Author Topic: 2 3/4hp - Does YOUR advance/retard lever make any difference on the road?  (Read 8632 times)

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Offline spency777

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Hi all,
It's been ages since I've posted a question. I'm the very proud owner of a lovely Banbury gold award winning 1924 2 3/4hp TS here in the UK it runs very nicely but refuses to haul my 14 stone up Sunrising hill no matter what I do.
I'm OK with that as the engine is still on its original bore and running cast iron pistons (albeit with new rings).

So here is the question, does your advance retard lever position make any difference to the running of the bike?

I've checked my ignition timing and it seems to be set up exactly as per the original manual and it starts beautifully with the a/r lever pulled all the way back (fully advanced). However once under way moving the lever anywhere forwards (less advanced) just seems to dull the performance.
Admittedly it's not a huge problem as it runs very nicely but I always thought that the lever would do something, at the moment I mey as well just set it to fully advanced and disconnect the control altogether.
Ultimately I'm poised to get the engine rebuilt but thought I'd just pose the question just to see if my bike is behaving as normally as can be expected.
Many thanks to you all,
Richard

Offline graeme

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Hi Richard

Have you checked your ignition timing with a degree disc? I would think 35 degrees is what you should be aiming for, maybe slightly more if you don't mind fiddling with the a/r lever on the run. I suspect your timing at the moment is a bit retarded from the symptoms you describe.

Cheers, Graeme

Offline spency777

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Hi Graeme,
No I've not used a timing disc as the original handbook just tells you to turn the flywheel until the rear exhaust valve just closes (putting the front cylinder at its firing point) and then with the advance/retard lever set at its mid point, rotate the magneto until the points are just opening and then mesh the magneto with its drive gear at that point.
Mine seems to be set at exactly that point.
I agree with you that the lack of response to the lever being retarded does seem to indicate that the timing is already slightly retarded (possibly one drive gear tooth out?) but according to the manual it seems spot on.
I'm really hoping that someone out there with a sweet running 2 3/4 engine can just let me know if their a/r lever has much of an effect on their engines performance or if "not to worry, they all that, Sir!".
I'd be quite happy to change the "mesh" of the magneto drive by one tooth or so if I felt it might make a difference but I'd rather not mess about with it if not as it starts and runs really well as it is.
Cheers for your reply,
Richard

Offline Frank Lyn

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Although my Douglas has an advance lever, in reality, I find that setting it to (nearly) full advance and not mucking with it further works well for me. 

I have a car of the same year as the Douglas that has a FIXED Magneto with no advance-retard mechanism of any kind and it works as designed. Full advance, all the time. When I tell people that I start it with the hand-crank (the only way) at full advance, they start looking for splints to set a broken arm :)

Just keep the revs up and avoid "lugging" so life will be good at full advance.

Offline spency777

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Thanks very much Frank, in many ways that's the answer I was hoping for. I've owned the bike for about 3 years now and it's always run better at full advance including hand starting.
I guess I'll just treat the lever as another almost useless ornament, a bit like the front brake now I think about it 😀.
Regards
Richard
🏍💨💨💨💨💨💨

Offline ian scott

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I cannot feel any difference on my 2&3/4 if I retard the ignition for a hill. I just leave it ar full advance.

Offline cardan

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Hi Richard,

The technique of setting the ignition timing in the original manual is a little bit obtuse, and requires that the engine is exactly as it left the factory. It doesn't allow for wear, or bastardry, that may have occurred over the life of the bike.

You can very easily check the timing on an outside-flywheel motor. Set the magneto to full advance and remove a spark plug. Move the engine by hand until the piston it exactly at TDC on the firing stroke. Mark the flywheel with a marking pen. Using a flexible tape (a dress maker's tape is ideal), measure the circumference of the flywheel, then make a mark on the flywheel at one tenth of this distance before the TDC mark. (One tenth of one revolution is 36 degrees.) Rotate the engine to this mark. If the timing is correct the points should be just opening.

From your description you may be running with the timing a bit retarded. One tooth change will probably make it over advanced.

Retarding the ignition should help when the motor is in "slog" mode before the snatch is made for first on a long hill. By this time the air lever would usually be closed a little also.

By the way, if you slowly pull the rear wheel of a TS you should feel strong compression for each cylinder, to the point where the belt my begin to slip a bit before the compression is overcome.

I suppose there are 1920s TSs that romp up Sunrising?

Cheers

Leon

Offline spency777

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Thanks again chaps,
I've now managed to retime the magneto by moving its drive sprocket one tooth.
In doing so I've proved to myself that the original timing was about right as now when I ride the advance/retard lever now definitely sets the engine too far advanced.
Therefore I think it's probably time for a rebuild, I've already bought new valves and guides so just need a reputable UK company to carry out the rebore and fitting of a pair of JP Pistons to suit.
If it won't go up Sunrising then I'd better just try to lose about 12 stone, that should do it!
Richard

Offline cardan

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Hi Richard,

I'm a great advocate for iron pistons, so do convince yourself that the bores are badly worn before you rebore them and fit alloy pistons. This doesn't cost anything, other than some careful measurement, and at least you then know that "it needed a rebore because the cylinder was worn xxx thou at the top".

