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Douglas Motorcycles - General Discussion / Re: 3.5HP timing
« Last post by graeme on 20 Nov 2021 at 08:59  »
Hi Kevin
Finding TDC can be done by removing one of the valve caps and poking a wire in, a bit of a fiddle I know but it is possible. Another method that works on any engine is to get a spark plug, knock out the insulator so that it is hollow, then put a balloon, or better still a condom over the plug body, and see when it blows up the most before deflating again. This is really quite accurate.
Cheers, Graeme
Douglas Motorcycles - General Discussion / Re: 3.5HP timing
« Last post by cardan on 19 Nov 2021 at 22:44  »
Hi Kevin,

The test of whether the valves are timed correctly is to turn the engine forwards - on the non-firing stroke the exhaust valve should just be shutting at TDC, and the inlet valve is just opening, or about to open in the next 10-15 degrees or so. When correct this is true for both cylinders.

If you don't have a degree disc, you can make do with a dress-maker's tape and a marker pen. Fit the flywheel. Mark TDC relative to a fixed point - vertical or a fixed wire pointer. Run the tape around the outside of the flywheel (360 degrees) and measure the circumference. Divide the circumference by 10, and mark this out out on the flywheel before and after TDC - this will be +/- 36 degrees. You can use the "36 degrees before TDC mark" to time the magneto (on full advance). You can use the 36 degrees after TDC mark to make sure that the inlets are not opening too late - they should be well opening by the time you get half way there - 18 degrees after TDC.)

OK - there's a problem with my instructions, which were to leave the half time pinion (gear) on the crankshaft (1), and to leave the gear on the camshaft (3). I had envisaged just taking taking out the intermediate gear (2), setting the engine to TDC, setting the cam so the valves are "rocking", then dropping the intermediate gear (2) into place. But I see the top of the oil pump shaft is in the way! Are you able to drop the oil pump out?

I assume in the factory the oil pump went in last!

If you can do that, my instructions should be OK.

Re the timing marks, when the engine is at TDC I assume one of the 180-degee marks on the half time pinion points directly towards the intermediate gear spindle, Mark A on the photo below lines up with it, Mark B then points directly at the camshaft, and the mark on the cam gear lines up with it. But, as in my opening comment, don't bet on it! Remember that the position of the intermediate gear is completely arbitrary - it will look good if the timing marks line up but the engine will run exactly the same regardless of where you throw it in. Even the number of teeth on it is unimportant! It is the position of the cam relative to the crank that is important, thus the importance of timing the engine.

Good luck. Be confident!


Douglas Motorcycles - General Discussion / Re: 250 crankcase breather
« Last post by Cliffy73 on 19 Nov 2021 at 20:27  »
Hi I have a spare 250 breather if you still require one.
Douglas Motorcycles - General Discussion / Re: 3.5HP timing
« Last post by kevinbush on 19 Nov 2021 at 19:36  »
So update . I have enclosed pic of my engine to prevent confusion. I removed gear wheel 3 ,then set bottom of engine at TDC as directed,then refitted middle section and top section of crankcases,then set valves as directed, I noted that exhaust valve closes a lot before inlet valve starts to be opened,so i set the valve position just as both valve springs under pressure.
I then found I could not fit the gear wheel three in position, so then removed top two sections of crankcase again ,refitted gear wheel and did same procedure best i could, note the timing  marks do not line up. I have found at this point the flywheel spline facing at 3 o'clock towards the front of engine,after 360 degrees rotation of flywheel, found  both valves in similar positions and the flywheel spline position.
What do you think, shall I refit engine and see if bike runs. I will check if points  opening just before TDC, I forgot to do this. Is there an easy way to find TDC as with cylinder heads fitted seems difficult?

Thanks again Kevin
Douglas Motorcycles - General Discussion / Gearbox engine spacers
« Last post by Pallijen15 on 19 Nov 2021 at 12:59  »
Hi, I think that I must have the adjustable type spacers fitted on my 1951 MkV. Not the same as to what's mentioned should  be in Spannerama on page 31, but the type fitted to Plus and Dragonfly models. Mine are a thin headed hollow bolt, two different  lengths for left and right sides with the wider adjusting nut on the other side. When I checked them both were a loose fit and could be turned by hand. Do these need to be tight and anything placed against the contacting points of the gearbox or/and engine? Is there a specific way or do I just align the final drive sprocket with the rear wheel by eye? Thanks for any advice. Paul Jensen
Douglas Motorcycles - General Discussion / Re: MkV centre stand
« Last post by Pallijen15 on 19 Nov 2021 at 08:27  »
Hi Eddie, I have taken up the looseness with a thin washer between the tube and the lug. Fits nicely now, no slop. I think the repair must have already been done anyway because even when before I put the washer in between the top of the stand was nowhere near the bottom of the gearbox, there's about a cm clearance at least. The stand, measuring from centre of frame to bottom is way over 10". Thanks for your advice, greatly appreciated. Paul J
Good day,
I'm interested in the timing cover if still available.
PM sent.  -Doug
Hi Doug how do I go about purchasing one of these brackets and more importantly paying for it.

Douglas Motorcycles - General Discussion / Re: TS Thread repairs
« Last post by chris mac on 17 Nov 2021 at 03:56  »
Don't underestimate the ability of high temperature epoxies such as Lab Metal or JB,  generally good to 1000F
Bore out the old stub, thread a new stub on the lathe and epoxy in place
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