Machining Cylinder Head Chamber Roof – DIY or Shop Tool

[William Harvey 1Participant @williamharvey1]

Bit of a mixed (but linked question here). I am modifying my own A Series Engine Cylinder Head. The chamber size needs increasing and I have been given technical advice from an A Series Engine Modding specialist.

I have a Warco WM180 Lathe and a Warco Hobby Bench Drill, I have zero experience

I need to raise the roof of the chamber and have been advised to machine out a recess around the top valve throat to a specific height and use that height as a reference for grinding out the chamber roof with a Mount Point tool in a Die Grinder. I have done one chamber as a test, but go a machine shop to cut the recess – I now want to do the rest myself.

The tool I need resembles a Fly Cutter, but needs to have a shaft that sits in the valve guide to act as a guide to keep in central.

Here is a pic of the tool in question (Home Made)

Sorry all I managed to get was some frame grabs from a video. If you have FaceBook, here is the video.

The guy was actually using the tool to cut recesses for Hardened Valve Seats, but it will do the job I want. He suggests that it can be used in a Pillar Drill?

Again information from the same guy that uses the above tool:

"So to sum it up we use a single point cutting tool mounted in a pillar drill with a valve guide pilot to machine the chambers to produce an even depth on all chambers and to take the chamber wall out to the gasket line save for a few thou. Use a 0.040" radius on the cutting tool so not to produce too sharp a corner in the chamber."

Question

– Would anyone be willing to make this tool for me or help me make it?

– The lowest speed on my drill is 600RPM (Warco Hobby Drill), for Cast Iron I have been advised that this is way to fast?

– I could use the Lathe, once I fashion up the facility to Mill on it using a modified slide mount and some Angle Plate (separate thread on this a while ago).

[William Harvey 1Participant @williamharvey1]

[nigel jones 5Participant @nigeljones5]

Thirty years ago I made good money modding 12G295 and 240 heads.Im assuming your increasing valve size? Cutter is easy to make if youve got a lathe – 120rpm. If your wanting high compression (13 to1 is as high as you go for normal fuel) then the chamber surfaces need to be ground smooth otherwise you will get detonation. Pillar drill – not a chance. An easier way to increase the seat size is with a conical grinder. If its just to lower the compression then die grinder – still got my Bosch die grinder somewhere – and wear goggles, forgot how many times I went to a and e with cast iton in my eye!

[William Harvey 1Participant @williamharvey1]

Best head is a Metro 12G940 with 35.6mm valves, practice head has the slightly smaller valves so, if I end up using this then yes bigger valves,

Chamber needs to be increased to achieve CR of 9.75:1

So how do I make the tool, it’s EN24 Steel and I’ll need some cutting tools for it?

[StueeeeParticipant @stueeee]

If you have a lathe you have all the tools you need to make a suitable pilot cutter. I have made a lot of these for cylinder head/block work. I usually drive them by hand.

This cutter is enlarging the valve throat in a 1928 Chevrolet head to accept slightly larger modern stainless steel valves. But the principle would be the same for cutting around the face of a valve seat. I always use knackered centre drills to make the actual cutter bit for the hand operated pilot cutters.

On the odd occasion that I do use a pilot in a machine, I use my Bridgeport mill, I don't think that anything with less weight would give a satisfactory finish on a job like this one.

This carbide cutter was made to narrow the cast in valve guide to improve gas flow in the valve throat. 'Before' on the left 'after' on the right. The first version I made with a cobalt HSS bit wouldn't touch what was obviously a chilled casting

Edited By Stueeee on 30/06/2021 22:13:19

Edited By Stueeee on 30/06/2021 22:17:39

[EmgeeParticipant @emgee]

William

Using a fly cutter will give you a vertical wall whereas the picture shows sloping walls.
I don't see how you increase the valve size as they are almost touching now.

The fly cutter pictured looks to have a round cutting tool inserted, possibly has a flat ground where the securing screw bears.
Any rod you use to locate in the valve guide will need to be polished and kept lubricated in use or damage may be done to the guide.

