Hitchcocks Forum

Please please someone help me solve my 1960 Connie from heaving oil out the breather. Have tried everything.... new pumps properly fitted including high capacity scavenge side only, new engine cases just fitted, all breathing mods tried including Soltau high capacity & Bunn, new piston and rings. This engine has been meticulously rebuilt a number of times and this problem persists to the extent that on a 160km run it threw 600ml out the breather. The return to tank on cold start up pumps solidly until it clears the cases then becomes intermitent as it should but on a run the motor is building up with oil and passing out the breather and up past the rings sometimes. Any ideas out there?
Desperate Mike

For the bike to be puking oil from the breather there are several possible issues, but what breather is currently fitted and how is it plumbed?
Regards the Bunn breather, if still fitted remove it. The valves are very problematic and at times cause more problems that they are supposed to fix. Overpriced and Over rated. 'OK' while they work, junk when they dont...


Why did you disconnect the original breather off the drive side to the top of the oil tank?


That was intended as an alternate oil return to the oil tank...


Have you checked the breather valve inside the end of the crankshaft nut?


Is the vent pipe from off the top of the primary cover open?

The sump is not being cleared of oil fast enough, which usually implies a blockage in the return lines, which is common to find the oil ways obstructed with wee bits of shattered oil ring lodged inside them, only problem is you really do need to strip the cases to get at one particular oil way with LONG drill bit...
Next problem is dealing with the oil that is being forced out of the breather: you need to vent the oil tank better; Ala Mk1 Interceptor, with a vent off the oil tank and to the rear. You will also need the Inter Breather from the crank case to the oil tank with a Banjo fitting.
Part of the issue with oil return from the sump is from oil passing out of the cam shaft tunnels and into the sump, instead of running into the timing chest...
But fitting the larger return pump should have addressed that?


Have you lapped the new return pump disc into its seat?


Is the pump disc spring strong enough?


Has the RH exhaust tappet been removed/replaced? if so then MAYBE the oil drain from the exhaust cam tunnel is blocked and ALL the oil is heading to the sump via the cam tunnel windows and the oil holes in the bottom of the barrel?


IF the oil way from the sump up to the return pump is blocked, there is a 'dodge' that will bypass the internal drillings: by fitting an external oil line from the sump to the pump suction! But it is only a temp dodge, as the max size of the oil way is limited by the size of the threaded plug that seals off the end of the suction drilling...

Thanks for the reply Tim was not watching the thread as assumed that UK was where the info would come from.
Soltau high capacity breather fitted currently.
New cases with original tappets already in place.
Oilways perfect.
New cases have no fitting for breathing into top of tank as old cases did. This is also found on other cases I have of same era so not unusual. Breather currently carried out to rear guard to spew onto following riders.
Crankshaft breather welded up as per breather mods when I got the bike years ago as horror stories of exploding primaries was enough to spur me on to do that. I am reluctant to reinstate this breather as I doubt it would make any diff. There is another Big Twin over here set up like mine and it has no probs.
Pump disc carefully lapped and has new spring.
There is no problem with the oilways I have just put this engine back together and the issue has always been there even with the old cases with oil tank return.
I reckon I have struck out all your suggestions Tim but thankyou for trying.

Forgot to mention that it almost seems as though the breather is too efficient and for some reason in creating a massive negative pressure in the cases thus making the scavenge less efficient when the motor is hot and running at high revs as opposed to cold and at idle when it seems fine. I might remove the valve and see what happens ?

Hi, for my 2 pence worth if it is breathing heavily then the pressure can only be coming from combustion gasses blowing past the rings And into the crankcase. What pistons do you have fitted? And what clearance have the bores been honed to.
my super meteor was wet sumping last year and also filled the primary case with oil very quickly. I found the cause to be a destroyed crank main bearing which in turn had bent one one of the conrods by 7thou, this also had a side effect of lining up the piston ring end gaps so that the combustion gases had a clear path down the barrel. This has caused me a massive rebuild cost this winter. I have fitted our hosts forged ally conrods and a set of forged JE pistons and 3 piece oil scraper ring to help combat any high oil consumption and crank pressure in future. ed

That is a very comprehensive and helpful reply from Tim.

The only thing I can add is that if the timing cover has been replaced at some time in the past the scavange drillings in the crankcase and timing cover are very small and dont always line up exactly causing this problem, no matter how good the scavenge pump is it cannot pull enough oil through return on higher revs, you can open the return oilways up if you wish but I have found that most times all you need is to countersink the holes lightly in both the crankcase and the timing cover also slightly increase the size of the hole in the gasket also be very carefull if using a sealant on this gasket.

Mike, if you've heard this, apologies: are you over-filling the oil tank? Ignore any markings on the dipstick, I find my Twins run best with the oil level about half way between High and Low. You will need to keep an eye on it as you won't have so much leeway on capacity. I tried the Soltau breather on my Meteor but it didn't work, to be fair Bill said it might not cure every motor! My Meteor (1953, not nearly as highly tunes as a Connie,) was completely dry when I got it but had a stripped rocker cover stud. I fixed that and it's leaked ever since! I got leakage under control by removing the breather discs from the base of the barrel and adding a rubber pipe from that pipe to the chain up to a catch bottle mounted under the saddle. A little oil collected there but once it had puffed a few millilitres into the container it stayed free. The pipe leading upwards maybe acted as a separator? I'm tempted to make a breather off a rocker cover replicating what was there before but some have suggested this will starve oil from the rockers(?). My Interceptor just uses oil rather than leaks it, even with modern pistons and valve seals! REgards, Mark

I'm with Mark on this. When I rebuilt my Connie (1959), my first ride sloshed oil over the rear tyre through my oil-tank breather pipe mod. Much head-scratching later and I simply lowered the oil level as per Mark's post and problem solved. Good luck, Stephen

Many thanks for your input guys. Here in Western Australia there are only 2 or 3 blokes with in depth knowledge of the twins and I am one of them so when we are stumped it's good that you are around.
Barnes: everything is new with standard 10 thou piston and rings as supplied from our hosts. They are not high compression and were fitted to specification. So I reckon that is covered.
Dennis C: I reckon you are right as I sleeved and realigned the hole for the oil feed Quill to the Big ends and I did check the oil holes for a match but was pretty superficial about it so will have a closer look.
Mark & PO: I am aware of this oil level issue but mine heaves that much oil out on a run it is well off the dip stick on return home. I assume it will just keep spitting it out until it runs dry.
I have tried a breather from the rocker cover in one of my attempts along with every other permutation. I am not joking when i say I have tried nearly everything. A set of SM cases I have has an original breather with no provision for the Pen steel disks ( ie no valve at all ) and a short stub to take a push on hose. I will try this alone with my zip tied catch can on the rear number plate, rejig the holes on the timing cover and fingers crossed. There may be hope for the Antichrist as I have come to regard this bike by now. I have had many bikes of all kinds including a Meteor ans SM but this one has truly done my head in.
Cheers Mike

Hi mike. I rebuilt a freids mk1 interceptor with standard pistons at the standard bore clearance from our hosts and it Blew out oil from every orifice Plus a few i didnt know existed. I then rebuilt it with the JE pistons which run a 3 1/2 to 4 thou clearance and a ring gap of 15 thou and it has cured it. He has done 350 running in miles and the bike is as dry as the day it rolled out my shed. Hope you cure it. Ed