Billy Golightly
04-27-2007, 07:27 PM
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.
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.