22 replies to this topic

[alsy]

Hi, so ive looked up on how to set tappets and i understand how to do it, and to follow the rule of 9.

But what confuses me is which should i set to 15 and which should i set to 12? how do i know which is exhaust inlet and which is the other...

also do i do it one way and then the other?

Thanks

[MRA]

It goes as follows

ex, in, in, ex, ex, in, in, ex

The A series is what is known as a siamese ported engine.

The head is a 5 port head as standard, this means that you have the following..

An exhaust port for cylinder 1,
Then a siamese inlet for cylinders 1 & 2,
Then a siamese exhaust for cylinders 2 & 3,
Then a siamese inlet port for cylinders 3 & 4,
And finally a single exhaust for cylinder 4.

Hope this helps ?

[MRA]

Exhaust by definition is out not in therefore there is no such thing as an exhaust inlet.

Once you perform the rule of 9 allshould be ok, you should not need to do it again until the next service.

You do not need to do it from each end just the one, cylinder no 1 being closest to the radiator.

Exhaust as it runs hotter and there is more expansion due to this increased temperature should in your case be set to 0.015" (15 thou, 15 thousandths of an inch)
The inlet should then be set to 0.012" 12 thou.

[IainStallard]

I read on an auto data program that 0.3mm is correct for all tappets? Correct me if this is incorrect.

[Vipernoir]

A 998 should be set to .012" on all rockers.
The different setting between inlet and exhaust was for the MG Metro (and probably the carbed Cooper).

[MRA]

0.3mm is 0.012" for those that don't know the conversion

0.3/25.4 = 0.0118"

[alsy]

Thanks everyone, so I can just set then all to 12thou and il be alright?

This is probably never going to be able to be explained over the net but how much resistance am I looking for? :<

[jaydee]

you have to be able to slide in the feeler gauge and move it side to side.

for a standard 998 nominal factory setting is 12 thou (0.30mm)
standard 1275 is 15 thou (0.38mm)
MG metro is 14 thou inlet 17 thou exhaust
for aftermarket cams and rockers make reference to what manifacturer specified

[MRA]

That's a good idea Dilligaf, practice on all by setting them the same, then move on and adjust the inlets to the smaller size.

[Vipernoir]

I thought the increase in exhaust clearance was more to do with cleaning up the emissions and the idle than anything to do with expansion.

[MRA]

Heat expansion causes various different thengs to occur, cast iron blocks don't expand as nuch as steel pushrods, rockers valves etc and as such extra heat as in a performance engine needs to be catered for.

Not sure about the emmisions, how would loose rocker clearances help ? Higher CR which helps emissions does create more heat, it would be good to find out more about this one.

[Vipernoir]

I've got so many books & publications that I can't remember right now where the obscure reference is...

Basically, by increasing the tappet gap the effective overall lift & duration is reduced slightly on the exhaust, therby reducing the overlap and makign for a smoother idle and cleaner exhaust.
I'll rack my brian and try and find the source.

The .015" change occured loooong before unleaded petrol was introduced.

[Cooperman]

Even at 0.012" on inlet & ex there will be a big tolerance so that in a worst case where the ex. valves are at a temperature where the engine will almost not run - like so retarded the exhaust manifold is glowing red - there will be no risk of the valve clearance disappearing. I've seen a competition Mini having its valve clearances set to 0.008" to try to gain a few tenths of a second a lap by increasing both lift & duration. Don't know how effective this might be - probably not at all.
It might be interesting to do the maths to work out how much the ex. valve and push rod expands at max operating temp and subtracting the amount the head expands depthwise.
But, setting 0.015" on the inlet and 0.012" on the ex is the best way to set them on a 1275 engine with a hotter cam, higher C.R., etc. Originally everything was set to 0.012", even on a modified Cooper 'S', but times and attitudes change. I still set 0.012" on my 'S' and that has a 286 cam and 1.5 rockers. Never had a problem though.

[tiger99]

You could use one of these, which also needs a 7/16" socket to fit the locknut. It works on a different principle, by nipping up lightly to zero clearance and backing off the appropriate number of clicks. Halfords and various accessory shops sell similar ones. I think mine is a Draper, but I may be wrong as I have long since lost the packaging. It was very much cheaper in about 1980!

http://www.amazon.co...ASIN=B002WT4S1Y

But to return to the question about getting the correct feel, it has already been suggested that there is a risk of being too tight. I will try to explain as well as I can, although you really need to be hands-on to appreciate the feel. If you expect any major amount of force to be needed to move the feeler in the gap, it is because the valve is lifting from its seat and you are actually feeling spring pressure. Just very light friction, an ounce or two, is all that is required. You should be able to insert and remove the feeler with no visible movement at the gap, if so it is just perfect. Don't forget to check again after tightening the locknut, as it will move slightly. You need to have a guess as to how much you need to adjust it, and repeat, until it is right. Not too difficult, if you are patient.

Make sure that there is no wear on the rocker, because if a groove has worn, the feeler will be bridging the gap and will lead to an excessively large clearance. In these circumstances, the above tool will still get it right, but obviously you would need to be thinking about having the rockers refaced.

One thing I always do is to loosen all the adjusters off considerably before I start. That way, you can see at a glance which have been done, and which are still loose, so that none get missed.

[MRA]

Basically, by increasing the tappet gap the effective overall lift & duration is reduced slightly on the exhaust, therby reducing the overlap and makign for a smoother idle and cleaner exhaust.
I'll rack my brian and try and find the source.

I don't have a brian to rack !

However in my Leyland workshop manual it says 0.012" for road use and 0.015" for competition use in the Cooper S section.

And in the latest Rover workshopmanual is says from 0.27mm to 0.33mm which is 0.0106" call it 11 thou and near as makes no difference 13 thou.

So fuel has little to do with it then.

Edited by mra-minis.co.uk, 12 March 2013 - 02:43 PM.