The other day the piston skirt shattered on my 2001 CR 250. I am wondering about causes. It has had about 3 Wiseco top end jobs in the past. This time we used Vortex because Wiseco was out of stock. The new Vortex had about 5 hours on it when she blew. I'm wondering how it is possible that there was too much clearance between the cylinder and piston??? Could the cylinder be worn out already? A piece of the piston went into the case and made it so it wouldn't turn over so I thought it was seized until I got it apart. I didn't force it or anything so the bottom end should be ok right?
Shattered Piston Skirt
- Thread starter derekb_55
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marcusgunby
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- Jan 9, 2000
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Vetex make the pistons in sizes to match the wear on the bore-if it was the smallest size they do, and your cylinder measures on the large size of its tolerance,you may well have had excessive clearance.
My TM dealer told me:
When you change from an ASSO piston (forged, stock piston) to a Vertex on a TM you have to carefully meassure the clearance between Piston top and cylinder head and adjust it by choosing the correct base gasket size. Vertex seems to work with other tolerances on piston height and so sometimes the engines have too much compression, which causes the pistons to break.
Maybe that applies also on Vertex pistons for a Honda.
When you change from an ASSO piston (forged, stock piston) to a Vertex on a TM you have to carefully meassure the clearance between Piston top and cylinder head and adjust it by choosing the correct base gasket size. Vertex seems to work with other tolerances on piston height and so sometimes the engines have too much compression, which causes the pistons to break.
Maybe that applies also on Vertex pistons for a Honda.
Last edited:
marcusgunby
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- Jan 9, 2000
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I wonder if TM frank is on to something with the crown height-is it possible to get a new one measured?also it was the same type as previous ie flat top or dome?
jmics19067
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- Jan 22, 2002
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Just a few ideas and possible things to check on /think about.
Wiseco is a forged piston, Vertex is a cast piston. The forged piston is probably a little bit more "rubbery"<?> and should handle the assorted problems of excess piston to cylinder wall clearances a "LITTLE better". Cylinders do wear and cylinders wear unevenly, if you didn't measure the cylinder in 6 places <top, middle and bottom front to back and side to side> it is quite possible the piston could be tight in one spot and too loose in an other.
Another thing to think about is the piston pin , bearing and connecting rod. if those pieces aren't in good shape the piston could easily be trying to ride up the cylinder sideways.
Didn't know about the different crown hieghts on the vertex piston but your problem could be any one of these or any combination.
About your bottom end full of junk , if you are going to send the cylinder out to get repaired my suggestion would be to take the motor out of the frame. Support it upside down over a drain pan and while you are waiting for cylinder to come back spray some Wd 40 ,CRC or something like that up into the crank area and spin the crank a couple of turns by hand to try and flush all of the garbage out. Do not use carb cleaner brake cleaner or anything that could harm the seals. A couple of minutes everyday while waiting will probably get the junk out. That is of course if you didn't actually do any damage to the bottom end.
If that is what you see then splitting the cases is in order. If you spin the crank around and move the rod from front to back you should be able to take a little look see at the big end rod bearing make sure you dont see any blue or scratches. Do a visual on the side thrust washers also , measure all you can and rotate the crank making sure all feels smooth and free. Although the seals and the tranny will give you some drag it should have a nice "slippery snug"<?> feeling to it. Definately don't want any looseness , binding or grinding feeling.
Wiseco is a forged piston, Vertex is a cast piston. The forged piston is probably a little bit more "rubbery"<?> and should handle the assorted problems of excess piston to cylinder wall clearances a "LITTLE better". Cylinders do wear and cylinders wear unevenly, if you didn't measure the cylinder in 6 places <top, middle and bottom front to back and side to side> it is quite possible the piston could be tight in one spot and too loose in an other.
Another thing to think about is the piston pin , bearing and connecting rod. if those pieces aren't in good shape the piston could easily be trying to ride up the cylinder sideways.
Didn't know about the different crown hieghts on the vertex piston but your problem could be any one of these or any combination.
About your bottom end full of junk , if you are going to send the cylinder out to get repaired my suggestion would be to take the motor out of the frame. Support it upside down over a drain pan and while you are waiting for cylinder to come back spray some Wd 40 ,CRC or something like that up into the crank area and spin the crank a couple of turns by hand to try and flush all of the garbage out. Do not use carb cleaner brake cleaner or anything that could harm the seals. A couple of minutes everyday while waiting will probably get the junk out. That is of course if you didn't actually do any damage to the bottom end.
If that is what you see then splitting the cases is in order. If you spin the crank around and move the rod from front to back you should be able to take a little look see at the big end rod bearing make sure you dont see any blue or scratches. Do a visual on the side thrust washers also , measure all you can and rotate the crank making sure all feels smooth and free. Although the seals and the tranny will give you some drag it should have a nice "slippery snug"<?> feeling to it. Definately don't want any looseness , binding or grinding feeling.
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