TRIUMPH 650-750 TWIN RETURN OILING
This may affect only a few but it has me. Because I have done so many triumph twin motors over the last 40 years would something like this appear. A while ago I built and sold a ’68 650. The thing would not settle down with a ring seal and therefore smoked badly at the tailpipes. Ring seal for sure as it smoked all the time. As most would know if the valves and or guides are badly worn then smoking only occurs when the throttle is shut, ie. on closed throttle over run and therefore idling. Smoke appears for a short while when the throttle is opened again, then clears. This happens because the cylinder vacuum will pull air from wherever it can and down worn guides bringing oil with it is one avenue.
So anyway this ’68 , I tried 3 sets of rings including Hastings and an new-old but decent set of Wellworthy. On a rebored and true cylinder this made no difference. All the time as I went, I was measuring the sump oil and finding 300ml. The pickup on this year was 1” up from the sealing washer shoulder. I checked on some other cases and found that after ’66 the pick up tube was ½” shorter. So from ’67 or ’68 all the way thru the 750’s the short tube is fitted. Why I’m not sure, maybe the factory was experiencing seizures with the longer tube and lower sump level, or not. They are “ dry sump” engines after all. Norton and A65 BSA had an oil drilling in at least one conrod to squirt oil up the cylinder wall. Never with Triumph. I prefer to block these anyway and keep the oil on the rod journal. The higher sump level didn’t seem to be any problem years ago but I believe the original Hepolite rings were better quality then, than what is available today???? Also when the factory first went 750 they fitted 3 piece oil rings, on the short pickup tube, that is a problem solver right there. They later went to one piece but with a coil spring expander behind and they seem to work ok, can be fragile though. I have been doing the 3 piece oil ring on certain rebuilds for a while now as a way to get a positive ring seal. By the way, that ’68 on had a perfect round bore, the poor sealing could be seen with all the one piece oil rings I tried , only touching at about 60% of ring circumference. I had a Morgo big bore kit do something similar 20 yrs ago and tried 2 sets of Morgo rings on a true bore to no avail then fitted a new old stock Hepolite A65 BSA set and problem solved. It too was a short pickup. On a bike I built my brother this problem arose and no amount of wishing and riding it would stop smoking, hoping it would settle down. So in went a new set of one piece oil rings but I made up and tapped on and glued in place with JB weld, an extension. The sump now had more like 150ml instead of 300ml. It stopped smoking with a one piece oil ring. The less oil flinging around the better, especially with one piece oil rings although 3 piece will seal ok on a short tube with 300ml sump volume. The best option is long tube and 3 piece oil. This is not a problem on pre-units as the sump pick up is very low as is any Brit twin with 4 bolt sump plate. The 650 pre-unit Triumph can have different problems though, smoking caused by bore distortion due to the lack of metal between bore material and bolt hole pattern. 3 piece rings will fix that. I have always used a serious hone , a Sunnen with correct grit, and the last 30 yrs any machine shop I have used had the same Sunnen equipment, as used by the majority of auto machine shops. These things can correct abnormalities in the bore. An ammeter showing cylinder wall drag on the big floor machine then a bore gauge with dial indicator shows this. Today it would be at least $1000 for a hand held Sunnen like mine and is the same unit as the big floor machines use. Using an auto shop $40 3 finger hone won’t cut it, they just follow the problem. So the bore sizing and reading has never been an issue. Triumphs will use oil for sure, they never had guide seals which is ok as a little oil down the guide may make the guide bore and valve stem last longer. The oil is much better now days. I think I remember seeing ½ to 1 pint ( 250 -500ml) if US pint, used per 1000 miles is normal. The rest leaks out. Norton twins never had this problem as they used 3 piece oils and had a very low pick up. Ditto BSA twin on the low pick up point. I am ok with using new Hepolite / Emgo piston and rings as the choice is slim to none, but will alter the pick up tube to make sure I don’t have a problem. The pick up tube is .300” OD, so finding a drill at .295 or so and boring a tube with a thin wall and useable outside diameter is not a huge problem . Especially when cases are apart. Altering the screen is best done with one that has a brass washer in the end. Fitting an external oil filter is the best thing you can do for your classic machine. I don’t know how many cranks I have cleaned the sludge trap on and they always have carbon build up ,some to the point of blockage and therefore starvation. Chances are you may never see this problem and maybe it is only because I have done sooo many, that I have.