Wiseco piston bottom hits crank flywheel on T350

[mike1161]

Has anyone had this problem? I just installed a brand new set of Wiseco pistons on my T350. Before putting the cylinders back on, I turned the crank to check things out. Seems that the bottom of the pistons are hitting the crank flywheel just before each piston hits bottom dead center. Compared side by side, they look pretty much identical, and the measurements from top of piston to bottom are exactly equal. Could it be the taper at the bottom of the piston? More importantly, how do I fix it? I guess the first step is I'm going to contact Paul Miller (where I bought them). I'm a little leery about machining any material off the bottom of the pistons, because they might not weigh the same afterward, which I'm sure would lead to vibration.

[jabcb]

Maybe Paul gave you pistons for a different bike.

[Suzinut]

With pistons over 1mm OS there is a possibility of the piston skirt hitting the crankcase casting ledge that sits directly below the bottom of the cylinder liner. This ledge needs to be ground back to fit the extra OS piston sizes that Suzuki never produced(Suz max OS = 0.5mm) There was a post about this by an old board member "Fang" when he fitted old style Wiseco .060 thou OS pistons (+1.5mm), but that post is lost I think.

[mike1161]

Thanks to all. I think they are the right pistons, since all the form factors and sizes (except diameter, of course, seem to be identical. Suzinut, that could be it. These pistons are the 3rd oversize (.060", or 1.5mm larger). And I did see those casting ledges, but didn't think much of it this morning when I did the install. I will look at it a little more carefully to see if that's the case.
Then will be the challenge of how to grind back that ledge without the debris getting into the crankcase. Even with stuffing rags down there, I worry about stuff falling in when pulling the rags out.

[Suzinut]

Good luck Mike, Fang had his cases split when he ground back the ledge!

[mike1161]

OK, well I looked at it more carefully last night, and the bottom of the piston skirts is indeed hitting on those casting ledges! So next step is to break out the dremel & see if I have enough room to cut them down just a bit. I will have to be really careful to not let anything fall inside! I hope there is enough room, since I really don't want to split the cases. But if that's what it comes down to, just a little bit more fun, right? I will report back later on how it goes...

[mike1161]

Well guys, I looked at this again pretty carefully last night and decided that I just couldn't do it the right way without pulling the motor & splitting the cases. I just don't think I could seal up the area well enough, and the crank flywheels are too close to those casting ledges.
So I thought what the heck, it's always fun to see inside the motor anyway. So in a little over an hour I had the motor almost ready to pull out. Part of what I love about these old bikes, they're so simple to work on! Hopefully during the next week or so I'll have it all done.

[ConnerVT]

It's the right call to pull it apart, and do it right. You'll be able to clean everything up after grinding.

I've shared this story before about my T500 (kinda embarrassing). But once you do this project the first time, it can be done pretty quickly:

I rebuilt my T500 motor on my workbench, down in the basement. Had almost everything reassembled, motor back on the bike. Only needed to install the main drive gear, clutch basket, and front sprocket. My brother in law was going to stop by after work, with his compressor and impact wrench, to make short work of it.

As I started to put these three items on, hand tight, I came to the realization that I had my crankshaft in backwards!

Engine off the bike. Engine down the stairs to the bench. Pull off the jugs. Off come the pistons. Split the cases. Clean up the sealer. Put crankshaft in correctly. Reapply sealer. Put cases together. Reinstall top end. Carry motor back up stairs. Install on bike.

All told, about 3-4 hours. Tired, but done with 30 minutes to spare, before my BIL arrived.

[mike1161]

Thanks, good story - I think we've all had stuff like that happen! Maybe how we learn I had something really similar to your story when I put this motor together for the 1st time. Had it all back together, ready to go into the bike, and just happened to be looking at some photos I had taken of the transmission & inside of the case, and noticed that the bushing on the transmission shaft (the one that has an oil groove on one side only) was in backwards! I saw it in the photo, but hadn't noticed it when I put things back together. You know, the one that if you reverse it, it won't get any oil & will burn it up? So I had to split the cases again to get that flipped around the right way! Good lesson learned, though!

[Coyote]

It's a long story, but just last weekend I installed the swing arm upside down. Got ready to put on a shock to hold the swing arm in place ----------- CRAP! Sometimes it seems like I have to do everything twice.
It's like putting a T-shirt on in the dark Your chances are 50-50, but 85% of the time it will be backwards. Murphy's Law.

[mike1161]

OK, got it all done. Had to make 3 passes, taking off quite a bit of material to get the piston skirts to clear those ledges.

Now a question: I started it up, and was letting it idle, with some light revving. According to Bill Bune with new pistons & a cylinder bore you have to start it up 3 times, letting it warm up a bit then cool down. But it seems to be really loud, kind of like piston rattle, but it really shouldn't have any since they are new. Is that just the way it is until broken in a bit? I did make sure to pre-lube the bores with a bit of 2 stroke oil.

[Suzinut]

Mike, if they are the new wiseco from PM they are very noisy even with only 2 thou clearance. Not sure why, but noticed it on my friends bike. Maybe the wrist pin is not offset like the factory pistons to keep them quiet, but I have not checked that yet. They seem to run fine, just noisy!

[mike1161]

Wow, thanks! Good info. Yes they are the Wisecos from PM. I will rest easier knowing that. I did have them bore with between 2 and 3 thousands clearance, so I thought it should be OK. Thought I might have messed something up, even though I was very careful with the install. OK, I will continue the break-in process tomorrow.

[joolstacho]

Bugger, that's just what I didn't want to hear. Good pistons not so good after all (Wisecos)
I might as well get the cheap ones then?

?

[joewillybob]

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.