Wisco piston that is round

[asasin]

Has any one ever struck a Wisco Piston that was round insted of oval?.I got my RM barrel rebored to a NOS 432 p8 Wiseco and it ran for 2 minutes and seized ( only around the bottom half of the skirt) Sent it back to enging guys who upon much crastination said that the Piston was round.

[Lozza]

Was it an old Wiseco in a blue box?

[lc4]

I'm told a lot of the Wiseco stuff is now made in good ol CHINA 

[Marc.com]

Yeah the Chinese do special oval bores to go with those pistons. 

But the Wiseco pistons I have are oval and tapered, says on the box which point to measure from, basically in line with the pin on the opposite side. Likewise crown has taper toward it and skirt. Diameter will be nominal bore - minimum clearance, or it is on the MX250 piston

[asasin]

It was a new. old piston judging by the box so should be USA made.I have asked for it back to measure it myself,and ordered a new one  They are going to measure new one against old one to see if there is a problem .It seems very weird as Wisco pistons have never been a problem when ive used them before.

[Lozza]

After thinking about this the person who did the rebore should have measured the piston before hand. I'm thinking that the 'round' piston story maybe a cop out.If it was in a sky blue box these old pistons expand rapidly when heated, they should be baked for 2-3hours at 200C and then bored to size off that.

[Doc]

personally never seen, had or heard of a problem with Wiseco slugs John (excepting the early blue box dykes type ring pistons as Lozza mentioned) I run NOS wiseco's in near all my engines and would be inclined to also say the bore job may have been sus. 

[asasin]

Thanks Guys I thought it was a bit odd, I have built lots of race engines ( and blown up a few !) I have never seen a piston seize like this one, I Think they got the taper wrong, Thanks for the info re blue box ones. It wasnt one but I have a DT one like it  spare for my Cooper.

[asasin]

Went into engine shop today, they showed me the piston and measured it in frunt of me. It has 2 thou of oval,the new one had 3.5 thou. So we thought we would use the new one , only problem is that the new one was 4 thou smaller than the old one,both 86 mm pistons with same part number.So now I have a beautifully ported and speced barrel that is knackered.Lesson learnt!

[Doc]

I have 2 of these #432 kits on the shelf. Will measure them out of curiosity. I don't ever work in 'thou' period..metric weights and measures only for this black duck

[Doc]

measured 2 wiseco pistons 4.3 and 4.5 thou respectively depending on how I held my tongue whilst 2 stock suzuki pistons both measure a touch over 3 thou. Physically measure the piston yourself with your own calipers as the measurement can easily vary a couple of thou via a little pressure on the calipers.   

[Freakshow]

why did you bore out to P8 ? if i'd spend money on porting id start at a sleeved P1.   or am i missing somthing here....

[Lozza]

You need to measure with a micrometer, still say the shop should have picked that up before hand.Measure twice cut once.  Doc I'm a metric man but for some strange reason piston clearences or small measurements I like to work in thousands of an inch

[LWC82PE]

i would not be surprised if you have found a piston not machined right. i had a dud pair of hepolites in a 750 triumph i could not  work out why they kept seizing. my self and my reborer have delt with these pistons for many years, and know what they are like and they are have been the best pistons to use in Triumphs and had always been good up until now so my borer probably didnt do a check as he would have done hundreds of these rebores for hepolites in Triumphs. After stripping the motor and measuring the pistons to work out what the heck was going on i found that there was no taper on the pistons. Phoned the supplier and they said thats the first time they have come across that in 30 or 40 years with these pistons and then gladly sent over a new set free of charge that had been machined correctly.

[STW996]

To use a piston straight out of the box with out measuring is a dangerous exercise at the best of times little long if you have spent money having a barrel modified. I use the micrometer but unless you are very good with them can get yourself in trouble, the old feeler gauge in the base of the barrel to measure is still a good way to measure and hone the cylinder to suit the piston (if you can't get another piston), Wiseco pistons are generally good but can differ from piston to piston. If you had a workshop do the work they should warrant what they have done as it is the first rule of engine building to measure ALL parts used.