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MG MGB GT V8 Factory Originals Technical - Plug Inserts

Does the factory V8 head have inserts in the spark plug holes or are the threads direct in the block? I ask because yesterday I spent an anxious half hour trying to get one new plug in without cross threading it. In spite of being ever so careful and starting it by hand it was almost impossible to get this plug to go in straight (second from rear on the RHS looking back - No. 6?), a process not helped by the dip stick tube and the impossibility of lining them up by eye. Also the low torque required makes it difficult to know when it is fully home and properly sealed due to the different "feel" of aluminium. I didn't actually use a torque wrench - I expect people will find this critical - just nipping them up by hand. Are there any sure fire ways of tackling this (grease the threads perhaps). Thanks

Ian Thomson
ian thomson

Ian,

The Factory V-8 does not use steel inserts in the plug holes, unless one has been previously damaged and has a Helicoil insert installed. I find that it may be easier to remove the plug in that position if you first remove the bolt that holds the dipstick tube to the valve cover. This gives you a little wiggle room to get to the plug. Put a little Copaslip on the threads of the new plug, also make sure that there is no dirt or grit built up around the old plug before you take it out. I use a blast of compressed air around the base of the plug to blow away anything before attempting to remove it.

On aluminum heads, don't try to remove the plugs unless the engine is cold. Make sure you eyeball and make a mental note of the angle of installation of the plugs in the Rover V-8 heads - they are angled slightly. If you forget to do this, check the corresponding plug on the opposite side of the engine. Buy a good quality spark plug socket with a rubber or foam insert to support the plug insulator. You can use this socket with a short 3" extension as a handle to install the new plug as well. It is sometimes easier to guide the plug in place by holding it in the socket with the extension, than it is to try to hold the end of the plug with two fingers as you attempt to guide it in place and turn it at the same time. I don't worry about specific torque values for the plugs, with new sealing ring type plugs, tighten them 1/4 turn after the gasket contacts the head. If you are putting a used plug back in, tighten it 1/16 turn after the gasket seats (just snug).

One other note on factory V-8 spark plugs - the factory recommends removal of the heat riser shrouds to get to the front two plugs. If you have a good spark plug socket that has hex flats machined into the drive end, you don't need to remove the shroud. You can usually sneak the socket in over the spark plug, then use a large open-end wrench on the socket flats to loosen the old plug and to tighten the new one.

Hope this helps,
Paul Kile
Paul Kile

Thanks Paul. I found that removing the top dip stick tube bolt and swivelling the tube made things a little easier - but only after I hit trouble. I have a good plug socket like you describe but the problem, as I see it, turned out to be the socket itself which was too thick walled and was rubbing on the sides of the gully in the head giving a false feel to the whole thing. It would go tight and then loosen off suddenly as if the threads had stripped; creating, as you can imagine, an exquisite sense of impending panic! Paradoxically a cheap (thin walled) plug spanner may have been better.

Ian T
ian thomson

Ian,
You're right, I had forgotten about the wall thickness issue on the spark plug sockets. Actually, if you can get hold of a really good quality socket from a company like Snap-On (and I know they have distributors in the UK), the wall thickness will actually be thinner than those of cheaper sockets. Better quality metal means it doesn't have to be as thick.

Cheers,
Paul Kile
Paul Kile

When I first had my V8 I found the same thing regarding my plug socket. Went to Halfords and borrowed one of their 'off the shelf' items and it fitted just fine.
Paul Hunt

Thanks Pauls, It's nice at least to know that I am not alone with these scares. I have been using the plug socket in qhestion for about 20 years with no difficulties up to now. I guess I will have to pension it off for a new model now. BTW I have now fixed my ongoing intermittent ign. warning lamp problem Paul (factory V8 - AC Delco Alt) - it was the field diodes! (but the local shop was had the parts on the shelf).

Happy Easter.

Ian
Ian Thomson

This thread was discussed between 25/03/2002 and 31/03/2002

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