4G Rocker box breather?

[Pete.Silson]

Does hole in the centre of a 4G rocker box lid serve any purpose other than to keep the underside of the petrol tank free of rust? When the engine is warmed up I find that I get a steady mist of oil from the hole - enough to eventually get onto the cylinder head resulting in a smokey haze every time I come to stop at traffic lights.

I have temporarily blocked the hole with a wooden peg and this seems remedy the oil loss but I assume the hole is there for a reason so I was thinking of threading the hole and routing a breather pipe to somewhere more useful - like the chain. Any suggestions.

Pete

[paul.jameson]

Just leave it alone. It allows steam out but very little in the way of oil follows the steam. You can always wipe the top of the rocker cover if you ever find it necessary.

[paul.jameson]

I attribute the "smokey haze at traffic lights" on my 1936 Square to the fact that it contains the pistons I removed from another Square about 25 years ago. I am coming to the conclusion that two of them may well be well worn but the other two are absolutely fine. And the bike produces nowhere near as much smoke as the engine I took them out of was prone to do.
Leave it alone for at least 1000 miles on running in oil and then another 1000 miles on normal oil. By that time you might have found out whether there is a need for anything else.

Incidentally, in case anyone reading this has not so far guessed this - I am a tight fisted Yorkshireman who believes in getting what he can do out of parts, particularly original parts, before I replace them with what are often inferior modern pattern parts.

[Pete.Silson]

Paul

Just leave it alone. It allows steam out but very little in the way of oil follows the steam. You can always wipe the top of the rocker cover if you ever find it necessary.

When I say a "mist of oil" from the breather I am talking about enough oil (after 20 miles or so) to be running down the rockerbox sides and dripping onto the cylinder head fins. The haze I mention is not from the exhaust but from this oil burning off the cylinder head. I originally thought the problem was due to leakage from the rockerbox gaskets but these are oil tight and anyway the problem stops when the hole is temporarily blocked. When first assembled I did find that the rocker oil feed was blocked (which might explain the original snapped rocker shaft). I cleared the oil feed pipe by running it through with a throttle cable inner and I now have plenty of oil getting to the rockers. Should there be a restriction in the oil feed pipe? I was wondering if I had opened out the feed pipe too much and was getting too much oil in the top end. Apart from this the engine is surprisingly oil tight (which is more than can be said of the gearbox - but that's another story).

Incidentally, in case anyone reading this has not so far guessed this - I am a tight fisted Yorkshireman who believes in getting what he can do out of parts, particularly original parts, before I replace them with what are often inferior modern pattern parts.

I wholeheartedly agree with reusing serviceable parts if possible. I reassembled the engine with original bores, pistons and rings and without deglazing the bores. The only new parts were four exhaust valve guides, piston circlips and split pins for the big-end nuts. I did get new countersunk screws for the sludge traps but these were so poorly made that I binned them and reused the originals. The engine does sound a bit piston-slappy but I am pleasantly surprised how little exhaust smoke I am getting.

Leave it alone for at least 1000 miles on running in oil and then another 1000 miles on normal oil. By that time you might have found out whether there is a need for anything else.

I did not use running-in oil since I didn't really see the need with no new components installed. I have been running semi-synthetic 10W40 from the start although I have fitted an oil filter and everythings seems OK so far. Time will tell.

Pete

[chris.shearwood]

Hello Pete,
To get that much oil out of that hole in the cover of the rockerbox something is not right. I have the same size hole in the rockerbox cover of my Sq4 and I would normally find just a smear of oil around the hole after dozens of miles. I do recall seeing a plume of steam coming out of the hole after start-up on a cool morning so I think the vent is beneficial. I've just been out to the garage to measure the hole in the "Oil stud for swivel conn." (1012-37) that connects the oil feed pipe to the fitting (1015-37) which is screwed into the rockerbox and although I couldn't find the exact drill bit to measure it, it appears to be around .055". I'm not talking about the hole in the end of the adaptor but the one which is covered over when the acorn nut is screwed on. I think it is this hole which provides restriction to the oil flow.
Regards, Chris

[paul.jameson]

You are definitely getting too much oil to the top end. Both my 4Gs have had this hole and neither has ever put more than the tiny amount of oil you can easily wipe off with a rag - and then put the rag in your pocket.
I wonder if the blocked oil feed pipe might be a clue? Could this have been blocked for some time, perhaps, leading to high wear on the rockers and shafts to the extent that they now leak lots of oil? Running the engine with the rocker cover off might prove illuminating here.
Is the pressure relief valve working properly? My bike runs at a pretty constant pressure between 20 and 30 psi once it has gone through the initial warming up. If you are getting a higher pressure than that consistently, suspect the pressure relief valve. If this isn't working, the excess oil might well be coming out via the rockers. You have got the oil feeds the right way round haven't you? The small diameter pipe feeds the rockers, the large diameter one feeds the oil gauge.

