That's good news. Thanks for the update.

Update - -
I took the cylinder jug and piston to a shop to check the measurements. I showed the shop owners the videos I had shared in this post, and confirmed that rattling noise was definitely piston slap.. Mystery solved I guess! He said there was a more-than-normal gap between the piston/cylinder.

Good news is, I have a standard-size piston/cylinder. Which means there's plenty of life left in this cylinder.
Now I'm looking to replace the Piston with the 1st oversize, which the parts catalog im referencing designates it as 0.25mm. As well as have the cylinder bored for this new piston.

Before I move forward with boring and buying the 1st oversize piston, I had a couple questions.

1. Does the cylinder need to be bored? Isnt the cylinder made of steel and the piston of aluminum? I would assume the aluminum piston is worn and can be replaced with another standard size piston?

2. Has anybody had any luck, or tried using these Vintco piston sets  instead of NOS parts?

The shop manual will give you tolerances for your cylinder before it needs a re-bore, have the shop you took it too measure it to see if it's within tolerance.

Be interesting to know what clearance they found & where the main wear is in the cylinder. I guess if worn around the ports then bore it. A new bore & yamaha piston only has about 1.5 thou clearance but wouldn't rattle much with almost double that if the bore is parallel. But if worn around the ports it'll rattle. Factory max allowable clearance i'm guessing go close to 3 thou max but could stand to be corrected.
So just thinking if you didn't want the expence of boring it'd be interesting to measure a new standard piston exact size compared with what you have. Or tell us what yours has now & we can get a good idea of clearance in a good std bore.
Hope that makes some sense--confusing myself & i keep changing it, so ignore if you want.

Rings are hard chrome plated and yes, bore does wear.  Only way to tell if it needs a rebore or just a new piston is very accurate measurements by a competent machine shop and compare to measurements on a new piston plus check for taper and out of round as per manual.

Never heard a complaint about Vintco...  they may only sell pistons in 0.50mm increments though? 

It is normal to send the new piston with the barrel when you rebore.  They can then bore the barrel and finish hone it to exactly match the piston size as every one is very slightly different.

After watching the video — before reading any of the comments, my first inclination was, the piston was in backwards with the arrow pointing towards the carburetor, and the rings were hitting the ports. That may not be the case but that was my first inclination. Good luck.

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Hey there! Sorry to see that shorn bolt, I quite literally had that exact same bolt go on my TT 350 in the same fashion, except mine sheared a bit lower if I recall correctly. Lucky for you (maybe) that bolt honestly looks like it might be recoverable. What you might want to try is to first hit it with some penetrant, try PB blaster or take your pick of some other penetrating oil. Use a center punch on the shorn face of the bolt and give it some strikes in conjunction with letting some penetrant sit on top of the whole thing, that will give you a good shot at letting some creep down in there. Do this every couple hours for a day or so and then you can do the next step(s). After this, in your case, what you perhaps should try is to use some kind of rotary tool with an abrasive cutoff wheel and to cut a small slot into the center of the protruding part of the bolt head all the way across the bolt and then go and find the widest screwdriver you can find and give it a shot. Bonus points if you if you can hit it with a torch before you give er the ol' twisteroo.

Outside of this, you have extractors which can be somewhat hit-or-miss. If it comes down to it and the shop has to get it out, there's not much more that they can do than to clamp it down and try to get it square for them to drill it out and use a tapped extractor, or just drill and tap it again, but locating that face is going to be challenging since the workpiece is not square to begin with. You may also know all of this already and I'm just preaching to the choir, but I thought if I could be helpful it might be worth it! Good luck, keep us posted!

Thank you for the feedback and advice all!

I took the cylinder in and had it rebored to the next size up, .25. They mentioned the tolerance was way off - the piston did have a lot of play while seated in the cylinder.

I also bought the next size-up piston and replacement bearings and piston pin.

I noticed that the piston pin I received was about 1/8" shorter than the original (picture attached).
If I use this piston pin that is 1/8" shorter, can this potentially cause damage? I wasnt sure if there would be any side-to-side play.

Or is the 1/8" difference inconsequential?


 

Surprised your new piston didn't come with a new pin too. I can't remember getting one that didn't. I had to buy new small end bearing separate though.