Can still hear the rattle in the first vid but you didn't at any stage have it idling as slow so nothing has changed. It's a Wiseco Piston & they run double clearance or they seize. Not called seizco for nothing--but mostly because instructions aren't adhered to when boring. Your's looks too good to go replacing or boring again. Just slide a feeler gauge in with the shirt to get a rough idea on clearance but i'd guess it's about a 4 thou rattle & should quieten a little when hot & expanded. My theories anyway lol.
While the piston is off have a good feel of the rod up n down & side clearance plus sideways rocking. I used a wiseco in my 360 for years vintage mx & it lasted good, albeit a bit rattly in the end after years of good service.

I agree that if you would have idled it slower in the first video the sound would likely have been the same.

Forgot to say that it sounds kind of normal to me.

I checked the connecting rod. It has minimal side to side movement but no “in and out” movement at all.

Crazy to think it’s a normal sound but I am a newbie to these bikes and I appreciate the help from everyone. I will jus put everything back together.

If I would like to go back to an oem piston would it be possible to get a .75mm over oem piston and bore the cylinder for it? It has the .50 over wiseco now.

Thanks again

With my headphones on [plus my hearing aids haha] it does sound bad. Cylinder looks ok so might get away with a 0.5 yamaha kit & save the bore cost but need to measure the cylinder for size incase a whisker over 0.5. If its 'on' size the Yamy piston 'should' give you about 2thou clearance & won't rattle at that. Get the bore measured top bottom & central area.

I listened to a few videos on YouTube and most seem to have a similar chatter but I was concerned mine was so loud.
Going to also have my piston clearance measured.

I can't find it now but Enduronut brought up the ring pin location... it's probably in another thread someplace... happens when someone asks same questions in different posts.

Anyway, what he said is extremely valid... I dug through my old pistons and found a Wiseco... which are great pistons and only need slightly more clearance than OEM, just follow the Wiseco specs... Too many shops "add a little extra" clearance which just ruins the whole bore job and gives you piston rattle right off the bat.

VERY common problem so make sure if you get it bored, you find a shop that will adhere to factory clearance specs and not some "expert" who is going to add extra clearance... easier said than done... also port edges need to be chamfered properly and the cylinder and ports need to be carefully cleaned after machining.

Anyway, your piston looks great and I wouldn't replace it... except for the ring pin location issue... You don't want a ring end catching in a port... Attached is a pic of a Wiseco like yours where I drew the ring pin locations on top... what you do is insert the piston in the bore and make sure the pin locations stay in the solid wall area of the cylinder and don't cross over an open port when the piston is down near bottom dead center. Hope that makes sense.

I can't find my 1975 cylinder but I think the ring end gaps are going to be pretty darn close to the rear port. "Close" might be okay but if the end gaps are exposed by the port you risk a ring end snagging in the port and creating massive damage.





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Thanks much mark.
I did read about the danger of the rings getting caught.
Also I took cylinder and piston measurements
Piston measured 66.50


Cylinder
From intake to exhaust
Top 66.58
Middle 66.57
Bottom 66.52

Left to right on cylinder
Too 66.57
Middle 66.58
Bottom 66.57

Using the measurements, you have just over 0.003" clearance... that's not bad at all... If I remember, Wiseco spec for new bore is 0.0025".

If you change the piston, you will need to go to the next bore... Yamaha piston will almost certainly be slightly under 66.50mm giving you even more clearance.

Please check the ring pin location against the port... if okay, I'd run what you have.

On the rod, it has to be really bad to feel "up and down" play. Sometimes you can tell the big end bearing is worn out by pulling up hard on the rod with one hand and then smacking the rod down with the other while continuing to pull up... if you hear a "click", the bearing is bad.

Best way to check is measure the "wobble" as shown in the service manual. Side play is normal but when checking the wobble you need to make sure you're not sliding the rod side to side... just wobbling the small end side to side. Any more than 2mm wobble is worn out. They do start to make noise at about 2mm...

Excuse my ignorance but what is the name of the T shaped measuring tool called?