Giving a Bezoat a Second Chance

[Albert]

51753BCF-F06E-49D6-8A56-60DD43871401.jpeg OK,
So since no one seems to want to recast and machine heads for an 80 and replacement heads seem scarce it was time to get creative.
Step one consult the manual:

27. It is legal to re-machine squish band area to the following measurement: angle 15° ± 2°, 2.350 ± 0.015. No changes may be made to the combustion chamber. There must be a visible ledge surrounding the squish band.


I assume there is also a minimum cc for cylinder head but I don't see it in the apba manual.
Regardless my squish band needed love and my by hand grinding job last year left a lot to be desired.

If only I had something like this die to work in some valve grinding compound to repair the squish band without putting it on a lathe or mill.

[ZUL8TR]

Luc
You are welcome. March on with the work it will be worth it and a great accomplishment. I look back at all the people along the way that helped me and pass on what I can to others.
Have a good day
Pete

[Albert]

Thanks for the words of encouragement Pete. I know this is stuff some experienced racers have been going through for many years. But it’s new to me, and I figure it may answer some questions for other rookies along the way.

Maybe the lesson to be learned here is start with good gear. Or don’t hack a motor together. Or don’t be a mechanical masochist. Or that you can start with garbage and end up with a pretty nice set up if you have helpful friends, are willing to read a lot and don’t place value on your own time invested in a project.

[ZUL8TR]

Keep us posted with pics on your progress. This is a great thread.

[Albert]

Your right once again its Lucas...not sure what I was thinking there.

[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]

F0E790BB-0ECD-4E95-A906-077B1D0A9C29.jpeg C52ADAE2-BEE7-4E26-9814-47A9E08EE8A3.jpeg


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.