650SS engine breather back to oil tank?

I wouldn't run the pipe direct to the back of the bike. It could get very messy. As I understand it, the breather pipe should go to the oil tank, then the oil tank breather goes to the rear chain.

I have a 1964 650SS engine, but in a wideline frame, with an earlier oil tank, which does not have the inlet pipe; just the breather outlet. When I had the engine stripped, I was advised by Norman White to remove the timed breather, cover the outlet with a blanking plate, and drill extra holes in the right hand crankcase into the timing chest. He then provided me with a large bore breather fitting; basically a part-threaded tube with locking nut, for which he advised me to drill a suitable sized hole in the back of the timing chest, alongside the magneto; a bit tight, but do- able. I then attached a suitably large bore pipe to the outlet, took it to a catch tank between the rear engine plates, from which another pipe then goes to the back mudguard, as you described. That pipe must not of course dip into any oil in the catch tank, as it will hose it straight out onto the back of the bike! It seem to work. The oil tank breather tube goes to the rear chain.

His explanation is that the timed breather simply does not allow the engine to breath sufficiently, hence the requirement for a large bore pipe. Presumably using both breather systems together does not work..... I believe this is the final breather arrangement used on Mk 3 Commando's, although I could stand corrected on that.

I had wondered whether a one-way valve in the large breather pipe is advisable, and would appreciate the views of others on that.

Ian

On my Atlas, there is a pipe from the engine breather to the oil tankand an oil tank overflow which is piped to the rear chain guard - the standard set-up. It works just fine. Well, except if you grossly over-fill the oil tank when you send the excess oil over the rear tyre. Not the bike's fault!I think Norman White's modification is only really necessary if you have excessive blowby. A rebore would be on the cards in that case.

I have a 1964 650ss engine in a slimline, built from bits.

I got fed up with a puddle of oil on the floor from the breather pipe when starting after a couple of days. Then I remembered an oil tank I had that came with a breather in. I had the tank chemically stripped, sealed up and powder coated. No more oil leak, from there at least.

Reporting back when I get the bike back on the road. I hope the 1960 99 does not drop so much oil from the breather.

I think Norman White's modification is only really necessary if you have excessive blowby. A rebore would be on the cards in that case.

Not that, really, because Norman has always raced, and built race bikes, so his engines aren't knackered! It is a mod. that Norton came to, bit by bit, with the Commando's, so is worthwhile considering, whilst the engine is stripped, but for normal light use, the standard set-up should be fine.

True enough Ian. Normal light use? Hmm, well, I always start out with the best of intentions, but the bike never feels right until it has been wound on a bit, so best intentions fly out of the metaphorical window. I have only raced 88 & 99s, in both cases with the standard breather, without problems. But I accept that the 750 and upwards engines may well benefit from better breathing under race conditions.

I tend to ride mine 'briskly', too! Schools of thought change with time, of course. I took these pictures of a 500cc Dommie Racer in the race paddock at the IoM Classic TT this year, and had a long conversation with the owner about engine breathing, when I caught up with him at Jurby a couple of days later.. You will see that it has 3 breathers; the big bore one I described previously, and one from the rear rocker cover. The 3rd is from the timed breather. As well as extra holes drilled in the timing side crankcase half into the timing chest, he has drilled extra holes in the drive side crankcase through to the gallery on the end of the camshaft which leads to the timed breather. I dare say he is using a 6-start oil pump.

Ian

i have a 1961 88 and that breathes into the oil tank and then to the chain but the rear end of the bike is always messy, and the oil discharged is frothy. so i think the breather is not clearing the moisture from tengine quick enough. my job this winter is to strip it down and investigate.i feel it may mean a rebore as was mentioned derek