Buzzie with her Douglas DT engine made it to Goodwood!

[Buzzie]

Buzzie made it to Goodwood! We had a great weekend rubbing shoulders with the motorsports gliterati at this famous track. I’d love to tell you that the Douglas DT engine ran perfectly over the weekend, blowing away the Norton and JAP powered opposition. Sadly the reality was a bit different! But we had a great time and Buzzie with her Douglas power unit attracted a lot of attention.

The headline is that the car failed in the practice and in the race itself. However we were granted a second chance to complete a flying qualification lap, which she did without issue. The problem with the engine was the same each time, which was that the exhaust valve pushrod adjuster on the rear cylinder shortened itself until the rocker end leapt out of the socket on the rocket. The same thing had happened in a test run on a local airfield the week before.

It took the three occurrences for us to work out exactly what was happening and that it wasn't due to component failure, wrong clearance adjustment or failure to lock the adjuster properly. There were a couple of people we met who actually owned DT bikes, and neither of them had heard of such a thing happening.

So if anyone has any experience of something like this happening, and what can be done to stop it please reply below. I am all ears !!!

[Jonathan Hewitt]

Morning, if the valve stuck in the guide momentarily, could the push rod  simply drop out ? This happens on Lister SR series engines when the inlet valves are clagged up and the piston then closes the valve but not before the pushrod has moved sideways
  Jonathan

[eddie]

Something else that might have caused a valve to stick. If you are still using cast iron valve guides, but with modern valves that are suited to unleaded fuel, these valves are known to stick unless they have had the stems specially coated - we had the same problem when involved with the LDMCC spares scheme with valves for the postwar motors.
   On my DT motors, I am using cut down bronze guides from an early 750 Commando motor and Kibblewhite oversize valves for a 650 Triumph (along with springs, top caps and collets).

   Regards,
                Eddie.

[Buzzie]

Thanks chaps for the useful replies:

Jonathan we wondered about a sticking valve causing it exactly as you say. But the adjuster had definitely unwound by quite a way, so far that the pushrod could never have stayed in. So we are pretty sure thats not the primary cause of the problem. However the self adjusting of the adjuster could have been caused by a sticking or indeed crashing valve.

Eddie, thank you for the suggestion about optimising the valve and guide set up to remove those potential causes of sticking. I will certainly look at fitting the parts you suggest before we run her in anger again.

One issue I also have is about measuring engine revs. I used an electronic tacho which is designed for a 4 cylinder engine. I fed it from the lead which earths the contact breaker when the emergency cut off switch was thrown. I assumed that this would read half the actual engine speed for the 2 cylinder Douglas engine. But when we ran the engine it seemed to us that wasn't the case. So we are not sure what engine speed was. I was working on a red line at 5000 rpm(tacho reading 2500 rpm) to be safe.