Hi all, I have owned an A65 rocket for over 30 years and probably due to the srm needle roller conversion, haven't had the engine totally stripped down in the last 20. Alas in march 2020 the big ends failed but now sorted and I was merrily rebuilding when I noticed that the breather pipe (and screw in union) above the final drive sprocket was missing. after researching on the internet and subsequent forums, I find no mention of this elusive part, nor did I find any mention of it in the bsa shop manual or parts book. do any of you folks have any knowledge/ tips/ where i could buy one? Otherwise, as the thread is standard BSF, I will head off to a plumbers merchant and see if I can make something work from there. Any advice is much appreciated. Simon.

I have worked on 1970 pre OIF and 1971 OIF A65 engines and on those there is just a plain hole for the cam breather outlet.. Are you saying that earlier engines had some fitting which would be strange given the angle of the hole in relation to the casting. Has your engine possibly been modified in some way?

Hi Ian, yep on mine it has a bsf thread ( i think 5/16")  My Rocket was manufactured in 1963. If I can find a fitting for it, I might be tempted to fit an ERG reed valve to it, do you have any experience with them? Cheers, Simon.

Hi,

I must say that having had several A65 cases in my possession I have never noticed a threaded breather outlet so this may have been done by a previous owner.  The only advantage of a pipe would be that any mist coming from the breather could be directed towards the chain or piped to the back of the bike.  The breather is timed so is in effect a valve that only works one way so an extra valve would not really have a benefit or could indeed inhibit the function of the breather even if only to a very small degree.

Dave.

Hi Dave, well it's a pretty early case, are the ones in your possession post 1963 or later? but what you say does marry up with the fact that the shop manual and the parts book make no mention of it  Cheers for your input, Simon.

Hi,

Not as early as '63 so perhaps they did have a threaded hole.  If so why was it not continued on later models? 
I suppose that the need was not there as an engine in good condition does not breath any oil out and maybe only the slightest amount of vapour.
I have high mileage A65 and as good as nothing comes out of the breather.

Dave.

 
I've got one on the bench that I've just looked at and cant find any thread. 1963/64
I must admit that I have never even noticed the outlet before. Having now seen it I must say its very tempting to run a pipe back to the oil tank. I'll give that some thought.

My A50 is breathing very hard and throwing droplets rather than occasional mist and I wonder how many of our untraceable oil drips are caused by the breather, and oil collecting around that outlet.

Mike

Hi Mike,

No doubt someone has done this but if running a pipe to the oil tank it would probably need its own inlet as it may cause a bit of pressure in the tank making the tank breather more important.  A 'T' in a tank breather pipe would probably be OK.
Droplets from the breather could be an indication of crankcase pressure being too high so may be worth investigating.  If it was an A10 I would guess that the cork behind the 'top hat' needs replacing but on an A50 it could be that the breather timing is not correct.

Dave. 

 

Hi. The A50 has been rebuilt and has probably only done 10 miles so I am hoping that its over pressure caused by the piston rings not yet bedded properly.

The point about the breather timing. I always understood that it was fully controlled by a very small spigot in the back(inner/fixed) plate and the the plate on the end of the cam shaft is also fixed by two "tangs" and with a spring to hold it in its rotational position. So I dont actually see how it can be the breather timing can be altered. Always a willing learner.

I didn't re assemble the bottom end and my fear is that the spring has been omitted.

Mike

Hi Mike,

Yes if fitted properly the A50/A65 breather should not come out of position but as you say, with only 10 miles covered then some bedding in of the rings still to do.  I suppose that waiting for a few more miles to be completed will not do any harm and will probably solve the problem.

Dave.

 

I hope its that simple. My fear is that the guy who did the bottom assembly omitted the spring. It would be extremely unusual for this particular fella to make sush a mistake.

Time will probably tell Oh! hum

Mike

Hi Rocket
I don't think the factory fitted one as standard. It (was) a plain hole on both my A65s and on my Royal Star. However, on the A50, I have fitted such a pipe.
I've seen a few where the owner has pushed a piece of suitably sized copper pipe in there, maybe loctited in. But, I drilled out the hole and tapped it 1/8 BSP and found some fittings on ebay that suffice.
My advice, as yours is already tapped, would be to get a 5/16 BSF bolt drill it out as large as you dare and cut it off so that it protrudes about 1/2" to 3/4". Find a suitable piece and length of flexi pipe and run it out the back and under the rear mudguard to exit at the rear.

I put a tee piece in half way up as it rises with the mudguard and a drain pipe (tail) runs downwards. I have plugged this tail with a bolt. This acts as a small 'catch' reservoir purely to see how much actually comes out over what mileage. If it's peeing out then I'd rather know sooner than find out when the rear wheel loses grip as the tyre is soaked in 20/50!!!

The problem with leaving the hole as is, is that the angle the oil comes out at doesn't point at the final drive sprocket but more at the front of the gearbox. This keeps that part of the cases nice and shiny underneath all the crud that the roads have thrown at it but it also then drips the oil off when stationery much to the amusement of modern bikers "You can tell its old British, just look for the oil." Oh how they laugh..........

Better to do it now. Whilst the engine is out. Much easier than trying to get to it from underneath when its in the frame.
Good luck!
Chris

when I rebuilt the the two Thunderbolts, the 1966 didnt have the spring and disc but the earlier 1967 rebuilt one did. Ive brought a spare pair of bits just incase for any future rebuilds. they were both rebuilt within a year of each other and both ridden at the same time, no noticeable difference in misting or fumes.

 

My thoughts are that if I do run a pipe, I''l either run it to a point above te oil level in the oil tank via a brazed spigot or run it up to the air intake via the filter housing.

Mike

Hi Mike,

It will be interesting to see how a connection to the inlet goes. This was done on lots of bikes for reducing emissions.  I wonder how it will affect combustion.

Dave.