In the absence of a milling machine I think you will be advised to use the lathe for this work, a drill press is not really suited to this work, the tool needs securing in the spindle and the rpm needs to be lower than your drill can go to.
Using a lathe will have it's own problems in securing the cylinder securely and accurately to the cross slide in a position where the work can be done, it seems it will need to be hanging over the front of the saddle with the combustion chambers facing the headstock with the centre of the valve seats in line with the lathe centre height, any support will need to extend for the length of the cylinder head from lathe cantreline to allow all parts to be machined.

Emgee

[William Harvey 1Participant @williamharvey1]

Posted by Emgee on 30/06/2021 22:32:16:

William

Using a fly cutter will give you a vertical wall whereas the picture shows sloping walls.
I don't see how you increase the valve size as they are almost touching now.

The fly cutter pictured looks to have a round cutting tool inserted, possibly has a flat ground where the securing screw bears.
Any rod you use to locate in the valve guide will need to be polished and kept lubricated in use or damage may be done to the guide.

In the absence of a milling machine I think you will be advised to use the lathe for this work, a drill press is not really suited to this work, the tool needs securing in the spindle and the rpm needs to be lower than your drill can go to.
Using a lathe will have it's own problems in securing the cylinder securely and accurately to the cross slide in a position where the work can be done, it seems it will need to be hanging over the front of the saddle with the combustion chambers facing the headstock with the centre of the valve seats in line with the lathe centre height, any support will need to extend for the length of the cylinder head from lathe cantreline to allow all parts to be machined.

Emgee

Emgee,

That’s not my cylinder head but yes on any 12G940 head the valves almost touch.

He is definitely cutting vertically as he is making a cut to fit hardened valve inserts.

I was planning on moving the backplate on the Warco which will give more room. And I will be fitting an Angle Plate on the cross slide to hold the cylinder head.

And any cutting is done whilst the old valve guides are still in.

Edited By William Harvey 1 on 30/06/2021 22:40:11

[Glyn DaviesParticipant @glyndavies49417]

If I understand the task here, it's to produce some flat area in the chamber that is a defined distance from the top face of the cylinder head so as to provide a guide when using a mounted point on a flexible shaft grinder to fully profile the chamber. Why not set the depth on your pillar drill and use a small diameter end mill (~5mm) to create a number of spot faces in each chamber? Or just use a 5mm drill instead of the end mill.

If the valve seats are already cut, you could make a pair of dummy valves that protect the seats and sit in the seat at the correct depth to act as a further guide when grinding.

I still have my 1973 Vizard's guide to cylinder head modification from my 998cc Mini days and scanned the 1275 Midget template:

Edited By Glyn Davies on 01/07/2021 10:46:59

[StueeeeParticipant @stueeee]

Posted by Glyn Davies on 01/07/2021 10:43:08:

If I understand the task here, it's to produce some flat area in the chamber that is a defined distance from the top face of the cylinder head so as to provide a guide when using a mounted point on a flexible shaft grinder to fully profile the chamber. Why not set the depth on your pillar drill and use a small diameter end mill (~5mm) to create a number of spot faces in each chamber? Or just use a 5mm drill instead of the end mill.

If the valve seats are already cut, you could make a pair of dummy valves that protect the seats and sit in the seat at the correct depth to act as a further guide when grinding.

I still have my 1973 Vizard's guide to cylinder head modification from my 998cc Mini days and scanned the 1275 Midget template:

Edited By Glyn Davies on 01/07/2021 10:46:59

Multiple spot faces with a slot drill should deliver what the OP needs. And more importantly should be doable with a pillar drill.

Here's a 12G940 head I did a while ago, very similar combustion chamber shape to the Vizard design. I traced the combustion chamber shape for this head from a head from a professionally built motor (Swaymar IIRC) that gave really good power on the Dyno.

[EmgeeParticipant @emgee]

Using a slot drill or endmill with plunge cuts only will not produce a flat combustion chamber, just a load of peaks and troughs, Those cutters have the lips ground to provide clearance so do not cut a flat hole.
Could be beneficial as it would certainly cause a lot of disruption to the gas flow.

