1930's 750cc S6/T6

[kmd]

Hi All

Can any one help me with a photo or a drawing of the workings of the 750's(sv) valve lifter parts as i think i have few parts missing for my next project.

Regards
Kevin

[Doug]

Kevin,

When you say valve lifter, do you mean the exhaust valve lifter, or decompression release? If so, you are not missing any parts as the S6 models and derivatives were not fitted with such.

Otherwise do you mean the mechanism for opening and closing the inlet and exhaust valves for conventional running?

-Doug

[kmd]

Hi Doug

Its a mix.
 I have crank cases that is T6(600)  but my barrels,pistons,inlet manifold and the cam followers (they have a roller on the out side)are off a 750 ,there is also a leaver which looks like  linkage or a cable  should attach to it.
Thanks
Kevin

[ChrisS]

Doug, Kevin.
I have an E32 [T6] which has exhaust valve lifter [decompressor] parts fitted these would appear to be Douglas originals and are worked by a cable which exits the timing gear chest roughly in the same place as the oil indicator but forward of the mag drive. the parts fit around the exhaust cam and when actuated lift both exhaust valves at the same time Could this have been something fitted at the factory on request.
ChrisS

[Doug]

I have an E32 [T6] which has exhaust valve lifter [decompressor] parts fitted...

Now that would be interesting to see. Mention of where the cable exits got me to thinking, the S6 engines do have a hex head plug fitted exactly there, and if looked up in the spares list (Feb '31), part number 810 is described as "plug in place of exhaust lift", interchangeable across all models. So Kingswood must have had thoughts on a exhaust lifter.

But no where is there a description of the parts for the exhaust lift in my copy of the spares list, or is mention of such made in the the 1929 T6, S5, S6, C31, D/31, and E/31 care and maintenance manual (which despite the title must have been issued in 1931!) Given the S6 and ilk have the pivoting roller followers and things appear a bit full in the timing chest, it would be interesting to see how a exhaust valve lifter was arranged internally around the other bits. I have been looking through my pictures of S6 and derivatives, and so far they have all had the plug.

-Doug

[Doug]

I did find one picture in the back of "The Best Twin", second printing (which has an additional chapter 17, Picture Gallery) showing what is captioned as a 1932 750cc H32 Mastiff engine (engine only) with a exhaust lift cable fitted. I wonder if this was something actually only fitted to the engine in stationary engine and stillage truck applications? It would explain it scarcity on motorcycles and absence from the motorcycle manuals. Though the engine shown does seem to have a primary chain case partially visible on the opposite side.

Any other S6 and derivative owners with a exhaust lift cable fitted?

-Doug

[graeme]

Doug,
I have seen a valve lifter fitted to a Mastiff - the outfit that used to belong to Andy Clark. A valve lifter would certainly be useful on my S6 - as you know Doug, you have to stall it by putting it in gear and let the clutch out a with the front brake firmly on. Bit of a pain really - I'm amazed that Douglas didn't fit a lifter as standard.
Cheers, Graeme

[MRD]

Hi All

I have recently spoken to a very knowlegable Ex president of LDMCC. And I am led to believe that the Valve lifter was fitted to the 750cc "Mastiff" only. I am also of the understanding that it used the same crankcase as the S6. Not sure about the crankshaft or conrods but other differences are heads, cylinders, pistons and although very similar the timing cover / induction manifold. The manifold being slightly longer due to the increase in capacity and also to take a side draught carb instead of the common S6 updraught.   
Hope this is of help.
Regards      Martin

[kmd]

Thanks  for your help.

I have had some luck and  have been giving the rocking horse **** ? from an other member of the LDMCC.

The operating arm sits between the  lobs on the exhaust cam

1 of the cam followers bolts is replaced with a post for the return spring

The cam followers have a bearing on the out side

Kevin

[Doug]

Kevin,

So that is how they arranged it. Not sure I care for it pivoting on the cam, even at half engine speed it is turning inside the 'rocking horse' all the time the engine is running; a lot of wear and tear serving no purpose. Still, they apparently were unable to come up with a better solution. The only saving grace is when not in use the loading and friction is minimal.

Graeme, I remember your S6 more for going than stopping! I should have noticed the cable on the ex-Andy Clarke outfit, but did not. I dug out a picture form the 2007 ADCR and there it was. I looked at the catalog pics and info for the Mastiff last night, and did not see or read mention of a valve lifter. Of course, catalog illustrations and specs are not the last word on what they actually shipped out the factory door.

As the Mastiff came along in ’32 and the boss was there right from the beginning, they must have had thoughts about fitting a lifter long before the T6/S6 got opened up to 750cc. From all appearances the Mastiff does use the same crankcase as the S6, with slightly larger cylinders and deeper heads. The timing cover and integral inlet manifold did change slightly.

The crankcase did change for the final two years when the Greyhound and Mastiff became the Z and Z1 of 1934 and then the Wessex and Powerflow of 1935. In 1934 they dropped the pancake dyno from the face of the timing cover and used a Lucas magdyno. There was the elimination of the oil sump which lowered the engine in the frame, fitting of a duplex geared oil pump common to the other big twins, and there is mention of a connecting rod with double roller bearing and durallumin cage (probably the same what was being used in the Blue Chief and Endeavour.)

-Doug