Atlas piston issues (oil fouling)

Triton Thrasher said:

I can’t much be bothered arguing, but if you think cold pistons are round, you know nothing about pistons. My second statement is right. You wrote a long post full of garbage that you’ve dreamed up.

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Triton, I welcome honest opinions. Your blatant statements are so refreshening!

I recently nearly scrapped a pair of decent pistons when I found 5/6 thou clearance ring to piston groove. A close check in good light showed the rings had worn a step and a check with a new ring showed acceptable clearance.I had expected the wear to be on the softer alloy,but it was on the ring.

mdt-son said:

Triton, I welcome honest opinions. Your blatant statements are so refreshening!

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You’re very gracious.

Many thanks for many replies. New pistons are here. Emgo w/ Hastings rings. Original piston c/w rings, pin and clips weigh 317.5gr and a new piston c/w rings, pin and clips comes in at 318.1gr. I didn't take the new rings out of their paper envelope so really they're pretty close in weight which is good.

Long story short, considering the current availability of pistons, +20 is really a first bore to me. I'm going to drop this all off at the machinist tomorrow since they keep "cycle shop" hours and aren't open on Mondays.

No taking the Commando to the OVM Corvallis show for Jeltz. The Ratlas barrel is ready for pickup tomorrow. Machinist said he didn't think the +10 over job was very good and he was barely able to take it to +20. Head gasket's cooking on the stove.

Good luck with the rebuild,check ring gaps in cylinders. I'm looking at some very heavy thick walled commando piston pins, were your proper atlas pins lighter? can you measure the wall thickness for me?. Or the weight?.

Bob, one of the original pins weighs in at 69.0gr. As far as pin wall thickness, it is tapered on the inside but the largest drill I could pass through it was .375" OD is about .687" Too early in the day for 'rithmatic. Won't have the new pins in hand until this afternoon.

Back from the machinist. LES took the Ratlas barrel to 2.8888 with a .0041 clearance. Other side was 2.8889 with .0040 clearance. He said while it was more or less round, it wasn't very straight top to bottom.

Emgo +20 pistons. Hastings +20 rings currently gap up at .006. Looks like just a little filing is in order.

I'm going to use the spec from the factory Commando manual of 10-12 for the top ring and 8-12 for the second and shoot for the low end.

Jeltz here, finally back on target. The Ratlas is back together and runs well enough for an eight mile tour. No stalls or poor running, it runs well but rather rich. I'm looking at two carb issues. First is that I believe I have the 2-1 manifold upside down resulting in a more downdraft position as well as upset float levels. Secondly, the bike came with a single 389 Amal and near as I can tell from the big Bacon book and Amal's website it should have a single 376.

Current carb settings for the 389 Monoblock are: #20 pilot, 106 needle jet, D needle on pos. 3, no. 3 slide and a 330 main.

It's in the shop now without any damage to Jeltz's toes despite the wearing of sandals. https://www.accessnorton.com/NortonCommando/maybe-i-should-wear-my-work-boots.27875/

We'll turn the 2-1 manifold the other way round and see if that makes a difference. If not, I'll dig into my big box of Amal leftovers and see what we see.

http://www.pharaohlan.com/~jeltz/misc/DSCN0397.JPG

According to my Norton manual Publication P106/P, The single carb Atlas used a 376/294, with configuration as follows:

Main Jet: 400
Needle Jet: 106
Pilot Jet: 20
Throttle Valve: 3 1/2
Needle taper: C
Needle Position: 4

Float chamber needle seating raised by 1/32" washer.

Slick

Oh yeah, Jeltz definitely had the 2-1 manifold upside down. Just got back from a 10 mile test, plugs are much better now. Still a little more colour on the right side, but these were used plugs that I cleaned up. Runs pretty well now, I like it.

Thanks for the info on the correct carb Slick. Pretty much agrees with what the Bacon book said it should be. I've got an old 376 body, but the wrong slide (#4) and a couple of spare needles with no markings on them. I think the 389 will work, but probably will want a larger main than 330.

About time to close out this thread and move on to https://www.accessnorton.com/NortonCommando/how-to-make-the-atlas-dominator-primary-oil-tight.26860/ now that it's timed and running well. Got a tub of Red Rubber grease and I'm going to try that before resorting to glue.