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Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Doug on 05 Mar 2019 at 05:38  »

I know it is a long and limber shaft on the timing side and the bushing in the timing cover will force it true, but the total indicator reading ought to be less than that. A run out of 0.2mm is going to cause undue wear on the bushing. You want to aim for 0.08mm or better.

Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 04 Mar 2019 at 21:20  »
Hi Eddie,

Thanks for that info. I turned the ignition timing round so to speak as you described. The engine fired on the rear cylinder about 5 times with plenty of oil smoke before stopping. I didnt have time to do any more today, but I think thats a step in the right direction.

Thanks for the warning about weak methanol mixtures. I am interested in the units of measurements for jet sized. Ive seen some Douglas data which says the jet sizes were 100 to 120 for petrol and 35% larger for methanol. I assume that the numbers stamped on my jets are the same units as these ones, but have no idea how those figures relate  to the hole size, or whether the sizes you use are on the same scale, and what sizes these hles are?

I didnt check the timing of the valve closing point, but will do so tomorrow, I also plan to double check everything again and get the engine running properly, At this stage I only plan to get it idling. I will need to get some proper head gaskets made and then fettle it to start producing power and then put it in the chassis when it comes back from Avit with its mounting kit installed.
Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Eric S on 04 Mar 2019 at 12:39  »
The crankshaft has been worked on and the cone rebuilt. However the machinist checked the other end of the shaft and found it was off by 0.2mm on  the end.
Since the bike was running fine until now except for the un-locked crankshaft, is it an acceptable offset or should he make it run straight? (or straighter as he said he had not yet checked if it was S shaped or just bent...)
Douglas Motorcycles - General Discussion / Re: Main shaft felt seal
« Last post by Bynorthsea on 04 Mar 2019 at 08:04  »
Thanks Eddie
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by eddie on 04 Mar 2019 at 07:51  »
Looking at the photo of the points end of the mag, if the valves on the rear cylinder are 'rocking', the mag needs retiming so that the points are to the left (that is, I think you have it timed on the wrong cylinder). An easy check can be done by removing the front HT pickup to see if the slip ring  brass segment is visible. Also, if you are running it on methanol, you will need much larger jets (and slides with a smaller cutaway than those used with petrol). To give you a guide, our sprint engines run 600 - 650 Amal main jets with 1" bore carbs, and about a no.2 cutaway. Methanol is very tolerant of rich settings (provided you have a good spark) but weak settings can quickly cause piston damage - so be careful!


  P.S.  When you set the valve timing, did you also check the point at which the valve closed? The reason for asking is that some manufacturers quoted timing figures obtained with increased tappet clearances because some ramp cams are difficult to time accurately at the start of their lift. You may need to experiment to get the factory figures.
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 03 Mar 2019 at 22:37  »
The engine is now complete and ready to be started. The carbs have been fitted, an under magneto inspection carried out, the valve clearances set and the valve and ignition timing set. So why wont it run? TBH I'm hoping some of you might have some ideas!

To put some meat on the bones. My inspection of the camshaft etc showed that there was no significant end float on the cam and the cam followers seemed to be running in the centre of the cam lobes and the cam drive gear was meshed in the middle of the idler gear. I couldnt make any meaningful measurement of the cam base circle though.

I timed the valves using my 360 deg timing disc on the flywheel rotating anti clock wise looking at the flywheel, so the inlet just starts to open at 10 deg BTDC. I timed the ignition so that the contact breaker is just opening at 37 deg BTDC on the front cylinder with the rear cylinder valves "rocking"

The magneto has contact breaker base plate marked with a cast L. The magneto rotates clockwise when the engine turns anti clockwise. The stud is opposite the front cylinder. I am not certain that the slip ring is the correct one, but it was recently professionally refurbished. This set up is pictured in the photos posted below.

Both spark plugs had good healthy spark when the engine was turned overtuned over with the plugs removed. The plugs are one NOS Champion COM6 and one used Champion COM5 cleaned and regapped. The gaps are around 12 thou. The contact breaker points gap is 11 thou fully open, and the opening point found when a 2 thou feeler gauge between the points is released.

The engine is running on methanol. The carbs are AMAL/AMAC type M's (I think). I have cleaned, readjusted them and blown through all the various orrifices. Everything runs freely in them, The jets are 150 front, 140 rear and the engine is fitted with domed topped pistons. CR measures at 10.1

When the engine is turned over with the plugs fitted I get good compressions in both cyliders, and I can see vapour being blown out of the exhaust ports. Apart from the occassional lone cylinder firing the engine wont start. I am turning it over anti clockwise with an electric drill on the flyweel nut. I have tried spraying Bradex Starting fluid and putting small amounts of methanol into the combstion chambers through the plug holes (on seperate occasions). Ive tried advancing and retarding the ignition at the magneto, opening the throttles. All to no avail!

I attach below a couple of pics of the magneto. The first one is of the engine at TDC with the rear valves rocking.
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 03 Mar 2019 at 21:45  »
Todays trials and tribulations!

Read more on next post!
Douglas Motorcycles - General Discussion / Re: Main shaft felt seal
« Last post by eddie on 03 Mar 2019 at 20:30  »
The gearbox coupling should be fitted with 2 pressed steel flanges pushed on to the plain spigot - the inner one throws any leaking oil into the catch channel around the input shaft - the larger outer flange covers the outer lip on the front cover plate. There should not be a felt seal in the channel around the shaft - the seal is in the housing that is inboard of the coupling, and is only accessible from inside the 'box. My advice would be - don't worry about the oil loss when the gearbox has been stood on it's front end, it is designed to do that! In normal use, any oil that leaks past the input bearing, gets flung out into the catch channel and drains through a drilling to pass through the front layshaft bearing and back into the gearbox. This drilling also doubles as a breather for the gearbox - so when you stand the 'box on end, the oil returns up the drilling and on to the floor!

Michael, I have had the same problem posting pictures so I now past the photo into a word doc and save the document as a PDF containing the picture.  This works well as a workaround.  Gord
Douglas Motorcycles - General Discussion / Re: Main shaft felt seal
« Last post by Bynorthsea on 03 Mar 2019 at 18:40  »
Forgot the pictures
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