Author Topic: MK IV Valve timing  (Read 337 times)

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Offline twirl

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MK IV Valve timing
« on: 18 Dec 2016 at 17:55 »
Overhauling my Douglas MK IV (7260/4), I found last year badly worn out sport-camshafts. This Douglas is not a sport-version, so I orded standard-camshafts from London Douglas Motorcycle Club. After fitting them into the crankcase I ensured that the timing marks for the gear idles were right. But, for my surprise, I got a different  valve timing on both sides. To get the same timings, on the right handed side (in driving direction) I had to go one theeth clockwards (see photo idle-gears).  With 0.05mm tappet adjustment on all valves I’ve got the following timings: Inlet opens 20 degrees bevor TDC and closes 54 degrees after BDC. Exhaust opens 57 degrees before BDC and closes 18 degrees after TDC. This times are different to the maintainance manual, especially the closing times concerned.  Maybe it’s not the best way to check the timing with 0.05 clearances only. Beside, the machine seems to work well last year. My questions are: did you ever hear of different timings when the timing marks are correct? Do you know a better way to check the Timing then my method (see photo Timing-check)? Should I worry about the closing times?  I am curious about your thoughts and advices. Thank you very much!
« Last Edit: 20 Dec 2016 at 05:25 by twirl »

Offline eddie

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Re: MK IV Valve timing
« Reply #1 on: 18 Dec 2016 at 18:42 »
Hi Twirl,
             For some strange reason, Mr Douglas decided to label most parts as Left Hand or Right Hand as you sit on the bike - except for the timing gears - these are marked LH & RH as you look into the timing chest. Now, you may think both gears are the same, but one has the keyway in line with a tooth and the other with the keyway in line with the space between 2 teeth. Your different valve timings may be due to swapped cam gears. The handbook gives the valve timing but it does not state the tappet clearance at which these figures are obtained. Most manufacturers quote figures at about .015" clearance so that the followers are on the main lift rather than the bottom of the ramp (where wildly varying figures can be obtained).
 Hope this helps,
 Regards,
               Eddie.

Offline twirl

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Re: MK IV Valve timing
« Reply #2 on: 19 Dec 2016 at 12:10 »
Hi Eddie,
thank you a lot for your hints. To be sure, not to have swapped gears, I first checked the standard position as you wrote in a thread of 2009. In TDC the crankshaft keyway was in 3 a'clock, but the timing line was not exactly in 6 a'clock, but one more tooth clockwise. Therefore I put the cam drive one tooth back. After that I checked the cam gears. The marks on the 17s and 11 ts theeth are correct as you wrote. With the teeth in line, and with 0.05mm tappet clearances to be able to compare the timing, I checked the valve timing again. On the right side (with the gear marked as left) exhaust opens at 60 degrees before BDC and closes 17 degrees after TDC. Inlet opens 24 degrees before TDC and 60 degrees after BDC. This seems to be the standard timing. But on the left cylinder now exhaust opens 40 degrees before BDC and closes 33 degrees after TDC.  Inlet opens 8 degrees before TDC and closes 70 degrees after BDC. That’s rather the same difference I ‘ve got the last time with all timing marks positioned as the manual mentioned. Maybe I’ve got one bad camshaft. I think, in this case I shoult write the Douglas Club to prevent other members from possible problems. What do you think?

Offline eddie

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Re: MK IV Valve timing
« Reply #3 on: 19 Dec 2016 at 12:38 »
Twirl,
         Another of Mr Douglas's eccentricities was that the crankshaft gear from a generator engine, whilst measuring up identical to that from the motorcycle engine, has the keyway half a tooth out of position. If you have a gear from a generator, that could be the reason the timing mark is not exactly at 6 o'clock!
 If you have managed to get the timing within a couple of degrees of the figures in the handbook, I would settle for that - I doubt that the factory managed to get much closer! If you want to get any closer, you will probably have to resort to making up stepped keys for the camshafts.
  Regards,
               Eddie.

Offline twirl

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Re: MK IV Valve timing
« Reply #4 on: 19 Dec 2016 at 17:12 »
Dear Eddie
Thank you for your advice.  As I think, the right cylinder is ok now, and I will try to settle the left cylinder valves within the same timings, without respecting the timing marks. Maybe Mr. Ernst Stärkle from Bale, who was a great motorsport enthusiast and imported Douglas postwar motorcycles in Switzerland, build up this engine with the sport-cams and just those parts, he found in his workplace.  On 1948, he and his wife Margrit visited the Douglas-Workplace in Bristol accompanied with a dozen fellows from the Douglas Club of Bale, dressed as Scotsmen. I found this story in “Motorradfahren in der Schweiz, Band 2” published by the friends of ancient motorcycles, Switzerland.
Thank you very much!

Offline twirl

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Re: MK IV Valve timing
« Reply #5 on: 27 Dec 2016 at 07:23 »
Now I've checked the valve timing as serious as I can. Maybe the keyway on the right handed pinion (plate 3, 7, 36252, marked with L) ore cam is exceptional, too. 
On this RH-pinion I have to line up the 18 tooth (and not as usual the 17one)  in line with the mark on the idler gear, as shown in the photo "idle-gears". This way I got a symetric timing on both sides as I reported . With 0.05mm tappet adjustment on all valves I’ve got the following timings: Inlet opens 18 degrees bevor TDC and closes 45 degrees after BDC. Exhaust opens 45 degrees before BDC and closes 18 degrees after TDC. I stepped foreward in steps of 9 degrees, using my indexion ficture. After all, this are definitly more moderate timings  as the maintenance manual explains.