Author Topic: Douglas EW valve timing  (Read 2792 times)

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Offline patrickhowell

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Douglas EW valve timing
« on: 26 Jan 2016 at 13:57 »
Is it possible to (accidentally) transpose the valve timing pinion/ cams, so that the inlet goes into  the exhaust bush and vice versa? If so, what would be the effect on the valve timing? If they were identical, I would guess none, but otherwise? Still looking for reasons for a no-go engine.

Offline Doug

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Re: Douglas EW valve timing
« Reply #1 on: 27 Jan 2016 at 03:24 »
Patrick,

It is possible to transpose the cam gears. From 1925 to 1926, the inlet cam is the one with the drive slot on its hub. This was to drive the gear type oil pump, used on engines up to about YE6500. After that, the oil pump was a rotary plunger type drive via a worm in the crankshaft. However cam wheels with redundant drive slots probably were still fitted to the inlet until stocks were exhausted.  By c1927 they must have deleted this drive slot, as the spares list for that year just shows one cam wheel for the inlet/exhaust; part number c/8316. I do not have a spares list earlier than 1927 for the EW, to know offhand what the earlier cam numbers were. But it really does not matter, because-

Both cams have the same 245 degree duration according to the EW handbook (including the 1925-26 models), so either can be timed as a inlet or an exhaust. Though if you are using the original timing marks, things could get a bit interesting in the valve event! If you ignore any spurious marks and time it to the diagram in the handbook, you will be o.k.

Or by the numbers:

IO 15 degrees BTDC
IC 50 degrees ABDC
EO 50 degrees BBDC
EC 15 degrees ATDC

Inlet and exhaust valve lash 0.006" engine cold.

Without having an engine apart in front of me, I never really understood why they included a distance collar (part #8412) for the cam wheel. The axial location is determined by the tappets (am followers) on either side, not the length of the cam hub.

-Doug

Offline patrickhowell

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Re: Douglas EW valve timing
« Reply #2 on: 28 Jan 2016 at 15:55 »
Thanks, Doug
My Nov. 1929 spare parts list gives different part numbers for the inlet and exhaust cam wheels. My EW was registered in early 1929. I wonder whether they changed the design, and if so, when?
Patrick

Offline Doug

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Re: Douglas EW valve timing
« Reply #3 on: 28 Jan 2016 at 16:26 »
Patrick,

Are you sure you are not looking at the cam wheels for the L29/B29 (pc/10729 & pc/10728)? Those were different becuase of the sump and the oil pump located therein. The exhaust cam drove the vertical shaft for the oil pump. The A28/B28/C28 used cam wheel c/8316. 

-Doug

Offline patrickhowell

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Re: Douglas EW valve timing
« Reply #4 on: 29 Jan 2016 at 14:28 »
Doug
You seem to bright about that, thanks.
Patrick

 

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