HPBCANADA.COM

Just about to have the cylinder sized to my new pistons for my 56ci omc. The box says only .004" The book says .0045"-.0055" for the OMC pistons. I've heard people say the Wiseco forged pistons should have as much as .007". I told him to give me .006" but he won't be doing it till tomorrow so if anyone thinks I should tell him otherwise, please let me know. I don't want a sloppy engine but I don't want to stick pistons either.

iv been told by my bike machanic that if i run a seiseco piston in my bike to let it warm up for no less than ten min before i ride.. the piston will expand alott faster than the cylinder... i'v also been told by an old sled race machanic, when your building a race motor build it lose,, it will spin up quicker,,and if your building a trail motor build it tight it will last longer..

Wiseco's run from .004 to .006 ,usually.004 to .005, they had issues in the 70's with a few single ring pistons, they are GREAT pistons, and will last a long time. ALL motors require a warmup time, taking a little extra care in assembling a motor with the correct ring gap and piston to wall clearance and heat cycling it a few times and breaking it in for a few hours just makes sence.I cant believe how many mechanics give these a bad rap . there are hundreds of big bore sleds out there running these pistons for thousands of miles without a problem, outboards too.

Steve

I'm gonna disagree with you Steve....Wiseco's need more room and more care than cast pistons. I'm sure they are great pistons if put together with great care...but cast pistons seem to have a greater margins of error. I've got a pile of 2.6L ones if you'd like them lol.

i here the new coated ones are good. they do need more clearance, and they rattle when cold. i had skirt collapse issues in my 49s, sticking with the stock ones for the 56.

Not saying that they do not require more care Rick, just that there is nothing wrong with them. In certain applications, like the big Tcat motors with the huge wide exhaust ports , they are stronger, and will take more abuse than standard cast pistons.I posted more because I knew too many people calling them "siezco's" because they did not take the time to clearance their motor and break in properly, more to defend Wiseco pistons than debate cast vs forged. The cast will put up with more cold start reving etc , and being tight. I've seen alot of scarred , but still running cast piston sled motors from guys nailing it as soon as the motor starts on a cold day.For under 7000 rpm in an outboard I dont see any reason not to run cast pistons.All of my experience so far is in sled and car motors, as far as pistons anyway.there are more factors to take in to account, such as iron or chrome walls, if installing forged pistons in an iron liner motor, alot of builders recomend a blended oil aswell, not pure synthetic.Sierra cast pistons are supposed to be a good alternative to stock omc's btw.

Steve

I call them seizco's lol...I honestly have two new sets with one scuffed for the exact reason you stated...now, good for me because I got motors to build but sucks for the guy who builds a motor to the factory spec using "good"/expensive pistons then BAM motor goes down during break in...which is the whole reason Kevi asked in the first place I guess lol. I'm glad someone knew the answer!! Luckily we got an Arctic Cat guy around!!

Interesting to hear everyone's thoughts on them. They are the newer coated ones. Even come in a fancy little black wiseco piston pouch now lol. I saw a bunch of posts on other forums saying to go as much as .008 or .009. Probably a little excessive for a slightly hopped up fishing motor. It's already been done to .006 so I guess I'll find out soon enough how it works. Sounds like proper break-in and letting it warm up before putting your foot into it will be most important on making it last.

pm instigator(Gary) or jphii (Joe) on scream and fly , they have built and clearanced a ton of forged wiseco's in omc blocks, and can set your mind at ease as far as clearance. another thing I have done and most do is heat cycle the motor at least five times, allowing it to reach full operating temp as the first part of breakin. my Arctis cat 2 cents!

Steve