Piston rings clearance

Hope someone can give me an answer to my question.
I have bore up my 850 cylinder to +020. The piston clearance is 0.10 mm, the top ring has a gap of 0.30 mm, the second ring has 0.26 and the oil ring has a gap of only 0.005 mm. This must be way too small? What is the recommended clearance on this type of oil ring?
The oil ring is very hard to get down into the cylinder. I had to take out the coil spring that is inside the oil ring to get it in. I‘m afraid that too small ring gap and the pressure that the coil spring creates against the cylinder walls will be too high and will lead to damage to the cylinder. Should I take off the length of the spiral spring? Point of views?

The rule of thumb is 0.1 mm gap for ever 25 mm of bore, That applies to all rings.

Can you post a picture of the oil ring? Having trouble picturing it. Most have an upper and lower rail, with a waved spacer in between. Is this what you mean?

I tried, but did not succeed. Will try again.

Derek Wilson said:

The rule of thumb is 0.1 mm gap for ever 25 mm of bore, That applies to all rings.

Can you post a picture of the oil ring? Having trouble picturing it. Most have and upper and lower rail, with a waved spacer in between. Is this what you mean?

Click to expand...

No, it’s one oli ring with spiral spring inside. See photos.

Kvinnhering said:

No, it’s one oli ring with spiral spring inside. See photos.

Click to expand...

Can you take out the spring and size the ring with the correct gap?

Derek Wilson said:

Can you take out the spring and size the ring with the correct gap?

Click to expand...

Yes. there is no problem.
The question is which clearance should I go for, 0.30 or 0.25? Next and perhaps the most difficult question is how much should I take off the length of the coil spring? How can you measure / test this so you have the correct length / tensions on this?

Kvinnhering said:

Yes. there is no problem.
The question is which clearance should I go for, 0.30 or 0.25? Next and perhaps the most difficult question is how much should I take off the length of the coil spring? How can you measure / test this so you have the correct length / tensions on this?

Click to expand...

If it were mine, I would be setting them all a 0.30. I would not touch the coil spring. The point here is to make enough room for thermal expansion of the rings, the tension of the coil spring has very little to do with this. Too little ring gap and you can lock up the engine (obviously).

Hoper this helps.

Derek Wilson said:

If it were mine, I would be setting them all a 0.30. I would not touch the coil spring. The point here is to make enough room for thermal expansion of the rings, the tension of the coil spring has very little to do with this. Too little ring gap and you can lock up the engine (obviously).

Hoper this helps.

Click to expand...

Appreciate your input. But I can‘t squeeze the oil ring together with my hands, when the spiral spring is inside. I feel this will make too much pressure against the cylinder wall.

Kvinnhering said:

Appreciate your input. But I can‘t squeeze the oil ring together with my hands. I feel this is too much pressure against the cylinder wall.

Click to expand...

I have a question about whether those oil rings are appropriate for a Norton. I've never seen that type oil rings before.
Other members please educate me.

Ed

The Cycle Craft rings USA, made by Grant for 750 T140s have a similar oil ring. I believe they are made that way because T140s have oil control problems, hence that type of oil ring. Nortons don't have that problem and the early OEM pistons do not like a one piece oil ring , so I would rather have a Hastings set with their 3 piece "Flex Vent" oil rings.

Kvinnhering said:

Appreciate your input. But I can‘t squeeze the oil ring together with my hands, when the spiral spring is inside. I feel this will make too much pressure against the cylinder wall.

Click to expand...

I feel that it won’t.

APRRSV said:

I have a question about whether those oil rings are appropriate for a Norton. I've never seen that type oil rings before.
Other members please educate me.

Ed

Click to expand...

If you go to Andover website, you will see that they sell oil rings with a similar design. Andover is a quality supplier of parts for our Norton bikes so it must be a recognized design I believe. But it seems that coil springs are of a softer version.

