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MG MGB Technical - Adjusting valves, (tapets)

I know this has been discussed at lenght in these threads, but as a first timer, can anyone provide a link to a site that explains how to adjust valves on a MGB? Also, has anyone used the Click-Adjust tool advertised in Moss? Is it worth the price?
Car facts- 74.5 mgb roadster.
Greg Bowman

Thanks, great site, it has been bookmarked.

Yes, rule of 9 Bill; 1 fully down adjust 8, 2 down adjust 7 etc. I use a 1 5/16" socket on the pulley nut, to avoid having to move the car, and a 15 thou feeler guage, 1/2" spanner and screwdriver are the tools. Rich.

You asked about the Clik-Adjust - you can check in the archives for pluses/minuses.

It has the advantages of only needing two hands to adjust the valves, and it can compensate for any dimpling or dishing of the rocker arm, which would throw off a feeler gauge.

The "three handed" process of working wrench/screw driver/feeler gauge simultaneously can be infuriatingly iterative.

Some posters talk about adjusting the valves while the engine idling. Now, that I'd like to see - several times - before trying.

No, I don't have one, but I'm strongly tempted.
John Z

Rule of nine: I have found that some of my valves are at less than their maximum clearance at the strict rule of nine point than others. Not only does this make repeat measurements difficult after rotating the crank but the valves are noisier. Setting the gap at the maximum clearance point has made mine quieter, and hasn't caused any other problems which was something I wondered about at the time.
Paul Hunt

Paul - i know we have been here before but I think you had better give us the formula if we are not to follow the factory advice.

I think it indicates that Pauls cams and tappets are knackered. Given a cam period of 252 deg crank, thats 126 deg cam. The opening ramp is probably 20 deg and the closing could be 30 deg cam then this means that there is no lift at all for over half the rotation of the cam. So you shouldn't have to be too precise about where you set them. I also had the problem Paul describes and I did what he did, turned the crank until I found the biggest gap and set them there. This made the tappets quiet and didn't seem to harm the engine in 12000 miles apart from it regularly chewed up followers. Ive just got the camshaft out and its well and truly F*cked. The lobes at the front are missing about 3mm of lift and half my followers are mangled again.
Paul Hollingworth

Rotate the engine back and forth with a steel rule against the open valve to check it is truly fully open - itīs hard to be sure to within several degrees otherwise - then you should have no problem. A friend of mine got a shock the first time he did the tappets on his newly aquired B and found one wasnīt opening at all - lobe worn off - it happens. Rich.

You turn the engine until the valve is wide open and then turn the engine one full turn, the follower MUST then be on the back of the cam. A bit of chalk on the front pulley helps.If you remove the plugs first the engine can easily be turned with the fan. Just mark the head beside the rocker last adjusted. This is by far the most accurate way to adjust tappets and it does not take much longer(even less time if it means you dont have to have a second go). Denis

I picked up at a flea market a while back an old valve adjusting tool. They used to be very popular because they work well. The handle has a half inch drive for a socket (for the lock nut) with a separate knob on top that drives a screwdriver bit. I've found that I can adjust the valves without a feeler guage by turning the knob (the adjusting screw) to snug and then backing off about 1/2 turn. You hold the knob in place and tighten the set nut. Double check with the feeler guage and move on to the next one. Way easier and more precise than the screwdriver and box wrench process.
Barry Parkinson

Without actually removing the camshaft I've checked the lift and for play in the bearings, and checked the cam followers and push-rods, and all seemed to be in order. This situation has pertained on my engine for the 15 years and 40k I've had with no apparent change over that time.

Another thing I have done in the 40 years I've been adjusting BL rockers is not to use the feeler gauge stated i.e. .015" cold but to use two, one thou either side of that. Much easier to judge one loose and one tight than just the right amount grip with the stated value.
Paul Hunt

Why not use a go-no go gauge? Each gauge has a .002 step in it. Bob
Bob Thompson

How about adjusting valves on an alloy head? I read from a couple sources that an alloy head will expand in height and change the gap by about 8 thou. I set my valves cold at 7 thou and it sounds and runs good.
Any comments or experience?
Barry Parkinson

If I read .007 right I feel that is a good canditate for burnt valves. Bob
Bob Thompson

This is supposed to be the "hot" stuff from Crane Cams. Who am I to argue with a manufacturer?

"Author: gary neely (
Date: 02-09-05 13:06

I called Crane cams again today and talked with Dave Womack , thier guru with brithish cars. He confirmed what was told to me earlier by another one of thier techs. His manual calls for valve settings with an aluminum alloy head and a cast iron block to be set at .06 LESS than the hot setting in this stenario. This is absoulutely hard for me to believe. Using a stock cam and an alloy head the settings would be .07 cold. That is an .08 spread from the .15 normally used on a cast iron head with a cast iron block. Using my spec. card on the 342-0010 cam,(.14 intake hot and .16 exhaust hot) the settings would be .08 intake cold and .10 exhaust cold. Anyone out there setting their valves on thier alloy heads with the stock cam at .07 cold, or with the crane cam at .08,.10 cold?"
Barry Parkinson


You and who-ever may be mis-interpretting Dave at Crane Cams. His .06 will be mm not inches. .06mm = .00236" (2.36 thou).

The B head is 3" thick. From cold to hot it will change 70 degrees C. The coefficient of cast iron is x.000011/degrees C.

