You do not want to use a bronze material for valve guides in a 'dry' application; inlet or exhaust. They are better suited for enclosed valve gear where there is a positive lubrication, like an oil mist. Douglas (and many others) use cast iron as it does have some inherent lubricity in between the infrequent applications of the oil can.

Some of the later racing models tapped oil vapor off the crankcase which coalesced in small oil lines that ran to the individual valve guides. They were drilled through the head/guides as you describe. I am not aware that the RAs would have this feature, but it could have been added later. Usually when encountered they are choked shut with carbonized oil.

-Doug

I've removed the valve guides from the two cylinder heads. The inlet ones are bronze and the exhaust ones cast iron. Both the exhaust ones have been broken. All four guides are stopped from rotating by pegs located in the heads that locate with cut-aways in the guide shoulder. I assume this is to maintain the alignment of small (2mm) lubrication holes in the guides and matching holes in the head. However, these holes have no evidence of external oil feed fittings and are just 'free to air'. 

I had planned to make four new valve guides from phosphor bronze, but a friend has queried whether the exhaust guides will be adequate in bronze rather than cast iron. Any advice from those better qualified than I in metallurgy would be welcomed.

 .

As I understand it, stepped rings come in two types - stepped compression and stepped scrapers. Normally, stepped compression rings are fitted as 'ridge dodgers' in worn bores (i.e., with the relief at he top). Stepped scrapers are usually fitted the other way up (relief at the bottom). In the case of the postwar Douglas, the stepped ring is fitted in the second groove, so can't be a 'ridge dodger' - so must be a stepped scraper (especially as it was listed from new - i.e. for an unworn bore).

Hope this helps,
                         Eddie.

Rings often have a dot near an end of the ring - to indicate the top or up side.
Nothing of that here ?

An oil scraper (ie lower/lowest) ring would generally have the stepped side facing downwards.
To gather and scrape the oil back downwards towards the sump.

But I personally don't know your ring set.
Nothing in the little instruction sheet that likely came with them ?
Knowing the recommended ring end gap is also vital info.
Too little can cause trouble, and equally so can too much....
Hopethishelps.

Hi See general tips below



https://www.thn.nl/en/product-line/piston-rings/piston-ring-types

Winter 2025 edition now available - French Motorcycles.

Download link - Winter 2025 - French Motorcycles

Which way round does the stepped scraper ring go, step up to piston crown or step down to bottom of piston?

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It was in the Whitewebbs Museum, where I saw it in 2003 (below). At that time the sump was off getting copied by someone in the LDMCC.



It seems to be a 1925 Works frame, in that it has the plate rear lugs like the RA/OB, though with slots to adjust the axle position. These are seen in other period photos of the factory entries at races. The following year when the model became cataloged and available to general public it had the cast frame lugs seen on subsequent models. Another 'early' feature is the RA (OB?) style foot peg lugs. They only wrap around the frame tube about 3/4s of the way, and are not the fully enveloping tee-fitting like on the DT models.

The engine is a slight oddity too. The bottom of the crankcase casting is extended and milled off in one great large planer surface.



In all other cases I have seen where the sump is fitted the 'window frame' in the base of the crankcase is a raised spigot. As in this example:



-Doug