CR250 2002 Top End questions- OEM or Weisco?

[john stu]

wiseco all the way............been using them 15 years no problems ever and bike seems like makes less engine noise (not exhaust i mean from engine itself) and wiseco claims lighter than stock

 

[Sandy Whoops]

I asked Eric about drilling the holes in my Wiseco single ring piston. Here is his response:

"Pistons are turned in an egg shape with the blunt side facing the exhaust. Exhaust bridges are relieved for extra clearance. The extra oil holes aren't neccessary, just a little more insurance."

 

[Rcannon]

I woudl never argue with Eric. He knows 10 times more than I will ever know.
On second thought, maybe I would. I have a destroyed CR 80 cylinder in my garage. I had neglected to read the weisco piston instructions and did not drill it. There is a visible gouge in the piston where it travels over the exhaust bridge. .This hole takes all of 30 seconds to drill. It really is no big deal to add.


Eric's book said this can also be caused by a bad crank seal...I wonder....

If anyone wants a picture, e mail me at jamesc4085@msn.com. I will send you one. I am too retarded to post the picture here.

 

[Studboy]

I guess that it depends on the bike, but I have seen the same bike (91 RMX250) both with wiseco pistons come out, one that was drilled and one that wasn't, and the one that wasn't had 1/4 the wear on the exhaust bridge that the undrilled one had.

 

[Thumpdaddy]

I bought an 02 CR250 3 weeks ago and it is in cherry shape - only on the second tire in the rear. I decided to do the top end this weekend just in case as I don't know how many hours are on it. I went with the Wiseco piston, Cometic gaskets and Honda wrist bearing for $145 from the dealer (Rockymountain & Motorsports Outlet have it for $120 but no gaskets in stock). When I got things apart the piston didn't look too bad but the carbon was starting to build up on the RC flaps - use Easy Off. I drilled 2 holes in the piston per the instructions using a 5/64 drill (.075) and it was no big deal. I got everything back together this afternoon and it started up on the first kick. Rode it down the street and it feels real tight. One thing about the 02 if you go with the OEM piston is that you have to know wheter it is an A or B piston (marked on the top) whereas with the Wiseco it doesn't matter. Anyways the project took me about 5-6 hours following the shop manual (first time as I have been riding Thumpers). I think I could do it in about 3-4 hours next time. Make sure you have a torque wrench, easy off, scotch brite, and some patience. :aj:

T-Diddy

 

[Micahdawg]

I've heard two conflicting views throughout this thread. One person says the Wiseco piston feels lighter than OEM...one person says the OEM piston is lighter than Wiseco.

Here is what I've been told and makes sense. When I was deciding which piston to go with on my older 97 RM250, the sales guy (a friend) told me this. The wiseco is forged (stronger) than the stock cast piston. So the wiseco can get away with being thinner and lighter. (KTM is the only manufacturer to use forged pistons for stock applications.)

The stock cast pistons are normally thicker and heavier to beef them up. So from a performance standpoint, the thinner wiseco would probably be the choice. A wiseco kit is almost always going to be cheaper than OEM also. So I went with Wiseco.

As far as long term durability...it sounds like both will last quite a while. But as for abuse (detonation, fire spiking)...I would rather have a thinner forged piston than a thicker cast one. Forged pistons should be able to deform, melt...and do all kinds of screw stuff while a cast one will probably just get a hole blown through it. At least this seems to be the case in my experience with car engines.

I think wiseco is also thicker/beefier in the pin area than stock.

So for me...I'll probably stick with Wiseco, but if I got a killer deal on OEM I wouldn't turn it down.

Micah

 

[crazyYammi]

i wonder how many of these guys going for the faster revving forged piston have flywheel weights

 

[Studboy]

A piston has to stop and start movement, whereas the crank just keeps on rotating.

I usually run the Wiseco pistons, but I put in a OEM this time. Why? Because for $105 for the complete topend kit (including gaskets, wristpin bearing, etc.) I couldn't pass it up.

 

[johnny 1997 cr]

Hey guys, took my 1997 cr 250 out this weekend and it seized, the bike just died, i kicked it about 20 times and then the kicker just seized up. Is it a big job to fix it myself? I sure would like to save the money. Thanks in advance.

 

[dirtbike_madness]

So, I talked to a friend of mine at a Honda dealer, and he recommended the OEM piston, and here's his reasoning.

He said that since the Weisco is forged, if it does go, it goes in a big way and can destroy the cylinder. Because the cylinder is nikosil coated, it cannot be bored. (is this true-anyone know that for sure?) The OEM piston is cast, and will not cause the damage that the Weisco will if it goes south.

Now granted, that was what the dealer said. Anyone here want to comment on any of this? To me, I would rather have long term operation than short term performance. A cylinder is not cheap. I'd hate to see a piston go to pieces in my engine, know what I mean ;-)

 

[Micahdawg]

There's not really any good way for any piston to "go". If you put a small chip in the plating or a FRIGGEN huge shread in the plating...guess what.........it's gotta be rechromed either way. Big gouges usually require welding which can cost an extra $30 typically (if US Chrome does it). So the price difference in that case would be $200ish for a rechrome only or $230 for a weld and rechrome.

In the end, don't let your pistons go boom. If they are cast or forged it won't be fun.

Micah

 

[Studboy]

If the a piston blows whether it be cast or forged, you are going to be screwed.

