750 Combat - oil tank pipe configuration

Glyn

There is a diagram on the OldBritts site which may help.

There are diagrams for other Commando models as well.

Andover Norton parts search has much the same diagram although it's not quite as clear, but easier for ordering parts.

Andy

Glyn

Just to add that in the factory 1972 parts diagrams the lines to the oil filter are shown incorrectly connected to the wrong oil feed pipe from the oil pump.Don't you just love the traps out there for the newbies and unwary!

Andy

This particular drawing is indeed wrong. If you look at the drawings for alll the other years- 1971 750, 1973 750 & 850, and 1975 850Mk3- those are correct.

Sorry about that, the mistake is in the original 1972 parts list.

I tend to refer to the coloured drawing in the 850Mk3 workshop manual when I look the routing of the oilpipes up.

Joe/Andover Norton

Joe

Thank you for confirming this.

Andy

Your oil pipes sound correct from your description. Yes the breather does go to the oil tank filler cap neck and yes there should be a bit of pipe between your carbs.

But not all the oil gets pumped up the breather staying in the engine causing problems and the return side of the pump runs dry as well.

Previously glyn_jones wrote:

Thanks Andy, Joe and Dave.

I've looked at the diagrams and have used them to confirm most of the oil/breather pipes. Dave agrees with the way that my crankcase breather is connected to the oil tank and it seems logical to me too.

The main thing that confuses me is that I've read many horror stories where the combat engine is supposed to lose oil from the crankcase breather if it's revved hard for long periods and there are different mods that can be carried out to cure this problem. If oil is pumped out of my engine breather then surely it's just going to end up back in the oil tank?

Glyn

Hi Glyn. You have to tread carefully when listening to the horror stories relating to the Combat engine. The possible problem you refer to with oil loss at high revs is the mystery of oil hiding in the Combat crankcase, away from the pick up,if revved for prolonged periods over 4000rpm thus allegedly starving the top end and engine in generalof oil. I believe this cameabout when the bikes were used at speed for long periods abroad on the autobahns for example, others may correct me on this. Many have had there crankcases adapted to avoid this. I have run a 72 Norton with a Combat engine for the past 4 years with some long fast runs with no problems bearing in mind if your engine gearingis in interstate trim then at 4000rpm in top you would be traveling at a fair old rate of knots. As for the breather pipe set up the breather should go into the oil tank you will now if its wrong by the amount of oil under your bike.

Mark

Hello Mark....

Check out this article from the Old Britts site in USA.

I've done the mod to my crankcases with excellent result.

Had a lot of trouble with wet sumping before.

Colin

Previously Colin Fairall wrote:

Hello Mark....

Check out this article from the Old Britts site in USA.

I've done the mod to my crankcases with excellent result.

Had a lot of trouble with wet sumping before.

Colin

Hi Colin. I had seen a very similar article a few years back. John Dunn our resident Commando expert had shown it to me. At the risk of taking this oil pipe questionoff track I was then,and as I feel Glyn is now, a little concerned about our infamous Combat engine but in my unqualified opinion unless you are planning to race, or tour Europe at vast speeds along long and boring autobahns you need not worry undulyabout wet sumping and your engine self destructing every other weekend although it is important to be aware of this little annoying habit these engines canhave. I admit I was very close to having my crankcase modified but being an old git whom is happy to keep to the speed limits these days and any longer than an hour in the saddleand I would have to be surgically removed from the bikeI chose just to enjoy it as it is. It is a fantastic bike, better I feel than my MK111, lighter, simpler and morerevvy. I alsoprefer the gearing with its long legs in first and its casual engine speed in top. Its your choice Glyn but if like me you just wanta bikefor casual rides out then enjoy it.

Mark.

Had a nasty experience with a Combat type crankcase on our newly-built Commando racer about twenty years ago- it threw all the oil out the breather onto the track even though I only revved the brand-new engine hardly over 4.500rpm.

Norton themselves gave out a service information "for racing" but knew no doubt all "Combat" type crankcases needed the mod. You find the original service info under www.andover-norton.co.uk/SI Combat.htm

Joe

The mods as per the Andover Norton site work but can be improved, the driveside milling away of area E leaves the return side pump completely unprotected from debris from major blow ups. So instead drill a series of small holes through area E so the oil can drain but any large pieces from a blow up stay inside the cases. You also have to extend the timing side oil drain hole into the driveside and make sure the series of small holes intersect this extended hole. I have also bought a magnetic sump plug on an M12 threaded bolt and plan to drill up from below and have the magnet site in the extended drain hole so any smaller iron/steel pieces that on the properly sump plugged crankcases get stuck in the filter screen will be on the magnet for regular removal.

Hello John..

What sort of blow-ups were you expecting ??

During my mod and re-build I inspected my con-rods very carefully

and polished out any nicks or scratches which could be stress raisers and then polished the rods and the end caps.

I had a mate which put a rod through the cases. but he used to go screaming about at over 6000 rpm most of the time !!!

When I was in the IOM I found the useful power was above 4000 rpm.

ride safe !!

Colin