Emgee

[old martParticipant @oldmart]

I did this years ago, not to tune the engine, but to lower the compression ratio when unleaded petrol came in. I did it by hand with a die grinder, fortunately the head was aluminium. Th match the volumes, with the valves and plugs in place. a piece of perspex with a hole in it covered each combustion chamber in turn, and a syringe was used with oil to get within 1/4CC each.

[William Harvey 1Participant @williamharvey1]

Posted by Stueeee on 30/06/2021 22:10:46:

If you have a lathe you have all the tools you need to make a suitable pilot cutter. I have made a lot of these for cylinder head/block work. I usually drive them by hand.

This cutter is enlarging the valve throat in a 1928 Chevrolet head to accept slightly larger modern stainless steel valves. But the principle would be the same for cutting around the face of a valve seat. I always use knackered centre drills to make the actual cutter bit for the hand operated pilot cutters.

On the odd occasion that I do use a pilot in a machine, I use my Bridgeport mill, I don't think that anything with less weight would give a satisfactory finish on a job like this one.

This carbide cutter was made to narrow the cast in valve guide to improve gas flow in the valve throat. 'Before' on the left 'after' on the right. The first version I made with a cobalt HSS bit wouldn't touch what was obviously a chilled casting

So how do I go about making the cutter? I have found a couple of possible ideas but nothing step by step. The main issue is the angle of the cutting tool in the holder and the shape and position of the cutting tip required for Cast Iron?

[William Harvey 1Participant @williamharvey1]

Posted by Emgee on 01/07/2021 12:42:41:

Using a slot drill or endmill with plunge cuts only will not produce a flat combustion chamber, just a load of peaks and troughs, Those cutters have the lips ground to provide clearance so do not cut a flat hole.
Could be beneficial as it would certainly cause a lot of disruption to the gas flow.

Emgee

The idea is to make a reference cut. The chamber floor will be ground flat to the reference point using an Air Die Grinder.

[StueeeeParticipant @stueeee]

IMO, If you're going to use a pilot cutter rather than make a number of reference cuts with a slotdrill as suggested earlier, what you're aiming for should look very much like the hand operated cutter in the photo of the early Chevrolet head in my previous post.

Machine the cutter from a single piece of mild steel. Doesn't need to be anything fancy; I usually use EN3B, EN1A should be OK too. 'A' series valves are 9/32 diameter, so that's going to be the size you're going to machine your pilot to. Once you've machined the pilot, put the job in a pair of vee blocks and drill across the piece immediately above the 9/32" section to the same size as whatever piece of round HSS you're going to use.

Once that's done, turn the piece 90 degrees and drill the hole for the grubscrew. The drilled hole needs to be the tapping size for whatever size grubscrew you choose. It needs to be smaller than the toolbit diameter; e.g. if you are using a 5/16" diameter toolbit, then aim for a 1/4" or 6mm grubscrew. At the top of the piece crossdrill again for the tommy bar.

Re. grinding the toolbit, to produce a flat cut, the cutting edge needs to be at 90 degrees to the pilot. Orientate the tool bit in the hole so that it has zero or negative rake, otherwise the toolbit will 'dig in' while you're cutting.

 

HTH. Stuart.

Edited By Stueeee on 01/07/2021 21:37:07

[William Harvey 1Participant @williamharvey1]

Posted by Stueeee on 01/07/2021 12:25:26:

Posted by Glyn Davies on 01/07/2021 10:43:08:

If I understand the task here, it's to produce some flat area in the chamber that is a defined distance from the top face of the cylinder head so as to provide a guide when using a mounted point on a flexible shaft grinder to fully profile the chamber. Why not set the depth on your pillar drill and use a small diameter end mill (~5mm) to create a number of spot faces in each chamber? Or just use a 5mm drill instead of the end mill.

If the valve seats are already cut, you could make a pair of dummy valves that protect the seats and sit in the seat at the correct depth to act as a further guide when grinding.

I still have my 1973 Vizard's guide to cylinder head modification from my 998cc Mini days and scanned the 1275 Midget template:

Edited By Glyn Davies on 01/07/2021 10:46:59

Multiple spot faces with a slot drill should deliver what the OP needs. And more importantly should be doable with a pillar drill.

