Tech Talk for Classic Nortons
Norton Oil Pressure
Since the mid 70’s and multiple Commando ownership, I have been very unimpressed with the stock rocker line (plastic). When it comes off the banjo it may give you a hot-wet sensation. The obvious and popular upgrade is braided line to the rockers. This has a 3 fold benefit: no leaks and an oil pressure gauge that can easily be routed to positions off the handlebar clamps (in your face); with the gauge on braided lines, you can now pack your oil pressure relief valve spring until you raise your oil pressure from a paltry 15-20lbs, factory set, (so as to not blow the plastic line off), to 50lbs or so and your rod bearings will love you for it.
Importantly, now you can see if your anti wet sumping device, (if turned on manually, or the ball that is coming off the seat under vacuum), is open, when the bike fires up. You can now monitor your engines lifeblood, via the gauge.
All my Nortons have been set up this way for over 30 years. I have seen my bikes start up with no oil pressure in the past and a quick tap on the aftermarket anti drain valve with the back my pocket knife sees the needle jump up to 60-70lbs cold. I use 20-50w in the winter and 40-70w in the summer. The gauge tells you how well the cold oil is pulling through during the warm up. Use a good high zinc oil to protect your cam and followers.
A gauge will tell you if the oil is low as the needle will start to flutter, also poor seals or pump and rod bearing condition can be seen with low oil pressure even after packing the oil pressure relief valve. It is invaluable as no light or gauge indication was fitted to Norton twins.
One step better is to put a “T” with an oil pressure switch (a single terminal as the braided line is grounded) and a warning light in the headlamp for those darker rides. It is a lot cheaper than a set of rods/cases/cylinder, etc. I put gauges on my Triumphs too, especially Twins as there is always a chance of the pump being compromised by a bit of grit on the ball seat, especially after an oil change. On Triumph Twins a gauge can also tell you rod bearing condition as you can watch how long it takes to bleed out to zero after you stop.
Be in the know and fit a gauge: without one you’re flying blind. I have seen two Norton 1972 models blown apart due to tacho drive seizures, stripping the cam drive and filling the pump with swarf as on this model there is no case filter. This caused the pump to jam resulting in no oil pressure and with no oil pressure indicator the motor internals were set free. So be careful when adding lipped or better seals to the tach drive on Commandos. They may stop the aggravating leak but oil down the cable to compensate.
Many times I’ve heard from owners, “but it wobbles at 70mph, it wanders.” Well these machines are fraught with problems but it can be rectified. I have fallen off Tridents, T140’s, A10’s and Suzukis ridden too hard, but not a Norton. The flexi flyer, as it should be called is designed with a hinge: it’s called isolastics.
What gives a tingle free ride @ 4000RPM, can also give a ponderous handling ride. Have you ever noticed when pitching into a corner, how the rear wheel comes with you a moment later? The isolastic design was good but flawed. In 1979 I made and fitted a third isolastic mount under the swing arm. My mate Neil and I pondered on this a while and reasoned that, with three mounts, the swingarm load would be better supported if triangulated. I made it a reality and it works great. I have done it to many of my personal bikes. You don’t need the top mount with the third bottom mount. The Norvil top mount helps with the STD 2 mounts. Three mounts reduce isolastic maintenance to almost zero. Anyway, even without this modification, by rebuilding your isolastics and adding extra buffers and shimming to zero, and then controlling tingles with the nylon nuts on the mounts, loosening a smidge as required, keeps the flop to a minimum. As the PTFE washers bed in, periodically tighten them. Obviously the best is to fit MK III type conversions if staying with the stock setup. The swingarm pivot pin wears (not the bushes, they rarely wear). As most Norton owners know, the swingarm pin becomes loose in the cradle. It is best is to remove the swingarm, drill 2 holes out wide, tap ¼-28, use plain nut with ½-28 bolt and weld nuts to cradle. Paint, refit swingarm with new bolts and pivot pin in place and tighten. End of story.
To fit an 18” wheel/tyre or not? Go ahead, it looks better, fills the void, offers better tyre choices and won’t affect the handling. I know some say it causes cornering clearance problems, but if you measure typical tyre sizes used, say 90/90/19 front and 4.10/18, there is no or little difference in diameter. I know a 90/90 front seems small, but when racing a track day once, I had a lot of head weave in corners and when I consulted a tyre tech, he said it was over tyred and we fitted a 90/90 and the shakes were gone. I only talk about my experiences on these pages not someone else’s. When using 110/80/19 on the rear, as you probably would, there is ¼ inch difference in diameter to the 4.10-18 or 110/90/18 using Avons. I prefer to use the rear shocks at least ¾ to 1” longer as it helps compensate for fat arses and keeps the bike more level and helps steering. A quality shock, tailored to suit your size, say a 100kg man, solo use, add ¾” & 130 springs. With an occasional passenger 70kg add 1”. This helps the machine from becoming a chopper when loaded. Check with the shock manufacturers. Low touring bars also keep some of the weight up front to help control wander. Fit a good steering damper if you want to but not before you make sure of wheel true, tyre condition, tyre type, pressures, wheel bearing condition, and wheel balances: all the things you should have done first. As Norton’s have notoriously stiff forks there are plenty of mods for damping, etc, but at least check the forks for tweaks and bent tubes. Sighting across the plane of the fork might reveal twisted trees. At least loosen axle pinch bolts, lower clamps, bolts and pump the fork up and down ½ dozen times then retighten all, preferably with fork pulled down. The last thing after you measure wheel alignment (string line) and tracking (tie a broom handle to front & rear wheels sticking up and sight) is to fit taper head bearings. Buy taper equivalent to the metric balls fitted. These balls cannot be preloaded and therefore cause steering to easily flop. Tapers should be fitted so that there is a minimum of preload, (not so floppy). It will probably solve the wander. Matter of fact, do it first, maybe you can live with the rest.