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MG MGB Technical - Engine rebuild advice

I seem to have started a number of related threads about basically the same thing.
I will ask all the queries in this one from now on.
Block is now with the machiners to get cleaned and rebored +0.60
The crankshaft is also with them to get reground, unfortunately when I removed it it looked in lovely condition but sized on one of the mains as oval and undersize. The spare is std/std but has been badly stored and would need reground anyway.
I am now refurbishing, renewing, checking all the other bits from two engines to make up the parts to reassemble.

The next question is that I have two cams, one from the existing engine and one from the spare.
The original is marked in electro pencil on one end what looks like "42AF", the sopare is unmarked.
Looking at them they look pretty much the same profile by eye but the 42AF marked one looks like it has been reground, there is less metal around the lobes.
How do I identify they, do the numbers, or lack of number means anything?

I also have the earlier lifter fitted to me engine, is there any good reason why someone whould do this to an 18v engine? Both engines I am using were rebuilt very recently, the one from the car badly, and the spare badly stored before I got it but unrun.

On the block, is there a date stamp near the sump flange on the filter side?
Often folk recon engines with whatever they have laying around, thus originality becomes irrelevant.
Buy a billet cam, there is no point in messing around.

Peter Burgess Tuning

I'm with PB. New cam and followers. I f you use the later, lighter followers you will need different push rods.
Allan Reeling

I only took out the engine to fix a noisy bearing, on what looks like a recently refurbished gearbox.
The engine was only supposed to be reshelling the bearings and giving it a paint, mainly because it was going to be out.
The costs are starting to run away already, machining is going to cost around me around 400-500, the new head a further 400+ plus all the other bits and bobs which will run another few hundred. This is in addition to other parts already purchased like new dizzy, carb rebuild kit and other parts.
I really don't want to send another 200+ on a new cam if I can possibly avoid it.
No markings anywhere apart from the 42 AF marking on the cam that looks reground, the other is completely unmarked and so are both blocks.
I have just found that the exhaust manifold is the wrong one and somebody had drilled out all the threads, at least I have a spare of the correct typ with good studs from the spare engine.

The annoying thing is it looks like the original engine was rebuild very recently, but fairly poorly.
The spare engine, which I addmitedely got for a tenner, had been rebuilt but put through a hotwash and not dried after being stored for a number of years which had damaged some of the components. However I have managed to get some usable parts from it!

Reusing one of the old cams is an exercise in futility. The older style followers are much heavier than those used in the later engines. A new set, along with longer pushrods, is fairly inexpensive. Trying to reuse the older followers, with either cam, will result in increased wear and you'll be replacing the cam and followers in short order. Do it properly the first time, even if it costs a bit more now, rather than having to do a lot of it over again in the near future. RAY
rjm RAY

I am aware of this, but think that it may not be understood I am not building a race engine, simply freshening up a road engine which I had originally not intended to do anything bar put new bearing shells into and check the bores.
It certainly isn't turning out the way I had expected.

I have plenty of engine building experience including building a 1950cc B engine, Ford Kent Engines and more recently an 07 Kia Sorento. I remember the 1950 pushing the B along at a respectable, for the time 120mph, plus.
Unfortunately suppliers and methods have moved on in the MG world since my last B engine rebuild, some 25 years ago!
I already have the longer pushrods and can see new standard cams for sale for around 80 or so.
This may be the answer if I cannot identify the current cams.
I would always use new tappets on any build unless I was replacing them in exactly the same place and they looked perfect. I have never came across this yet on a rebuild so it remains theoretical.....


I am also wanting the engine to look original from the outside, hence the retention of the standard exhaust and manifold, the original air cleaner boxes (with K&Ns inside) and all the ancillaries standard.
The spec I am working towards is +60 overbore to give around 1870cc, econotune head, standard cam, K&N filters and new needles, and electronic ignition. The remainder is simply tidying up and repairs/reconditioning.
I use my car to go to work most days so while a little more power would be nice, reliablity and usability are the main plans. I also want it to look original as far as reasonably practicable.
I have found I have forgotten an awful lot about engines over the years, or possibly am just getting senile in my old age.....

I pulled the gearbox apart tonight while awaiting the return of my block and crank.
This was the original reason for pulling the engine in the first place, a noisy gearbox.
When I split the motor/gearbox I noticed the spigot bush was not installed, probably the origin of the noise as the bearings would have been protesting if the clutch was not fully centred when engaged.
Since I had bought a rebuild kit I ened up stripping the gearbox and replacing the layshaft and most of the internal bearings, the gears and synchro rings look fine.
This brings me to the question, how much play should the double ring rear bearing have, it has some but the balls look perfect. I would replace it as a mater of course but it is really expensive and very hard to obtain.
It is a double row bearing so I assume some play is required to ensure the double row doesn't bind when it warns up but roughly how much is too much?

