Author Topic: 250 comet petrol tank  (Read 7991 times)

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Offline sidecar willy

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250 comet petrol tank
« on: 05 Aug 2007 at 07:21 »
Hi....More questions on the 250 cc Comet petrol tank for the forum. [a 1935 model]

1. What colours should the tank be.
2. I have knee grips and the plate that fits behind them..but the question is..should there be a spacer fitted behind the plate?
3. Like wise for the hand gear lever bracket ...is this flush fitting or should there be spacers fitted for the two screws.

Any photos would really help.

cheers

Bill

Offline Doug

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Re: 250 comet petrol tank
« Reply #1 on: 07 Aug 2007 at 00:30 »
Bill,

Rather than post directly here, I have put some pictures of my 600cc Aero Douglas petrol tank, before, after, and sketch, in the Reference section. Use this link. Hopefully, this will make it easier for someone else in the future that needs similar information to stumble across it, and still provide an answer to you query (via the link.)

It is a 1936 petrol tank, but should be identical to what was being used in 1935, judging by the catalog illustration. I do have full size tracings of the panels on tissue paper, but copying these is problematic.

The plates will need to be contoured to match the curvature of the petrol tank, to maintain a consistent gap just larger than the thickness of the flange on the knee grip rubbers. To be quite honest, I forget if there are thick washers under the mounting plates, or if the gap is archived entirely just by contouring the plates to a more gradual curvature than the sides of the tank (the sides of the tank 'fall away' from the plate.) Those bits are buried in a cupboard and not presently accessible. Note- modern reproduction 'grips are cast in urethane and are not vulcanized rubber. They are very susceptible to tearing when trying to stretch them over the mounting plates.

The back of the hand change gate is contoured to fit tightly against the tank.

-Doug

Offline sidecar willy

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Re: 250 comet petrol tank
« Reply #2 on: 07 Aug 2007 at 08:30 »
Doug...As previously you came up with the answers. Thank you.

Indeed the timing was perfect...as today I am taking the petrol tank to a refinisher to carry out the minor repair and restore the tank. The engineer had an idea of what the tank should like and this included some chroming. Your pictures provide an exact photographic template for him to work to. I do like the blue on top of black with the gold pin stripe.

The last thing I wanted really was spend what will be quite a lot of money ...and then be told........." agh thats not what colour the tank should be..."



Offline Doug

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Re: 250 comet petrol tank
« Reply #3 on: 07 Aug 2007 at 13:09 »
Bill,

Many 1934 tanks were shown cataloged and described in chrome rather than black. I have heard some say that black was actually the standard and chrome was offered as an option (contrary to advertising, but then the catalog is not always right.) I do not doubt that if a customer really wanted it, he could have his 1935 model with a chrome tank too. I have not seen any advertising that such was offered in 1935, nor can I imagine anyone spending the money on a 250cc economy model where price mattered most, but given the right incentive (!) I am sure the factory would oblige. So if you found traces of old chromium plating on your tank and have a large wad of discretionary cash to part with...  8)

-Doug

Offline sidecar willy

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Re: 250 comet petrol tank
« Reply #4 on: 07 Aug 2007 at 21:38 »
Doug...the previous owner had the tank chromed...some 6 years ago or so. Unfortunately the preparation was not carried out very well and now the tank is badly corroded. The corrosion has come through from the inside to out with some severe bubbling....and as such the tank will require some serious repairs with both sections on the side cut out and re-welded. The end result means its too expensive to prepare the tank for chroming after the welding.

So luckily for me you sent some photos of the tank with Black under Blue panel and a nice gold pinstrip round the blue....so I will be having the paint as per your link photos.

I must admit for a few minutes today I thought.." sell the bits on eBay and sell the number plate. ...cut my loses...especially when the restoration chappie told me the tank was seriously corroded. But I am not to be beaten on this set back...but going to carry on using your photos as my template.

But before the work starts  I require to get the oil feed and return brass fittings [male connectors] ....as I would go bonkers if the tank was re-welded/repaired and painted then find ..no fittings.  Looking at the thread sizes..it appears to be BSP thread...could you or anyone else on the forum let me know if indeed they are BSP ...and what size?

cheers
Bill

Offline Doug

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Re: 250 comet petrol tank
« Reply #5 on: 08 Aug 2007 at 18:29 »
Bill,

The oil tank inlet/outlet openings shown (1934 lightweight tank) have a thread where they enter the oil compartment are 3/4-26 with a 60 degree thread form. I had a look at a 1934 large tank (with inset instrument panel) and the 1936 petrol tank that I posted images of in the Reference section, and they both have a similar configuration of the 3/4 opening for the oil cock (via a screw in adapter and strainer) and a smaller opening for the return standpipe. I would assume your 1935 Comet tank has this configuration. I do not know what size the smaller thread is, as the one tank examined is full of oil, and the other (that I took the pictures of) the thread is choked up with tank sealer. I will need to check the oil return pipe to determine what size tap to use to clean out the threads, that is when I find where I stored the return pipe. I think I know where it is, but it will mean shifting quite a few boxes to get to it! I already checked the more accessible locations.

