Piston Rings

swooshdave · Jul 11, 2019

Rings installed. Circlip facing up. Oil ring not over lapping, you can see the red and green marks. Inside bevel on top two rings facing up. Does it matter where the two oil scraper rings have their gaps at? And where do you like to set the top two gaps at? @comnoz mentioned it doesn’t make too much difference as they are going to move anyways. Planning on putting them in nearly dry bores so they bed nicely. What else am I forgetting?

Time Warp · Jul 11, 2019

Did you deburr the top rings so they do 7 rpm with no drag in the ring land ?

comnoz · Jul 11, 2019

The oil ring rail end gaps should be 1 inch away from the expander end. One gap to the left and the other gap to the right, so there is roughly 2 inches between the rail end gaps.

swooshdave · Jul 12, 2019

comnoz said:
The oil ring rail end gaps should be 1 inch away from the expander end. One gap to the left and the other gap to the right, so there is roughly 2 inches between the rail end gaps.

And then how dry should the bore be? Wiped clean or wiped with a bit of oil?

Fast Eddie · Jul 12, 2019

From your picture it looks like the circlip is are in ‘back to front’ as it look like I can see the ‘rounded edge’ face of the circlip (I could be wrong here though).

My understanding is that these style of circlip is are stamped out. The stamping process creates one face with a very slightly rounded edge, and one face with a very clear and sharp edge. The sharper edged face should go against the pistons as it helps it ‘bite’ and increase security of the circlip installation.

Fast Eddie · Jul 12, 2019

swooshdave said:
And then how dry should the bore be? Wiped clean or wiped with a bit of oil?

I’ve personally never put pistons in a Norton dry, so I may be missing a trick here!

But I suspect that it’s a practice done more commonly in modern racing engines, which have modern oil pumps.

The Commando pistons and bores are fed by splash. On a freshly rebuild engine I worry that it would take quite a while for the crankcase oil content to reach the point whereby the ‘splash’ is serving its function.

(Same argument for the cam. Which is why I always lather the cam and followers in assembly lube).

Whilst I can see the logic re the ring bedding in process, I worry what’s gonna happen to those soft alloy pistons being pushed and dragged up and down freshly honed (and thus rough) bores.

I’d be happy to hear from those who can demonstrate that I’m wrong though...

MexicoMike · Jul 12, 2019

Well - when you say "splash" it's not actually splash like an old Briggs and Stratton lawnmower motor. IOW, the crank does not dip into the oil (once any wet-sumped excess is returned to the tank!). Oil is "sprayed" ("splattered" might be a better word) onto the walls by the oil from the crank journals. So oil is almost immediately deposited on the cylinder walls when the engine turns/the pump supplies pressure.

When I last rebuilt my Commando, I installed the pistons/rings totally dry. The only lube present was a wipe of WD 40 on the bores to prevent surface rust after honing/cleaning with soap/water. So far (8 years later) no sign of oil use/no smoke at all. Not claiming a one-time result proves anything but I wanted to try it and if was rebuilding another one I'd do the same again.

Some folks that I used to work with building automotive race/performance engines now use ONLY the dry method. But, as I often say - do what you are comfortable with!!

kommando · Jul 12, 2019

Bore dry with a drop of oil on front and back of piston well below rings is how I do it.

Triton Thrasher · Jul 12, 2019

Fast Eddie said:
From your picture it looks like the circlip is are in ‘back to front’ as it look like I can see the ‘rounded edge’ face of the circlip (I could be wrong here though).

My understanding is that these style of circlip is are stamped out. The stamping process creates one face with a very slightly rounded edge, and one face with a very clear and sharp edge. The sharper edged face should go against the pistons as it helps it ‘bite’ and increase security of the circlip installation.

From the photo, it looks like you’re right.

Fast Eddie · Jul 12, 2019

All good points ref the dry piston assembly guys.

I guess the caveat being ‘do what you’re comfortable with’ !

Triton Thrasher · Jul 12, 2019

FastEddie said:
I’ve personally never put pistons in a Norton dry, so I may be missing a trick here!

