Drags Hawker singles oil pump

Singles, twins and fours.
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Holder of a Golden Anorak
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Drags Hawker singles oil pump

Postby alan.moore » Fri Jan 17, 2020 9:42 pm

Ariel increased the bore of the feed piston around 1950 (based on the part number). I had an early small bore one (0.186" dia piston) reconditioned by Drags and it came back at 0.267" (They sent me a reconditioned later body not the 1936 body I sent them :D ). Working out the surface areas of the two (0.027" and 0.056") that's just over a 50% increase in piston surface area. So in theory (stroke was unaltered) that should give a 50% increase in pump output per stroke. (The recon return piston was only slightly bigger (20 thou) and was therefore still 2x the surface area of the feed at 0.120").

Looks like Drags don't do exchange recon pumps anymore, they do their Hawker brand which is listed as 50% increase flow rate over standard. They list it under the older pumps part number (2212-29). So I wonder if that 50% more flow than standard relates to the old small bore pump or the later large bore pump? If its 50% more than the large bore then that's a lot of oil flow !!

I will give them a ring next week to see.

1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single

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Re: Drags Hawker singles oil pump

Postby will_curry » Fri Jan 17, 2020 11:10 pm

Apart from the irritation of the return ball valve holding off its seat and subsequently
having to drain the magneto in over 50 years I've never felt the need to replace a pump.

The engines don't seem to need a lot of oil, except in the timing case for the cam and they don't
wet-sump either. My BSA single with a gear pump is an absolute s*d for that.

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Re: Drags Hawker singles oil pump

Postby nevhunter » Sat Jan 18, 2020 12:26 am

It's logical that a 500cc would need a bit more oil flow as it's a bigger motor and revs slower. For normal use I reckon the 49 0n pump is completely adequate especially where the valve gear is fed from the return line to the tank Later models. The open valve gear models don't feed the rockers at all so the small pump is probably OK there too. It certainly is Perfect on my W/NG which got an award basically for it's easy starting and not leaking or dripping oil and has no oil control ring (as original) and blows no smoke and hasn't been worked on cylinder head wise since it went together in 1997. I just couldn't be more pleased with it in that respect. It's worn out a rear tyre and then some so isn't just a static exhibit. '
The small pump plunger might be a little more sensitive to wear reducing the flow . It's only the very end that does the work in sealing. Nev

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