MG T & Y Type Rocker Covers

MG T & Y Type Rocker Covers



MG T-Type and Y-Type Rocker Covers and Side Engine Plates sustain oil leaks for a variety of reasons. However, once these factors are identified and then action is taken to rectify the common areas of concern, MG owners can assuredly have totally leak-free results in at least this part of their XPAG/XPEG.

The original Rocker Covers on T-Types and Y-Types were manufactured in pressed steel. From experience of working on T-Type engines, I can say that the Cover’s original integrity is almost invariably compromised in some way or another. Like chassis frames, what appears to be accurate may not be the case when careful examination of Covers occurs.

Firstly, before attempting any work to be carried out, it is preferable to thoroughly degrease the Rocker Cover and strip off all paint/chrome. Also bead blasting, particularly after reverse electro chrome stripping, saves a lot of time in surface preparation. Remove the brass “Rocker Clearance” plate by carefully grinding off the pair of brass rivet tails located inside the cover. Use a fine punch to finally drive out the solid rivets. These brass rivets can be re-made up using a lathe. The brass plate itself will usually be in excellent, readable condition providing it previously hasn’t been linished over when former owners had the Cover chrome plated. Light buffing will bring the brass back to its former sheen. The polished finish will be maintained for a long time by dipping the plate in a clear lacquer such as Incralac or spraying with Holts Auto Clear Lacquer. I like to rivet this plate back into position on the Rocker Cover after final painting of the Cover is completed. Use of a suitably sized/shaped dolly turned up on a lathe to enable the head of the rivet to be supported without damage during the peening procedure, together with the application of a small Ball Pein Hammer, assists in effective closing of the solid rivet.

To check for unwanted dents, imperfections, etc. on the Rocker Cover’s surface, use a fine abrasive paper over the surface to obviate the problems. This procedure defines the point in the surface of a dent where the previous impact occurred and from which direction. I usually recommend using mallets first in some beating processes, but the steel cover is fairly rigid and major dents may require the use of appropriate steel panel beating hammers. Typically, a major area of damage can result, for example, from an engine toppling over when being moved across a garage floor. Don’t ask me how I know!

The Rocker Cover is held down tightly on the gasket situated between the Rocker Cover sealing flange and Cylinder Head surface by a pair of Bakelite thumb nuts. Often the correct sized fibre washer which goes between the thumb nut and the Cover is missing. As a result, indents can occur at this point. Using a round bar for a dolly, you can tap this area of the Cover back to its original position and form. A good seal at these points will then again be possible. To assist in getting the Rocker Cover to sit squarely, on the sealing surface, ensure the studs for the thumb nuts are in fact vertical.

It pays to closely check the sealing flange on the Rocker Cover. Look for localised indents on the flange. I suspect these imperfections are often the result of screwdrivers being used to prise off the cover from the Cylinder Head upper surface when the Rocker Cover over time becomes stuck fast. These indents need to be eradicated before filing of the delicate flange surface is initiated. Usually it is perhaps prudent to use wooden dollies to knock out the indents when panelling. However, because the flange is very narrow and rigid a metal dolly may have to be pressed into use. Grind up the end of a metal bar approximately three-quarters the width of the flange. Place the Rocker Cover on a steel bed and use hammer and dolly to remove the sealing flange indents. To assist you in identifying where flange imperfections are located, a hand block with fine abrasive paper will soon show up the tell-tale damage.

Once you are satisfied with the paneling process, Mill 2nd cut files can then be used across the entire flange of the Cover to true the surface. During the 60’s and 70’s, many owners delighted in having their Rocker Covers chrome plated. Quite often the linishing, which occurred as part of the chrome plating preparation, created thinning and undulation on the already meagre sealing flange. Non chrome plated covers are therefore easier to restore. Mill 2nd cut files help preserve precious metal, they plane off, rather than tear off, the metal.


Restorers can use a piece of sheet glass and a feeler gauge to check the “truth” of the cover or offer the Rocker Cover up to a spare Cylinder Head. It is easier for checks to occur at bench level.