From the Grandini Web site. Luckily the pictures translate most of what you need to know. But It would be handy to see it in English. It seems the 750 rings have a coating on the top ring and the 850 rings are more Plain Jane.​

*** If the pictures don't show up,, Go to their web site***

https://www.gandini-industria.it/catalogo/serie-segmenti/serie-per-motori/norton/SFP775-050

NORTON SFP739-050​

NORTON SFP775-050​

​

Kvinnhering said:

Appreciate your input. But I can‘t squeeze the oil ring together with my hands, when the spiral spring is inside. I feel this will make too much pressure against the cylinder wall.

Click to expand...

Kvinnhering said:

Yes. there is no problem.
The question is which clearance should I go for, 0.30 or 0.25? Next and perhaps the most difficult question is how much should I take off the length of the coil spring? How can you measure / test this so you have the correct length / tensions on this?

Click to expand...

Why not use stock OEM Norton ring gap specs. As far as the oil ring I would put oil on it to see if that helps compress it and then use a ring compressor to insert the oil ring in the bore and check the gap . then and use the piston to push it up and down in the bore to get a feel for the friction. You could also contact Grandini direct and ask them about specs and why that type of oil ring.

Re: difficulty getting oil rings in bore

Use a ring compressor. Sometimes, the compressor refuses to cinch up on its ratchet, in which case shim it with a band of thin shim stock.
Hastings three piece oil rings are a bear to get in the bore. I had to work on getting the oil rings in first without the top two rings, then after getting the oil rings in the bore, I used the ring compressor to get the top two rings in.

I would not cut anything off the rings, especially the oil control spreader. Place the ring in the bore without a piston and measure the gap. File if necessary to meet the gap spec.

Slick

texasSlick said:

Re: difficulty getting oil rings in bore

Use a ring compressor. Sometimes, the compressor refuses to cinch up on its ratchet, in which case shim it with a band of thin shim stock.
Hastings three piece oil rings are a bear to get in the bore. I had to work on getting the oil rings in first without the top two rings, then after getting the oil rings in the bore, I used the ring compressor to get the top two rings in.

I would not cut anything off the rings, especially the oil control spreader. Place the ring in the bore without a piston and measure the gap. File if necessary to meet the gap spec.

Slick

Click to expand...

To get rings in I make the bottom chamfer bigger so it lets the rings enter easier. After a rebore the chamfer gets quite small .

I have ring compressors but for the Norton I made one out of 1 -1/2 inch wide [ or wide enough to cover the three piston rings ]strip of panel steel, which I prepared for the job by rounding off its edges and bending 4 tags out of one edge. [ just like real ring compressors ] The ends of the strip were bent out with a hole in them to take a bolt and when the bolt was done up [ snug enough to slide on the piston easily ] the compressor band had slight gaps between the ends. This tool can then be used when you have the pistons fitted to the rods. [ a standard ring compressor wont come apart ]. It comes apart easily after the barrel has slide down over the rings. Of course you do need a couple of say blocks of hardwood to rest the barrel on when removing the compressor band.

There are idiots on this forum who are proud to say they have cut the expander on Hastings oil rings. Don't be one of them.

Carl H said
To get rings in I make the bottom chamfer bigger so it lets the rings enter easier. After a rebore the chamfer gets quite small . DONT DO IT.

Not necessary if you use the right ring compressor. Most Auto engines have only a very slight chamfer at the top of the bores.

The Oil ring end gap is checked without the expander fitted , do not cut the expander it is designed to compress on installation
use a motorcycle type ring compressor as the pistons are fitted from the bottom of the cylinder the chamfer needs to be re machined to help enter the rings
some advice above like DO NOT DO IT is wrong a Factory fresh standard bore Norton cylinder will have a chamfer at the bottom

it is normal practise when re boring motorcycle cylinders to re machine the chamfer once the cylinder reaches larger over sizes the chamfer is removed
Auto engines have a slight chamfer at the top as THE PISTONS are fitted from the top ? says it all

I'm dealing with +40 and +60 over bores, Or new sleeved down barrels ,so I put back the chamfer that was about what Norton had OEM new. I have altered my ring compressors to make them work a little better, But putting a cylinder on it a little tricky and you need good tooling and techniques and patience. Mistakes are costly.