04 CR250 new piston questions

[El-Senor]

Hello all! New guy here....
I have 70 or 80 hours on my 04 CR250. I ride only trails and haven't really noticed any problems. I want to put in a new piston and top bearing so I bought the stock size Wiseco replacement 801M06640, the Wiseco top bearing B1003, and a Cometic top end gasket set. My bike has a few mods for trails:
Phathead head (1 over dome)
Boyessen rad valve and flange
FMF Gnarly pipe and Q silencer
Steahly 11 ounce flywheel weight
Clarke 3.2 oversize tank
Talon sprockets/ DID ert gold chain
Kouba lowering link
Renthal Fatbar
Trail Tech computer
DeVol rad guards
Magura Hydraulic clutch
and a W/C skid plate
I run C12 50/50 with 91 octane at 32.1 with HP2 oil. I would like to have Swain tech coat the new Wiseco piston but I don't know if it will increase the diameter too much? All I've read here states that the Wiseco is universal for A & B cylinders and drilling the bridge holes is optional.
If anyone has any opinions on the Wiseco/Swain tech, Drill or don't drill theories I would appreciate the help!!
Thanx for reading...
Pictures

 

[jmossbarger]

Generally you do not have to compensate for the clearance that the coating takes up. If you want to have it coated, you should have no problems.

Good luck and you made an excellent choice in the 801 piston, but why the 801 and not the 802? Just curious.

Thanks,
Joe

 

[jmossbarger]

Oh, I almost forgot. You don't have to worry about the holes. They are insurance, but that piston doesn't need them. The shape is made to keep it off of the bridge in the exhaust port.

Joe

 

[Faded]

El-Senor,

No worries, have the piston coated and you'll be okay. I had Swain Tech do the same thing to a Wiseco 802M06850 before putting it in my '02 EG CR265. I drilled and de-burred the piston before sending it out though. :ride:

 

[Wilky]

I put an uncoated Wiseco piston (no holes) in my 04 CR250 about 6 months ago, it has about 30-40 hours on it and it is still running strong. Like the previous poster said the holes are insurance to help get some lube where the piston and port bridge meet. Although I do not see how this could help much because the bridge on mine was clearly machined so the piston never makes contact with it. Since I am the original owner and the only one that has had it open, yours should be the same.

If this is your first top end here are a couple of things to note:


Read the cylinder prep thread in this forum, it has some real good info in it.

Remove both radiators. It is a whole lot easier removing and installing the cylinder with them out of the way.

As soon as you get the cylinder off put a clean rag around the rod to cover any holes that could let anything get in the bottom end. Do not remove this rag until the circlips are in and you are ready to put the cylinder back on.

Use a wire brush the get the corrosion (if any) off of the head bolts. Do this with the old head gasket installed between the cylinder/head surface and the wire brush so you do not scratch the cylinder/head surface.

You will need to gap your rings. I gapped mine to .016", I think the service limit is .022" Verify these as I am going by memory

Getting the power valves out to clean them took some patience. I used a utility knife blade to scrape the carbon of the PVs because I didn't have the patience to use the oven cleaner others suggest.


Now a couple questions for you. I see on your list of mods you have a Kouba lowering link and am wondering what you think of it. Which one did you get CRF2 or 3? Did it have any negative effects on handling? What did you do to the front end to compensate for the lower rear?

 

[rmxtwofitty]

I would recomend drilling the holes for the exhaust bridge. It doesn't hurt anything, and provides extra insurance for the longevity of your piston and cylinder. My .02.

 

[El-Senor]

Thanx for the help guys!
The 801 was in stock no real preference. So it's off to SwainTech!

Now a couple questions for you. I see on your list of mods you have a Kouba lowering link and am wondering what you think of it. Which one did you get CRF2 or 3? Did it have any negative effects on handling? What did you do to the front end to compensate for the lower rear?

Besides the flywheel weight I think it is the best mod you can bolt on to tame a MX bike for trails. I have the CRF2 which lowers the bike about an inch. I still had the stock Renthal bars on when I first installed it and I just pushed the fork tubes up til they touched the bars. Handling was fine and I had a hell of a lot more confidence with my feet touching the ground!
Now a warning! When I put on the Fatbar with the universal mount I gained a little bar height (the mount) so I pushed the tubes up again to touch the bars. It was too much, it changed the geometry of the bike too much and because of it I got tossed and broke 2 ribs. The same day I put the tubes back down a half inch and the bike was fine (still is.) Anyone who is uncomfortable with the height of their bike or just want their feet to touch the ground should look into a Koubalink. Thanx again all!