Making new tappet adjusters.

The tappet adjusters (basically a threaded rod and adjusting nut) need replacing.

I have sourced some long, high tensile, 1/4" UNF grub screws and grade 5 nuts. The grub screws have a hex slot rather than a screwdriver slot which is easier when it comes to adjustment.

It is the other end of the grub screw that presents a small problem. I need to make them hemispherical to fit into the top of the push rod.. I don't have a ball turning device and apart from the use of warding files, I don't have a good idea of how to do the job!

I am sure I am missing a trick here or overthinking the solution, so any suggestions? Otherwise it will be files and Mk 1 eyeball.

Andrew.

Maybe an HSS form tool and a basic lantern chuck in the lathe
If you can find one the correct diameter, you could even use a woodworker's carbide tipped router cutter in the toolpost, as the form would then be ready ground.

Bill

Bill has it ! A form tool at that size, ground from HSS. Rough out screw end to 45* to get rid of the bulk then finish with the form tool. Noel

Now why didn't I think of that. Thanks Bill and Noel. I have this vision of form tools as being for much larger jobs.

Thanks again,

Andrew.

How about a ball ended endmill in the drill chuck?

Probably showing my ignorance, but isn't a ball ended end mill, one that has a ball or hemisphere on the end? I want a ball or hemisphere on the tappet adjuster, not on the cutting tool, or have I totally misunderstood your suggestion?

Regards,

Andrew.

You are quite right. I was thinking of the end of the push rod.

I was wondering if a grub screw will be hard enough for a tappet adjuster? They are usually very hard whereas socket headed fasteners are made from material selected and heat treated for toughness. Depending on your application the grub screws may have a shorter than hoped for life. Of course they may last for ever if they are relatively lightly stressed.

Mike

I have made similar form tools by using silver steel,driling a hole at an angle,to give the wanted radius Grind away to leave half of the drilled hole , harden.Usualy works quite well.

Keith

I tend to make my tappet adjusters from silver steel and simply harden with a blow torch. Works for me but the old Sloper only does around 300 miles a year.

I thought of using grub screws (with a hex hole) as most of the work has been done. The ones I have ordered are quoted as being high tensile and meeting AINSI B18.3 standard. Anyone know if that spec is suitable for my intended use?

Like Chris, the tappet adjusters will get a very easy life in my Petter driven alternator. Used for power cuts only, apart from annoying the neighbours when test running and annoying them even more when there is a power cut.

Andrew.

Edited By Andrew Tinsley on 19/02/2023 22:34:17

They might last an hour or two unhardened or maybe a bit more. But they might mess up the ends of your pushrods and fiinish up costing you more money in the long run too. I would buy the correct parts. They take quite a hammering due to the tappet clearance and there is a reason every manufacturer hardens them..

There is a technique for turning small ball shapes which might work for this. You take a piece of silver steel rod a little larger than the ball size, and drill a hole in the end a little smaller than the ball size.Face the end and then harden. Fit the other end into a file handle, and arrange a rest in the tool post close to the job. Having roughly formed the ball end with a 45 degree chamfer, use the hand turning tool to form the ball, moving it around the end of the job so that it can cut. The circular cutting edge on the inside of the hole will form the ball. The outside edge is not a cutting edge and should never contact the job.

I've used this technique to form ball ends on tiny handles as small as about 1/8 inch or so. A refinement is if you can manage to face the end back at an angle to give some relief to the cutting edge. This sort of tool will work for a range of sizes, the smallest being the size of the hole.

Otherwise, you can make a form tool from gauge plate by drilling a hole the size you want and then cutting away the bits you don't want to leave a half or quarter circle cutting edge.

Case hardening should be enough for the tappets for a vintage style of engine.

regards

John

Hopper

Unfortunately the tappet adjusters are no longer available to buy, hence making them is the only solution, So you give the home made ones a couple of hours before they ruin the push rods? Goodness knows if the grub screws can be hardened, I wouldn't know where to start looking for AINSI standards.

Looks as though it might be better to go Chris Evans route and make them out of silver steel and harden them? I have never had much luck threading small diameter silver steel, I always finish up with a very ragged thread. Doesn't matter if I use a die or screw cut, the silver steel is good quality stuff (Coventry Grinders).

Andrew.

I don't know how long they would last for sure. The only way to really tell would be to run them for an hour and inspect carefully. May well be all right for occasional emergency gen set use. But I would not expect them to last too long if not hardened.

I don't have trouble threading silver steel but use good quality dies. I don't know if high tensile bolts would have enough carbon in them to harden like silver steel. I think they are more of an alloy steel than high carbon content, but have never looked it up. I am sure it is out there somewhere.

1/4 UNF tappet adjusters from something else might fit? Lister?

The ball ends will have to be polished to match the pushrod cups, case hardening may be the best way .

Allen screws are probably some alloy steel, we need a metallurgist to comment on whether case hardening is a good idea. Above my pay grade.

Try A series tappet adjusting screws

Robert Butler

Hello Robert,

Good thinking, but A series tappet adjusters are 7/16" UNF. As I found out long ago!

Thanks,

Andrew.

Sorry but 803 A series are 1/4 UNF