Wiseco piston bottom hits crank flywheel on T350

[Coyote]

I bought a first over Wiseco kit from PM for my 550. He sent me one first over and 2 standards. 2 first over rings and 4 standards. I sent the whole mess back to him after letting know he screwed up. About 10 days later I got another box. In it was all Suzuki stuff. 3 correct pistons and 6 correct keystone rings. No Wiseco anything. At first I was pissed off. Then I thought it over and said to myself "I KNOW these will work". But it still bugs me because I didn't get the Wiseco that was in his ebay ad.. Now that I hear you guys are having noise problems with the Wiseco pistons, I figure he did me a favor by sending me OEM stuff. He also put $20 in the box to cover the return shipping I had to pay to ship the incorrect stuff back.
There seems to always be an issue when I order from PM. I bought #1 and #2 wiring harnesses when building my Buffalo. I received 2 new harnesses, both #1's. He made it right and sent me the #2 harness after I returned one of the #1's. Again it's just pointless delays and unneeded hassle. But he has it and I don't, so I deal with it.

[mike1161]

Just did the top end on my 71 T350 w/1st over Wiesco's from PM. Cylinders were bored by Bill Bune to fit the pistons.Mine is very noisy also. Thought maybe it was just faulty memory. Bike runs fine, over 1500 mi. since rebuild.

Well, guess this is just the way the forged pistons are (vs. cast). But, man, are they noisy!!! Kind of a bummer, because that's the reason that I did the bore & next size up pistons in the first place (thought I would get rid of that piston slap noise). At least I know nothing's wrong. I actually pulled the heads to check the cylinder walls yesterday (after about 15 miles of break-in riding), and everything looked perfect. Guess I will just continue the break-in & live with the noise.
Any coyote, yes, probably a good thing that you got the OEMs instead. To me, the noise from these Wisecos is pretty bad. You don't hear it too much at speed, but it's embarrassing while warming up in the driveway. Sounds like the whole thing is going to blow up.

[ConnerVT]

Well, guess this is just the way the forged pistons are (vs. cast).
<snip>
You don't hear it too much at speed, but it's embarrassing while warming up in the driveway. Sounds like the whole thing is going to blow up.

This is counter to what I would expect, based on what I've read about cast vs forged pistons, and cold seizing in engines.

There are two dissimilar metals making up the combustion chamber - aluminum (piston) and steel (cylinder liner). Aluminum thermally expands more/faster than steel, which is why you need to gently run your cold started engine to prevent cold seizure. The piston to cylinder clearance initially begins getting smaller at start up, then increase again until the entire engine (both piston and cylinder) come to operating temperature.

I've also read that forged pistons expand less than cast pistons, allowing for tighter (cold assembled) clearances. More care is needed during start up, but the over operating clearance would end up being smaller once at operating temp.

As piston slap is generally due to excessive piston to cylinder clearance, perhaps something else is responsible for the sound?

[mike1161]

ConnerVT, I agree with everything you've said. That has been my exact understanding of the forged piston advantages, too. So I really don't understand the noise. But several others here, and some guys over on the Kawasaki forums have had the same experience, but they say the bike runs great & reliability is good - but these Wiseco forged pistons are really loud. And so far, mine has been running great during the break in. So it's really a mystery to me.

[Coyote]

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I've also read that forged pistons expand less than cast pistons,

I can't say I totally agree with that. The reason I say this is because Wiseco pistons require a larger initial bore than stock pistons. I had a set (since sold) and the paperwork in the boxes stated this fact and recommended .002 - .0025 oversize bore. I can't find in any of my manuals but I believe to stock initial oversize is .0012 - .0017. This suggests that the forged piston expands MORE than a cast piston.
BUT, that's the advantage of forging over casting. Forgings are much tougher and more flexible than a casting. Castings are inherently brittle and can't move much without breaking. If you break the skirt off a cast piston, you will see a crystalline like structure at the break. Do the same to a forging (you'll have a tougher time) and the break will be smooth. That's because the molecules are arranged differently in a forging.

