Ring end gaps

[Rusty McNeil]

Trying to decide where to go with this.

Yammy spec for ring end gap for the stock pistons and rings is 0.0295 total/measured, no stipulation whether it it's 1st, 2nd or oil ring.

General consensus from current info is that a n/a hot rod motor needs about 0.004-0.0045 per inch of bore if for for the top ring and about 0.0045-0.055 per inch of bore for the second ring. There's some current science behind making 2nd ring gap larger than 1st ring gap having something to do with "ring flutter"

For the oil ring rails 0.015 total is a fixed value across most Mfgr.

Yammy's spec works out to about 0.010 per inch of bore, Sounds kinda big to me from the info. I'm seeing out there on the current rings available. Blown nitrous race only motors don't even call for gaps that large.

Are Yamahas specs just a reflection of the knowledge base back then, having never been updated? Or based on the materials they were working with back then? Or does ring end gap really need to be that big in spite of the current technology?

From what I'm reading those huge ring end gaps leave power on the table for no reason.

 

[bazwell]

I think you are on the mark 100%
Standard manufacturers specs are usually conservative.
When building a performance engine those specs are mostly ignored and you only look at things which would make you want to deviate from the norm. ie. massive turbos and mega octane fuel would mean more temperature and therefore more ring expansion.

The v-max has a pretty normal water cooled 4 stroke motor. Go for the tighter tolerances and set the horses free! :biglaugh:


(I'm guessing that this is for a big bore motor, unk: and that it has been rebored to suit the pistons you have. Worn bores aren't the same.)

 

[Rusty McNeil]

I think you are on the mark 100%
Standard manufacturers specs are usually conservative.
When building a performance engine those specs are mostly ignored and you only look at things which would make you want to deviate from the norm. ie. massive turbos and mega octane fuel would mean more temperature and therefore more ring expansion.

The v-max has a pretty normal water cooled 4 stroke motor. Go for the tighter tolerances and set the horses free! :biglaugh:


(I'm guessing that this is for a big bore motor, unk: and that it has been rebored to suit the pistons you have. Worn bores aren't the same.)

Yes, it's a 1540 stroker. All new machine work so bores should be square and correct. Sean did a good job of coordinating machine work and speccing sizes. Every thing I've plastiguaged or measured so far has been spot on.

 

[06VMAXIMUS]

Curious about this too....what does Sean suggest ?

 

[one2dmax]

I typically use close to the stock spec. There isn't going to be a ton of power lost due to excessive ring gap. I've seen a few where there wasn't enough ring gap so it wasted the cylinders when it got good and hot.

 

[bazwell]

I typically use close to the stock spec. There isn't going to be a ton of power lost due to excessive ring gap. I've seen a few where there wasn't enough ring gap so it wasted the cylinders when it got good and hot.

Not enough ring end gap does make a f*ing mess! Wears your motor out real fast!
Could it have been from people not gapping the rings at all that caused the problem? You could probably answer that Rusty. What are the ring end gaps without touching anything? (I'm just curious. I'm assuming that you have to file the rings to get them to manufacturers specs.)

Because Sean supplied your stuff, I say the safest action is to take his advise. He's selling the kit. (Also it's bad voodoo to tell people to ignore their parts supplier, unless you know he's a cockhead. :biglaugh

For the record... I'd close them up. F*# the warranty!

 

[Rusty McNeil]

Not enough ring end gap does make a f*ing mess! Wears your motor out real fast!
Could it have been from people not gapping the rings at all that caused the problem? You could probably answer that Rusty. What are the ring end gaps without touching anything? (I'm just curious. I'm assuming that you have to file the rings to get them to manufacturers specs.)

Because Sean supplied your stuff, I say the safest action is to take his advise. He's selling the kit. (Also it's bad voodoo to tell people to ignore their parts supplier, unless you know he's a cockhead. :biglaugh

For the record... I'd close them up. F*# the warranty!

"caused the problem"??
I'm not sure what you mean. If your talking about my motor it's down because the tranny was trashed.
The rings, out of the box, are too tight by any ones standards, just barely fit in the bore.

I ended up going withe the general industry specs but opened them up a little towards Sean's numbers just to be on the safe side
0.018 on top ring
0.020 on second compression ring.
0.015 on oil rails

If I had have gone straight with industry standards it woul have been
0.015 top ring
0.017 second compression ring
0.015 oil ring

Yamaha calls for 0.0295 all rings but those are with stock pistons and completely different design philosophy.

 

[bazwell]

"caused the problem"??
I'm not sure what you mean. If your talking about my motor it's down because the tranny was trashed.
The rings, out of the box, are too tight by any ones standards, just barely fit in the bore.

I was wondering if the ones that Sean has seen blown up were because of people not even knowing they had to gap the rings. Sounds like it could have been.

In a lot of stock applications for cars, the rings can go straight in without a problem. For some reason people don't check ring end gaps, or plastigage, or check bearing crush any more.

 

[one2dmax]

There aren't many in the blown pile with bad ring gap. I had a 2006 from Scott Sharp that was that way and Yamaha refused to warranty it. I also know we sold Rick Rash a set of 1260 pistons years ago that ended up failing and it was due to ring gap issues (his mechanic put it together without checking).

Sean