Cylinder Head Identification

A friend was looking at my cylinder head and he noticed that it doesn't have air rail holes drilled for the air pump. Hmmm. Very puzzling. On the suggestion of folks at MGExp I pulled the valve cover gasket and made a note of the number. The head is a number 12H4736. Pat# 565394. This is actually a British Leyland produced replacement head for the B. I think they came without the air rail holes drilled so that they could be sold in both the US and UK market.

If you want to ID you cylinder head, here are a couple of useful sites...
http://www.flowspeed.com/cylinder-ident.htm
and

http://www.mgbmga.com/tech/mgb25.htm

Ray, owner of the famous supercharged B writes on his site...

The MGB engine used four basic cylinder head designs. The fourth version of the cylinder head was a slightly modified version of the 12H4736 cylinder head first introduced on the Austin Marina and used in the UK/European market RB MGB (74½-80) as Original Equipment.
This cylinder head was also used as a replacement cylinder for the CAM1106 on the US RB MGB (74½-80). They are essentially the same as the CAM1106 with slight modifications. It was referred to as the "lead-free" cylinder head and was induction hardened to withstand higher combustion temperatures of lead-free fuel.

The process involved 1% tin being added to the molten iron before casting, additional depth was used which was machined off before the induction hardening process was applied to the valve seat area, all valve seats. This was a complex process and applied only to the US market cylinder heads. It used 1.5625" inlet valves and 1.343" exhaust with a more efficient "Open" Kidney-Shaped combustion chambers featuring a larger squish area as well as reduced promontory between the valves, a chamber height of .375" with a volume of 39cc, (UK 43cc). The rear rocker shaft pedestal had an offset oil feed in order to accommodate the redesigned cooling passages that assisted in preventing overheating of the rear cylinder. These larger coolant ports also provided a greater service area to assist in dealing with higher combustion temperatures that resulted in efforts to reduce emissions. It has air injection ports and a water choke outlet at the rear of the cylinder head. The main difference compared to the CAM-1106 was a slightly more improved intake port design and the outer shaping of the head was revised giving a much smoother appearance. The Patent Number 565394 located by the thermostat housing was removed and marked inside the cylinder head.
We felt this cylinder had that little extra and when ported would provide us with low and middle range torque & power for increased street performance that we wanted.

Most likely the original head cracked and was replaced with this one. All fascinating stuff...

Brakes and a tuneup.

Its been a while since I posted, largely because I haven't done any work on the car - which is good!! I've driven it quite a bit in the meantime. I did replace shoes and rotors on the front brakes a while ago and today I took a look at the back brakes.

Before you get started take a look at this video by John Twist. It goes through the components and assembly nicely.


To do the back brakes, its worth taking a look at them before you buy any parts. (If you can't get the drum off - check you don't have the handbrake on!) Here is what one side looked like

 

Clearly there is plenty of life left in these shoes, although the cylinder is leaking. I checked for movement in the components by depressing the pedal and making sure everything moved it should. Then I put the wheel back on. I'll order a new cylinder and do that replacement another day.

If you have a sharp eye, you'll note that both shoes are in the same way. This is not how they are supposed to be. One should be up and one should be down - they are not supposed to be symmetric. I actually just realized this and I'll fix them next time I have the brakes apart.


I also have a pinched brake line which was probably caused by someone trying to pull the car with a rope or chain around the rear axle. I'll replace that when I do the brake cylinder as bleeding the brakes will be called for.



I also did a few other maintenance items. I had noticed a little exhaust noise from under the car, so I re-positioned and tightened the exhaust brackets.

I also did a tuneup. This involved:
1. Check spark plugs and gaps. - The plugs were all nice a clean with no bad discoloration or oil.
2. Check timing. Its where I left it at 14 BTDC.
3. Check valve clearance. This is something I haven't done before, but it is pretty easy. Check out first these two videos.

First, it helps if you can turn over then engine from under the hood. This video shows you how to do it. But basically you run a wire from the brown/white pin on the ignition starter relay to the bottom fuse of the fuse box. I also disconnected the HT lead from the top of the coil.



The second video shows you how to set the valves - basically we are adjusting the gap between the tappet and the top of the valve. The system is easy once you see it! You follow the rule of 9. There are 8 valves. When a valve is in its lowest position, its' pair (they should add to 9) is the one to adjust. So the pairing is as follows:
1 - 8
2 - 7
3 - 6
4 - 5
5 - 4
6 - 3
7 - 2
8 - 1

You get the valve in to its lowest position by just turning over the motor.

I did this with a cold engine and set the gap at 0.015. It'll be a bit narrower when warm - and the shop manual recommends 0.013 for a warm engine. I'll probably go back and check it in a few days.

You do not want to set it too tight!!!! You'll wear out the cam and you'll hurt performance. If it is set right, the valves should sound like a sewing machine!



Finally, I put a 180F stat in and took out the 195. Its been running a little warm and I want to see if this makes a difference.