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MG MGB Technical - Tappet chest gaskets

I carefully installed new cork gaskets about 35,000 miles ago and suddenly both were leaking considerable amounts of oil. The tappet covers take a thick gasket. I found one in rubber and replaced the worst offender while tightening the bolt on the breather cover.

I was able to obtain two thin cork gaskets, too thin to fill the trough of the covers. The rubber gasket was the only option and it seemed to have shrunk slightly.

This is a hot spot, on the block behind the exhaust manifold. has anyone tried the silicone gaskets offered by Moss? It is definitely a severe application, a poor design really. These covers were eliminated on A Series engines between the 1098 and the 1275.
Glenn Mallory

Napa auto parts sells an adhesive called "The right stuff" I used it on my MGA side covers! It works great! Don't get it on you! see picture!


S

Replaced mine (73, I think they changed in 76). One cork and one rubber, the rubber was slightly too small for the groove in the rear chest, the cork was fine as it basically sits against a flat flange. The rubber seal I lightly clamped into place in the cover overnight using some wood strips, and that stayed in place when unclamped as long as I fitted it immediately. Non-setting sealant on both side of both gaskets and they have been fine. It's important that the rubber seal on the bolts is sound, and the cup washer is fitted. As the bolt is tightened the rubber wants to spread, but is restrained by the cup, and clamps into the threads.
paulh4

Glenn. When I replaced the tappet cover gaskets on my 79,some 12 years ago. With the engine warm, I used cork gaskets and Permatex sealer on both sides of the gaskets. Also put a dab of Lock-Tite on the bolt threads. Check the condition of the covers to see if the bolt holes haven't collapsed at all from over tightening. That will reduce the "holding pressure" of the cover to the gaskets.

Cheers

Gary
79 MGB
gary hansen

just last week, i was watching a john twist video.

he said for the B, use MGA gaskets. the rubber one.

G
Graham Moore

Glenn-
The tappet chest covers were redesigned as the years went by, along with their gaskets. What year is your car? During the course of its production life, the 1800cc version of the BMC B-Series engine was produced with a series of four different front tappet chest covers.

1) 18G engines employed a front tappet chest cover (BMC Part # 12H 950) that has an angled tube pointing up and back for the basic breathing system with a 'road draught' tube and hose from the rocker cover to the front air filter housing.

2) 18GA, 18GB, 18GD, and 18GF engines employed a front tappet chest cover (BMC Part # 12H 1399) with an internal oil separator for the PCV valve ventilation system.

3) 18GG, 18GH, 18GJ, 18GK, and early 18V engines, i.e., with the carburettor ventilation system, employed a front tappet chest cover (BMC Part # 12H 3684) with an external oil separator.

4) 18V-797-AE, 18V-798-AE, 18V-801-AE, 18V-802-AE, 18V-846-F-H, 18V-847-F-H, 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L, 18V-891-AE-L engines, together with reconditioned 18GG to GK and early 18V (Engine #s 18GK/RWe-H/101 to 14,364) engines, employed a front tappet chest cover (BMC Part # 12H 4395) which had an improved internal oil condensation / return chamber along with an improved external oil separator, the combination of which minimizes the transfer of oil mist into the fuel induction system. It is preferable to preceding designs due to its more open design that permits better breathing characteristics.

Only two rear tappet chest covers were employed. The early design (BMC Part # 12A 1386) was sadly prone to distortion and consequent leakage if its mounting machine nut was overtightened. Its cork gasket was prone to failure as a result of prolonged exposure to heat radiating from the exhaust manifold. The later rear tappet chest cover (BMC Part # 12A 1366) has the advantage of being less prone to distortion and leakage, partly as a result of stronger design that minimizes distortion, as well as its having a groove for retaining the later synthetic rubber oil seal (BMC Part # 12A 1175) that is less prone to heat-induced failure.

