for the service, I remembered that the service manual says to get the diameter of the cylinder measured to ensure proper clearance for the new piston and rings. . . . . and to determine if previous rebuilds involved increasing bore size. Well well WELLLLLLL. The previous Owner failed to mention that he put a big bore kit in the bike, maybe it had something to do with the fact that nobody makes that size piston anymore.

The piston that's in there now is a Pro X part number 1320BB. My cylinder measured 68.47mm diameter. Stock diameter is 66.4 mm.

I shouldn't say that nobody makes a larger size piston, Wiseco makes one (68.5), but I have heard so many things about them being easy to blow up or seize, that they take a LONG time to warm up, and that they are not meant for riding within a large temperature range. I ride all summer (hot), and i use this bike for hunting (cold as Sh!t). soooo, I don't want a Wiseco.

Here's what bums me out the most. This bike is going on 12 years old, I REALLY don't want to spend any money on this, and I can't justify spending much more on it to my wife, as the kit that I already bought (stock 250) cost us $250 with all lubricants/sealants/misc parts. Sooo, even if I decided to get the Wiseco, I'd still have to pay for the cylinder to be bored out to fit the 68.5mm piston.

Does ANYONE know where I could look for a new piston to match the one that I have? Pro X does not have a link for "Contact Us", unless you are a distributor. I have tried some google searches, with no luck.

Thanks in advance for any advice.

ckholloway

If you have already purchased the stock piston and rings then look on servicehonda.com and see what a new cylinder would cost. they are very reasonable.

IDAHOBALLER

That sounds like a 265cc motor then. As for pistons buy a wiseco! Forged pistons are much better in every way than a cast piston. The only thing you have to watch is that you make sure to warm the bike up before you ring its neck to prevent cold seizure. You should warm up a cast piston too anyways so that is not an issue. Its not really a big deal just let it idle or ride it easy for 5-10mins before you get on it hard and you will be fine. What they dont want is for people to start it totally cold and take off WOT. Cast pistons can cold sieze in that situation too! The only advantage of the cast piston is they tend to be slightly quieter but the bike makes enough noise on its own that you wont hear the difference without a stethascope (sp?).

I would say either buy the oversize wiseco piston or find yourself a different stock bore cylinder.

Are there any identifying marks on the piston that came out of it? It is most likely a wiseco being a big bore....that lasted 3+ riding seasons without mechanical failure...just sayin..

Ryan@IdahoSportBikes

I raced with Wiseco pistons for years.

JJSPRINT

I Completely agree with this post!! Forged Is the better way to go... my buy the wiseco Piston and bore it out an .010 bigger which Is like One pass lol

BuellCru

I always ran Wiseco with no issues.

BLIZANTHIMUM

actually a forged piston should be quieter than a cast piston since forged ppistons are less prone to thermal expansion and can be machined to fit in a tighter cylinder tolerance.

cylinder scuffing and piston slap is a common occurrence with cast pistons due to the loose tolerances to accommodate thermal expansion.

LckyTylr

Stock piston does have markings. "Pro X 1320BB".

Anybody know how much it costs to bore out to the larger 68.5 bore that I would need?

As I said, I REALLY don't want to sink any more money into this thing. I'll be getting a brand new bike this coming December. If I can make this bike last through this summer, and more importantly, through hunting season, then I'll be happy.

I can't justify putting a total of $500 of parts/labor into a $1000 bike that I'm only going to use for one more season. . . .

Thanks for the input, keep it coming.

IDAHOBALLER

I should have said that the forged piston is less quiet before it is at operating temperature. Once warmed up all the way the difference should be minimal unless there is cylinder taper or some other issue allowing for a looser fit. It should be mentioned that I am talking about these pistons in aluminum cylinders. There is different expansion issues when used in a steel sleeve vs a nikasil coated aluminum one.

