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Discussion Starter #1
First time doing 750 rings. Two questions;

I know that on my 750-four engine, the maximum end gap for the two upper piston rings is .7mm (according to my shop manual) but does anyone know what the minimum ring gap is? Since the rings expand a bit with heat, this measurement seems important to me, since too small a gap can lead to bore damage. But oddly, the minimum gap is not covered in the manual!

Second, the rails for my old oil rings hardly stick out of the grooves at all, like the compression rings do (before being compressed), although the engine wasn't really a smoker. Indeed, when I place a rail down in the bore, there is hardly any gap at all. Is that normal?

I'm planning to buy new rings, but want to understand this before I do. Who can explain it to me? Thanks!
 

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Discussion Starter #3
That applies also to the oil ring rails? When I push a rail into the bore, there is barely any gap at all.
 

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4" bore?? You realize we're not talking small block V8 here, right? :)

I think the stock 750 four bore is around 66mm, or about 2.64".
 

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Discussion Starter #7
Thanks guys, good info.

My main concern now is the oil rings. I just went out and tried fitting the rails in the bores (like with compression rings-I put the oil rails in the bore. Better then half of them were loose enough to just drop through the bores! What? So I realize that the expanders keep the rails apart, but do they also somehow force the rails outward? When I remount the old oil ring assemblies on the piston, they are flush with the pistons, and there's little or no gap in the rails. I don't see how this can work? I had planned to use the old rings again as they are otherwise in good shape. So I'm wondering if new oil rings would be the same way?
 

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Why would you use the old rings again? And why go to the trouble of removing them if you are going to go back with them unless you are broke. My atv warrior's crank locked up so I rebuilt the crank but went with the old rings because the bike had not been smoking or using oil and I was trying to save a little money. Well after I put it back together it started smoking and I decided that next time I would not go with used rings.

Get some new rings and run a hone down the bores. And do not worry about too tight an end gap. That is not going to happen with a worn bore.
 

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Discussion Starter #10
Well, this all started because I was blowing some oil smoke. I couldn't tell if it was rings or valve guides/seals, so I pulled the engine uppers to look. Haven't yet looked at the valves, but the compression rings looked fine and had the proper gaps. As I am unemployed and...well, poor, I was hoping to reuse them, but am not sure about the oil rings. I suspect that the oil is coming from bad valve seals (and possibly guides) and will check on that this weekend.

I certainly would rather like to hone the bores a bit (which measure out okay but are a bit glazed) and use new rings, but the cheapest I have seen on the web (Z1, and other sites) is around $130 and I just don't have that. Who has seen them cheaper?
 

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I know where you can buy a set for $100.00 shipped in the US for a new set of standard rings for a 81 or later 750 four .:wink:
 

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I know what you mean bro. I am sans job myself and have had to scratch up a few dollars to spend on my bike.

I don't think you can buy just the oil rings but the compression rings are the ones that control oil anyway are they not?

From my experience valve guide seals only cause smoking at start-up and when you shift. A steady smoking usually indicates your rings are worn. Also you can do a cheap hone job with sand paper if you do not have access to a hone. It will give that glazed cylinder a rougher finish which helps seat the rings.
 

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Discussion Starter #13
Yea, I now suspect that someone stuck these rings in recently without bothering to hone. I've seen that really bad valve seals will smoke even at idle, but I think it's poorly seated rings.
 

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shoulda done a leak down before tear down... but since youre there replace the valve guide seals anyways.... so whats your ring end gap on the rings ? are they in spec ?
 

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Discussion Starter #15
Well, the book says .7mm max. All my compression rings come in at about .4 to .45mm, so that seems okay. I have not measured gap for the oil rails, but they are closed when loose off the piston, or when trying to set them in the bore, but they open up a bit when installed with the expander on the piston (not sure how to measure the rails, or if it's necessary-they do grab the bore when installed on the piston).

I do intend to hone a little, and have posted another question about that.
 

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Discussion Starter #16
Well, the book says .7mm max. All my compression rings come in at about .4 to .45mm, so that seems okay. I have not measured gap for the oil rails, but they are closed when loose off the piston, or when trying to set them in the bore, but they open up a bit when installed with the expander on the piston (not sure how to measure the rails, or if it's necessary-they do grab the bore when installed on the piston).

Yea, I don't have a leak down tester. I may try to make one.

I do intend to hone a little, and have posted another question about that.
 

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Yea, I now suspect that someone stuck these rings in recently without bothering to hone. I've seen that really bad valve seals will smoke even at idle, but I think it's poorly seated rings.
Could be.
Years ago I used to help my uncle a bit as he was always tinkering with cars. He would put the news rings in but never bothered to hone them. He would just cut the ridge from the top of the bore. Those engines took quite awhile for the rings to seat because there was not a proper hone job done on them. You need to break that glaze so the rings mate quickly.
 
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