If you are using an Original Equipment cast iron exhaust manifold, then use either Permatex Ultra Black RTV Gasket Maker, Permatex Aviation Form-A-Gasket sealant, or Loctite Hi-Tac in order to glue the gaskets onto the tappet chest covers. Press the gasket into place on the tappet chest cover, and then place a weight on it in order to seal it flat. Allow it to cure for 24 hours before installing it onto the engine block so that they will not move during installation. Should you decide to use a tubular steel exhaust manifold that is not Jet-Hot coated, be sure to use a synthetic rubber tappet chest cover gasket (BMC Part # 12A 1175, Moss Motors Part # 296-375) as the cork tappet chest cover gaskets that are employed in this location tend to fail under prolonged exposure to the extreme heat radiated by such exhaust manifolds. Use of the more warpage-resistant rear tappet chest cover (BMC Part # 12A 1366) from the 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L and 18V-891-AE-L engines cover will assist in this as well. However, if you do elect to use a cork gasket, then always use the thin cork gasket on the front tappet chest cover - it lays flat and is actually the right size. Both the thick cork gaskets and the synthetic rubber gaskets are too small to fit properly on the front tappet chest cover. When installing a front tappet chest cover onto an engine that has an uncoated tubular steel exhaust manifold, it is advisable to apply a thin coat of Permatex Ultra 'Copper' RTV to its sealing surface as it is difficult for the gasket to seal against the crimp-welded surface of the cover. Although expensive, this is the most appropriate sealant for this particular purpose. It has an impressive temperature range of -65 degrees Fahrenheit (-54 degrees Celsius) to 700 degrees Fahrenheit (371 degrees Celsius). It is also three times more oil-resistant than conventional silicones and eight times more flexible than cut gaskets. Do not use silicone-based Permatex Blue RTV or Permatex Red Ultra RTV sealant on any of the engine gaskets as they are both prone to failure and consequent contamination of the engine oil under hot operating conditions. In addition, they can also substantially contribute to swelling of the seals. Incidentally, excessive swelling of a shaft seals elastomeric lip is a good indicator that the lip material and the lubricant that is being employed are incompatible. Swelling of the seal material can be particularly problematic if some materials, such as silicone, come into contact with oil at high temperatures. Under such conditions, softening, swelling, and reversion of the seal material can occur. If material swelling becomes an issue, then check to be sure that the elastomer that is being employed is compatible with the lubricant and any other fluids coming into contact with the seal, either during cleaning, installation, or operation. This includes any solvents that may be utilized during the disassembly process. You should also check to be sure that system fluids are not being contaminated in some way; contamination could cause an otherwise acceptable seal material to either swell or degrade.

Do not be misled by any product with a term such as 'gasket maker' that is included in its name. The use of this term is merely a marketing ploy. There is no reason to feel confident without the structural element of the actual gasket, therefore never attempt to use any sealant as a substitute for an actual gasket.

When installing the gaskets onto the covers of the tappet chest, remember that the rubber grommets (BMC Part # 12A 1176) and cup washers (BMC Part # 12A 1177) on the fasteners tend to take a set when left in place, therefore always replace them with new ones in order to obtain an effective seal. This is important as many tappet chest cover leaks originate at the mounting hole. The use of Stat-O-Seal washers in this application can also make for a more oil-tight assembly (Stat-O-Seal Part # 600-31 43-5/16).

The 5/16"-24 UNF machine nut for the shallow rear tappet chest cover should be torqued to 2 Ft-lbs (dry), while the 5/16"-24 UNF machine nut for the deeper front tappet chest cover of should be torqued to 5 Ft-lbs (dry). Be sure that you have cleaned all of the threads first; otherwise, you will get a false torque reading. Exceeding these torque values may result in distortion of the tappet chest covers, as well as crushing of the gaskets, leakage being the result. It is also a good idea to use Loctite 222MS on the fasteners because of the need to not over-tighten them, as the Loctite 222MS will keep the fasteners secure.

