Setting ring gap on home honed pistons.

[martythemad]

150 yamaha 2-stroke, overheated and scraped up 3 cylinder walls pretty good. I gave them a deep honing until the scratches were about 85-90% removed. The undamaged lightly honed cylinders are showing a ring gap of about 13-14 thousandths. The deepest honed one is showing a gap of 18-19 thou. Would you still consider this fairly passable? Is there any benefit to matching the ring gaps by enlarging the tighter ones slightly? Will this much gap affect compression?

[Chaz]

What's the old saying .. If it will rattle, it will run ..

As a general rule of thumb .005 - .006 per inch of bore is considered normal.

I don't know the bore size on your Yamaha, so hypothetically :

3.500" x .005 = .0175 / 3.500" x .006 = .021

So unless you have a real small bore, I'd say your pretty tight @ .013". Which can / will cause the ends to butt together ,, nowhere for the ring to go except dig into the bore or twist in the land .. Both causing excess heat / wear / broken ring lands.

[H2OPERF]

What kinda hone did you use...

[martythemad]

3 stone hone on a drill. Since I was removing material not just glaze breaking I was concerned a ball hone could make it out of round around the ports.

[martythemad]

Yup, the bore is 3.5". The old rings measure the same, maybe .001 more. Im pretty sure they are original, I dont see any signs anyones ever put a wrench on this engine. A shame someone blew this engine up, it doesnt look like it has hardly any hours on it. Good to know i at least wont be hurting things if i open them a touch.

What's the old saying .. If it will rattle, it will run ..

As a general rule of thumb .005 - .006 per inch of bore is considered normal.

I don't know the bore size on your Yamaha, so hypothetically :

3.500" x .005 = .0175 / 3.500" x .005 = .021

So unless you have a real small bore, I'd say your pretty tight @ .013". Which can / will cause the ends to butt together ,, nowhere for the ring to go except dig into the bore or twist in the land .. Both causing excess heat / wear / broken ring lands.

[Chaz]

What kinda hone did you use...

Yup, the bore is 3.5". The old rings measure the same, maybe .001 more. Im pretty sure they are original, I dont see any signs anyones ever put a wrench on this engine. A shame someone blew this engine up, it doesnt look like it has hardly any hours on it. Good to know i at least wont be hurting things if i open them a touch.

.004 per inch .. a little tight for my liking. And for those times when the water pick-up gets clogged with grass .. beeppp - beeppp -- beep ..

But to each their own ..

Pat Musi built a motor for an Outlaw-632 car I did the chassis on. We saw him at a race, I said, I've got a 706 ci (4.600" bore) motor in my car. Every time I turn the second gun on, it kills the ring lands. First thing out of his mouth was you need to be .038 on the top and .040 on the second ring. I was at .032 and .030 I thought he was nuts .. but no more issues. The leak down tester might not have liked it .. but I never went down the track with one of those things anyway ...

Keep in mind that a two stroke tends to run the piston crown temp a touch hotter than a four stroke ..

https://auto.wiseco.com/blog/everyth...about-ring-gap

[Chaz]

What's the old saying .. If it will rattle, it will run ..

As a general rule of thumb .005 - .006 per inch of bore is considered normal.

I don't know the bore size on your Yamaha, so hypothetically :

3.500" x .005 = .0175 / 3.500" x .006 = .021

So unless you have a real small bore, I'd say your pretty tight @ .013". Which can / will cause the ends to butt together ,, nowhere for the ring to go except dig into the bore or twist in the land .. Both causing excess heat / wear / broken ring lands.

So I got a text .. that basically said I was a dumbazz and can't do maff ...

OK , I think it really said for me to check my math ..

The mornin sun was in my eyes ..

I hadn't had my 5 th cup of coffee yet ..

I was late for honey-doo's ..

I was on the phone with Governor DeSantis ..

New keyboard has smaller buttons ..

My proofreader is on vacation ..

Fixed it ...