Pre-dirt-track OHV Douglas rocker arms: S1, S2, RA, maybe even TT, OC

[cardan]

I've been sorting out - or trying to sort out! - a set of rockers suitable for an early RA/TW motor, c1924. A good opportunity to post some photos of the different types I've encountered.

There are a couple of rockers I'll ignore for the moment: OB rockers fitted with adjusters, and later DT-style rockers with the part number forged into the cylindrical part of the rocker between the arms.

This leaves three basic styles of rockers, with variants on each of the three.

The first photo shows the lightest style of rockers. These run directly on the spindle, with no bush. Very light weight, so I suppose they are either for the Sports Model, or maybe even for the 350cc version of the RA (RW, TW).

The rockers in the second photo are heavier, and use a full-length steel bush between the rocker and the spindle (bottom left). The rocker arms are strengthened with a spine down the back, which extends around onto the collared end of the rocker body. Possibly suitable for 24-25 RA?

The third photo shows rockers where there is a gusset between the arms and the body. These still have the pronounced collar at the two ends, but are otherwise similar to the DT pattern. I only have three of these. Maybe suit later RA/TT?

Odds and ends in the fourth photo, including one-return-spring and two return-spring versions (for Sports Model I think).

Comments welcome. Yell if you need any of the odds and ends, or if you have an odd rocker to complete set number three.

Cheers

Leon

[Alan Cun]

Hello Leon,
A quick trip to the shed and my info tells me they are probably DT. All my DT motors have no adjusters on the rockers. My OB and OC motors have valve clearance adjustment on the rocker at the valve collets and for whatever reason at the cam end of the push rods as well. I dont have an RA but assume some would be like the S1 which appear to be longer and smaller shaft dia.

Thats the way mine are anyway and as some me bikes were put together from what was on the shelf I could be wrong.

regards Alan.

[Doug]

Leon,

First picture, S1/S2 rocker arms. They ran direct on the spindles, no bush. According to the 1921-23 spares list, they did not change the rocker arms during the production run, though many other components were improved (particularly for 1923).

Third picture, RA rocker arms. Two variations of spindle size have been seen, but both use a hardened steel bush between the spindle bolt and the rocker arm.

Second picture, RA rocker arms. Same forgings as in picture three, but the center barrel section has been turned down in a lathe. There seem to be quite a few engines around with this type, which suggests that the factory did this modification.

Forth picture, S1/S2 rocker arms. From time to time you see these with one or two lugs for auxiliary return extension springs. Seem to have been only for use when you took your S1/S2 racing, so is not shown in the road model spares list. You also occasionally see these same 'helper' springs on RA rockers.

-Doug


[Fix typo.  18Jun14, Doug]

[cardan]

Thanks Alan and Doug. I should have mentioned that these rockers came loose or on a range of heads, including OB. They are obviously among the items that mix and match well across the range of OHV motors. All the rocker shafts I have seen on pre-DT heads are nominally 5/16", and the various RA/S1/S2 heads I have seen are machined to take 5/16" spindles. I've also come across quite a few OB rockers with adjusters fitted - perhaps they did have adjusters both on the tappets at the cam end and on the rockers but I can't think why.

Doug I hadn't noticed the similarity between the rockers in photo 2 and photo 3. Yes it looks like those in 3 could be machined to be converted into those in photo 2. Given the variety of finishes and dimensions within the same style of rocker, there must have been some hand finishing going on at the factory, at least on the OHV bikes.

Cheers

Leon

[cardan]

"Don't always believe what you see in a catalogue".  That said, interesting that the illustration below appears in the RA24 catalogue. Although the rockers are cut away in the drawing, they are clearly that bush-less type (as used in Sports model S1/S2 and shown in photo 1). Also the rocker oil box has vertical finning all around; more Sports than RA. Not surprising that the prototypes/race RAs in 1923 drew on parts from the Sports Model.

Leon

[Doug]

Leon,

The catalog illustration is definitely of a 3-1/2hp Sports.* The buttress for the rocker perch on the cylinder head is different between a S1/S2 and an RA, and this shows the S1/S2. Not sure why it is being passed off as an RA in the catalog, other than as an expediency. Oh, and there is no RA airbox visible.

-Doug

* Errata, see later post.  -Doug

[strike out incorrect text and add footnote. 18Jun14, Doug]

[cardan]

Agreed that the heads in the drawing are same as S1/S2, but the rest of the drawing is RA. Perhaps the artist was given a prototype or very early RA engine to draw.

Leon

[Doug]

Leon,

Ah, yes definitely intended to be an RA.

However I was a bit hasty, as even in the cropped illustration one can see the end of a horizontal crankcase bolt. The S1/S2 would have vertical bolts like the 4hp engine. My bad. The piston should have been a give-away too. Though some racing S1/S2 models might have had a slipper type piston, they would not, so far as I have seen, have had the forked little end to the connecting rod.

And for some reason the artist omitted the airbox.

Don't always believe what you see in a catalogue.

True, the 1924 and '25 RA catalog images continue to show the 1923 style frame.

-Doug