A short trip to the petrol station, 5 miles down the A46 at 65 mph and then 10 miles on B roads and a bit of stop and go in our village for about 15 minutes Suprisingly comfortable, nice low pegs, vibration less than expected. The engine ran perfectly and always returned to a steady idle when stopped. Engine starts easily and runs smoothly although I did not push it. Dunstall front disc brakes worked and I didn't expect them to, quite basic but functional meaning not a lot of feel. When I first went out on it the clutch was slipping in high gear (the bike has been sitting for a year or two) decided I would continue and just go easy and ride around it but after a few miles it seemed to stop slipping.....time will tell.
The one issue that did occur is a bad oil leak in and around the left side rear of the engine. I suspect it's a crankcase breather issue. A little unsure of the source but suspect it's the hose to breather outlet on the engine itself , the copper pipe that exits on the left rear of the crankcase.
The previous owner had just built the bike and had incorporated a PCV valve between the crankcase breather outlet and the oil tank in an attempt to improve the crankcase ventilation but not allowing tramp air back into the crankcase as the pistons rose up in their bores. A well made item (brass PCV valve) but was slightly restrictive when tested so I've removed it and piped straight into the oil tank from the crankcase breather vent. I'm interested in member comments re this issue. Once I wiped the bike down and it was not running there were no oil leaks not even from the primary chain case.
All in all I'm very pleased with the initial result and once the oil leak is resolved will venture further a field.
All comments and suggestions welcomed.
Engine breather
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The earlier disc brakes were…
The earlier disc brakes were fitted with larger bore master cylinders relative to the slave, so the RGM (or other) small bore type might improve the feel of the brake. The later Norton oil tank had a "froth tower" arrangement where the engine breather arrives on one side of the "tower" and the exit pipe goes to the chain. I've never had tank overflow. With a non standard tank, maybe you could try similar?
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Master cylinder
Good to see you out riding that beautiful bike. My mate at work loved that of pic of your red Dunstall 650, any comparism with your current bike?
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Once again, thanks for your…
Once again, thanks for your helpful comments gents please keep them coming. Neil, it's been 45 years since I rode the red Dunstall so recollections are a bit fogged. The feather bed feels very stable compared to my 1960 Triumph with it's slightly steeper front forks when out on the road at speed.
Just want to make sure I've got the function of the standard crankcase breather right, if not please correct me. As the pistons go down the timed breather valve opens thus relieving any positive crankcase pressure to the oil tank and then to atmosphere via the oil tank vent line. As the pistons rise in their bores the timed breather valve closes thus causing a low pressure or slight vacuum in the crankcase, this cycle should not cause oil leaks in the up stoke as it is trying to draw air into the crankcase and not let oil out. If this is true my problem is during the downstroke, by removing the extra PCV valve that caused a slight restriction in air getting to the oil tank the situation should have improved. Will test it out today.
I am convinced that the major reason British twins leak oil has nothing to do with vertically split crankcases but mainly to do with two pistons rising and falling together and the inability to adequately relieve the positive resulting crankcase pressure that pushes the oil out of the engine. As I have requested, comment please.
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It's quite likely..
.. that the engine has wet sumped while standing and some of the excess oil in the crankcase has emerged via the breather. I'd just wipe it off and see if it reappears while using the bike more regularly.
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And I said it all so confidently!
Well just back from the ride out. Oil leak still present. It does appear to be more on the left side of the engine and maybe from the barrel/head junction. Ian, the oil feed has an isolation valve that is always closed when the bike is not running (plan on changing to an electrical interlock type that prevents the bike from starting unless valve is open) but I had the same thought and will pull the brass drain plug once bike has cooled to see what comes out of the wet sump.
Is it possible that an oil gallery between barrel and head is leaking? Don't have a manual as of yet and obviously I need one.
Now the good news, bike runs very well and clutch is not slipping, pushed it a tad harder today. Your comments please.
I do apologise if I appear to be hogging the forum ,it's my obsessive nature that sometimes offends
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You shouldn't need a pcv valve in the breather side. The oil tank breather/overflow should be piped to the top run of the rear chainguard. Overfilling the oil tank will result in oil over the left side of the bike (and rear tyre). I'm sure most of us have discovered that at some point...