The main reason why manufacturers use cast pistons as OEM is because they are slightly cheaper to make in addition to the fact that the cast pistons have almost the exact same expansion and heat absorbtion properties as the CAST aluminum cylinder around them making warm up a little less of an issue. The forged pistons absorb and expand at a much different rate than cast (making them noisy when cold...) which is good because you have a stronger piston that is more resilient in high heat (detonation...) situations. Obviously that is why the forged must be warmed up more so than the cast but thats not to say that cast dont have a weak point as they are the most prone to having the intake skirt break off and drop down into the crank case. This is due to the massive temp difference between the exhaust side of the piston vs the intake side being much cooler at all times. Temp cycles over time make cast become brittle (especially in an area of uneven heat distribution) but doesnt effect forged as much in the same way.

Basically what I am saying is at this point in time cast works fine but forged is clearly the better way to go no matter what type of engine it is (2 stroke, 4 stroke, gas, diesel, alcohols, boosted, n/a, etc...)

ckholloway

I agree with what everyone is saying but I would get pricing on everything before you make a choice. You said you already had a top end kit (piston and such) for the stock bore cylinder. You also said you want to spend as little money as possible. To do the big bore you are going to need a new top end kit and the cylinder bored. You can get a stock cylinder from service honda reasonable price. I don't know the year of your bike (maybe I missed it before) but I looked and this is what I found.
CYLINDER A
12101-KZ3-B10 001 $478.89 $326.60

So if you can do new top end kit and the machine work for $326.00 or less I say go for it, thats what I would do. However if not I would buy the stock cylinder, put it together and ride it through the season. Just my opinion.

IDAHOBALLER

That is definately a prox cast piston then. If they are still producing that particular piston then you should be able to order a new piston and rings from prox using that part ID number. I have used prox in the past in both 4t and 2t builds that I have done for others (I will ONLY used forged on my own stuff...) and have had good luck with them but these motors were vet ridden and didnt get ridden super hard all the time plus they are good about maintnance schedules and such which I am sure helps in the reliability spectrum...

I can say that I personally have broken quite a few cast pistons over the years but have only "hurt" one forged one and that was in one of my 450's that was a stock bore/stroke 15:1 compression big valve huge cam huge carb meth drag motor that I was spraying a 30 shot of go juice on. That motor made 62rwhp on motor and 91hp on spray. The piston in it ( a custom made for me CP forged piston) ended up crackingthrough the center of the dome (along the same plane as the wristpin) but still ran like a champ with the huge crack in it. The only thing that happened was it would smoke a bit when cold but seemed fine once warm. My buddy drag raced that motor for a whole season on that cracked piston with no ill effects other than cracking the cases around the main crank bearings (but that was the cases fault for not being stong enough around the bearings to hold the extra hp/tq).

IDAHOBALLER

I agree! Shop around and see what makes the most financial sense before making any further purchases. I have seen cylinders in great shape some even being brand new sell for cheap on ebay.

My buddy blew up a CR250 last year (same motor as tylers not the newer case reed motor) pretty bad because the cast piston in it dropped the intake skirt but it somehow got wedged in the intake port which ruined the cylinder but didnt hurt the bottom end at all. He ended up finding a brand new never ran cylinder on ebay for like $160 something dollars. There are great deals to be had if you look long enough. We put the motor back together and got it jetted right and it ran great until he forgot to check his sparkplug torque and the thing backed out on him while riding allowing the cylinder to temporarily lean way out which ended up melting a whole through the top of the piston dome (was an OEM cast piston again...). Long story short he got tired of working on it and sold the bike and gave up riding for a while. sad story.

IDAHOBALLER

Since the bike in question has a nikasil coated aluminum cylinder it will require the ports to be chamfered and the cylinder recoated at the minmum after it has been bored to be usable again. It might also have to have the powervalve modded slightly as well depending on how far they cut it back during the original big bore work. If a person were to just bore it and run it they would quickly find out how much harder of a material the piston rings are then the bare uncoated aluminum cylinder wall. The rings would eat the cylinder walls in no time.

Ryan@IdahoSportBikes

Jet engine?