3 x 70 x .000011 = .00231

That is the amount the iron head will expand by. The coefficient of expansion of aluminium is approx x2 that of cast iron so the ally head will expand that amount again. You can see the figure agrees with Crane Cams.

I'd set your tapets 13 thou cold.


Why not set the valves hot per the spec. and re-measure cold? Heck, if you don't like getting burned on hot pieces, just set ONE hot and let it cool to measure cold? That way you'd know "fer-sure" what was up.

I have heard lots of opinions on the "rule of nine" and they all fel into one of three camps...

-That's how I do it and I'm happy.
-That's how I did it and I was unhappy because re-checking showed variable gaps and it ran noisier.
-That's how I do it and I don't worry about it.

I use the manual method as it takes half the time.


I tried the empirical approach as you suggested. I set the clearances at .006" with the engine at about 55 degrees f. I then drove it around for a while until it reached the thermostat 195 f operating temperature.
Parked it, immediately pulled the valve cover and voila! the clearance is 14 to 15 thousandths, just like the book says. The alloy head expansion as it heats certainly changes the valve clearances.
Barry Parkinson

Barry - I don't have one, I have never seen one, but I do have .014 and .016 in a set and using them positioned side by side suits me fine :o)

Mike! - what's this 'manual' (aren't they all 'manual'?) method and how does it save time?
Paul Hunt

Mike Adjusting the valves as per the book is fine on an engine with a stock cam but the system I use can be used on any engine, hot cam or not. You can still adjust two at a time as one inlet and one exhaust open together. DEnis


But the pushrods and valves expand too - so the net difference will be head expansion minus (the valve expansion plus the pushrod expansion)- you need to work out the expansion rates for all three materials..
Chris at Octarine Services

That's said it all Chris and you got there before me. This is all getting very complicated chaps and it is a relatively easy task. Maybe its because we all have hydraulic lifters on our everyday cars. On the basis that we all normally run our engines hot, and I mean hot and not just when the operating temperature is reached but after about 20 mins I would advocate that this is the only setting that really matters. Set the rocker to the specified setting either as in the engine manual or as detailed by the cam manufacturer. Make sure the engine is really hot and use the rule of nine. If you don't believe in that turn the engine until the valve to be set is fully open and then rotate the crankshaft one full turn and then set the clearance. Better still, do it with the engine idling but don't use a new set of gauges, use shim steel cuttings.

Don't try to get the B quiet by reducing the clearances as you'll alter the valve timing and spoil the running and don't expect it to run as quietly as a modern car, it just won't do it
Iain MacKintosh


But the pushrods and valves expand too - so the net difference will be head expansion minus (the valve expansion plus the pushrod expansion)- you need to work out the expansion rates for all three materials..

<<That's said it all Chris and you got there before me.>>

Thanks, just looked at it again. The temp change is the same so the valve and pushrod expansions are the same in both cases.

My simplistic calc is way off though as I didn't consider there would be extra clearance BOTH sides of the rocker pivot :-( Only bother reading further if you are in pedantic mode.

The head expands an extra 2.3 thou so the rocker pivot moves up an extra 2.3 thou. That gives an extra 2.3 thou clearance on the pushrod side of the rocker. The rocker ratio is 1.4:1 so that makes 3.2 thou on the valve side.

On the valve side the valve tip clearance will increase by an amount equal to the extra expansion over the distance of the valve seat to head top, approx 2.5" x 70 x .000011 = 1.9 thou extra.

Add 3.2 to 1.9 makes a total of 5.1 thou extra at the valve clearance. So 10 thou cold should be right.

Only a cold figure of 15 thou is given up to 18V. At 18V we then get 15 thou cold and 13 thou hot. But 18V uses longer ally pushrods than the early engines so may not be the same. Hot setting is tricky as the engine cools a lot in the 20 mins it takes to set the tapets.

Not if you set them with the engine idling Rich
Iain MacKintosh

Never tried it Iain, don't you get burnt fingers, induced DTs and oil up your sleeve he he! No good for me anyway as I have 18GB engine. Suppose I could set one carefully to 15 thou cold then run it up to temp and check it hot to get a hot setting but, err, what's the point, why not set them all cold :-) Rich.

I started this thread and am now totally confused, at what do I set the clearances? Please keep it simple, I was never a whiz at math, even with a calclator.

Forgive the irreverence. The first link, as posted by Greg, is as per the BMC manual,
The order of adjustment shown there is to avoid un-needed crank turning and let you adjust them all during just 2 revs of the crank.
You will see the procedure is known as "the rule of 9" wherebye the number of the valve fully open (down) and the number of the valve to be adjusted adds to 9. Number the valves from the front, 1, backwards. Check for a fully open valve using a rule set against it to find it's lowest point if you are not sure.
Clearance is 15 thou cold all engines (or optional 13 thou hot from engine number 18V onwards). Feel for a slightly dragging fit of the feeler and re-check after tightening the locknut as they may move.

Took me a loooong time to realize it - if you put the car in 4th like in the article, instead of pulling you can reach down and move it by rolling it back/forth with the front wheel. Seems to give me more leverage so the crank moves smoothly and it's easier to see when the valves are fully open.
Mike Polan

This thread was discussed between 17/02/2005 and 23/02/2005

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