Here's a 12G940 head I did a while ago, very similar combustion chamber shape to the Vizard design. I traced the combustion chamber shape for this head from a head from a professionally built motor (Swaymar IIRC) that gave really good power on the Dyno.

I replied to this yesterday morning, but the post seems not to have uploaded. You have understood the task correctly. Vizards Cylinder Head Modification Book is on eBay for £38, but I am cautious about buying it as a lot of his info has now been superceeded due to modern fuels, would it be worth buying? You don't still have the chamber profile template do you All the experts do not want to give away thiers I have managed to get a photo of a modified cylinder with a ruler as a guide and I am trying to make up a template but it is very difficult. I have been getting guidance from a renowned expert but its very bitty.

[William Harvey 1Participant @williamharvey1]

Posted by Stueeee on 01/07/2021 21:35:14:

IMO, If you're going to use a pilot cutter rather than make a number of reference cuts with a slotdrill as suggested earlier, what you're aiming for should look very much like the hand operated cutter in the photo of the early Chevrolet head in my previous post.

Machine the cutter from a single piece of mild steel. Doesn't need to be anything fancy; I usually use EN3B, EN1A should be OK too. 'A' series valves are 9/32 diameter, so that's going to be the size you're going to machine your pilot to. Once you've machined the pilot, put the job in a pair of vee blocks and drill across the piece immediately above the 9/32" section to the same size as whatever piece of round HSS you're going to use.

Once that's done, turn the piece 90 degrees and drill the hole for the grubscrew. The drilled hole needs to be the tapping size for whatever size grubscrew you choose. It needs to be smaller than the toolbit diameter; e.g. if you are using a 5/16" diameter toolbit, then aim for a 1/4" or 6mm grubscrew. At the top of the piece crossdrill again for the tommy bar.

Re. grinding the toolbit, to produce a flat cut, the cutting edge needs to be at 90 degrees to the pilot. Orientate the tool bit in the hole so that it has zero or negative rake, otherwise the toolbit will 'dig in' while you're cutting.

 

HTH. Stuart.

Edited By Stueeee on 01/07/2021 21:37:07

Hi,

I picked up some mild steel from a fabrication company a few weeks ago, but I have no idea what grade it is? Yes the old guides are 9/32", so that's the pilot size.

Here are some scans of a similar tool to the one you are describing that I managed to pick up on the Mig Welding Forum from the Vizard Book mentioned in these threads (not great quality and I cannot read the detail). It says the tool is for cutting radiused valve seats, not sure what these are, based on that all the research I have done is that valve seats are 30 / 45 / 60 degrees? The same tool with a different shape cutting tip could be used to cut hardened valve seat recesses of depth guide like I want. Also seems to be used in a drill and manually, but my drill is too fast, hence using the lathe.

This tool also has the cutter at 90 degrees to the pilot as opposed to the others which are angled (angles seem to differ, are there particular angles for particular cuts?).

I am a little confused with the shape of the actual cutting bit and what I should use to make it.

In your reply you said:

"Re. grinding the toolbit, to produce a flat cut, the cutting edge needs to be at 90 degrees to the pilot. Orientate the tool bit in the hole so that it has zero or negative rake, otherwise the toolbit will 'dig in' while you're cutting."

So the cutting face would be along the bottom edge of the cutting bit in the image above.

Here is another scan from the same source showing the cutting bit (albeit not for the use I need, but I can use it to describe what I think you mean)

In the image above I assume we are looking towards the tool and the tool bit is facing us.

If I understand correctly the rake shown above is positive and will dig in, however you are suggesting the opposite? I can't get my head around how a tool with a negative rake will cut, but I found this explanation and negative rake seems to be better for harder materials such as steel (and I guess cast iron?).

Without having any clear guidance on tool dimensions (as the detail is unclear in the scan) I will for the time being start with the following:

Shank Length – 70mm (long enough to fit tightly in the chuck)

Tool Head (The part the cutting bit is mounted in) – Dia less than valve throat, length 35mm (about 4 times bigger that the diameter of the cutting tool?)

