|The MGA With An Attitude
ENGINE OVERHAUL - BE-201A -- Pg 1 of 5
General and External
I have been resisting this for a long time, particularly reproducing what is already in the workshop manual or that which should be common knowledge. However, as the factory workshop manual was written for use by competent mechanics, it is generally lacking in fine detail and the common knowledge stuff. Since there are now a lot of novice collector type people interested in restoring or repairing their own car, I have been getting enough inquires to merit posting a beginning to end description of a complete engine overhaul.
This will be organized in the same general sequence as the Workshop manual. Where possible I will try to make reference to the shop manual for the common procedures rather than reproducing it here. I will have plenty of additional notes for more detail (and some tech tricks). The Engine section in the Book does not detail an engine overhaul start to finish in the complete logical sequence, so there will be some occasional cross reference notes here to clarify the sequence where necessary.
Step 1: Read in detail everything in section A of The MG Series MGA Workshop Manual, (hereinafter referred to as "The Book"). Read it a few times for review, as it is a mere 23 pages with index and pictures.
Step 2: Read everything in the MG Engine General Tech section of this web site. That will occupy quite a lot more of your time, but it is important, as I will be referencing many of those articles here to avoid repetition.
Step 3: Read all of this page (and the sequentially linked pages which follow). Pay attention to the links to other articles, as this page is a general outline, and much of the detail will be found in the linked articles (most of which preceded this page in publication).
Step 4: If after all that you still have more questions, feel free to ask, and I will consider adding more notes here when warranted.
"The Book" - Section A, General Description
I might first remind you that you are dealing with a 1950's vintage vehicle which was built with 1920's technology. I get a lot of questions about upgrading the engine for more power. Upgrading things to late 1970's vintage technology is a significantly large undertaking. Don't even think about trying to upgrade this engine to 21st century spec's, as the iron lump (fond as I am of it) does not lend itself to such a leap of faith. This article will deal primarily with repairing and restoring the engine to original specifications (including some period factory changes). Performance enhancement has an entirely separate section on this web site.
When dealing with the engine, the Book is arranged to deal with R&R and repair of external parts first, followed by working inward until dealing with the innermost parts of the engine. When it comes to reassembly much of the procedure is assumed to be "reverse of disassembly". So for assembling a complete engine, starting with a bare cylinder block, you need to read the entire chapter multiple times to become familiar with it, then essentially read it backward to define engine assembly procedures.
Section A, Lubrication System
Reference articles on Oil filter assemblies and Oil flow path.
Section A.1, Draining the Sump
Add that it is a good idea to install a magnetic oil drain plug. This is especially important for a newly rebuilt engine which will generate a certain amount of fuzzy iron powder during initial run in and the first 500 miles as the piston rings seat and polish the cylinder walls.
Section A.2, Oil Pressure
Also reference articles for Priming the oil system and Oil coolers.
Section A.3, Oil Pressure Relief Valve
Also see Oil pressure relief and and gallery plugs and the Relationship between oil pressure, flow, and lubrication.
Section A.4, Removing and Replacing the Water Pump
Add to this that some modern replacement water pumps have cast aluminum body rather than the original cast iron part. Aluminum itself is not bad, but the most common aluminum casting is quite thin and weak and prone to break in the area of the generator attachment point. Original iron water pumps are generally quite durable. Given a choice I would rather have an iron water pump rebuilt rather than installing the aluminum replacement part.
Also notice that some of the threaded holes for water pump mounting bolts may go through into the water jacket. When installing the water pump you should apply thread sealant to these bolts to prevent coolant from weeping out through the threads. Leaks here could cause rusting of the threads and bolt shanks and the bolt holes in the pump housing.
Section A.5, Removing and Replacing the Carburetors
Disconnect the vent hose, fuel hose, two control cables, four nuts and washers, and lift out the carbs. I find it easiest to leave the cable trunnions attached to the cables, pull the split pins to disconnect the trunnions from the levers, and remove the cable bracket from the top of the intake manifold. This will retain the position of the trunnions on the cables so there is no adjustment required on reassembly. Also refer to Choke adjustment and other articles in the Carburetor section.
Section A.6, Removing and Replacing the Manifolds
Here I might note that the manifold mounting nuts should be brass to best tolerate the heat and to prevent rusting in place. Brass threads are easily damaged with excess torque or repeated assembly, so you might plan on replacing the brass nuts occasionally. Or replace the brass nuts with stainless steel nuts.
The four manifold studs in the middle are longer than the end studs, and they also run through into the vertical holes for the head bolts. Here you should use a thread sealer on the base of the studs during assembly to prevent oil from weeping out onto the hot exhaust manifold when running. Also use studs with correct dimensions. If the base thread on the manifold stud is too long they can run into the head studs and lock them in place like set screws, making the cylinder head impossible to remove.
If you are not an originality buff, you might consider replacing the two end manifold studs (front and rear) with hex head bolts of appropriate length. This would allow in the future lifting off the cylinder head for separate service without having to remove the exhaust manifold or disconnecting it from the exhaust pipe or from the bellhousing bracket.
On the bottom of the exhaust manifold the fasteners were originally tall brass nuts with spring lock washers. The brass threads are easily damaged, and these nuts have a habit of falling off. Steel nuts would quickly rust in place from the heat cycling. I heartily recommend double nutting these studs with stainless steel hex nuts (3/8-24 UNF or SAE fine threaded). Also see notes on Broken exhaust manifold.
When it comes to reattaching the exhaust down pipe to the bellhousing, I can recommend tossing the longer brace strap in the trash, as it never seems to be the right length, depending on the position of the welded bracket on the pipe. The shorter brace strap is generally very useful for stabilizing the pipe and preserving the integrity of the flange gasket ring. However this short strap is prone to breakage. The cure for that is to double up on the short strap bracket for extra strength, or make one from 1/8-inch (3-mm) thick steel strap, in which case it may never break again.