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[Adrian]

Cov Lad,



no, I don't mean tapered. Were you thinking of counterSUNK? Have a close look at the second picture, you see where the valve body sits IN the top of the head a bit? To do the modification as I did you have to drill right through the combustion chamber with a 1/2" drill, then you have to drill out the same hole PART WAY with a bigger drill.



The thickness of the casting at that point means that once you have drilled and tapped the hole for the valve body, you can screw the thing in but it it is recessed into the head somewhat. Whilst it is probably OK to use like that it does still mean that you have increased the combustion chamber volume slightly, causing what is an admittedly minor drop in compression.



To get the head of the valve actually to sit flush with the combustion chamber surface I then had to partly re-drill the hole from the top side of the head with a larger bit (I think it was 22mm) to remove JUST ENOUGH of the newly-threaded metal so that the remaining amount of thread matched the length of the threaded portion of the valve body, including the tip of the valve head. Think short-reach 14mm spark plug. This process also left a nice seat for the valve body to sit on/in. Do NOT drill down too far with the bigger drill or the valve body will protrude into the combustion chamber. Also you will not be left with enough thread to hold the valve body securely, which leaves you with a scrap head.



I have a couple more heads to so, so I will try and remember to take some work in progress pictures.



A.

[Norm]

Hi Adrian, the 14mm hole probably doesn't need to go all the way through, all you need is enough clearance around the actual valve in the decomp, in actual fact the hole going through into the head might only need to be a 1/4 inch it means the plug hole thread would be in a blind hole. Just a thought, it is only needed to remove a small volume of air at the time

[Adrian]

Hi Norm,



my intention was just to restore the missing classic Bullet feature to the AVL head, but as you say the 14mm hole only needs to be drilled deep enough for the fitted valve to have room to operate. In practice I have had no clearance issues with the decomp valve head and the inlet valve, but your method would remove the risk altogether. Semper Reformanda.



I think Tim NZ uses a similar set-up (with an extra adapter) on twin-plugged classic Bullet heads where the original decomp valve hole is in use for a twin-plug conversion.



A.

[Norm]

Adrian another thought I had was to tap into the head and fit a bit of copper tube out to the side and fit a lever type ball valve on it. Always good for a laugh when people see it and go "what tha" in particular when outside the pub. I fitted a little brass bilge pump on my Electra cross bred, got so many laughs when, before starting it up I would stand there pumping away on it

[Adrian]

Since we're wandering so far off the original topic, our hosts could market those bilge pumps as a white smoke prevention device on wet-sumping Bullets, just a question of plumbing one into the sump! Do you have a picture of it, Norm?



A.

[Norm]

Sorry Adrian I don't have any pics of although I put plenty of the internet while I still had it. My original idea (over a few beers of course) was because the Electra had no seal on the timing side, which meant they could wet sump, not a problem with the Electra piston rings being capable of handling a wet sump type motor using scraper ring type, but as I was fitting a cast iron barrel on mine I figured wet sumping was a possible issue so I went with the little pump. I welded a fitting into the front sump plug and ran the discharge from the pump back in through the tank breather fitting. I guess I should have kept some picks of it, but it always got a laugh

[Norm]

Adrian I have found some pics of it on Aussie Enfields I just have to work out how to lift from there to put on here. I will need my sons help with it. Maybe I should put it in a new topic, we have drifted a long way off the electrical problems