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1914 HUMBERETTE "Cyclecar" Valve Timing

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Lillianbrooks:
Hello all, I guess I'm an imposter because my "bike" is in fact a Cyclecar - a 1914 Humberette, 998cc, 84x90, 50 Degree, V-twin.  In an attempt to get more sting out of it, I'm appealing to the experts - YOU, for advice. i believe original timing was Inlet opens TDC, closes 50 past BDC and Exhaust opens 50 before BDC, closes TDC.  It's very like an early J.A.P. motor and from what I've read on your forum, the J.A.P. Inlet opens 16 before TDC, closes 65 after BDC and the Exhaust opens 65 before BDC, closes 25 after TDC - which is a hell of a difference.  Then I look at other British bikes of that era and get more confusing stats.  My dilemma is do I leave it alone or go for the J.A.P. or similar setting - so I'm asking any old blokes on the Forum, what do you think. (I've never found an original SMITHS carburettor and have previously run brass Zeniths.  I'm now about to fit an Amal model 289, my limited brain-power reasoning that if it feeds a BSA 500cc. it should feed my 998cc twin.). ANY SOUND ADVICE WELCOME.

cardan:

--- Quote from: Lillianbrooks on September 15, 2020, 05:27:43 AM ---It's very like an early J.A.P. motor and from what I've read on your forum, the J.A.P. Inlet opens 16 before TDC, closes 65 after BDC and the Exhaust opens 65 before BDC, closes 25 after TDC  - which is a hell of a difference.

--- End quote ---

Hi,

Yes indeed a hell of a difference, because those numbers go with a JAP racing engine of the late 1920s - something like a KTOR fitted to a bike lapping Brooklands at 100+ mph, not a 1914 light car. A pre WW1 engine with any overlap of the valves is a rare thing indeed, and only a handful of wizard tuners of the day would dare to suggest anything other than closing the exhaust valve before opening the inlet. Much was learned from aircraft engine development during the war.

Your dilemma is easily solved. Leave it alone, or sell it to someone who appreciates it for what it is. The Humberette is in many ways the prototypical "sports car" of the veteran era. Standard, and well sorted, they run along very nicely and climb most ordinary hills, and a hoot to drive. Find a Smiths carburettor and get all those little jets just as they were intended to be in 1914...

Not sure whether this is "sound advice" as I don't classify myself as "any old bloke", but at least I haven't resorted to fitting AMAL carburettors to my veteran bikes.

Cheers

Leon

chaterlea25:
Hi,
The 16/25 timing also applies to the 500/600 "sports" sidevalve 
(only this afternoon I was timing up a J.A.P KT V twin (1929) and it has overlap , I have not measured up the amount yet as I put the crank pinion for a minute down and it seems to have gone AWOL  >:(

Some years ago I was asked to come up with cam timing for a 1904 Minerva single cylinder car when a new cam had to be made. I suggested the J.A.P 16/25 timing , It worked out well, The owner of another Minerva visited and test drove the car commented "I wish mine went that well"

I know that owners of Veteran Triumphs play with the cam timing to improve performance and hill climbing by advancing the inlet cam (?)
Does the Humberette have a single or separate cams? experimentation is more difficult with a single camshaft
The J.A.P KT has three key ways in the crank pinion so the timing can be fine tuned

John

Lillianbrooks:
Thanks Leon, you certainly don't mince word.  Not used, here, to such "direct" advice. you are my first experience with a Forum. Here's a few facts from an old bloke. You're talking to an Australian who's had the Humberette for about 14 years  (and has had genuinely restored veteran and vintage cars. with correct parts, including carburettors, for 50 years), does appreciate his Humberette and certainly would fit a Smiths carburettor if I could find one.  We don't drive cyclecars around villages here but punish the poor little things on 100 km rallies at times, sometimes on inappropriate roads.  There are about 14 Humberette in Australia and none with a spare Smiths carburettor. (I have searched Ebay for 14 years for said carbie. Find me one and I'll fit it!)
Thank you for your advice.  I will leave the timing alone.  The rest of your advice and opinions was unnecessary.

Thanks John for your answer. It's appreciated. The Humberette has separate cams but Leon seems to have given me good advice, in his charming way, to leave it alone - so will do so.

cardan:
Here's some JAP timing figures, from the 1920s.

The Collier brothers' Matchless that raced at Brooklands pre WW1 had 0 degrees overlap, with both exhaust closing and inlet opening at 20 degrees after TDC. http://earlymotor.com/leon/misc/html/timing.htm

Hope you've swapped out the original rods for a pair of Carillos! Enjoy "punishing" the Humberette, but don't expect everyone to be impressed.

I have a Smiths carb somewhere, or I did have, but I think it was a bit large for a Humberette.

Leon

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