Countersink

Hi Folks

i need to create valve seats for a small IC engine. The plan calls for the use of a No 4 Countersink can anyone help in telling me how these countersinks are measured and identified. ? as there is a no 4 I assume there are Nos. 1,2,3, etc.any help would greatly appreciated.

Assuming plan calls for centre drills not counter sinks a no 4 should be 3/8 diameter. Loads of hits for info on Google, one here **LINK** .

Countersinks are sized by diameter and angle not numbers.

Clive.

Hi Clive

The plan I am working from says to use a No:4 countersink to achieve the valve seat geometry, I was wondering what the specification of a No: 4 was hence the post.

What is the engine and what is the angle on the valves?

I have seen the odd one where you get a double angle on the seat in which case a BSNo4 centre drill could possibly be used this is 5/16 body and 1/8 pilot

Hi Jason

The engine is a 3 cylinder 4 st. LME-370 designed by Todd Snouffer, on the plan the "Valve cages" indicate an external seating of 45 degrees for seating into the cylinder head, however the internal "valve seating" says use a No 4 countersink to achieve a 45 degree angle for the valves.

I'll have a look at what I have though I think I gave my PIP drawings to someone else.

The only reason I could think of you a specific size is if the CSK seat is set below teh surface of teh head and a specific OD is required

I think the No 4 will be a specific diameter, there is not a great deal of material in the valve cage left to cut the seating, sods law if I try something else it simply will not work.

Just had a look and it seems that all the build article was printed as a pull out in MEB mag so I must have given that away with the drawings.

Does sound like a specific size as you say maybe designed for a #4 UNC CSK screw and possibly a pilote dcountersink which would ensure the seat is concentric with the guide

I have asked on one of the other forums where there are more American members and they also tend to make engines there too.

Edited By JasonB on 18/06/2017 13:40:19

Thanks Jason

I have dropped of an email email to Todd Snouffler to ask his opinion, I have a feeling that i will be in contact with him on a regular basis lol

Alan,

are the valve cages cylindrical, if so why use a countersink?

Hi Bob

My problem is that the plan I am working on states using a NO:4 countersink to cut the seating's for the valves, what I am trying to do is find out what is the specification of a No: 4 countersink.

Regards

Alan

What follows is based on the fact (unstated - my guess) that this is an IC engine with conventional poppet valves.

The important detail when cutting valve seats is that the valve guide and the seat should be concentric. Full size tooling involves a conical cutter (or grinder) with a central spindle, which goes down the valve guide. An unguided conical tool used on its own is not likely to produce exact concentricity, unless you can manage to cut the guide bore, fit the guide and ream it, and then cut the seat at the same settings on the same machine.

Most 'ordinary' countersinks are made at 45 degrees, which seems to be what you want - but suitability (and availability) also depends on what material (hardness, especially) you are using for the seats. The final operation should be to grind each of the valves in to its seat - a sort of lapping operation. As soon as you start this, you will see whether your concentricity is OK - if not, the fine grey lapped surface will only show at one side of the seat, even after several arm-aching minutes.

The exact size of the cutter is not related always to the seat itself - as long as the blades of the cutter sweep the full radial width of the seat, that should be fine. But you also need to ensure that the cutter does not remove metal elsewhere, too. How likely this is will depend on the layout of your engine. A side-valve with removable head is the least problematical. A fixed head design, side-valve or overhead, is much more of a problem.

Hope this helps

Regards, Tim

Not a good photo but it looks like the cage is inserted and then the seat cut which cuts both the surrounding alloy head and also the brass/bronze cage which would be one reason for a piloted CSK

Quite interesting stuff on Todd's Littleloco's facebook photos, interesting to se the developement of a couple of engines from drawing, 3D prints, Patterns, Casting and making. Don't go looking for locos though!

Edited By JasonB on 18/06/2017 19:11:23

Why not google 'number 4 countersink'?

You'll discover it's a piloted countersink for a number 4 woodscrew, these days typically with a 3mm drill fitted.

I assume the outer diameter is not critical as long as you can fit a 3mm rod in it to act as a pilot.

Neil

I think your valves might leak with one of those. Would not even want to use my Carbide tipped combined drill/csk bit son an engine

There are engineering piloted CSks about the one for a #4 unc screw has a 0.252" OD which looks about right have a look at this catalogue

Hi Jason

Thank you for the photos, The valve "cages" are machined and screwed into the head, the seating for the poppet valves are machined before the cages are screwed into the head, hence the need for a Number four countersink . All work is done on the lathe a No 4 Countersink would be simply held in the tail stock chuck

Edited By Alan Gordon 4 on 18/06/2017 20:08:01

Edited By Alan Gordon 4 on 18/06/2017 20:10:39

By the looks of it, the "cages" are in fact the valve seats. They should be locked so that they cannot unscrew, otherwise things could get terminal. (Make sure that the locking cannot find its way into the cylinder, or the cure will be as bad as the disease!)

Ideally, there should be a very slight (1 degree) difference between valve and seat angle, so that the valve makes a line contact with the seat at the outer diameter of the valve. In this way, there should be no hot gas between the valve and seat when the valve is seated. A seat slightly wider than a line should be acceptable, since it increases the area to conduct heat from the valve head into the seat and the parent metal of the head, to keep it as cool as possible.

It is important, as already said, that the valve guide bore and the seat are concentric. Otherwise there will not be a good seal between valve and seat, unless a huge amount of lapping in is done, and possibly not even then.

The bore of the guide needs to such that the valve stem is a close fit (not so tight that galling occurs), but to prevent the valve and the seat being worn to a radius form.

The rocker pad needs to of such a radius that minimal side thrust on the valve stem is produced (Which is why O H C engines use bucket tappets to take the thrust from the cam lobe into the head, and not to the valve stem.

Howard

While looking for something else I did find a company in teh states tat does centre drills with various angles to them not just 60deg. They do a 90deg one in #4 size and describe them as "combined drill countersinks" could be what was described.

Thanks for the info guys, much appreciated