Hitchcocks Forum

Can anyone tell me how to distinguish the various cylinder heads fitted to the post war Bullets, both English and Indian Graham

Hi Graham, two things I can think of are the pre '55 types had an external exhaust pipe stub, for the pipe to clamp onto, the other is the pushrod tunnels are a bit closer to the combustion chamber on the earlier ones, meaning the head and base gaskets required are different. There may be other differences on top of these, but those are the ones I know of. I once saw a late engine fitted with an early head - or was it the other way around - but head joint sealing and clearance for the pushrods in their tunnels was badly compromised. The stud hole spacings are the same, around the cylinder, apart from maybe the short one at the top of the barrel, where I seem to recall seeing some bodgery.

Just checked through my pictures and it was a late head and barrel on an early bottom end, with the stud hole in the barrel above the tappet cover re drilled to suit the earlier, narrower engine.

If the exhaust valve seat falls out onto the floor when you take the valve out, it's probably an Indian one.

There's a school of thought which says the Redditch heads were better quality castings. I wouldn't be worried if an Indian-made head wasn't quite such a neat job, though I'd want my valve seats to stay put! I have heard of this issue before, though I'm not sure it's a particularly widespread problem.

Redditch also made a version of their 350 head in cast-iron as an economy measure on the 1958 350 Clipper (the budget version of the Bullet).

Very late 350 Indian Bullet heads (pre-UCE) also had an extra alloy lump in the casting near the exhaust port on the left hand side, which suggests that the factory had been considering moving the Pulse Air Valve input from the exhaust pipe to the head itself, much the same as the 500 Electra-X cylinder heads.

I assume that the 350 AVL and UCE heads are not what you're referring to in your original question.

A.

I think Paul was referring to my bike asbo 30 Redditch head and bottom end with Indian aluminum barrel
I think it's in one of the build videos that Paul (Bullet Whisperer) did of my bike look up asbo 30 on YouTube to see most of the build
Time to say yes the devcon is still there
A big thank you to Paul for putting up with my endless visits
Cheers all merry Xmas all Dai

Hello, Dai and Happy Christmas to you, too. No, it wasn't your machine, but a pre '55 engine, with later, post '55 wider pattern alloy head and barrel I was referring to above [see my first ever picture on here and check out the stud holes at the bottom of the barrel, above the tappet chest].
That said, we had a good bit of fun with yours leaking oil, thanks to very out of step gasket faces between the later pattern alloy head and barrel on yours, even though all components were meant to be correct and match and, yes, Devcon came to the rescue to put this right in the end!

Here is Dai's cylinder head, with added Devcon, to build up the gasket face and stop the leaks. There was only a few thou of metal overlap between the barrel and head joint faces at the outside of the pushrod tunnels and building it up allowed better sealing of the oil with the gasket. That old head gasket was just used as a template, by the way!

I do wonder if those barrels would be better with a groove machined round the pushrod tunnels for an o-ring/crush washer and just missing them out from the head gasket asembly altogether, similar to some of the liquid-cooled 2-strokes where the water-jacket connects to the head. Some of the composite gaskets do have an integral bead of goo round the pushrod tunnels

There was also an article in The Gun a while back about someone cutting down head gaskets so they effectively formed a very thin strip round all the necessary mating surfaces. Effectively a wire skeleton of a head gasket. As I recall they used the concept on some WW2 aero engines. Less surface area but a much greater degree of compression of the gasket material and more tolerant of imperfectly flat mating surfaces.

I have converted a number of alloy barrels to use o rings around the pushrod tunnels - they don't always want to be concentric to the holes, which may be slightly out of step with those in the head, so I like to place a barrel and head together and look down at the tunnels where they meet, to decide how to position the o rings. With this set up, I always lap the liner spigot into the recess in the head, to seal compression.