Wiseco piston differences.

[Billy Golightly]

In the interest of sharing information, I thought everyone would like to see a few changes Wiseco has made to its pistons for the CR500, and probably other models.

I recently received a new Wiseco piston from LA Sleeve after having my cylinder worked on b y them. As I took it out of the box I noticed quit a few differences between another older piston I had (from a CR500) laying around.

http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010044Large.jpg
http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010055Large.jpg
First of all, there are no cut outs around the wrist pin area. This makes the piston heavier, but also will have a less chance of the transfer port charge short circuiting via that cut out to the corners of the exhaust port. Very common on ported engines using the style of piston on the left. The newer piston (On the right) also has more built up around the bottom of the wrist pin boss area.

http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010059Large.jpg
http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010058Large-1.jpg
Secondly, from these pictures you can tell the difference in the skirt thickness between the two. I'm assuming that because the newer style piston has the lack of cut out around the wrist pin area Wiseco has removed some of the skirt thickness in order to keep piston weight down. The new piston is a stock bore, and the older one is an .080 over one. Even with the size differences I believe the newer piston weighs more. Its my opinion, that the additional weight of the piston combined with the thinner skirt on both the intake and exhaust (The newer piston's skirt measures slightly under 3mm thick, with the older style measuring slightly under 5mm thick) makes the newer style piston more suspectable to cracking on the intake side. I have a Wiseco for an ATC/TRX 250R engine that has a hairline crack right in the center of intake archway, and it is thin skirted piston similar to what I'm showing here. I do not want to open up the whole can of worms of cast vs forged pistons again (yet anyways, hehe) but lets take a note of the skirt thickness on any piston that develops a crack on it. In addition to all of that, you can see Wiseco also wisely has added a small oiling hole to each end of the pillar that the wrist pin rides in.

http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010067Large.jpg
Heres a shot of the label on the box the new piston came in.

http://i150.photobucket.com/albums/s100/HondaATC/CR500%20piston%20comparison/P1010063Large.jpg
And heres a shot from the underside of the old piston.

[cr480r]

How does a '82-'89 piston compare to these?

[Billy Golightly]

85-88 pistons you mean? They are, as far as I know, the same. Wiseco does list a different part # but I don't know why. The earlier 500s used a shorter connecting rod, kinda like the 250Rs were. But the difference is that instead of changing the piston to make up for the height difference, they changed the cases where the cylinders go on. All years pistons, and cylinders will interchange. Its the cases and connecting rods that are different.

[cr480r]

85-88 pistons you mean?

No I mean '82-'89... 480's run the same piston too...


They are, as far as I know, the same. Wiseco does list a different part # but I don't know why. All years pistons, and cylinders will interchange.

Are both of piston you have shown the same part number? I was just curious if maybe one of those shown was the earlier style... Wiseco currently offers a 554MO and a 636MO for 500's... I am curious if maybe the newer piston could be an upgrade for my old bike('83)...

[Billy Golightly]

I'm pretty sure the 480 pistons are different. I know the 84 Aircooled CR500 does share the same crankshaft and piston as the 85-88 watercooled engines. The 480 has a different bore diameter, its smaller. I could be wrong, but I'll check the catalog later this evening.

[Bryan Raffa]

the 82-83 480 and the 84-89 500 pistons are the same,, billy that piston is for a 90-01 CR 500,, the 84-89 are still the same as your old piston

pro X only lists a piston from 84-01

[Liquid-Darkness]

So what is the good side to a forged piston, other then the different design and oil holes to the wrist pin? So far the cast piston has better sides and weighs less. Its also thicker then a forged piston making it less susceptible to cracking? Supposedly the reason for the forged metal was for a stronger material and be less heavy. What do you guys think? To be honest, I used a stock piston and forged piston in both my two and four strokes. I like the cast pistons more. They seem quieter then the Wiseco's.

[3Razors]

It depends on the application. Forged pistons are stronger for high performance applications ie supercharging, nitrous.. But properly set-up cast piston will have a longer engine life. You can set the piston to cylinder clearence much closer with a cast piston.

[burnoutboy]

So are oem piston rings interchangebale with wiseco forged pistons?

[3Razors]

Wiseco rings, clips and wrist pins only fit Wiseco pistons. However, alot of Pro-x (cast) piston rings will interchange with oem pistons.

[BigGreenMachine]

If you've ever seen a cast piston come apart under load you would not run one in your machine.

Worst case senario is the piston disentigrates and the rod rotates through the cases.

[3Razors]

Yes they do make a mess of things, but if that happens it is not the pistons fault whether be cast or forged, it is from extreme neglect or improper tuning.

[burnoutboy]

Just measured up a set of oem and wiseco rings. both measured exactly the same and looked identical. think i would be fine running oem rings with a wiseco?

[Liquid-Darkness]

Is it safe to run high compression with a cast piston?

[Billy Golightly]

if you control your detonation with proper fuel yes

[Liquid-Darkness]

Sweet. Have you ever raced with that kind of setup Billy? Cast piston with high compression and race fuel?

[Billy Golightly]

the 270 flat tracker motor is around 185psi on a pro-x piston. I'm still getting by with pump gas though.