[Pete.Silson]

Paul

I wonder if the blocked oil feed pipe might be a clue? Could this have been blocked for some time, perhaps, leading to high wear on the rockers and shafts to the extent that they now leak lots of oil? Running the engine with the rocker cover off might prove illuminating here.

The rockers and shafts are quite sloppy. The replacement I got for the broken front rocker shaft (kindly donated by a club member) was quite pitted but works perfectly adequately. I have run the engine without the rockerbox lid and I do get a fair amount of oil splash from the rockers. This was with a cold engine and I suspect that it would increase as the oil warmed up.

Is the pressure relief valve working properly? My bike runs at a pretty constant pressure between 20 and 30 psi once it has gone through the initial warming up. If you are getting a higher pressure than that consistently, suspect the pressure relief valve. If this isn't working, the excess oil might well be coming out via the rockers.

When I first ran the engine the oil pressure was quite erratic so I fitted a new ball and spring to the relief valve and set the pressure at 45psi as per Pitman book. With a cold engine the pressure remains steady at 45psi from tickover to full speed. When the engine is fully warmed-up the pressure drops to 20-25psi at tickover but rises back up when riding and stays around 40-50psi.

You have got the oil feeds the right way round haven't you? The small diameter pipe feeds the rockers, the large diameter one feeds the oil gauge.

Yes - narrow bore pipe to rockers.


You are probably correct that more oil than normal is getting to the rockerbox but, apart from the leakage from the breather, is this necessarily a problem? The excess oil drains down to the cam followers and that must be better for the camshaft. I am still considering a simple expedient of running a hose from the breather hole to direct any oil away from the cylinder head - maybe tee-ing into the oiltank breather hose. I also don't think excess oil is going down the valve guides since the plugs appear to be quite clean.

Interestingly the 1939 basket case 4G engine I got last year had a small brass tap fitted in the rocker feed pipe. Maybe this was an attempt to remedy a similar issue?

Pete

[paul.jameson]

When you had the engine apart, did you take the cam follower guides out of the cylinder block and clean the drain holes through them? I'm just thinking that if they were partly blocked, you might get a build up of oil in the rocker box after a time.

[john.whiting]

I think you must have excessive blowby from the pistons to force the oil out.The crankcase is being pressurized blowing out the oil mist......I had an iron S4 years ago with the same problem,because in those days there were no spares.(that I could afford)....run with the cover off ,the motor was full of blowby smoke.As you mention,I added a breather to keep oil off the motor.....I also put a small flat baffle inside the cover ,so oil couldnt be thrown out the hole directly.Many engines have this arrangement...I read somewhere that the iron head was arranged so that the valve springs were in pools of oil just lower than the tops of the guides,the idea being to heat and agitate the oil and boil off any condensation ,which had caused problems with earlier motors,especially the Matchless Silver Hawk.

[Pete.Silson]

Thank you all for your advice/comments. I suspect the issue may be a combination of a number of factors including a bit of blow-by from the old bores compounded by additional oil getting into the rockerbox from sloppy rockers. I don't think the follower guides are blocked since these were removed and thoroughly cleaned along with the rest of the engine internals.

I can understand the comment about "boiling off condensation" since, even after a long fast run, the oil doesn't seem to get particularly hot. This suprised me somewhat having heard dire tales of overheating iron engines.

Maybe, in hindsight, I could have gone down the rebore/regrind/club rods route but I was curious to know how the engine would run with all its original parts intact. I'm sure I can live with a bit of oil, a few rattles and smoke at the traffic lights - it just adds character doesn't it? I will probably follow John's advice and live with it and fit a breather pipe with a baffle to reduce direct splash.

Next job - try to keep more of the lubricant in the gearbox and not on the rear wheel!

Pete