-Doug

Offline sidecar willy

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Re: 250 comet petrol tank
« Reply #6 on: 08 Aug 2007 at 19:34 »
Doug

The post you displayed previously with the two fittings...one with the oil filter gauze and the other with the return header appear to me to be the same diameter as the holes in the oil tank. One is as you suggest about 3/4" diameter....whilst the other is about half that size. Looking back on my time when I piped up small bore tubing in the oil industry many moons ago...they look like 1/2 BSP and 1/4" BSP...both parallel threads.

Back to my petrol tank...which is now in the capable hands of a company called Metal Magic...also named now Heritage Motor Works...Hampshire who phoned me earlier today. They think the tank can be salvaged ...a final inspection will be done tomorrow and a verdict given. At best it means cutting out the bottom section...removing all the dead metal, welding in new sides, re-weld the bottom back in...then prepare the tank for painting.

At worst it means making another tank...ouch.....or start looking out for a 2nd hand one. But then that may well be the same!!  The joys of a restoration project. Having said that the remaining tinware/cycle parts all look in very good condition...and save the odd bracket and spacer that is missing then the restoration should go well. Engine and gear box...for the winter evenings!!!!

I do value your contributions..thanks


Offline Doug

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Re: 250 comet petrol tank
« Reply #7 on: 08 Aug 2007 at 20:59 »
Quote
The post you displayed previously with the two fittings...one with the oil filter gauze and the other with the return header appear to me to be the same diameter as the holes in the oil tank.

Yes, those fittings were from a 1934 lightweight model, and both threads are 3/4-26. A smaller tank than yours; the same shape petrol tank as the A31 model. For 1935 the lightweights got the bulbous tank as used on the big twins, and the different size oil fittings (the smaller one of the two yet to be determined!) If it were the aperture for the oil cock, then I would say yes, probably an industry standard to match a purchased-in valve. But as it is for the standpipe, a item they likely manufactured themselves, then they could have used something funky if inclined. On the otherhand, Douglas probably purchased in the saddle tanks, and they would have whatever threads the vendor standardized on. I have heard Ariel mentioned as a supplier of the Douglas saddle tanks, but I do not know the Ariel models that well to say yea or nay definitively. The few Ariels that I have seen from the mid-thirties did not seem to have the same shape tank. But that is not to say that Ariel supplied them with one of their tanks, but instead manufactured Douglas' petrol tank for them (to Douglas' design.)

If the catalog illustrations can be believed, in 1936, the lightweight models reverted back to the smaller tank as used 1931-34!

-Doug


Offline sidecar willy

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Re: 250 comet petrol tank
« Reply #8 on: 08 Aug 2007 at 21:34 »
Might be in luck with the oil filter gauze fitting...one of the chaps that looked at the tank [with a view to restoration]...reckons that the Triumph 120 Bonnie has the identical fitting for its oil tank outlet. He has an old one in his garage and going to dig it out this weekend and try it for me. He also suggests that the smaller diameter fitting is easily converted from a 1/4 NPT male fitting then have the stand pipe welded in. Things can only get better




Offline Doug

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Re: 250 comet petrol tank
« Reply #9 on: 09 Aug 2007 at 18:49 »
Quote from: Bill
At best it means cutting out the bottom section...removing all the dead metal, welding in new sides, re-weld the bottom back in...

Bill,

Actually, taking the bottom out of the tank is often the preferred way of making repairs, it does give good access! Oil compartments do complicate matters, as you have more than just the perimeter weld to grind free and re-weld, but the seam joining the oil compartment as well. But in the case of your tank, this is just the two circular welds around the oil tank fittings that pierce the floor of the petrol tank. The oil compartment has its own separate floor which can remain untouched.

If you go easy with grinding the weld, you can often re-weld the original bottom back in (assuming there are no rust issues.) But it sounds like there are, and it has affected the sides as well. Replacing the lower edge of the side is a tricky process as you have to form up curved matching repair pieces, and the welds between the patches and the sides are much more prone to warping than the joint configuration used to connect the sides to the bottom. A good shop will hammer and dress these down flush while the bottom is out. A lower class organization will hammer it all below the surface and fill in with body solder, or worse, polyester body filler. (Neither or which, can be used on chromium plated tank.)

-Doug

Offline sidecar willy

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Re: 250 comet petrol tank
« Reply #10 on: 09 Aug 2007 at 21:28 »
Doug...thanks for the advice. I am still waiting for Metel Magic to get back to me about the work to be carried out on the tank. But will let you know what they come up with.
cheers
Bill

 

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