IDAHOBALLER

I would imagine that there are plenty of forged parts inside of a jet turbine engine...but I doubt you will find a wiseco, cp, je, cosworth, mahle, wossner, etc... forged piston inside.

BLIZANTHIMUM

i had no idea anything but steel cylinders were ever used.

THUMPER

soooo im sure ill get all sorts of sh!t for this.. but would it be possible to buy the 68.5 piston, and then have that machined to fit the current cylinder? just a thought rather than buying a stock piston/cylinder or having to bore the already bored cylinder?

BuellCru

Hand over the bike and I'll gladly take over where you left off.

Sethg1981

I worked at Chaparral for years and never once heard anything bad about wiseco. I rode wiseco pistons for years and never had any issues with them. Speaking of Chaparral, give them a call and once you get back to parts ask to speak to Dave Williams. He has worked there for like 15 years. that place can get ahold of a ton of shit and if anybody knows where to get stuff for this size cylinder he would be the guy. Tell him Seth Greene sent you. Hopefully he remembers me and will give you the employee discount.

IDAHOBALLER

In theory yes this could be done but it would be pretty extensive machine work because not only would the overall od of the piston need to be machined down but the ring lands would also have to be recessed deeped as well and that might cause ring fitment issues as well as you might have comprimised the structural integrity of the piston by removing that material. I would say not to do it.

Tyler can you measure the bore in inches? It has probably been bored in in increments of hundredths of inches. example being "bored .030 over" etc...

IDAHOBALLER

I agree! I am sure I can fix it!

IDAHOBALLER

One thing to think about tyler since you are looking at both retaining the big bore as well as going back to stock bore. I dont know how much experience you have on 250-300cc 2 strokes but I wanted to mention this anyways. with the big bore you have much more usable off idle torque and generally a less peaky power spread vs a 249cc engine which tends to be more hard hitting in the mid and top end.

What type of power do you prefer? low-mid, all around, mid-top, revvy wheel spinner or more of a smooth tractable type power?

LckyTylr

I'm really not sure what kind of power I prefer. This is the first dirtbike I have ever owned. Took me a summer to figure out what I was doing on it, nearly unmanageable for me to ride as a rookie. Now, 3 summers and many riding-hours later, I have come to really enjoy the power that it makes. Prior to my bike producing less and less power, I let some of my 2-stroke riding buddies take her for a spin. They both did a 1/4 mile or so before they came back and said "Here, take that F$&kin thing BACK". Apparently there was little comparison next to their own stock YZ250's that were half my bikes age. Now that my bike seems to be losing power, I feel more like I'm riding a kids bike. I'm having trouble with power in the upper rev range, so when I try to get up a hill, by bike won't stay in power band. I could be WOT in 3rd gear, giving it hell, and at some point she just falls out of the power band, loses revs, and I decelerate. This causes me to either clutch or grab 2nd gear to get back into the power band. Clutching overheats the bike on such a long hill, 2nd gear spins me into a hole, and I end up trying the hill all over again. These are all hills that I have done easily in summers past. I wish I could say that I have spent more time on different bikes, but I haven't. I don't really know if I would be willing to put up with 0 torque down low and a snappy lil b!0tch up high.

Either way, I can't afford ANY kind of engine work. If a mechanic has to touch my cylinder with any kind of bore drill, it's too rich for my blood.

BuellCru

Since nobody else did it here you go,

LckyTylr

:-)


That's AWESOME!

Much appreciated this morning. High-five to you, Sir.

LckyTylr

YAYYYYY!!!

I found a Piston that will work for my cylinder. As ordered, piston and rings fit into my cylinder, but it's pretty snug, and as it's a Wiseco piston, we were concerned with cold seizure. A nice guy at MotoTech, Joe, said that a rigid hone would take off just that tiny little bit that I'd need to ensure adequate clearance, and since MotoTech doesn't have a quality Rigid Hone, he offered to take it to CWI and get 'er done for me.

I'll have my cylinder back tomorrow, and will start reassembly soon. I'm SO STOKED!!!

:-)