Cheers

Leon

Offline spency777

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Wise words once again Leon,
In my case I've already ascertained when I replaced the piston rings that my rear cylinder has an ancient score from top to bottom and the front one is wine bottle shaped so I think I'll have to finally give up my cast iron pistons.
Rest assured I'll be following the guidance from this forum on piston to bore clearance before fitting the alloy versions.
Cheers again

Offline cardan

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Hi Richard,

It must be my training as a scientist - it's just nice to have numbers. I recently bought myself a proper (Mitutoyo) bore gauge which is great because it allows accurate measurement of "features" in the bore, like scores and ridges. It's sometime surprising just how small a variation is detectable with the eye or the finger tip. Certainly less than 1 thou (0.001").

Does anyone have a good estimate of what constitutes "worn out" for a 2 3/4 cylinder? With a bore of only 61-ish-mm, I suppose 6 or 7 thou wear (at the top, almost always in a four stroke) and you'd be thinking a rebore might be appropriate? But if the iron pistons were little worn, as is usually the case, the motor might be good for a lifetime of gentle rally use.

Similarly a score of a thou or two from an errant gudgeon pin might not be the end of the world.

For reference, I've been using skirt clearances of about (1 thou + 1 thou per inch of bore) for iron pistons in air-cooled cylinders with excellent results. For a TS this would be about 3 thou. As well I've been reducing the piston diameter at each ring land by 1 thou or so.

Even in a worn cylinder with original pistons the skirt clearance may still be close to 3 thou. Even with no tools general wear in the bore can be measured by putting a ring in the bottom of the cylinder and looking ate the ring gap. If the cylinder is worn by 10 thou at the top, when you slide the ring up there (use the piston to keep it square) the gap will increase by pi x 10 = 30 thou or about 0.75 mm which is easy to see with the naked eye.

Of course alloy pistons need much more clearance. I did OK with the JP piston in my 1914 Rudge until I rode it up a long hill on a 45 C day. I guess you don't have that problem in the UK!

Cheers

Leon

Offline graeme

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Can I add that in checking the ignition timing on my 3 1/2, to get the right setting I had to remove the key from the magneto, and just fit the gear on the taper. In other words I found that I couldn't get accurate timing with a "whole tooth" movement of the magneto

Offline Ian

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The biggest difference I have found is giving our TS new valves/guides/etc. Made a huge difference. Another one of our locals finds that his needs the valves re-lapped every so often to maintain the power.

I assume you also have the heated inlet or similar to remove any possibility of carb ice ?

Offline spency777

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Hi Ian,
I had to replace one of the valves and its guide when I first acquired the bike so this time I'm taking no chances and have bought a new set of four valves and guides from the LDMCC.
I'm also hoping that whoever I give the job to has the ability to re cut the valve seats (or even insert hardened seats) to do a proper job which hopefully will last for years to come and restore my Dougie to full strength.
I certainly won't be throwing away my original pistons as who knows, maybe a future  owner of my bike will need to rebore and fit cylinder liners next time around in which case the old Pistons could go back in and offer another 92 years of service!

Offline ian scott

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Would be a lot more trouble than JP Pistons but cast iron blanks can be bought from Bert Pol.

http://www.bertpol-vintagemotorcycles.com/parts%20Douglas.htm

Offline cardan

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Pretty solid blanks. It might be hard to get the weight down to that of the original pistons, so faced with these I'd be going for the JPs!

Leon

Offline chris mac

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Might I just make a comment about measuring bores, when they are worn they are not round, so putting a ring in hits the high spots on the sides and daylights front and back,similarly the bore gauges that 3 point the bore. Leon has the right stuff, measure side to side and fore and aft you can see the eccentricity
I also agree about the CI pistons, I pulled some favours to get a pair here in the US, that's a big lump of iron
Best. Chris Mac

Offline ian scott

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Chris,

I am interested in how close the inside of those castings is to the size of the inside of an original piston.

How did they measure up?

Offline Ian

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The JPs have worked fine when I have used them - as Leon says they just need more clearance. In fact we have found that the clearances they specify in the writeup they send is nowhere near enough.

Offline chris mac

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Ian, probably others on this site can reply better, I have not attempted to do anything with them at this point.
I can't imagine that they are close to dimension at all, anywhere
Best,  Chris Mac

Offline oily bloke

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I rebuilt an EW 350 a few years ago. The Iron/JP/Other make piston argument was prevalent then. I ended up fitting Honda pistons from a CB750. Minor mods were required but nothing too serious. My theory was that JP pistons were renown for over expansion due to the excessive heat generated by a side valve engine. Iron was not available to me, but Honda pistons designed for a high performance air cooled engine seemed the way to go. Bored to 2.5 thou piston to bore clearance then honed to 3 thou. Careful running for a few hundred miles. Jobs a goodun. It might pay to research what is available for the 2 3/4 before committing.
Cheers
Andy

Offline graeme

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Ian Coulston

I have seen numerous original Douglas cast iron pistons, and they have very thin skirts indeed, the Bert Pol blanks would need a lot of machining.

Offline ian scott

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I picked up a couple of cast iron blanks of unknown origin at the Kevin Cass sale Graeme. Will use them one day. But definitely not taking out the working JP Pistons whilst they have life in them.

Offline patrickhowell

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To change the subject slightly, how do you stop the advance/ retard lever winding itself back? I have done the obvious, by tightening the thread on top of the lever.

Offline graeme

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Perhaps the return spring is a bit too strong?

Offline cardan

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Or you might be missing a wave washer, friction washer, ... from the lever. Often levers have come from swap meets etc. with incorrect parts fitted, or parts missing entirely. One of the common disasters is for the central bolt to be sheared off from excessive tightening, so be careful it shouldn't need to be really tight. There is nothing mysterious inside the lever, so take it apart and see what's in there.

Cheers

Leon

 

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