Running in

[Minto]

Thanks all, didn't get as much done as I wanted today, other jobs getting in the way. Barrels are now on and a few other little bits done. Ignition timing and head tomorrow and hopefully quite a bit closer to starting up.
Jase

[RDfella]

Don't wish to labour the point, but the idea regarding the 2nd ring completely escapes me. The top ring takes the full force of the 'explosion' on its top face, pushing the ring against the supporting land and pushing the ring out to the cylinder wall by getting behind the ring. If the 2nd ring is getting equal or near equal pressure, summat's wrong. Maybe the top ring is too tight in its groove, denying gasses getting behind the ring (which is what forms the seal to cylinder wall, not the ring's springiness as is often assuimed). Whatever, if the 2nd ring is doing anything more that backing up the top ring, the engine needs taking apart to discover why.

[Triton Thrasher]

Pressure escapes through the top ring gap, to the space between the top and second rings.

The pressure that forces the top ring out against the bore is the difference in pressure above and below the top ring.

A bigger second ring gap relieves the pressure between the rings, so the pressure differential above and below the top ring is better maintained.

Nowadays, they can measure pressure above, below and between the rings on a running engine.

Under normal circumstances, all the second ring does is some oil scraping.

To have this conversation usefully, you’d have to buttonhole an automotive engineer.  I’m just a nit having a go at old bikes.

[Minto]

Thanks everyone,
Regarding the rings, the manufacturer advises not to do anything as they are pre gapped for optimum performance, so that's the way I'm going (lazy? Maybe!)
Cheers folks
Expect imminent incoming update of disaster.
Jase

[Greybeard]

Thanks everyone,
Regarding the rings, the manufacturer advises not to do anything as they are pre gapped for optimum performance, so that's the way I'm going (lazy? Maybe!)
Cheers folks
Expect imminent incoming update of disaster.
Jase

Just check the gaps please.

[Triton Thrasher]

Yes, assuming gaps are not too small is a big risk to take.

[Colsbeeza]

Hi Jase,
I fitted IMD pistons recently. I had the crank balanced, and the pistons came back with rings removed, so I took the opportunity to check gaps ( at the bottom of the bores). Otherwise I would not have checked. All were 12 thou except one of the top Compression rings was 9 thou, so I opened it up to match the others. Traditional recommendation was 4 thou per inch of diameter, although the tech world has moved on since then. I have also read that 2nd Comp ring is often set at 25% bigger gap than 1st Comp ring as TT suggests.
I suspect that unless you are going to flog the motor that may not be so important.
The IMD top ring is Moly coated, so recommended hone is 280 - 320# with a 400# plateaued finish. That is very different to traditional hones for cast iron rings - 150# seems normal. IMD didn't provide the recommendations for honing or running in, but the machinist who honed the bores did.
If you have had cams or followers or other rubbing parts renewed, then a high zinc oil with no friction modifiers is advised for break-in. If you go supermarket cheap oil, it still may have friction modifiers. Quite a few companies supply running-in oil.
Col

[Minto]

Cheers lads
Unfortunately the barrels, head and rocker box are all back on. I did however, check the compression ring gaps when I got the pistons, 12 thou, I didn't check the oil rings though.
The bores have been honed a further couple of thou since as well so should be ok for clearance.
Do wish I'd rechecked after I got the barrels back from the engineer's.
Cheers
Jase

[Minto]

Ok, I'm sufficiently unsure and concerned that I've made the decision to strip it back down and do some more measuring, ring gaps and piston to bore clearance (the bores were done at a MC machine shop, but I hadn't checked them after I picked them up, and am starting to wonder if they have been honed out as much as was required). It would be daft not to when it's only rocker box, head and barrels, hopefully I can leave the magneto in situ, ignition timing was a right faff, way more fiddly than siting the push rods in the rocker cups.
So, current status, going backwards!
Cheers all
Jase

[Minto]

Well rocker box, head and barrels off by 7.00am rings removed and gaps measured in the bores, 12.5 thou top ring  14 thou second same for left and right, also rechecked the piston/more clearance, a gnats sneeze over 4 thou, so I'm happy to proceed, barrels and head back on by 9.00am. leaving the rocker box as I want to helicoil one of the screw threads for the tappet cover studs which is barely hanging on. Helicoil kit hopefully be here in a couple of days.
It was definitely worth getting up early for, I feel much happier about things now.
Thanks for the prompts guys
Jase

[Greybeard]

Good work! 

[Triton Thrasher]

12.5 thou top ring  14 thou second

So they made rings with the second ring gap 12.5% bigger than the top ring gap.

[RDfella]

Probably didn't make them that way - they're just a used batch thrown in.

[Minto]

12.5 thou top ring  14 thou second

So they made rings with the second ring gap 12.5% bigger than the top ring gap.

It would seem they did, and as they were the same on both pistons I assume it was by design not chance.
I don't really get the science behind this but would welcome enlightenment if anyone could translate it into English.
Cheers
Jase

Never mind, just re read your post on the last page, not sure the extra 1.5 thou gap in my case is going to do that much.

[Scott and Jay]

Hi Minto, I put IMD piston and rings in during 2017. I couldn’t actually get the rings out to gap them because the are “modern” - deeper and thinner. I took Adrian Wright’s (IMD proprietor) advice and made no further attempt. I trusted my good reconditioner to follow IMD’s detailed “boring (and honing) instruction”. I was concerned about glazing so I put the rings in dry with just a little light oil on the skirts. I followed the “Klaus” method of “static” running in - see earlier posts. This was still with good high-zinc oil in 3 10-minute stints on stand with fan, changing oil (1 litre only needed each time) and tightenig tspprrts. This was st 3k rpm. No
Long idling. Lugging or too high rrve for 1st 500
Mile. Still running fantastic burns no oil...