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MG MGB Technical - A Bit of Advice Please

3 quick questions to the knowledgeable many!

1. I need to change the gearbox mounting rubbers on my 1978 B. MGOC spares sent me 2 but said they were substitutes for the originals but will be OK.
How long should it take? I have been told it can be difficult - any tips?

2. What is the easiest way to replace the heater cable - the one that controls the wateer valve?

3. Tappet clearances. I believe the engine should be hot. Is there a measurement for a cold engine?

Thanks for any help.

A Stubley

2. I bought a new cable from a farm supply store, as a universal choke replacement cable, $5. Removed the old cable, cut new one to match and replaced. It works best to remove the control valve from dash though. Then you have an opportunity to clean the control valve too, of all the old waxy buildup, etc. I greased the inner cable before inserting it back into outer sleeve.

R.W Anderson

Adrian. 1.What do you mean by, "the gearbox mounting rubbers"? Do you mean the two gear box mounts or do you mean all of the rubber parts associated with the cross member?

The two rubber pieces associated with the engine steady rod are no problem to replace.

The two round rubber pieces between the two sections of the cross member can be difficult to replace. It helps to heat the new pieces in a pan of hot water and to lubricate the metal with some silicone grease when assembling them together.

The rubber mounts between the cross member and the transmission are relatively easy with a standard four speed transmission and almost impossible with the four speed with overdrive transmission. If you have an overdrive box, consider modifying the cross member to make the job easier. Ollie Stephenson (sp?) has posted about this in the past and it should be in the archives. The photos on his web site make it clean what needs to be done. I have done this modification on three cars, making installing the cross member to the transmission much easier.

When dropping the cross member, the rear of the transmission will need to be supported in some fashion. The prop shaft does not need to be disconnected but doing so makes the job easier for me.

2. With all of the known problems with replacement heater control valves, I no longer use the factory style valve and have switched over to Bob Muenchausen's design. Cannot be adjusted from inside the passenger compartment, but I have never found any great need to do so anyway. Bob's design allows the valve to be shut off completely and, when turned on, has a potential to provide a higher flow of water through the heater. If you are interested in reading about it, do a web search for "Muenchausen's Garage".

3. As I remember it, the MGA had a specification for both hot and cold setting of the tappets with the cold setting being .002" larger than the hot setting. But, I always set the tappet clearances hot because it seemed a more accurate method and is no harder to do than setting them cold. At least for me.

Les Bengtson

Tappet adjustment is normally done cold (according to Haynes Manual) ... standard setting is 15 thou (0.015").
Geoff Everitt

Thanks for the replies:

1. The original handbook says that the tappets are set with a warm engine - I just wondered how much difference there is with a cold engine.

2. The gearbox rubbers I need to replace are the 2 between the cross member. Mine is an overdrive car. I am going to also replace the prop - the front joint has a trace of play in it.

3. When replacing the heater cable ( I have to do the valve as well - it had been weeping onto the distributer causing it to seize on the clamp!) I wondered how to access the back of the control knob in the car - is there an easy way to get at it!
A Stubley


1.The factory workshop manual gives a tappet clearance of .015" (Cold) on the early engines and a tappet setting of .015" (Cold) or .013" (Warm) on the later engines. With the rubber bumper cars, the factory workshop manual gives a specification of .013" (Warm) and does not list a cold engine setting. Either of the two specifications should work.

2. This is going to be interesting. Without modification to the cross member, it is almost impossible to install the cross member to transmission mounts. I say almost impossible because, one time, I saw someone with very small hands and a great deal of patience install these mounts on a stock cross member. But, I have never been able to do it myself, nor have I ever met anyone else who could. Much information on this in the archives.

The rear of the heater control knob is most easily accessed either through the opening where the radio goes or by removing the center console, then the upright panel containing the knobs and radio.

Job 1 is relatively easy. Jobs 2 and 3 are complex, time consuming, frustrating and not fun at all.

Les Bengtson

I have to say I have installed the OD gearbox cross member (sans modification) on a couple of occasions. Not easy, as those above attest, but can be done if all thread holes are thoroughly clean, very lightly oiled to assist the turn of steel bolts into aluminium housing holes, great patience is displayed and you have been to Church somewhere in the past year - wedding using wedding cars sevenoakss do count. I do think though that I will adopt the modification next time I have the bu***r out.

My factory manual (Leyland Australia, covering local cars up to 1972 only, local production ceased then) only lists 15 though cold for the tappets. Les and others know the US market and cars later than that date. Go with their advice.

Roger T

With the UK tin dash you simply remove the knob from the control (depress the plunger on the side of the knob) and undo the nub behind it, the control can then easily be withdrawn and hand down below the dash to get at the cable inner and outer clamp and screw, and this applies to both controls. For the later plastic dash with the heater controls in the centre console (which I'm asusming your 78 has) this must be unscrewed (two screws each side) and pulled forwards before you can get the controls out from the back, and to do that you will have to remove the arm-rest part of the centre console.

Where the 1976 Leyland Workshop Manual only quotes one figure it is always cold. This is the case for the 18G to GG, at .015. For 18V 581/582 and 583 it quotes both, at .015 cold and .013 hot. For 18V to ECE15 and 779/780 it goes back to quoting cold only as .015. For the 18V 846/847 it quotes both again but as .013 cold and .015 hot, which is obviously an error i.e. reversed. Then for this last engine for 1976 it goes back to one figure again which it gives as .013 cold, but given the undoubted error above I'd say this is also an error and it should say .015 cold. I can't see any advantage to adjusting warm apart from keeping your hands warm in winter, and how warm is warm? Depending on how long you take a warm engine will be continually cooling during the process, whereas a 'cold' engine is stable.

Paul Hunt

All B series standard cams use the same valve clearance of 15 thou cold or 13 thou hot.

Non standard cams use clearances specified by the cam grinder - it is a function of the cam profile.

The x member can be fitted most easily by bolting the mounts to the gearbox, then hooking one side on the protruding stud, loosely fitting the washer & nut, then "pinging" the other stud into the hole using a long screwdriver or short jemmy bar for leverage.

Taking the air vents out of the dash gives access to the back of the heater controls.
Chris at Octarine Services

Thanks for the replies!
A Stubley

This thread was discussed between 24/07/2009 and 26/07/2009

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