Non standard oil tank on a -69 Commando

When looking for oil tank spare parts for my -69 Commando I discovered that the tank does not appear in any of the spare part documentation I have seen. It appears to be a none standard tank.

The bike had been fitted with a bunch of Dunstall parts in the early 70's and my guess is that this might be one of the 'improvements' the previous owner had made.



The 'dome' on the top of the tank had been covered with 'plastick steel' compound which has started to peel off. Underneath the compound i discovered three holes.



The top left hole is connected to an internal pipe which exits at the back of the tank.



The other two holes are just vent holes between the tank and the atmosphere.

The internal pipe appears to have (it is very difficult to see) some vent holes just underneath the dome ceiling.

Has anybody seen this type of tank before?

Why would the previous owner have drilled the vent holes in the dome and then covered them up with plastic cement.

Would the recommendation be to seal up the three holes and focus on solving the crank case ventilation issues in one of the several othe recomended ways?

Any suggestions would be welcomed.

dda in Sweden

dick danielson said:

Has anybody seen this type of tank before?

Click to expand...

It's a standard '69-'70 750S or early Roadster tank.

L.A.B. is correct. It is also an early model tank. The later ones had the breather from the engine going into the tank beside the 'top hat'. I'm not sure when they changed in '69.

I can only assume the PO was trying to improve the motor venting, as the early 68-70 models had the timed breather out of the left side of the crank. It usually went to that tube that sticks out of the 'top hat' unless it is a later tank and it went into a tube beside the 'top hat'. I have not personally seen a later one, I would love a picture of one of the later tanks. At any rate, the PO was probably trying to vent the tank better than it was originally, because most of the early bikes would leak out of the hole in the front of the tank, the one you can clearly see in the last picture. That would drip down on the gearbox and make a mess. Several things help. As Mark says, don't put too much oil in the tank. Somewhere between the upper and lower mark is fine, for sure don't over fill it, and be aware of sumping.

Let me try to explain the tubes in the tank. The hole in the front of the tank in the last picture goes straight back, curves up and ends up in the 'top hat' thingy, that tube that goes into the 'top hat' just goes in and ends just inside the 'top hat'. I conjecture that oil from the timed breather on the crank, especially if it has sumped and all the oil is in the crank, is pushed up into that tube, and some amount of oil is pushed up into the 'top hat' where it splashes into the tube that connects to the front of the tank, which is the breather for the tank to atmosphere and the oil drips out.

It looks like to me that the PO was drilling holes in your top hat to find the vent tube and vent it somewhere else. That's my guess. I have entertained the idea of cutting the top of that thing off and re-arranging the tubes.

Nelson and I surmise Norton changed the location of the crank breather to alleviate this situation, but it is all conjecture. Nelson bought a newer tank to see if it helps the dripping from the front hole. I plan to remove the tube into my top hat and replace it with a bent tube that bends down and dumps the oil into the tank without splashing into the tank breather tube.

I hope I'm making sense, but I'm not sure. PM me if you want lots more info.

Dave
69S

Hi Dick I have that exact oiltank on my 1970 Roadster don't think I waste time on your tank looks pretty beat up. I see them on Ebay alot for not much money! I am running a single carb on my bike with after market air filter I tapped the small hole in the front of the tank srewed in a 1/4 in. nipple and ran a hose to the ground no more dribbles of oil all over the trans Ziggy

OOPS make that a 1/8th nipple! Ziggy

Thanks guys, I really appreciate your help.

I never realised that the firts batch of Commandos were fitted with this type of tank. All the spare part catalouges that I have seen (including the on-line one at Andover Norton) show the side mounted tank only.

Is there a spare part list out there that covers the -69 model?

I agree the tank looks a bit beaten up, but its actually quite sound. I'll have it soundblasted and see what it looks like.

The idea of fitting a pipe to the lower vent hole which carries excess oil past the transmission sounds like a good way of dealing with the problem of airborne oil residue.

Filling the tank to the half way mark only is also something I'll bear in mind.

Once again thanks for your help

dick danielson said:

I never realised that the firts batch of Commandos were fitted with this type of tank.

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Not the first, as the original Fastbacks and 750 'R' models had a different tank.

dick danielson said:

All the spare part catalouges that I have seen (including the on-line one at Andover Norton) show the side mounted tank only.

Is there a spare part list out there that covers the -69 model?

Click to expand...

Andover Norton parts book 06-3065.
Unfortunately the '69-70 parts supplements included do not contain any drawings or diagrams of the 69/70 parts.
http://www.andover-norton.co.uk/JRP/JRNORTON.HTM

dick danielson said:

I never realised that the firts batch of Commandos were fitted with this type of tank. All the spare part catalouges that I have seen (including the on-line one at Andover Norton) show the side mounted tank only.

Is there a spare part list out there that covers the -69 model?

Click to expand...

Yes, there is: 06-3065 but without illustrations for the 1970 bikes. There are quite a few differences between a 1970 and a 1971 roadster (which is an S with low pipes): Oil tank as you just found out;Side covers; Yokes (almost identical to the Dommie/Atlas ones except for the front lamp bracket fixation); Lamp attachment aka the Halo; Seat .....

Look for 1970 in the forum search, it will turn up tons of hints. Get yourself one of the succession lists (I got mine from Les Emery) as the early parts follow the old part no. pattern. With these tools and the ANIL web shop it is feasible to identify most parts - I'm doing exactly this atm and it takes a hell of a time.



Tim