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[Andy C]

I took my recently re acquired 612 out for its inaugural run this weekend, a few teething troubles as expected but generally performs reasonably well, however. It is fitted with our hosts oil tank breather and during my previous ownership I had never experienced any issues with the engines breathing, for some reason it is blowing oil our around the breather pipe where it connects to the crankcase. All breather pipes are clear, and no duckbill. It is not burning oil and bore checked out as OK so should not be blowing past the rings. It looks the engine has been apart so will be checking later today to see that the pumps have been fitted in the right place – scavenge at the front! I’ll also check that the gasket in the timing cover is not partially blocking the oil ways – things which I understand may cause this sort of problem. Anyone any suggestions what else to look at?, oil level is correct by the way. Apart from that it goes pretty well, not quite like it used to, but I guess if there is a breathing / oil issue that may be part of the reason. It also looks to be running pretty rich – sure it is not oil related and having looked at the needle it appears to be badly scored in a couple of places so new needle jet / needle / main on order.

[Bullet Whisperer]

Look out for blowing between the head gasket and any barrel stud holes, this can cause loss of power and compression, the lost compression finding its way into the crankcase via blowing the base gasket internally and causing excessive breathing. I have also seen a loose barrel liner cause the same, worth checking that as well, if you are planning to strip the top end. I also fit proper one way valves to the breather pipes on my machines, which make a world of difference.

[Andy C]

Hopefully not a head gasket issue – fitted a composite gasket and was very careful to make sure that everything was clean before fitting and I torqued it down properly. It is a new alloy cylinder from our hosts so hopefully not a liner problem – it did do it with the old iron cylinder anyway. No sign of anything coming out past the base gasket, it seems very localised to the cast in breather stub – wondering if there is some porosity in the casting or a small crack. As I say, it never used to do it. What are the benefits of the 1 way valve, and is it a simple “in line” valve?

[Bullet Whisperer]

Hi Andy, I wish I was capable of posting pictures on here! The one way breather valves I use have an alloy body, which can be dismantled and contain a disc which is lightly spring loaded. They have an 8mm bore [smaller and larger sizes are available and I buy mine from a motor factors van which calls by occasionally for less than £10 each. You can pay over £20 for the same thing, if you buy an anti wet sumping valve for a Norton Commando! I cut the breather pipes close to the engine and fit these one way valves to the short bit of pipe left on the outlet, then fit what's been cut off on the outlet end of the valve, with any duckbill removed. The composite head gaskets are the most prone to internal blowing, a chunk can break out adjacent to a stud hole, causing what I have already described. The stud hole above the original breather location sometimes breaks through into the breather outlet from the crankcase and if there is a blow by the head gasket to this stud hole, it may not be obvious at first. Regards, Paul.

[Andy C]

I would be surprised if it is the composite gasket as I have only covered about 75 miles with it fitted, and I re torqued the head after 50 miles so don’t really want to pull the head off just yet. I’ll investigate the pumps & timing side gasket first. Thanks for all the info.

[Carl C]

Hi Andy, Until my modification which loses no oil on my 612 I had a very similar issue with oil pumping from the engine through the duck bill breather so fitted the OIL BREATHER MODIFICATION KIT part no. 90060 after drilling the holes out to 9mm, then I connected the crank breather into the lower spigot on the breather and the upper spigot to a 0.3L Universal Oil Catch Breather Can Baffled Aluminum Reservoir. The can has an input, output and a breather spigot on top which I used a hose to the filter supplied with the can. The input to the can was from the crank and the output fed a hose over the the rear wheel frame to the number plate. No oil leaves the hose over the rear frame. The can was attached with a home made bracket and since I went to all this trouble the engine breathes without oil loss and you can really hear the engine pumping when lifting the oil filler cap. I hope this helps. Carl

[Andy C]

Carl - I have 90060 fitted to mine and with the filler cap removed as you say you can certainly hear the engine "breathe". I checked pump installation last night and they are fitted correctly. Engine seems to have really good compression so I don't believe that the head gasket is leaking as suggested by Bullet Whisperer. I am going to check the return pump filter tonight just to make sure that is free. Enlarging the holes in 90060 might not be a bad idea as they are a bit on the small side, mind you so is the bore of the cast in breather on the crankcase.

[Adrian]

If bore of the cast in breather on the crankcase isn't that big, presumably our hosts had no real incentive to fit bigger bore inlet/exit pipes in 90060. Late Redditch and early Indian Bullets had a breather union fitted by three screws, part no. 41540, if you were to grind off the cast-in breather stub and form a large enough flat surface you could possibly fit one of those, or make your own with, say, a 3/8" BSP fitting on.



The other alternative would be to plug the breather stub and drill and tap for a suitable BSP fitting right next to it, so it is fed crankcases gases via the same crescent-shaped recess in the l/h crankcase mouth that feeds the current breather.



The 612cc conversion will of course give whatever breather you have more work to do.



A.

[Andy C]

Update. Put the duckbill back on - made matters worse, much more oil comming out arouund the breather pipe, also some from around the tappet inspection cover. Not yet checked the timing cover gasket to see if the oil ways are partially blocked by the gasket, job for tomorrow. Just wondering if perhaps the rings are shot, when I had it apart I checked piston bore clearance and it was within tolerance, but did not look at the ring gap. Would a worn oil ring cause this problem ? No signs of it burning oil, no cluds of smoke on the overrun. Good news is that it pulls like it used to now that I have put a new needle and needle valve in it - running way too rich before. If only I can fix this breathing issue. Anyone any further thoughts?

[stinkwheel]

Oil passing the tappet cover suggests the timing side is pressurised. How? Gasket blowby into the pushrod tunnels? The only time I had this happen on a bullet was when the breather was physically obstructed by a huge slug of mayonaise but that was one with the "late" breathing system with the hole into the oil tank. So an obstructed breather pressurised the oil tank which in turn pressurised the timing chest.



If you have a "standard" crankcase breather below the barrel, how is the pressure getting from the crankcase to the timing chest?