13 replies to this topic

[Ell.s]

Hi All, I need to set the valve clearances on my RSP Cooper which has the MG metro lump, the Haynes Manual states 0.013" to 0.015" I have gauges for both of these and in between at 0.014", the question is which measurement should I set the gap to? I don't see why there is a range, surely one is better than the other?

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[beardylondon]

I have a Cooper mainstream and asked the same question recently, it should be 12 thou, some say 15, but it will be much noisier apparently.

[Ell.s]

My old Carb 94 Mayfair was 0.012“ too however I don't believe the MG engine is?

[Cooperman]

All A-series engines are fine with the valve clearances set to 0.012". The tolerance of 12 to 15 thou is fine and makes setting the clearances easier.

[minidizzy]

The official Rover Repair Manuel AKM 6353 (2nd edition) states under Engine Tuning Data:

Model: Mini Cooper with Catalyst  Year 1990 on

Valve rocker clearance (cold) Inlet and Exhaust. 0.013 to 0.015 in   0.33 to 0.38 mm

However it doesn't answer your question and Cooperman's advice is always worth listening to.

 

I see you have the original red ht leads. Never let those go.

[Cooperman]

The valve clearances are there just to ensure that even when the engine is hot and the valves are, therefore, at maximum length, clearance will still exist and the valves will close fully during the cam dwell periods.

Why clearances have been increased in later manuals is something which has no logic.

An exhaust valve can reach a temp of c.750 deg C. That gives a certain expansion figure (I can't be bothered to work it out). Now an old A35 valve and a Cooper S valve will still get to 750C and have identical expansion. They both had clearances quoted by BMC as 12 thou. Why would higher lift rockers, or an injection engine, or a higher-lift cam cause the valve to expand more and thus end up with less clearance when hot?

I believe BMC set 12 thou as the best compromise between ensuring that clearance always existed when hot and an as quiet as possible valve gear when running. It is what I always set, but then I first set A-series clearances in about 1959 when the only recommendation was 12 thou.

The only case I can think of when a bit more might be advisable would be the use of aluminium push rods, which will expand a bit more than the steel ones. Incidentally, the push rod expansion is not a real issue as the block and head expand as well, but the running tems of push rods, head and block are insignificant. I mean, you can take off the rocker shaft and push rods immediatel;y after switching off the engine. They are quite warm, but not red hot.

[sonscar]

There is also a slight alteration of the valve opening and closing times with different clearances.Steve..

[Ell.s]

All A-series engines are fine with the valve clearances set to 0.012". The tolerance of 12 to 15 thou is fine and makes setting the clearances easier.

I have never realised these HTs were original, I would have more than likely replaced them as well!

Thanks for the advice guys, think I will set them to 0.013" and see how it goes.

[Wise Old Elf]

All A-series engines are fine with the valve clearances set to 0.012". The tolerance of 12 to 15 thou is fine and makes setting the clearances easier.

I have never realised these HTs were original, I would have more than likely replaced them as well!

Thanks for the advice guys, think I will set them to 0.013" and see how it goes.

If you want to wind up the guys over on the Facebook page tell them you threw the red HT leads out and replaced them with new ones. Lol

I have 2 sets they are my retirement fund :)

[Cooperman]

There is also a slight alteration of the valve opening and closing times with different clearances.Steve..

 

I did mention that in my earlier post, but pointed out that the effects are really minimal. A tighter setting will just very slightly increase the valve opening duration.It is unlikely that you would notice it, even on a race circuit where timing is to tenths of a second. Having the cam timing a degree or two out from optimum would have a greater effect and not many cams are timed in that accurately.

[Ell.s]

All A-series engines are fine with the valve clearances set to 0.012". The tolerance of 12 to 15 thou is fine and makes setting the clearances easier.

I have never realised these HTs were original, I would have more than likely replaced them as well!

Thanks for the advice guys, think I will set them to 0.013" and see how it goes.

If you want to wind up the guys over on the Facebook page tell them you threw the red HT leads out and replaced them with new ones. Lol

I have 2 sets they are my retirement fund :)

I never thought they would be so valuable makes sense considering they are a service item. Almost makes me want to take them off and put them in a box. They could so with a clean up to be honest. Slighty perishing.

Update on the valve clearances. I've set them to 0.013" 7 out of 8 were at around 0.009" to 0.010" and one (number 4 was huge and took 4 full turns to tighten up. Went to start it to see if my tappety sound and rough idle had been cured and the battery is flat . Trickle charger now fitted.

[Ethel]

I think the 15 thou comes from the high compression, big valve original MG Metty engines. They were buggers for running on and pretty close to detonation. The bigger gap meant they were on their seats for a bit longer to aid heat transfer.

[absx2]

I remember the larger gaps being a revision to the Rover service manual to make the idle smoother and it worked.

No doubt someone will have a copy somewhere. 

[Cooperman]

I remember the larger gaps being a revision to the Rover service manual to make the idle smoother and it worked.

No doubt someone will have a copy somewhere. 

I guess it might do that. It makes the cam opening periods a bit less, but that is very slight in the real world, especially when you consider how far out the actual cam timing can be with dot-to-dot timing gears and no fine adjustment. I have seen a standard engine where the cam was over 8 degrees retarded as it came from the factory.