adjusting valve timing + clearance

[Pascal]

How big a job is it to adjust valve timing and clearance? The first challenge will be to remove my rocker cover which is stuck on the head, but after that how much time should I expect to spend on this?

Regards

[Stig]

At most 30 minutes, it's very straightforward. Then add the time it takes to clean off the stuck-on bits of old gasket and lining up the inevitably egg-timer shaped new gasket so it doesn't leak oil everywhere!

[bmcecosse]

Adjusting the valve timing is not for the beginner! Valve gaps are easy - get a new rocker cover gasket and a set of feeler gauges. I set inlets to 12 thou and exhausts to 15 thou - this to allow for the additional expansion of exhaust valves when running, to help make sure the gaps never close up. I assume you know/understand the Rule of 9 ?

[Pascal]

What is the rule of 9 about? I've read the workshop manual and they mention .3 mm clearance - can't remember the imperial values. What is '12 thou'?

[Welung666]

According to all the manuals it should be 0.012" for all valves. The rule of 9 is basically this. If you number the valves from front to back as 1 through 8, inlet and outlet, you adjust number 1 with number 8 fully open (or all the way down) IE. adds up to 9, so 2 & 7, 3 & 6 etc. etc. A tip for refitting the rocker gasket (as they are never the right shape!) is to thoroughly clean the rocker cover and use a few spots of superglue to glue the cork gasket to the cover only, this will make it easier to fit the cover back on and never tighten the cover really tight, just nip them up and turn another quarter turn with a socket or spanner.

[Stig]

Er, shouldn't that read 0.012"?

[bmcecosse]

Indeed - 1mm = 40 thou (near enough). So 0.1 mm = 4 thou. And so 0.3 mm = 12 thou which is 0.012" . The exhausts are better to be at 15 thou for reasons given above. Due to slight recession and /or valve stem expansion with the higher exhaust gas stream temperature the gap ever closes up (perhaps when powering up a longish hill) then the seat and/or valve is ruined.

[Welung666]

corrected now, stoopid fingers

[Axolotl]

Another useful tip is to adjust the valves in the following order, to minimise the number of times you have to turn the engine over by hand. Also, take the spark plugs out to make it easier to turn the engine.

Adjust in this order:- (Counting from the front of the engine)

1 with 8 fully open.
3 with 6 fully open.
5 with 4 fully open.
2 with 7 fully open.
8 with 1 fully open.
6 with 3 fully open.
4 with 5 fully open.
7 with 2 fully open.

I find a smear of grease on the cork gasket keeps it in place while you get the rocker cover on and helps stop oil leaks better than a dry gasket.

[Willie]

If you are using a standard engine, and especially if you have an unleaded head you should set the valve clearances to the official settings of 0.012thou". This will give you no problems, I have had no burnt out exhaust valves in over forty years of using this setting. If you really want to alter the setting you could set the INLET clearances to
0.008thou" as they run cooler but it is a personal choice. The proof is in the pudding, check the clearances when the engine is really hot.

[Pascal]

I have a standard engine (I guess) with the original (leaded) head.

When valve 8 is fully open (adjustment nut fully up), valve 1 is fully closed then? (adjustment nut fully down)

I guess you turn the engine manually using the starting handle, right? By how much do you have to turn it when getting to the next valve?

Do you check visually that the adjustment nut is fully down (or up), or do you check the position of the notch on the pulley?

[Willie]

You mark a piece of paper with the numbers 1 to 8. You then turn the engine until you see say valve number 1 (radiator end) go down as far as it will, at this point you would adjust valve number 8 (1+8 = 9) to 12thou" and then mark it off on your list. In practice you will notice that
there are always two valves which go down at the same time so you can
adjust two at a time.

[bmcecosse]

The two valves are only 'almost' open at the same time - best to adjust each one on it's own fully closed mark - ie when it's partner in the rule of 9 game is fully open. In fact A series engines run better with wide valve gaps (and it's a dodge used on Minis to help squeeze them through the emissions test at MOT) , supposedly something to do with more suddenly opening the valves instead of 'creeping' them open and this more than off-sets the tiny loss of valve lift - but of course there is then more valve noise.

[Packedup]

I turn the engine till the rockers on a given cylinder are clearly fully closed and do a cylinder at a time.

The theory behind larger gaps is, IIRC, the inlet charge will rush in at greater velocity, so increasing volumetric efficiency. I'm not convinced this is good for the valvetrain (larger gaps mean more hammering of the rockers/ valve stems IMO) or that it really gives a worthwhile performance increase in real terms.

I do agree there's no harm is widening the exhaust gap a little though, for the reasons given about cooling and expansion. Someone i used to know who worked on the OHV Triumphs at BL reckoned 12 in and 14 exhaust was the best way to go and the usual procedure, even though the under bonnet sticker and manual said 12 for both. Goes to show book spec isn't always even factory spec!

[Pascal]

I'm not sure I fully understand the logic of a bigger gap on the exhaust valve. If there is a bigger gap the valve will open later and close earlier so will be open a shorter time. How does this help with the cooling?

[Axolotl]

I think the theory is that the valve is cooled mainly when the rim is in contact with the valve seating in the cast-iron head, so if it is open for as short a time as possible, consistent with the engine running well enough, the cooling contact time is maximised.

I stand to be corrected, however.

(and no-doubt will be).

[bmcecosse]

Nowt to do with cooling - it's simply that the exhaust valve gets very hot - even hotter these days with the unleaded fuel which burns hotter than the old leaded fuel. So, exhaust valve stem expands more than the inlet stems meaning the gap will close up slightly. So the idea is to make SURE that even under the worst hard slog full throttle up-a-hill conditions the gap reamains. If it ever closes up then the seat will be damaged. The inlet valves are constantly cooled by nice fresh charge of evaporating petrol - and so their expansion is very much less and the 12 thou gap there is fine. But hey - it's just a suggestion based on my years of experience, run whatever gaps you like lads!

[Pascal]

By the way is it obvious which valves are the exhaust ones when you look at the rockers? Are the exhaust valves aligned with the exhaust manifold? (I'd rather know before I get started!)

[Packedup]

Starting at the front of teh engine the valves are:

1 - Ex
2 - Inlet
3 - Inlet
4 - Ex
5 - Ex
6 - Inlet
7 - Inlet
8 - Ex

The A series has three exhaust ports and 2 inlet at the head/ manifold join, hence the slightly odd looking pattern.

[bmcecosse]

Which is why it generates less power than say a Ford engine of the same capacity and era. there are of course fabulous 8 port heads available for these engines - and what a diffrence that makes ! But sadly, not inexpensive. there is also a 7 port version (4 inlets and 3 ex) but it's hardly any less expensive although it does use the standard camshaft and exhaust manifolding where the 8 port needs specials. And of course - there are overhead cam heads available too - but only at really crazy prices.