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MG MGB Technical - Engine info

I have recently purchased an 1800 Block ,head, pistons and rods,crank and cam. All parts disassembled ,but machined.Unfortunately I dont know the year of the engine.There are "raised" numbers on the block but no numbered plate.I will need info for rings,push rods, lifters ,bearings, etc. Does anyone have a clue on determing what year the block may be or does that not matter.(Since all 1800's are the same ?) The head is pre-air pump. Thanks for any input


seems to be a pre 18V.

There were blocks with three main bearings up to 18 GA. The 18 GB started with the 5 main bearing crank, still using the angeled conrods as known from the MG A.

Conrods for post 18 GB engines were changed, but there are a lot of other details to be explained first.

There are a number of experts on the board who can help with further details if they know about the main points listed here:

Which type of crank came with the kit ( 3 ore 5 main bearings)?

What type of conrods are used Angeled, pitch bolt at the small end or none of these)?

Is there a single or a double row timing chain used?

How long are the followers and the pushrods?

Are there spring clips on top of the valve springs added to the stems of the valves?

Are double valve spings used?

Just answer these questions and you will get an answer that will be precise enough to quote the main details of your engine and it's production series code.



Hi Tim The piston being used will determine which rings ars needed as will the size that the crank has been machined to. It doesnt matter which block is used once you have determined how many main bearings it has. The early cam followers were long and heavy and used short pushrods but you can use the later lighter followers with the later pushrods in any block. Four different cnnrods were used but all are the same length and carry the same bigend bearings. The early engines ran a two row timing chain and the 18v ran a single row system but either can be used. Jim
j soutar

Sorry should have said that size of crank will determine size of bearings needed Jim
j soutar

Further thoughts on your engine. Up to early 18v engines inlet valves were 1.56 in diameter, then incresed to 1.625 from 18v101 to 18v797 then back to 1.56 1975 on. the units fitted with 1.625 valves need the cutouts in the cylinder block to ensure sufficient clearance. With this in mind any head will fit any block. Two types of oil feed to the rockers were used utilising different drillings in the head and rocker pillars. Make sure these line up correctly. Hope this helps. Jim
j soutar

Why does it 'seem' to be a pre-18V? There's not enough information to tell.

The block will be 3-main, pre-18V or 18V. There could be differences for engine mounts, water pump, dynamo/alternator, oil cooler port, filter, breather system, etc. Pistons and rods need to match by type too. You need to know what pistons you have and whether it is a high or low compression head. Not all 18Vs had single chain. And if you've got a reconditioned unit (which may already have been reconditioned before) then all bets are off for what you have got. It doesn't really matter as long as everything matches where it needs to.

Also, the cut-outs in the block are to clear the exhaust valves, which didn't change in size over time. (Anybody know why cutouts are needed then? Is it that the chamber depths got smaller?)

Why not take some photos of the bits and we can have a proper go at identifying them?

Hope this helps (it's a bit negative, but meant to help),

Neil Lock

Tim. All good information and the parts about "we need to know more" are valid. One distinguishing thing on the 18V engine is the fact that it was set up for use with a mechanical fuel pump in other applications. Thus, an 18V block will have a blanking plate on the lower, left side near the front of the engine. Something of a shield shape. All of the 18V engines had the relief cut for the larger intake valves, but this is not a definitive indication. Other blocks have been modified for that relief cut when going to a cylinder head having larger intake valves.

The cylinder head was the same on both the high and low compression engines. It was the pistons which were changed to select the compression ratio and aftermarket pistons were available giving an even higher compression ratio.

The volume of the combustion chambers did change during the production life and this will affect engine operation, as will whether the head has been skimmed to either raise the compression ratio or to remove any warping which may have developed in use. Late model cylinder heads have the offset oil feel line which has been mentioned while the earlier model cylinder heads have the inline oil feed. Late model cylinder heads have a hole at the upper, rear where the water choke take off was fitted. There was a stud on either side of the hole in a crosswise direction. All US cylinder heads, from 1968-80 have the holes for the air injector rail.

The slab sided crankshaft is often considered to be more desirable than the other models.

The 18V connecting rods are considered to be better than the earlier models having the angled separation.

Again, more information would be of use.

Les Bengtson

If the engine identification plate is missing, there is a way to date the age of the block. On the Right Hand Side of the block, in the area between distributor and oil filter, there are three numbers that form a circle and that are slightly raised, e.g. 30 12 71, which tells the day, month, and year during which it was cast. This will help "narrow the field".
Steve S.

Steve. Good to see you back again. Assume you are resting up between trips and all is well.

Sorry to change the subject here. But, in the tread on poly bushings you mentioned using the rubber bushing for the anti-sway bars rather than the poly bushings. No reason given.

Could you expand on this, please?

Les Bengtson


The cut-outs are for the EXHAUST valves... presumably for higher lift camshafts?

Also, earlier heads can have take-offs for the heater tap too.

Don't all 5 bearing engines have blanking plates for the mechanical fuel pump take-off?

As I said, other than identifying the block (and hopefully the matching crank!) as 3 bearing or 5 bearing, there's not much difference in the block other than the valve cut-outs.

The engine plate is only of use if it is 'up to date' ie if the engine has not been changed/modified! It'll no doubt be on it's original block, but the internals may be 'mix and match' - even if it was an 'official' reconditioned engine.

Neil Lock

This thread was discussed between 28/04/2007 and 30/04/2007

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