J.A.P. EXHAUST VALVE TIMING

[TONY REGAN]

Hoping someone out there can help;I have an early 6hp JAP V-twin engine from 1909 so it's atomospheric inlet(no problem there but side valve exhaust. No marks at all on the sngle-lobed camwheel etc . The crank pinion screws on (left hand threaded) so could be finely adjusted perhaps by shims behind. I'm thinking 50 degrees before bottom opening and maybe 25 dgrees after TDC closing ? Ignition timing too would be handy ,it twin contacts and coils,not magneto,bit of a rarebird perhaps, thanks if anyone can assist,T

[cardan]

Hi Tony,
Sounds like an interesting engine - a photo would be nice. Do you have a bike for it to live in?
I assume you have the exhaust cam and followers, so the best plan would be to measure the dwell first. That is, for how many degrees are the exhaust valves open? Given the early date, you might find that it is not much more than 180 degrees; perhaps 200 - 220. In this case you might just set the exhaust valves to close at TDC, or maybe 5 degrees after. With atmospheric inlets, it was not fashionable to leave the exhaust open much beyond TDC. (Valve overlap was being used by some racers before WW1, but it was not universally adopted.)
For the ignition, try 35 degrees before TDC fully advanced. Should be plenty.
With the atmospheric inlets, make sure the valve spring tensions are accurately matched, and restrict the opening of the valves so that they don't get too excited and flutter everywhere. Try something like 3/16" maximum opening.
Good luck!
Leon

[TONY REGAN]

Thanks for replying so quickly. I agree with you about effect of too much overlap on Atomospheric valves as these rely on depression caused by piston descent,I knew it would be modest.I had a picture in this laptop but I appear to have not put it in a folder correctly so I'll take another. It's actually a water-cooled version and has lived in a cyclecar built in 1914 so I'd really like to hear it run this year. The cylinders are blind-head so I can either make a dummy cylinder's or chance drilling through the existing blanks inside the water-jacket ,they won't budge of course to determine bottom and top dead centres. The brass contact housing which is pear-shaped rotates on the brass timing chest seemingly only held by small arm though the which holds the cap on also and perhaps one stud at the top,no sign of advance mechanism at all,may be good idea to make something up to play with timing. Once again many thanks,I dig out that picture,TR

[chaterlea25]

Hi Tony,
The rotating contact housing is the method used to alter the ignition timing
With the automatic inlet valve housing removed you should be able to access the tops of the pistons with a cranked piece of wire
It has survived a hundred+ years with out having holes drilled in it so I would advise against it
These engines are basic in the extreme, so do not need very precice valve timing, the nearest tooth on the gear wheel (ex valve closing) at TDC will work, you can always try it a tooth either way later on

On these early engines the ignition advance control is as important as the throttle control, learning to drive these is a whole new experience 

Regards
John

[cardan]

Hi Tony,
I'm with John - keep those drills away! I suspect the "blanks" you're referring to only get you inside the water jacket anyway. Presumably you will lift the cylinders off to have a look inside before you start it. Give it a good internal clean and lube, and set the exhaust timing while a cylinder is off when its easy to see TDC with good accuracy. Don't forget that the V twin has two different firing intervals, so if you set the exhaust valve of cylinder no. 1 (rear) to close at TDC, check that no. 2 closes at 360 + 50 = 410 degrees later (i.e. at TDC of the front cylinder). If it doesn't, you're timing it on the wrong cylinder for that lump in the cam.
Presumably your motor looks something like the illustration below. Later versions - JAP probably built them up to 1911 or 1912 - have strengthening ribs on the cases but are otherwise similar.
Do tell more about the cyclecar to which it was fitted in 1914.
Leon

[TONY REGAN]

Thank you both; very helpful and if they are not that particular the bent wire idea sits well with me . I have the cylinders of presently because I wasn't sure of internal condition,but it's very good. Yes my engine is similar to your picture,apparently these ended production in 1909 the year of this engine and then JAP's just converted the inlet side to pushrod operation to use up spares it is said. The contact housing presently only has that retaining arm and post on lefthandside of timing cover ,no clamp or advanve mechanism,guess I will have to make something up for that,oddly the tapping in the top of  contact housing lines up with stud hole in top righthand corner of timing chest. Anyway a long way to go on this cyclecar . Oddly enough the motor runs a Chater-Lea 2-speed gearbox. thanks for now T

[cardan]

Like this one (from the 1907 Chater Lea catalogue)? Or the later motorcycle style?

Leon

[chaterlea25]

Hi Tony, Leon,
Isn't the world full of coincidences?
Tony and I share the same surname and have machines with Chater Lea connections,
Only last week I visited Letchworth to do some CL research and went and saw the Factory buiding CL moved to in 1928, its still called Chater Lea House. The pre 28 building in London is still pretty much externlly as it was, It looks to be a block of flats now??
I'm hoping to have my 25CL finished for its 90th birthday in 2015

Regards
John

[TONY REGAN]

Nice to know some of these old buildings survive and put to good use. I wish you luck with your 2015 deadline,mine is a little tighter,but it will motivate me,thanks T

[cardan]

Here in Adelaide, local firm Lewis used Chater Lea cycle parts - frame lugs, wheel hubs, pedaling gear, etc. - to build 1500+ motorcycles between 1902 and 1918. Lewis also sold tri-cars around 1907 that were likely Chater Lea, as well as genuine Chater Lea cycle cars around 1914-15. http://earlymotor.com/lewis/index.htm

Other firms used CL parts also, so there is likely more veteran CL stuff out here in Australia than in the UK.

Leon

[P.V. Motorcycles]

Interesting thread - I'd concur with the suggestions about having the exhaust close on TDC, and full advance at 35 BTDC.

Nick