[Vintageman]

+1 forged typically expand more than cast.

#2 any extra clearance is very noisy

#3 It doesn't matter who you pick to do the bore job, they can go too far and will. You need to check it yourself after and let them know you will ( I can't anymore for just changed jobs, and previous employer of the past last 11 years had all the expensive and calibrated measuring tools). But too late if they go too far I think I found a local place. the guy is older, experienced, has good tools and in no hurry (everyone can mess up if not 100% focused). It is a great fear-anger of mine and I always emphasize that (as if that matters... for who am I). I asked if I could observe the process for was curious. He said "sure thing" I plan to send him my mildly ported GT380 cyls soon to fit 1.0 mm OS cast pistons

#4 Break in: means just that things are breaking -in. If you tore your engine down after a brief run-in you may find high spots or build up on the skirts. Smooth these only. This is something I have read about in the past and have tried a few times and noise level was reduced significantly. It does not take much build up/roughness to make noise.

#5 if your clearance did prove to a little more that it should be, try having your piston skirts coated. There are some companies (can find link if interested) if you tell them your clearance and they will build up to zero it . You will have to fit once you get. Better the fit the longer these soft coatings last.

# Also there is a company in CA for example that does an Anodizing like coating and can build up forged pistons 0.002" lager dia.. It cost more. Cast piston more porous and only get 0.0015". This is hard stuff permanent.

Last year I did t350 top end. 0.5 mm OS OEM piston, Done by Sanel machine is Concord NH. "This" time they did clearance perfect. They usually do OK , but have messed up before. That engine is relatively quite.

My T305 clearance has ~0.001" more than from new specs and is a little noisy. just tore it down. Was going to have it Anodized or coated. The cylinders looked great and the pistons were nice too, but did have some high spots. smooth them out and Opted to just reassemble.

Like was said a little extra gap OK, engine runs well, just a little extra noise/vibration.

[Vintageman]

+1 forged typically expand more than cast.

#2 any extra clearance is very noisy

#3 It doesn't matter who you pick to do the bore job, they can go too far and will. You need to check it yourself after and let them know you will ( I can't anymore for just changed jobs, and previous employer of the past last 11 years had all the expensive and calibrated measuring tools). But too late if they go too far I think I found a local place. the guy is older, experienced, has good tools and in no hurry (everyone can mess up if not 100% focused). It is a great fear-anger of mine and I always emphasize that (as if that matters... for who am I). I asked if I could observe the process for was curious. He said "sure thing" I plan to send him my mildly ported GT380 cyls soon to fit 1.0 mm OS cast pistons

#4 Break in: means just that things are breaking -in. If you tore your engine down after a brief run-in you may find high spots or build up on the skirts. Smooth these only. This is something I have read about in the past and have tried a few times and noise level was reduced significantly. It does not take much build up/roughness to make noise.

#5 if your clearance did prove to a little more that it should be, try having your piston skirts coated. There are some companies (can find link if interested) if you tell them your clearance and they will build up to zero it . You will have to fit once you get. Better the fit the longer these soft coatings last.

# Also there is a company in CA for example that does an Anodizing like coating and can build up forged pistons 0.002" lager dia.. It cost more. Cast piston more porous and only get 0.0015". This is hard stuff permanent.

Last year I did t350 top end. 0.5 mm OS OEM piston, Done by Sanel machine is Concord NH. "This" time they did clearance perfect. They usually do OK , but have messed up before. That engine is relatively quite.

My T305 clearance has ~0.001" more than from new specs and is a little noisy. just tore it down. Was going to have it Anodized or coated. The cylinders looked great and the pistons were nice too, but did have some high spots. smooth them out and Opted to just reassemble.

[Suzukidave]

That does seem to be a issue with Wiseco pistons is they expand a bit more when hot so have to be fitted a bit more loose than stock pistons so they do rattle more when the engine is cold .