"I noticed the spigot bush was not installed"

Yikes - I'd expect that to cause intermittent massive clutch judder as well as significant stress on the first motion shaft bearings.

Yikes is right! A missing spigot bush in an old Sprite resulted in teeth missing from the lay gear for me.

Richard Smith 1

The more money you spend on good bits the more reliability you will have - it is really up to you what you want from the engine similarly with the gearbox.
Mike Ellsmore

I ordered the bearing kits and when they arrived they were not Knig as I had been told but County and the thrusts were an unknown indian make.
I wil not say where are they have agreed to swop them ut insist the indian thrusts are all that is available in the UK.
I find this hard to swallow, are there better ones around to match the King bearings I am going to use?

I have reassembled my gearbox, replacing the synchro rings on first and second, the layshaft plus all the bearings apart from the rear one.
I have hit a couple of snags. The front cover instructions are not 100% clear in the manual.
is dimension A, when calculating against dimesion B including the .012 gasket allowance or not?
The first part seems to says so but then the next part just says A, rather than A + C which seems to indicate B is going to be larger so negative clearance for the bearing?
I also have excessive play in my layshaft but the shims for front and rear are currently unavailable, how do gearbox builders get round this?

This s easily fixed and several different thicknesses are quoted in the manual but how do you do it if they are not available?

You say 'layshaft' but those calculations refer to the first-motion shaft.

It's not clear, but looking at it logically I'd say you would want to end up with light pressure on the outer/non-rotating race of the bearing when the joint washer is compressed. No pressure i.e. insufficient shimming might allow the race to rotate in the bell-housing, and too much pressure i.e. too much shimming could allow the joint washer to be under insufficient compression and so leak. That would mean that the shims would apply 0 to 1 thou of pressure, so it would be A plus C.

If your shaft is moving back and fore then it could be because the bearing outer isn't clamped, and so does need shims. If the shaft doesn't move when you hold the bearing outer into the bellhousing i.e. cover removed then that would tend to confirm it.

The only one of the usual suspects not showing a price for the shims is MGOC, half a dozen others do and/or say they are in stock.


I think you answered his question about the first motion shaft, but when he asked about end play in the layshaft, I believe he meant the end play in the laygear cluster. Two questions.

CR Huff

Ah right, although it looks like it's selective thrust washers for that, rather than shims, which changed for rubber bumpers. B&G have the later 22B692 and 22B696.

Maybe my query was a bit muddled.
The front cover calculation is a bit unclear.
I assume that calculations should show that a slight pressure should be on front and rear covers/retainers to ensure that the bearing is kept in the recess.
The workshop manual is not clear to use and seems to imply that there will be a clearance, mainly because of the calculation missing out dimension C when calculating at the end.

The other query is around layshaft endfloat. The proper eared thrust washers seem to be unavailable anywhere. All that is available is the ealrly non eared rotating versions. is there any reason why you cannot use these is a later gearbox?

I think the reason for the confusion is that there were two very distinct (but three versions) of the gearbox and two types of overdrive, plus non OD versions of the basic gearboxof every kind. The manual usually only shows instructions for the older box and is usually not fully detailed because nobody really does gearboxes really.
It does get a bit confusing trying to work out clearances, parts and defects when the manual isn't 100% clear and some of the parts are now unavailable!

1970 mgb is their history problem with #3 cylinder
Dm Matias

I ended up tracing a rear mainshaft NOS bearing and a layshaft NOS rear thrust washer so am going to replace every bearing and seal now as well as sort out the correct endfloats.
It took a bit of searching to find the bits, obviously made of unobtainium but eventually managed it.
Hopefully the egarbox will be back together by later this week, with every part back to factory spec.

I got my new cam (standard) today and need to time it in.
My engine should have simplex chains fitted but it actually has a duplex fitted.
I'll stay with the duplex but have read that the timing marks are different, thereby changing the actual timing.
For an 18V engine fitted to a 73 car what would the standard timing for the cam actually be?

We found the most effective timing for a Leyland spec standard cam to be number one inlet fully open at 108 degrees after top dead centre. Use offset keys to do the job as you cannot assume either the dots or cam are spot on as supplied.
Peter Burgess Tuning

Many thanks, hopefully get this in over the rest of the week ready for returning to the car.

This thread was discussed between 21/05/2016 and 15/06/2016

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