Drapers Windmill (Margate)
A little while ago, Tim Keenan contacted Richard Amos for some help with a Crossley gas engine that is used to power the mill. Richard asked me if I would help as I have some experience with the Tangye at Cobbs. A suitable date was found and Richard Amos, Mark Tewkesbury, Bill Ovenden and myself set off for Margate! Now this is not an engine you will see every day. It is a 30hp type GE117 single cylinder, single flywheel, open crank engine. Originally configured for town gas it is complete with gas bag/regulator although this is not in use. The information was that the engine would run for short periods and then peter out. The group had sent the low tension magneto off for rewind and had the ignitor rebuilt. The result was the same hence our involvement. We checked the condition of the magneto and ignitor and found them to be electrically sound. The return spring on the magneto was fouling the support housing spoiling the snap action. Refitting the spring with the offset the correct way round soon fixed that. It was also noticed that the tappet that strikes the ignitor was too long, holding the contacts open at rest. This was easily adjusted and we moved on.
A test run was tried and the engine proved difficult to start as getting the gas ratio correct is “trial and error” on a regulator valve. The gas system is extremely rudimentary and basically pours Propane gas into the inlet tract whether the inlet valve is open or not! Eventually the “sweet” spot was found and the engine started firing. Now this engine is cranked by a small lister diesel that engages a rubber wheel onto the flywheel face to turn it over. There is no over running clutch as installed at Cobbs Mill so a helper has to be very quick at disengaging the lister before it explodes!!
As the engine speed increases, the gas flow has to be increased to meet demand to keep it firing regularly.
The governor mechanism started to take control and then another problem showed itself. The system on this engine uses a “flying” pivot on the inlet valve actuating rocker arm. The pivot position is controlled directly by the centrifugal governor. At rest the pivot is very near the push rod end of the rocker and so opens the inlet valve fully. As the engine speed increases the pivot moves towards the valve end of the rocker and in a linear way reduces the valve opening. It is a very clever mechanism and effectively “throttles” the engine in the same way a butterfly would on a traditional setup. In this case there was insufficient clearance for the “Flying” pivot at the minimum stroke end and it jammed up. A quick adjustment of the valve clearance fixed this issue. Another start was made and this time the governor took control as it should and it was all looking good. After a few minutes the engine started miss firing and we were treated to some decent bangs from the exhaust before it died as described! A check revealed “no compression” due to zero clearance on the exhaust valve tappet. A quick adjustment cured that and another start was performed but same thing happened again …
Initially it was feared the head of the valve was unscrewing from the stem. Removal of the inlet valve cage to get access to the exhaust valve showed this not to be the case. Further examination proved that the valve spring retainer assembly was unscrewing from the valve stem and taking up the tappet clearance ! It looks as though there should be a lock-nut on this part to stop it from happening but we did not have one. A hole was drilled and tapped in the side of the retainer to take a suitable bolt. This works well as a temporary fix until a 1¼“ Whitworth thin nut can be found. This time it started and then ran correctly. We ran it for about ½ an hour before it frosted up the gas cylinder and stopped through lack of gas.
An interesting day and most of the objectives were achieved. The trouble is the distance, a 2-hour journey each way so it can’t be a regular thing.
The men operating the mill are not “engine men” so there will be other issues here for sure. We all hope that they learn to manage this very impressive Crossley for all to see and wish them well for the future.
Latest update, we have since heard from Tim Keenan that the volunteers operating the mill have successfully started the engine but the ignitor developed a leak. This was fixed by Tim allowing them to start and run the engine successfully.