The Cover should also be checked for wind or twist. A visual check first, followed again by use of a glass sheet, will soon obviate any problems in this regard.

The Rocker Cover is fairly easily “wound” back to a flat profile by the use of one’s hands. Work at it and keep re-checking against the glass sheet or Cylinder Head surface.

On TF’s at least, the Rocker Cover Oil Cap has a safety chain attached to the Rocker Cover by a solid aluminium rivet. Sometimes the rivet works loose (allowing leaks to occur) or is missing altogether. This rivet is easily turned up on a lathe. I like to have a small base or “land” on the rivet as well as the original flat type rivet head. The rivet can be readily peened over on the inside of the cover to effect a perfect seal.

The Rocker Cover Cap on TF’s was generally supplied in cadmium plated steel with the top centre finger hold release knob being nickel plated. The original cork junk gasket material used on the cap invariably results in a poor seal. Nitrile sheet is a far superior product and seals very well. To renew the seal and re-cadmium plate the cap, the riveted end of the finger hold’s shank located under the cap will need to be carefully ground down to just enable the retaining washer to be released. The finger hold can now be re-nickel plated at this stage. For re-assembly to occur, use a lathe to turn down (2mm approx.) the “shoulder” of the previously ground down finger hold shank. This procedure will enable the washer to be again held in place by re-peening the end of the finger hold shank over it. Don’t forget to fit the nitrile seal and then the circular Enots copper patented (Pat. No. 280261) locking tabs first. Incidentally, the reproduction safety chain holding the cap to the Rocker Cover rivet is often the incorrect size. This rather tedious work on the Rocker Cover Cap will be worth the effort, with no leaks resulting.

There appears to be some controversy regarding the paint colour of TF Rocker Covers. Some say the Cover was a rather drab looking greenish-grey colour yet others feel the colour was a light aluminium-grey tone. I have restored nine (9) TF Rocker Covers. In each case the brass Rocker Clearance plate had not been removed ex factory. Upon removing the plate, the paint underneath in each and every one, was the light aluminium-grey colour. I have found Acrylic Lacquer paint type works sufficiently well on Rocker Covers. A spray putty coat, followed by undercoat, then top colour coat, is effective. A clear lacquer over the final top coat helps seal the colour from oil, etc. Rubbing back between coats gives the desired finished result. Mask off all orifices on the Rocker Cover before any painting commences.

When finally fitting up the Rocker Cover to the Cylinder Head, a smear of the good old ‘tried and true’ sticky Permatex Aviation Gasket Cement applied on the underside of the surface of the gasket is very useful. This helps keep the gasket in the same position when the Rocker Cover has to be removed, for example, to check and adjust the valve clearances.

The Engine Side Plate Cover can also be prone to leaking oil. Again carefully check for, and rectify, localised imperfections, warp or wind. The original grey ‘muck’ metal (Mazak) three (3) setscrews which hold the Side Plate to the engine block, often stretch over time thereby losing Side Engine Plate pressure onto its sealing gasket. I have seen the hex heads of these dreadful original setscrews crack off their shank altogether!

Instead, brass setscrews (with a fibre washer placed under the head) are now available and work splendidly. For the Concours buffs, a flat grey colour painted over the brass hex heads will keep even the most fastidious Judge guessing.

Whilst discussing Rocker Covers and Cylinder Heads, confusion exists on the correct number that came originally with TF1250 Cylinder Heads. It is often erroneously written up by various authors that the cast number ex factory for TF1250 heads was 168422. This is not correct. TF1250’s had the number 168425 cast/stamped in with the first five (5) digits cast in and the number 5 stamped in.

MGTF Engine Bay and Rocker Cover.

In summary, attention to detail on Rocker Covers and Side Engine Plates will bring the reward of leak free seals. Correct, efficient gasket sealing is reflected in the accurate surfacing on which gaskets are to be applied.

Rob Grantham

TF3719, TF5164, TF9177

Perth, Western Australia

March 2012