SPQR/Draper ClickadjustTappet adjuster-Principle and instructions

This tappet adjuster first appeared under the German name SPQR and was later marketed in the UK under Draper and subsequently Gunsons. In the US it was sold under the Snap-on Brand. I do not know if all these adjusters are exactly the same but I do know that used items make frequent appearances at Autojumbles- by which time they have usually been separated from their instruction sheets so I reproduce the SPQR instructions here.

The tool is shown below, its usually supplied with only 2 sockets although others are available as extras and there is space for 5. I have tracked down some others and my set now boasts 5, but I don't know if other sizes were available

Tool in its case

Case opened- I don't know what the strange ladder like object is for blocking weak valve springs to stop them compressing as the tappet adjustment is closed down to the loud click stage. I've never had to use it.

The sockets I tracked down for mine are listed below- seems a bit light on metric sizes' but then this tool dates from the imperial era!

1/4 BSW; 9/16 AF; 1/2 SAE; 7/16 AF and 11mm

Note SPQR branded sockets- all 1/2" sq drive but with a 3/8" locating hole

These are all branded as SPQR and all have the 3/8 locating hole drilled in the centre of the 1/2" drive socket. There is a small blue plastic detent that engages into this hole although unlike many such socket handles there is no way to lock and unlock the detent for loading and unloading sockets. You need to push the detent back in manually to remove a socket! This is a primitive design and I think a design fault as it ensures this plastic ("plastic" for Heaven's sake???) detent will wear quickly. Fortunately, although the instructions emphasize the importance of this feature - I personally doubt that it matters at all and I suspect any socket will be fine as long as the screw driver head can penetrate far enough to engage the slot in the adjuster screw.

Plastic detent on the tool itself. I think this is a poor design.

I have read that many people distrust this tool- largely I suspect because they don't understand how it works so I'll state here that the tappet gap is measured and set by these tools using the thread of the tappet adjuster screw in the vehicle: The measurement system is not in the tool itself! The tool is in effect a micrometer which also uses a screw thread to determine a gap and in theory should be both more accurate and reproducible than using a feeler gauge. Its also quicker once you get the hang of it. The tool simply allows you to make a measured and reproducible turn of the adjuster screw by dividing one complete revolution into 30 clicks (I believe some give a finer adjustment of 1 turn = 40 clicks). You will already know that setting the gap means turning the adjuster- this tool just allows you to do that in a more precise way. Its simple to use, you don't need to know how it works, you just count "clicks". The number of clicks you need is thoughtfully laid out in a datasheet originally supplied with the tool (and obviously covering only vehicles current at that time), or it can be calibrated for any unlisted model.

If you're interested in some more theory read on- otherwise skip to the instructions and data sheets below.

There are of course variations in vehicle design which mean that the meaning of "one click" in terms of "thou set at tappet gap" isn't the same in every car. The most obvious of these is the thread on the adjuster itself- some are SAE-others metric, most are fine pitch but some, somewhere might be standard pitch.

The second point is that rockers rock! As one side goes up the opposite side goes down, and this movement will be equal on both sides only if the pivot point is in the centre of the rocker arm. Some may not be centre pivoted and nor are they all necessarily pivoted at the same point. You don't need to know anything about this to use the tool as its all worked out for you in the data sheet or automatically sorted out when you calibrate the tool on your car- and I would definitely recommend this as in my case at least (MGB) the data sheet was wrong. Most of us of course being amateurs, do not regularly adjust that many different vehicles and once you know what you need for your own, then its all very simple- just count the clicks.

While Im here I'll just explain that the datasheet for my car assumed the adjuster screws are 20tpi. In fact they are 5/15 UNF which is 24tpi. This finer pitch means you need more clicks to achieve the same disrance- in my case 10 not 8 clicks.

There is one much vaunted advantage of using this tool and one disadvantage, both of which I'll quickly describe.

Firstly the advantage- as a rocker arm wears the valve stem head gradually impresses a shallow depression into the the centre of the rocker arm push-pad. The actual valve clearance is then between the end of the valve stem and the bottom of this small depression or pit. Obviously this pit isn't going to be huge- and if it is then you need new rockers, but it may well be a thou or two. A feeler gauge cannot measure this clearance as it will simply bridge across this small pit resting on the rim. Consequently if rockers are worn, using a gauge alone can set the gaps too big. This is where years of old-guy experience come in- "pencil-behind-the-ear time" to sort out what's going on and modify the setting according to "feel". I don't have that wisdom. The SPQR tool of course determines the clearance starting from a fully depressed rocker- i.e. with the valve already at the bottom of any such pit, and so will give a more accurate gap setting.

Secondly then, the disadvantage: the tool depends on the thread of the adjuster screw. This has to be free and undistorted. If some previous owner has over-torqued the adjuster locknut it may have distorted the thread. Personally I think this is unlikely to be significant because the thread that matters is that inside the rocker arm and thus below the lock nut. This should be protected even if the nut is overtightened- Think about where the thread would strip if you really went for it and overtightened the locknut- the thread would give within the locknut not inside the rocker arm. All the same if your locknuts don't seem to stay tight for very long in use then maybe its time to replace at least the adjuster screw if not the whole rocker.

Below I'm simply reproducing the instructions and data sheet from the SPQR tool- As you will have gathered I like these tools- largely because I like objectivity and hate having to use "best judgment" to set anything. I don't doubt that "best judgment" can really be "best" when judged by a motor guru, but sadly I don't count myself in that category.