 

[jmossbarger]

dirtbike_madness, I think your dealer has it backwards. Since the Wiseco is forged, it is malleable (aka flexible to some degree). The cast piston is very stiff and will not flex. This sounds good at first, but think of it as a china plate, its really strong, until it breaks without warning. A forged piston will tend to "wear out" before a failure occurs. You will see a drop in compression, maybe a little noise from piston slap before its time to replace. A cast piston can just fail, without warning, generally either a piece of the top ring land breaks off or the skirt itself will break off.

The Wiseco Prolite is lighter than the OEM, the Wiseco Single ring race part is closer to the OEM weight, but still a little lighter. I just put a Wiseco single ring race piston and crank into my bike this week, went together perfectly and fired right up. Haven't ridden it yet, but should by the weekend.

As for the exhaust bridges, the pre 2002 motors should not have exhaust bridge oil holes drilled in them. Almost all of the modern 125's have bridges and can benefit from the oil holes.

Good luck in whatever you choose!
Joe

 

[dirtbike_madness]

Joe, quick question... You say the "pre 2002 motors". Mine is a 2002. Is there a way to know "before" I tear it apart if the holes are needed? Also, I hear lots of mention about Weisco drilling, but no mention of drilling the OEM piston. Do both benifit from drilling?

Thanks!

 

[Faded]

... You say the "pre 2002 motors". Mine is a 2002. Is there a way to know "before" I tear it apart if the holes are needed?

2002 has the exhaust bridge, the holes are not "needed" but rather recommended.

Example: Wiseco 801M06850 for a 2002 CR ready for installation.

 

[soulmate33]

2002 has the exhaust bridge, the holes are not "needed" but rather recommended.

Example: Wiseco 801M06850 for a 2002 CR ready for installation.

Faded,

Did you chamfer/debur the holes you drilled?

Tracy

 

[Faded]

Faded,

Did you chamfer/debur the holes you drilled?

Tracy

Yep. :ride:

 

[jmossbarger]

Faded, nice setup. Have you used the 802M? It has the electra coated ring grooves and pin hole. You can forget micro welding the ring with the e-coating and pounding out a wrist pin to disassemble is a thing of the past. The pin just slides out just as when it was new. Granted it is a single ring, but couple that with a TiN and you will have a pretty slick setup.

Nice skirt coating, what did you have put on it? Who did it?

thanks
Joe

 

[jmossbarger]

Man, just re-read your post. 802M isn't available in the 6850 size. Oh well, it was a good thought!
joe

 

[pace]

So, I talked to a friend of mine at a Honda dealer, and he recommended the OEM piston, and here's his reasoning.

He said that since the Weisco is forged, if it does go, it goes in a big way and can destroy the cylinder. Because the cylinder is nikosil coated, it cannot be bored. (is this true-anyone know that for sure?) The OEM piston is cast, and will not cause the damage that the Weisco will if it goes south.

I'll echo what others have said. Your dealer needs to back away from the crack pipe. Either piston is going to score up your cylinder bore if it lets go. The Wiseco is just much 'less likely' to let go, insofar as it will tolerate more detonation, provide longer service intervals, etc.

-pace

 

[Micahdawg]

Welp...just as we are discussing "blown" pistons...I discovered that mine was bad last night.

The bike was detonating badly and I didn't realize it (never had that experience before). I just popped the head off to look inside and a piece of the piston was gone. It's on the exhaust side, top edge right above the ring. It started peeling back along the ridge, but only 1/3 of what loosened up was completely broken. Looks like the chipped piece of piston passed right out the exhaust. I don't see any marks on the exhaust valve or the cylinder so it looks like I've gotten pretty lucky.

The cylinder head has ZERO pitting, the very middle-to exhaust valve side of the piston top has some very slight pitting which I guess is evidence of detonation. The top side of the rings and piston are a little dark looking (kinda blued) which I guess is evidence of high temperatures.

The bike still pulled 200 psi compression when cold and the ring didn't look bugged out. I'm not sure a cast piston would have "let go" like this. I can't imagine the remaining ring groove would have been strong enough to hold the piston ring in place if it were cast. So all things considered, I don't think this was as bad as it could have been.

Wiseco Pro-Lite.

Micah

 

[Faded]

Nice skirt coating, what did you have put on it? Who did it?

Swain Tech ( www.swaintech.com ) did the coating on the piston. They used their PC-9 on the skirt and TBC on the crown. You can click on the link to read more about it if you're interested.

If the 802 series was available I would have considered trying it, but since it's not this is what I ended up with.

 

[Studboy]

Have you ran the coating before, and if so, can you tell any difference in longevitey or power? What is the pricing like?

Thanks.

 

[Faded]

Have you ran the coating before, and if so, can you tell any difference in longevitey or power? What is the pricing like?

This is the first time running w/the coated piston. Currently I have about 3hrs on it including break-in and riding an unfamiliar track. Lots of changes after this rebuild so it's hard to comment on performance of the coating alone but the bike runs really strong. Price was $35 for the coatings. I've heard mixed emotions but it was one of those things I've always wanted to try myself, so I did. No plans to ride really soon either, still waiting on the weather.

 

[NateZ]

Is it safe to say that this discussion about wiesco or OEM is for all brands of bikes and not just honda's? Thinkin about pickin up a wiesco for my YZ250.

Nate