But I suspect that it’s a practice done more commonly in modern racing engines, which have modern oil pumps.

Modern engines are the ones that don’t need it.

cliffa · Jul 12, 2019

Fast Eddie said:
From your picture it looks like the circlip is are in ‘back to front’ as it look like I can see the ‘rounded edge’ face of the circlip (I could be wrong here though).

My understanding is that these style of circlip is are stamped out. The stamping process creates one face with a very slightly rounded edge, and one face with a very clear and sharp edge. The sharper edged face should go against the pistons as it helps it ‘bite’ and increase security of the circlip installation.

+1 on that. The “sharp” side should face outwards on grooves which have a semicircular cross section. It will offer more resistance to the clip creeping out under side load. Of course if the groove is square cross section it makes little difference.

cliffa · Jul 12, 2019

Triton Thrasher said:
Modern engines are the ones that don’t need it.

I thought dry run in was more to do with the materials used for the liner and rings ?

kommando · Jul 12, 2019

Modern engines are already run in as the dimensional tolerances off the machines are so good so the rings touch the bore all the way round, that allows a good surface finish to the used, that plus most engines are water cooled and so less heat distortion. On old engines the tolerances are not as good so the rings only touch in a few area's, so the surface finish is deliberately rough so the rings wear to the shape of the bore. The dry bore accelerates the wear in the first few seconds of running in and guards against glazed bores ie the rings are still only touching in some area's but the bore is too smooth to wear the rings to fit the bore.

swooshdave · Jul 12, 2019

So here are the two circlips. From the photo which one has the sharp side up? I know the answer because I can feel the difference. The holes (which are mostly what you can see in the previous photo) are rounded on both sides.

cliffa · Jul 12, 2019

swooshdave said:
So here are the two circlips. From the photo which one has the sharp side up? I know the answer because I can feel the difference. The holes (which are mostly what you can see in the previous photo) are rounded on both sides.

The left one.

comnoz · Jul 12, 2019

swooshdave said:
And then how dry should the bore be? Wiped clean or wiped with a bit of oil?

First, to clean the bore of any metal residue left in the pores, you take a few pieces of paper towel dipped in a little motor oil and wipe the bore. You will see the paper towel gets black. Continue the wipedown until the paper comes out looking pretty clean.
I then do the same thing with the piston.
The oil left on the bore and piston after wiping it down with a dry paper towel is enough for the assembly.

cliffa · Jul 12, 2019

swooshdave said:
So here are the two circlips. From the photo which one has the sharp side up? I know the answer because I can feel the difference. The holes (which are mostly what you can see in the previous photo) are rounded on both sides.

I see what you mean now Dave, it looks as thought the holes were stamped (punched) the other way round to the circlip itself.

swooshdave · Jul 12, 2019

comnoz said:
First, to clean the bore of any metal residue left in the pores, you take a few pieces of paper towel dipped in a little motor oil and wipe the bore. You will see the paper towel gets black. Continue the wipedown until the paper comes out looking pretty clean.
I then do the same thing with the piston.
The oil left on the bore and piston after wiping it down with a dry paper towel is enough for the assembly.

Would you have washed my barrels after you bored and honed them? Should I give them some soapy warm water then wipe down?

comnoz · Jul 12, 2019

swooshdave said:
Would you have washed my barrels after you bored and honed them? Should I give them some soapy warm water then wipe down?

I would have washed the barrels after I bored them and then wiped them with a little honing oil to keep them from rusting.

They will still benefit from an oiled towel wipedown.

You will be surprised at how much crap is on the towel on the first wipe.

Piston Rings

swooshdave

Time Warp

.......back to the 70's.

comnoz

swooshdave

Fast Eddie

Fast Eddie

MexicoMike

kommando

Triton Thrasher

Fast Eddie

Triton Thrasher

cliffa

cliffa

kommando

swooshdave

cliffa

comnoz

cliffa

swooshdave

comnoz

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