Giving a Bezoat a Second Chance

[ZUL8TR]

Luc
Good to have a 2nd opinion that both of us agree. So you will have a used piston for the shelf?
The 18:1 is good but I thought all Amzoil oils are full syn not semi syn you note? I prefer higher viscosity non injection oils that maintain a greater vis at high temps and revs.
Pete

[Albert]

So I stopped by a local engine builder this morning, we had a look at the piston and cylinder. He did spot two small spots of aluminum in the bore but said they would clean up with a hone. Otherwise he said he wouldn’t hesitate to reuse the piston and he agreed the lines visible in the cylinder wall are minor and will clean up.

He immediately asked how big my ring gap was and I told him too big. He agreed.

Pete,
I was running 18:1 Lucas semi-synthetic for injection oil.

[ZUL8TR]

That is a good question as to why certain parts are not off the shelf, in cars as well and other things!!
Just to know what oil mix ratio and brand/ type (full syn or dino) were you using that steamy engine day?
Hope the bores are OK.

[Albert]

I'm going to get the cylinder measured today or tomorrow depending on when I can sneak away from work.
As for the Piston I'll measure it when it arrives.
The motor definately got hot, real hot. We tried raising it to 1/2 below and by the time I came in from two laps it was pumping steam. Hopefully not enough to warp the bores...but I'll know soon.

I sure wish Yamato had used an off the shelf piston.

[ZUL8TR]

Luc

If you go the used piston route measure same as old to make sure the piston to cylinder clearance you will measure is ok. What happened that the engine suffered a cooling issue?
Good travels with your engine work
Pete

[Albert]

Pete,
You’re probably right but I’m still leaning toward getting another used piston.
I also found two spots where the ring snagged the port. Not sure if that caused the piston damage or vice versa. Regardless some sandpaper will clean the port edge up.

It will go back together and it will be better than ever.

[ZUL8TR]

Find out the piston clearance and if OK then knock down what appear to be some high spots on the piston where you cleaned it. Might need that flat stick I noted above. It will be fine if no cracks out and inside.

[Albert]

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If I had to race tomorrow I wouldn’t hesitate to put this in and run…the question is do I trust it long term. Some 1500 wet then a finish pad cleaned a lot of it up quite quickly.

[ZUL8TR]

I doubt if weakened, not enough scuff to cause that but inspect carefully for small cracks outside and inside. Don't get to aggressive with the 1000 or 1200 wet paper in the circumference direction just cleaning up here. Might help to put the paper on a flat stick and roll along the arc as you sand this keeps your fingers from digging on the paper. Never been into my Y80 but on the Merc racers I get the piston largest OD dimension about 1/2" up on the skirt at 90 degrees from the pin and compare that to the smallest ID in the bore at the same relative running orientation position of the piston in the bore to get the tightest the engine will deal with. Note there is no piston to bore clearance listed in the Y80 manual but in the 102 and 302 they list 0.003" clearance, I think a bit tight. If you get 0.004" OK

Maybe other HR guys will step in here on Y80 piston clearance and other suggestions?

If the bore is egged a lot use the smaller bore ID and the largest piston OD at the specified OD measured location.

Here is a video of measuring done on a 2 cycle Yamaha with OD mic and a bore gage (he has expensive accurate tools). Note with his tools all that matters is the difference of the Piston and bore measurements for the clearance which he explains.

https://www.bing.com/videos/search?q...6FORM%3DHDRSC3

Pete

[Albert]

Zul8ter,
Im not sure what the acceptable spec is on the cylinder. I was just going to see a friend with a dial bore gauge and see if it was “close”.
This piston was replaced when I did the crank as the original piston played pinball with some bearing material.
My first thought was to wet sand the piston smooth but I was worried about it having been weakened.
If I get both kids down for a nap at the same time today I’ll try and clean it up real well and have a better look at it.

[ZUL8TR]

Is there any aluminum on the cylinder wall, might be hard to see? If so remove it (not with sand paper) before a deglaze. If cylinder still round that would be amazing considering age and use! If out of round a spring hone not good for that could make bore egg worse. For deglaze I use ball hones for the Mercs (haven't done my Y80 yet), they do zip on the metal removal if not excessive, just get the rpm and stroke right and do CW 1st then CCW to finish and lots of outboard oil. That piston is not that bad the ring lands not folded and look ok per pic. I have reused pistons with light score like that with a light clean up using 1000 or 1200 wet paper in circumference direction. Based on your stated goal for the engine might consider a reuse of that piston since already fits the bore with lots of hot cold cycles, a used one could be a worse fit or not any better? Just get the right rings and end gap on them.

[Albert]

Bill,
I’ve had a night to sleep on it and you know what? This is as good as it could have of gone. I wasn’t able to get out to test a final time last fall. We knew it got hot and I ran it one more heat. Thankfully only one more. The cylinder is fine, new rings and a good used piston and this will be back together with a hone.
I am going to have the cylinders measured to be sure they are still round…but I think it will be ok.

Obviously I’d rather not have to deal with this. When you build a motor from spare parts and leftovers you have to expect things won’t be perfect. This motor needs to be good enough to lend to a local racer later this summer for a weekend. Maybe not win but be reliable. That’s the goal.

[bill hoctor]

[Albert]

Sigh,

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[Albert]

Ok,
Time to come clean. When I put this motor together last year we all knew it wasn’t perfect. I ran all last year with stock sized rings on .015 over pistons. Truth be told every time the motor was out my ring gap that started at 0.08 was growing and growing. Compression was dropping and so was power. There were also some things I’ve learned since that I just plain did wrong. Time to give the basket case 80 some love for getting me through the summer. It will be better and good practice before I tear into my hopefully nicer “new” motor.

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