600 aero tappet blocks

[polly]

more probs!! does anyone know how the tappet blocks are fixed in the 600sv engine, as mine are fitted with a rubber o ring and just pushed into their respective holes, but push out quite easily!! is there  a retaining clamp used? as there is a small hole adjacent to each but it is not threaded!! regards david

[Doug]

There is a sheet metal bridge clamp made from spring metal. This is clamped by the cylinder base stud between the tappet guides, and has a finger at each end that tucks in and bears against the face of the guide. I will see if I can find a picture of it, as it is easier to show it than describe.

-Doug




[photo added.  19Jul15.  -Doug]

[polly]

many thanks doug, I can now get on and make a couple, mine were just held by centre punching the alloy edges!!, one further question if I may, the breathing of the engine can only be achieved through the two small holes drilled in the crankcase adjacent to the tappet blocks on the front cylinder, (the tappet blocks themselves are sealed by rubber o rings)  thence to the breather pipe, is this sufficient? regards David

[Doug]

David,

There should be a tapped and spot-faced hole in the top of the front tappet chest. This has a fitting and an tube that leads over the top of the cylinder base and then tucks into a hole in the primary chain case. The hole is drilled at a bit of an angle, about the 10 o'clock position on the engine sprocket. It is a bit home-engineered look, but I have seen it on several other Aero models so it apparently was the factory's afterthought as to how to provide some engine breathing!

I do not have a good picture of mine while it was assembled, so am substituting the best I could find, taken at the (wet!) 2007 Bristol cavalcade.




Fleeting glimpses can also be seen in the Photo Guide section for the "1935-1938 Models 5Y2, 500, 600, 600 Aero, DC/38" models.

-Doug

[polly]

many thanks Doug, I have managed to obtain a pair of tappet block retainers from a member, so all is well!!, re the breathing, yes, mine is exactly as you describe, and is per as your picture, I attach two pics of the crankcase, front half through via these two small holes the engine breaths into the tappet area is this sufficient?, also I show the area around the main bearing, a breather slot??but to where?.
has anyone installed a reed valve breather or, is it necessary?
best regards david

[Doug]

David,

The slot through the crankcase works in conjunction with a timed disc valve. This is driven by a flat on the crankshaft and held against the crankcase wall by a wave washer bearing against the timing pinion. I do not have a picture of this from my 600 Aero, and indeed it was so long ago I do not even have a clear recollection of it. But attached is a image of a 1935 250cc timed breather valve which shows you the idea.



The timed breather vented the crankcase to the timing chest. This filled up with oil until the lower edge of the timing gear was submerged. Above that it overflowed the weir and was picked up by the scavenge pump. Pressure in the timing chest blew oil mist out into the tappet chests via the upper small holes. The smaller hole at the bottom drained coalesced oil back to the timing chest. Excess pressure vented via the tube from the top of the front tappet chest to the primary chain, and probably via every joint and crevasse possible! 

-Doug