I am hoping to get some help with an issue I have finishing my Wyvern IC engine. I basically finished it over a year ago but couldn't get it to run, so I put it aside for a bit.

I think that one issue that is stopping it running is that the valve housings are not properly sealing in the cylinder head. With the head, valves and valve housings fitted to the engine if I cover the inlet and exhaust holes with my fingers and rotate the engine I can feel (high and low) air pressure – with the valves fully closed. So air is getting from the head, past either the valve seal with the housing or past the valve housing seal with the head.

The housings should seal at the end. I machined the head and housings carefully and then used a fine grinding paste to get a close fit and the fit seems ok, I have blued the mating face of the housing and it seems to be a good fit with the head. I machined the 45 degree back face on the valves at the same topslide setting as the valve housing and again using grinding paste to get a good fit between the valves and the valve housings.

I would be really grateful if anyone has any advice on this. Can I use some sort of a seal or do I just need a tighter fit?

Thanks in advance. Andy

Brian – thanks for these thoughts. Your first suggestion may have hit the nail on the head and I have to say it's something I hadn't even considered. The stuff I used was part of a kit I had lying around designed for grinding valves in car engines – probably too coarse. After reading your reply I just used some Peek fine metal polish on the valve seats and then twisted the valves by hand for a few minutes until it felt very smooth, cleaned it all up and refitted the valve housings. I am now struggling to feel any air getting past. So I will now fully reassemble the engine and see if I can get it to fire up. If I can I will be extremely happy. If not it will probably be the next issue to do with the carb or the timing or the points

Yes, the valves are closed when the rockers are relaxed, I have been testing this with rockers removed to rule out that possibility. The valve springs feel strong enough – but I don't really know.

Rod – thanks for that. I have some of that product and thought about using it but wasn't sure if it would work at the temperatures next to the exhaust valve. Did you use it on the end of the housing that is inserted into the head or on the flange that is bolted on the surface of the head – or both?

One issue I have found with the head in this engine is that the alloy casting, once machined to drawings, is very thin and weak in places. One tapped hole for a valve housing had to be so shallow that the thread stripped – I have got around this for now by loctiting the stud in place.

Thanks again and I will post an update.

Thanks Roger and Jason

The fuel is petrol, fresh and expensive low sulphur stuff for 4 stroke lawn mowers. The spark plug is commercial and does spark at the correct moment. I am getting that bounce albeit not as strongly as in that video – it's a smaller engine though.

The timing seems fine when I move the engine slowly by hand, but something must be wrong. Fuel is dripping from the carb air intake on the intake stroke and I don't think any is making its way into the head.