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MG Midget and Sprite Technical - Beginners guide to tappets.

I recently tried to adjust the tappets on my 1977 1500 (due to a strange clacking sound emanating from underneath the rocker cover when the engine is put under load). According to Haynes and YouTube this is a 15minute job.
However I keep on finding that when one valve is opened e.g. no8 (which is the furthest from the radiator… yes?) no1 is closed tight. This seems to happen with all of the pairs.
Am I doing something fundamentally wrong?
BH Harvey

Sounds like you've discovered the rule of 9. Rotate the engine until one valve is maximum open and then adjust the valve clearance for the valve whose number added to the open one gives nine. Repeat until you've done all 8 valves.
David Billington

Sounds like someone has set the tappets far to tight! The rule of nine is one way and the way you describe it is correct (assuming you equate an open valve as the tappet fully down?)
To go back to the original noise. How do you know it's coming from the rocker cover area? It sounds like it could be pinking as a result of the tight tappet or some other fault like ignition timing or a weak mixture.

Set the tappets correctly (cold), check the timing and then the carb balance and mixture setting.
If it's still making the noise get back on the BBS.

good luck

M McAndrew

Best way to set valve clearance is with the engine running and hot, takes up all the working tolerance and takes less than two minutes once you have the method worked out, the hot oil can be a bit off putting but its the only way to get them spot on.

Al Charles

"assuming you equate an open valve as the tappet fully down"
Ah that will be where I am going wrong then, should have thought of that sooner.

How would you adjust the tappets when hot? The Haynes guide only gives cold clearances (0.25mm)and doesn’t recommend adjustment when hot.

BH Harvey

Al, that method is for those who have had lots of experience and don't mind getting oil everywhere. Not recommended on a 1500 which lies slightly higher at the front and hence oil pools at the back of the head and will be all down the back of the engine by the time you have half of them done!
Cold and stationary for amateurs like me;o) Even if you need to do them three times to get it spot on!

BH, if money is no option you could invest in a gunson's Click adjust which will help get the job done easier.

M McAndrew

I have had a "click adjust" for years.I never use it. I know they are supposed to allow for wear in the rocker ends but I just cannot get on with the thing. - there is no "feel" to it.

Adjusting tappets hot on a running engine is not for the faint-hearted. Fun, but messy with oil spraying around. I too wouldn't recommend it to an inexperienced novice.

Ordinary feeler gauges, spark plugs out, in gear, rock the car to rotate the engine and use the rule of 9, doing pairs of valves at a time

As Guy, plugs out, rotate only in the direction of engine rotation - I usually pull it round with the fan belt/blades - small garage !
No Eight fully open, adust clearance No One - No One open adjust No Eight - hence as others the rule of nine.
Similar 7/2 etc.

richard boobier

Guy, I've not tried using a click adjust but was thinking of getting one. If yours is gathering dust can we do a deal? What don't you like about it?

M McAndrew

You have mail.

As far as I can recall, what I didn't like about it is that it uses an enclosed socket over the locknut. This obscures the slot in the end of the tappet adjusting screw and although the screwdriver blade is engaged, you cannot see the movement of the adjuster. I prefer to be able to see what's going on as the locknut is tightened.

I must confess I used to slightly tighten the adjustment for noisy tappets... slip a 2-thou gauge on top of each valve stem when running to see if it becomes more quiet.

But on un-known engine, would always adjust using standard method first, to make sure that none were over-tight (leads to loss of power, burnt valves...; ie quiet does not nec mean good!).

Anthony Cutler

BH, if your tappets are all tight as you suggest, you wouldn't be getting any tappet noise. It seems like you are not getting them fully open. They should be done with the engine cold.
Also it is better to use a gauge that is about 4mm wide, so that it just fits on top of the valve stem, and not right across the rocker face. This give a true reading, and isn't affected by by the indentation caused by rocker face wear.
Cheers John

I use a dial test indicator (DTI) to gauge when the valve is fully open. use a .009 and a .010 as go/no go. .011 and .013 on a 1275 like mine. this gets the valve clearance spot on every time.
P Ottewell

Maybe I misunderstand this, but surely the period when the valve you are setting is fully "off cam" is far greater than the peak of the fully open valve. So it isn't that critical that you are on the maximum lift point or not, for the valve you are setting to be on the base circle part of the cam.

I do wonder why the thread pitch on the adjusters is as course as it is. You would think that for accurate adjustment, a finer pitch would have been better. I guess the reason is because it would have put the original costs up as special threads and lock nuts would need to be used.

Just your eyes a set of feeler gauges screwdriver and spanner is all you need.

Just think about the click adjust for a minute.
It divedes the rotation of your screw driver in little steps...
As a result the tapets are always slightly to tight or loose.

Onno K

I'd agree with that Onno.

I was reading about how those things work, and as you say, there is no fine tuning. It's either this click or the next one, and nothing in between.

And as they aren't that cheap, and I don't think they save much time, I reckon the feeler gauge wins out ove the click adjust everytime.
Lawrence Slater

Thanks for the advice, the tappets are now adjusted correctly (I think..) and only emit the occasional humming clack. The banging only occurs when running on three cylinders or in high gears, and is easily remedied by easing off the accelerator. I doubt it is serious.
BH Harvey

Running on 3 cylinders or in high gear banging (under load) are not good!

Metalic sounds under load point to pinking/detonation.

And the running on 3 cylinders could be a result....

So investigate!!
Onno K

fr some reason your email didn't reach me! I do have an outstanding issue with my ISP... could you resend and cc to


M McAndrew

You want to cure this running on 3 cylinder thing, start with electrics. A "banging" could be a badly aligned exhaust.
R Fowler

I'm with Guy on the click adjuster - mine's an SPQR or something and has been used once in about 25 years. Feeler gauges much more preferable and trustworthy.

Jeremy 3

This thread was discussed between 18/12/2011 and 20/12/2011

MG Midget and Sprite Technical index

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