Pre 1912 Valve Timing?

[Frank Lyn]

Hello All,

I am having trouble  deciding where to set the valve timing on my 1910 Model C (for which I do not have a manual......)

It has 20 teeth on the crank gear so that the increment of adjustment is 18 degrees.  With reasonable clearance (0.006") I have a choice of having the exhaust valve close at either 2 or 20 degrees beyond TDC.  Two degrees seems like too little and 20 seems like too much. 

With automatic inlets, the suction valve cannot open until the exhaust closes and the piston moves down a bit.

Any insight would be appreciated

thanks,

[Doug]

Frank,

Bruce Main-Smith Ltd (carried on by Don Michell) does a photocopy of the 1910 Catalog/Handbook/Spares list. There is no mention therein of what the exhaust timing is, but in the timing of the magneto it implies the exhaust closes at TDC.

In the 1911 edition, after proper warning against owners venturing inside the crankcase (verses returning to the makers for servicing), they describe re-timing the exhaust cam. The tappet is set so the valve is just closed and "turned a shade further" in the direction of running (on the cylinder being timed). Then the engine is rotated so the pistons are at their extremity (TDC). The crankshaft is then dropped into position without disturbing the cam position (within reason).

So 2 degrees before TDC sounds to be right in the ballpark.

Doug

[cardan]

Hi Frank,
I agree with Doug - you won't get into too much trouble with the valve closing at something close to TDC. When mechanical inlet valves came in, it was not uncommon to find the recommended opening 5 or even 10 degrees after TDC and this was often partnered by exhausts closing at or near TDC. The idea of overlap took a while to fall into place.
While you've got easy access to the cam, just check where the exhaust opens; don't be surprised if it isn't too far before BDC (20-30 degrees), but for peace of mind it's nice to know that it isn't ridiculously early (in which case the 20 degree after TDC may be a better option).
By the way, there is a lot of "tuning" to be had by correct adjustment of the automatic inlet valve springs. Not only does the "spring constant" (the amount of opening for a particular applied force) have to be correct, but also the maximum opening should be limited. Do you have figures for these? The weight of the valves is also important.
Leon

[Chris]

Hi Frank
Other factors to take into account with these engines is that the opening of the inlet valves is also dependant upon the compression available within the engine which is affected by the bore wear/ring condition etc. and whether original pistons with correct height of crown above gudgeon pin centre are fitted. The strength of the valve springs also affects performance in that weak springs permit easy starting but limit top end performance while stronger springs make for more difficult starting but higher top speed. To assess the equality of inlet valve springs  the two inlet valve assemblies can be put back to back between finger and thumb and compressed when both valves should be seen to open simultaneously and by the same amount. Chris.

[Frank Lyn]

Hello Again,

Thanks to all on the suggestions on how to deal with automatic inlet valves and the lack of original specifications for the Douglas.  It looks like trial and evaluation is going to be my lot during the first season of riding this bike.

As Doug wrote "So 2 degrees before TDC sounds to be right in the ballpark",
or as Leon wrote "in which case the 20 degree after TDC may be a better option",
indicating that a definitive answer is not forthcoming so a bit more research is needed.

I measured the dwell of the cam with 0.006" clearance to be between 235 and 240 degrees, then found the specifications for two other Air-Cooled engines with automatic inlet valves.

Gnome 90 HP Rotary: Dwell 258 deg, Open 65 deg. Before BDC, Close 13 deg. After TDC
Franklin 12 HP 4 cyl.: Dwell 237 deg, Open 38 deg. Before BDC, Close 19 deg. After TDC

The Gnome is a strange engine by anyone's standard and the designers were mainly concerned with the maximum full-throttle power with the lowest possible weight so its very early Exhaust opening is probably not the best analog for the Douglas.  The Franklin, on the other hand, is very similar in dwell, purpose, and general layout to the Douglas.  Plus both Franklin and Gnome call for a fairly late Exhaust Valve Closing.  The piston has not really moved down much even at 20 degrees so the thought might have been that you want to make Sure that there is NO residual exhaust pressure when the piston starts moving seriously so that the inlet valve opens promptly.

