Atlas White Smoke (again)

Thanks for the advice! I think I will give the restricted rocker feed option a try to get me going for a while (I couldn’t find a suitable jet but a small TIG torch collet fits the oil hose perfectly). However, I am tempted to revert back to the 3-start set-up eventually to avoid all the other changes (the rings are Hepolite R26260 btw). The idea to pressurise the crank is a great idea - I will do that when the head is off for the valve change anyway, removing the barrel should make it easy enough to observe the oil holes and also to check the piston rings. If the oil holes are in use, I have to bite the bullet, taking out the engine and to split the cases…

Hi Tomas and Robert, the valves and guides are definitely on the cards sooner rather than later, as they havent been done in the time I had the bike, nearly 30 years (even if 15 years off the road)… It being a ‘63 model, I will probably stick with the shorter valves, rather than changing the pushrods as well. I read various opinions on wether to go with the silicon bronze guides or the standard cast iron type. Tending towards the bronze - which ones did you go for?

John - I will try blocking the feeder for a short time to get a better idea where the oil comes from…

Hi, just ran her without the rocker feed as suggested by John and there is still a lot of smoke and wet plugs, so it appears to be the new rings! That makes sense as I don't remember to have the white smoke problem in the past and only changed the pistons and rings recently. The Hepolite oil rings are single piece items (with a spring), while the previous ones were triflex rings. I might try to fit the old rings as they have done less than a thousand miles and the ring gap in the pistons is the same. There still appears to be a lot of oil in the rocker area after re-connecting, so I might try restricting the flow a bit too as suggested.

Thanks for the info on the valves, Tomas. I will see what is available - I know that RGM does valve overhaul kits, so will check with them.

That’s a revealing experience, Philip - in theory both cast iron and silicone bronze should be self-lubricating. I wonder if the seizing had to do with wrong tolerances and different expansion rates of the various metals in the head. Maybe sticking with the iron ones is the way to go, so - RGM are offering both iron and bronze with inlet seals for early Atlas heads. Were the guides standard size or did you have to lathe them down to fit?

I took the head off yesterday to check valve and pushrod lengths and there was a lot of oil… The barrel will come off today to swap the oil ring for the previous triple scraping ring. I am a bit unsure about what head gasket to use - it is an early head with 5/16” bolts but the spigot has been machined off, assume when the cylinder liners were fitted. No rings were fitted to he head, but I will get two from RGM. I dont really want to go down the route of changing bolts to 3/8”, if I can avoid it. Not sure to use copper or the copper composite? With a smear of Wellseal or not?

Robert - yes, you are right - about twenty years ago, Norvil did a major job on the cases and barrel. Pistons were then so oversize that they recommended to fit liners and bring it back to standard. The crankshaft was balanced and the journals submersion welded back to standard, as the they were too worn and later conrods with oil holes were fitted. I think then, using a 6-start pump and cartridge oil filter was then recommended, which started my current over-oiling troubles. Strangely, I laid up the bike shortly after that major work was done and I only pulled her back out of the dusty corner last year…

No worries, Robert - you left the important ones! 

Ok, just took the barrel and pistons off… Turns out rhs had triplex oil ring, lhs a single one fitted - that’s the side that was smoking! I also discovered pressure marks on the skirt of the lhs piston, so I will get the piston clearance of the Norvil-fitted cylinder liner checked and honed to 4-5 thou in an engine shop.

I also pressurised the crank to see if the conrod oil holes are working as suggested by Robert. They indeed open when the piston is down and squirt out oil, as I learnt the hard way (I was covered in it…). 

I am considering to stick with the 6-start pump for now, fit back triplex oil rings on both pistons and upgrade the a valve gear to iron guides and seals from RGM. As the barrel is in the machine shop anyway I will get the oil return bore widened from 3/8” (4.5mm) to 7/16” (5.5mm) and do the same to the head and crankcase, as everything is off. Leave low pressure return feed and scrolled rocker spindles as is.

Btw, does anyone know if the RGM valve guides need to be reemed and are they standard or over-size, i.e. need to be turned down to the head?

In the past I had guides (not on a Norton) that had to be reamed to fit the valves. RGM does not specify any oversize dimensions, so I suspect they may come oversize to be turned down to size. Waiting for their response at the moment… a bit of Wellseal is a good idea.

Normal tin bronze is somewhat porous and the silicone has the ability to fill pores during the casting process, making it denser and harder. As an added benefit silicon adds a limited self lubrication quality to the metal, making it ideal for valve guides. Many bronze bearings are essentially compressed bronze powder with lubricant inclusions, as such self lubricating, but I dont think this applies to the Colsibro guides. Very interesting website, btw!

Maybe worth sticking to the old rule iron for roadwork and bronze for racing? In the end the advantage of bronze guides is improved heat transfer (but only 25% through the guide according to that website, 75% through the valve seat) but cast iron guides offer a reliable compromise between durability, lasting tolerances and cost.

Just a quick update on the above query and discussion. The Atlas runs fine now after more work over the last weekends. Happy days!

- I changed the rings back to the Twiflex (spring and two rails) oil scraper rings. I had to use the old pistons as the grove was not deep enough in the new ones which meant having to polish out a few marks and light scratches. Got the clearance checked and the cylinder liners honed to 4-5thou. The rings cured the smoking, so I did not have to change the pump or BE shells in the end.

- I ordered iron guides and valve kit from RGM, but left the old guides in for the moment as the play is still acceptable (healthy plop when valves are pulled). Turns out inlet guides are bronze already with seals but the exhaust are iron.

- Despite reconditioned carbs, complete magneto overhaul with EasyCap condenser, new plugs, checking ignition and valve timing several times, new leads and caps she still ran on one pot. The magneto cam is 3 degrees different for the two cylinders, but acceptable when difference is divided. This nearly drove me demented… In the end it turned out that one of the brand new Champion plugs was faulty! It produced a healthy spark when out but was dead under compression! First time I experienced this…

Thanks everyone for the help, advice and suggestions!

Holger