Tappet Clearances

[David Stepney]

I am sure that my Seven, whilst lying idle in the garage, which, as some of you may know, is not ofter, thinks up new and improved ways of making mischief.

For a week or so, although the car seemed to be running well, I noticed a slight decrease in performance coupled with the occasional backfire on deceleration. The engine was running sweetly - almost too sweetly, so, yesterday evening, I thought that I would give it a bit of a tune up.

The pints gap was correct, the timing was right and the carb seemed not to need much attention, with good pickup and a nice even tickover. As part of the operation, I checked the tappet clearances to find that they had closed up almost to nothing.

Now I am a bit fussy about tappet clearances, preferring them to be a touch on the generous side rather than the other way about. So I reset them to my accustomed setting of 4 thou inlet and 6 thou exhaust and a short test drive showed an immediate improvement. The car almost felt lively (if one cans use such an expression about an RP saloon in standard trim).

All the locking nuts were tight when I came to them but the adjusters themselves all required turning back several flats to get the required gaps. I should perhaps record that my car, for some reason now lost in the mists of time,is fitted with the later 'pin type' valve spring retainers rather than collets.

I must also admit that I haven't looked at the tappets since I last had the engine apart to fit new pistons, which is now some while ago, as the job with the engine in the car and the manifold in place is not the easiest of jobs.

The question is this: Has anyone else had experience of this phenomenon? If so, is there a solution, or should I be checking the tappet clearances more often?

[Chris KC]

Setting tappet clearances in situ is not my favourite job David. I also find it is very easy to make an error. I nowadays have the habit of setting them all, then making (at least) a second pass to make sure they are all where I thought I put them, which often flags up the need for some minor re-adjustment. I also try to re-check them after a bit of running. That's about all my back can take...

Could it be that your block to crankcase gasket / joint has "settled" a little over time? Likewise I go around the block fastenings with my spanner several times after making the joint and at least 24 hours later, as some compression can occur (depending on what you make your joints with, of course).

[John Mason]

Hi David, I set my tappets with a wider gap than you do. 6 for inlet and 8 exhaust. I use the rule of 9 when setting them. No. 1 valve fully open so adjust No, 8 (1+8 = 9. Then No.2 open adjust No 7 and so on until all are done. I also find it easier to remove the inlet manifold to do this when the engine is in the car.

John Mason.

[David Stepney]

Thank you, gentlemen, for your comments.
Chris. Setting tappets on the car is not my favourite job either! Not only are you bent into a most unnatural position, with your head upside down (which presents problems if, like me, you wear glasses), but there isn't that much room to wield spanners in there. That is probably why it is not on my list of service items, being a job (almost) of last resort.

It is entirely possible that the block to crankcase gasket has settled over time. It was a paper gasket liberally covered with silicon gasket cement and the nuts have been checked for security and tightened as required on several occasions.

John, yes, I too use the 'rule of nine' to set the tappets on a four cylinder engine It appears that you set your tappets as per Doug Woodrow's recommendation. if memory serves me correctly, the factory setting was 4 thou all round. I should perhaps mention that I trained as a motor mechanic before I retrained as a legal exec, and I recall that, with my first Seven, my them boss always thought that 4 thou was a bit tight for exhaust valves and used to suggest that 6 thou was better. He also taught me that tappet settings should be an easy fit, more generous being better than not.

[Chris KC]

I have no doubt that many people use 4 thou and have no problems at all, but back in the 80's I suffered a spate of burned valves and decided to adopt a slight "safety margin" - nowadays I use 6 & 8 (same as John) without any issues.

[Nick Lettington]

I recently bought a rolling chassis with a fresh looking engine built up with a 9E1 head, bunch of bananas exhaust and lightened flywheel. I had great hopes that it would be the perfect basis for building up a second Speedex Silverstone. The first surprise (and warning sign) was finding no thrust bearing in the gearbox when I separated it... next, although the engine turned over, it locked up until I removed the petrol pump... then the starting handle had a jury rigged spring that somehow held the shaft against the starter dog and today I thought it prudent to check the tappet clearances before attempting to start it. 6 of 8 were somewhere near where you might expect them, but the last two appear to have been set using a spanner in place of the feeler gauge... although the lock nuts were tight, I don't think the valves lifted in the slightest... I suspect the old boy who built it up had also used the rule of 9, but forgot himself and set the clearances on the valves that were up not down!

Still... it is the problem solving that makes this hobby of ours interesting.

I went for 6 thou and 7 thou... certainly better than the 243 thou I started with.

[Parazine]

if memory serves me correctly, the factory setting was 4 thou all round. 

The Austin Motor Co recommendation was for 4 thou hot. How one is supposed to achieve this, I do not know. 

I use 6 and 8 thou, cold, which has been successful for the last forty years.