So I have set the exhaust to close at 20 degrees after TDC and will give that a try.  If the performance is lacking (and after trying other aspects of the engine), I will move it one tooth earlier and try that.  After all, working on an old bike is almost as enjoyable as riding one.

[Frank Lyn]

An Update on the 1910 C:

I set the valves to close at 20 degrees beyond TDC with zero clearance.  When I introduced 0.020" clearance, the valves close at about 5 deg beyond TDC.  All this is COLD.

When both cylinders are firing, the bike goes like the wind, pulling hills easily at 25-30 mph (I put on a bicycle speedometer to keep track)

It seems to work best with the spark plugs set at 0.016" which by my standards, seems very close but they do no fire under full compression any wider.  I will charge the magnets on the magneto and see if that helps.

There is a lot of fussing with the air valve, throttle, and magneto while speeding along to keep both cylinders running.  It will fall back to one cylinder occasionally, sometimes the front, sometimes the rear. 

I had the float too high at first and found that I could not restart the engine after it had warmed up and was shut-down hot for a few minutes.  (this stranded me about a mile from home and I pushed the bike back.  After that, stay close to home until fully sorted out).    Not starting hot is classic for a float too high, but now I have gone too far the other way and have to pull the tickler occasionally while driving at low throttle.  To adjust the float, you have to drive a spool that is press fitted to the stem up or down on the stem.

So many things to fiddle with! It is good that it is so much fun when it runs, otherwise I might give up....   

[eddie]

Frank,
         .015" to .018" is the normal reccommended spark plug gap for use with early magnetos. It is only since the introduction of coil and electronic ignition on more modern machines that the plug gaps have slowly increased to .030" to .035". Also, magnetos are more suited to running with non-resistor plugs and without using suppressor plug caps.

     Regards,
                 Eddie.

[cardan]

Hi Frank,

At least it's running, which is a good start.

Check the induction system for air leaks - my favourite candidate for vague running on small machines with automatic inlet valves.

If you do give up, put it in a big box and send it over to me!

Cheers

Leon

[Frank Lyn]

Thanks Eddie...  I guess that I was thinking automotive rather than motorcyclic

When I consider the Bosch DA1 (two spark 180) on the Douglas compared to the Bosch DU4 on my 1910 car, I wonder how the little magneto works at all.  The DA1 has small magnets, a tiny coil, and runs at half engine speed.  The Douglas has significantly higher compression than the car also.   I run 0.025" on the DU4 quite successfully. 

 In the open air, the DA1 will light this gap nicely.  I started at 0.020 on the DA1 and the engine ran ragged so experiments were in order 

When it was running on only one cylinder, I put a inductive pickup timing light on the other side and could see the plug fire when the compression release is pulled but stop when under compression.  That is when I started closing down the plugs. 

Maybe I will go down another thousandths or two.

[cardan]

Did you get it running nicely Frank?

Leon

[Frank Lyn]

Sorry for not following up.

With the plugs at 0.014", points at 0.018",  Exhaust closing 1 tooth AFTER TDC and set to 0.018" (at which point they close close to TDC), and inlet springs perfectly matched, it climbs hills with great aplomb. (at least it did Last summer).  The only problem is that the belt slips on steep hills and sometimes when first dropping the exhaust valves.  It also runs best at one particular throttle/air lever position which is about 30 mph on the level.  (magnetic bicycle speedo).  Pedaling for a few yards, dropping the exhaust and having the engine fire up gives the impression of a sudden rush of acceleration.

I am looking forward to the next season and trying different belts, tensions, and dressings.  (I just bought a new Bremmer Belt)

[cardan]

Thanks for the update and photo - you have a very pretty little motorcycle there! Well done, and enjoy the ride.

Leon