Stephen Strange

stephen
I am struggling to find further info on the external oil separators you reference above (points 3 & 4).

do you have any pics or part #'s please?

G
Graham Moore

Graham, it is just a metal mesh pad that is incorporated in the tappet cover - oil mist hits the mesh, agglomerates and the larger drops drain back to sump. Sorry i dont have a pic. Mike
Mike Ellsmore

Oops Graham. I miss read your post - I don’t have any info on the external separator. Mike
Mike Ellsmore

Graham
Can't find a part No. on this but it matches the description of Point/3
Point4 has this same external seperator plus a larger box section type cover with a seperator built in internally
William Revit

People have fabricated them, basically a pipe at the bottom of a can that can drain the can back into the front cover, and another at the top providing the suction from the PCV or carbs.

I've never seen a picture or example of the thing, but the parts catalogue does appear to show 12H3684 as a cover with a large-ish can attached to the front cover, instead of just a pipe from the cover which had internal mesh as earlier and later, for 18GG (1970) to 18V prior to the 18V797 (November 73), which should apply to a lot of cars. Item 8 in the attached, centre left. It also says they weren't used on reconditioned engines. Googling throws up nothing except to use the later item.

But the bottom line is it shouldn't be necessary, as millions of these engines didn't need additional separation.



paulh4

Who's a donkey then-??I forgot the pikky.
Outside view


William Revit

Inside---

And as mentioned No.4 is a combo of this one with the ext. sep, and the top one in Paul's pic with the larger cover including an internal screen as well


William Revit

So, it does exist!
paulh4

Willy

Is that definitely from a B?

The 1098 midget had one just like it.


Dave O'Neill 2

A little like those 16mm hex, 12.7 reach plugs, i'm sure i've seen and the Yet, which i haven't.............I think!
Allan Reeling

Not 100% sure at all Dave
It came with a heap of US 18V engine parts
I wish it had a part No. on it
I might just clean it up and see if it has any id
I notice that Midget one has 2 grooves around it whereas this one is straight and the plate itself appears a flatter shape but then this one could have been bashed / damaged as I don't know it's history - I'll check it out
William Revit

Maybe not, there are any number of Mini and Midget/Sprite items around without the grooves.

I find it odd that with 186,000 MGB engines that apparently had that style of cover, there is not one Google image of it on an engine that I have found, and only one supplier reference to the part number - Australian, as it happens.
paulh4

The dismantled engine that this cover came with was an 18v single carb engine with a cat. converter
William Revit

Graham-
The front tappet chest cover that had the external oil separator (BMC Part # 12H 4395) also had an internal mesh that was much like that employed in the earlier tappet front chest covers. As William Revit indicated, it was employed on the later North American Market air pollution control engines that had a single carburetor. He provided images of the version that was employed on the A-Series Spridgit engines (no internal mesh).
Stephen Strange

"it was employed on the later North American Market air pollution control engines that had a single carburetor."

Don't see that. The single carb wasn't provided until the 1975 model year, and the cat not until the 76 model year. The Parts Catalogue (and earlier posts) describe this front cover being used on 18GG engines from 1969 through to 18V engines up to the end of the 74 1/2 model year. What comes on a car today, let alone a box of bits, could have been mucked about with to any extent, maybe by someone trying to cure excessive oil burning.

Also it was Dave the provided the image of the Midget item, not William as implied.
paulh4

Paul-
I made no mention of catalytic converters, but thanks for the complete information. Just to avoid confusion, my parts manual shows the front tappet chest cover that I referred to (BMC Part # 4395) as being introduced on engines 18V 797. The one used on the 18GG engines was BMC Part # 12H 3684.

My apologies to William.
Stephen Strange

Stephen - see William's last post on 14th October. That engine is obviously a 'bitsa' as it should not have that front cover with a cat, or a single carb. With both a single carb and a cat the implication is that it is a late engine and the front cover came from somewhere else.
paulh4

This thread was discussed between 02/10/2017 and 23/10/2017

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