Pilot Size: Dia 9/32", Length 80mm (about the thickness of the cylinder head)

For the diameter of the tool head, inlet valves are considerably larger than exhaust, could I make the tool suitable for exhaust throats but also use it on an inlet by moving the tool bit out to suit?

 

 

 

 

 

Edited By William Harvey 1 on 02/07/2021 10:29:11

Edited By William Harvey 1 on 02/07/2021 10:32:05

[not done it yetParticipant @notdoneityet]

It would be of interest to know:

What head you are modding.

Hardened seats?

Increased valve sizes.

Target head volume (plus volume over the pistons, if dished.

Anything else that might be relevant, like increased cam lift, are you cutting pockets in the deck, etc.

[Nick WheelerParticipant @nickwheeler]

William,

Vizard's tool goes back over fifty years to when the equipment to cut multi-angle valve seats was rare and expensive. It's intended to radius a single 45degree seat into the the chamber, and get most of the improvements without spending a lot of money. The other edge would be done as part of the valve throat shaping with a die grinder.

It uses a HSS bit(another use for a broken centre drill) with the radius ground and polished, in a drill press. It's not going to work very well if there are hardened valve seats, which is a real concern when doing these jobs today – an A-series in a road car is going to want them for modern fuel.

[StueeeeParticipant @stueeee]

Posted by William Harvey 1 on 02/07/2021 10:27:05:

Posted by Stueeee on 01/07/2021 21:35:14:

I am a little confused with the shape of the actual cutting bit and what I should use to make it.

In your reply you said:

"Re. grinding the toolbit, to produce a flat cut, the cutting edge needs to be at 90 degrees to the pilot. Orientate the tool bit in the hole so that it has zero or negative rake, otherwise the toolbit will 'dig in' while you're cutting."

So the cutting face would be along the bottom edge of the cutting bit in the image above.

Here is another scan from the same source showing the cutting bit (albeit not for the use I need, but I can use it to describe what I think you mean)

In the image above I assume we are looking towards the tool and the tool bit is facing us.

If I understand correctly the rake shown above is positive and will dig in, however you are suggesting the opposite? I can't get my head around how a tool with a negative rake will cut, but I found this explanation and negative rake seems to be better for harder materials such as steel (and I guess cast iron?).

Without having any clear guidance on tool dimensions (as the detail is unclear in the scan) I will for the time being start with the following:

Shank Length – 70mm (long enough to fit tightly in the chuck)

Tool Head (The part the cutting bit is mounted in) – Dia less than valve throat, length 35mm (about 4 times bigger that the diameter of the cutting tool?)

Pilot Size: Dia 9/32", Length 80mm (about the thickness of the cylinder head)

For the diameter of the tool head, inlet valves are considerably larger than exhaust, could I make the tool suitable for exhaust throats but also use it on an inlet by moving the tool bit out to suit?

Edited By William Harvey 1 on 02/07/2021 10:29:11

Edited By William Harvey 1 on 02/07/2021 10:32:05

Hi William, yes, the cutting edge would be along the bottom of the tool in the example I gave. If you haven't come across negative rake as a machining concept, just think of how someone scrapes the butter off a block of the stuff, the knife rake is negative but you get a nice curl of butter on the knife without it digging in. As Nicholas Wheeler says, the radius tool in Vizard's book is intended to radius the top and bottom edges of a 45 degree valve seat and pre-dates the modern implementation of three angle valve seats.

I can't say for the factory fitted hard valve seats in the late A series motors, but the ones I have dealt with in other motors can certainly be cut with a sharp HSS tool.

Re. the steel you have, if it has a bright finish, it is almost certainly an engineering steel; having come from a fabricators, anything with scale on it might be 'black mild' and not really very suitable for machining. There are lots of sellers on ebay who should be able to sell you a known quantity.

If you haven't done head work before on an A series motor, this Vizard book would probably be worth a read, there's some good stuff on porting, although I don't remember Vizard having cottoned on to the importance of the 'short side radius' as against the rest of the inlet valve throat as regards gas flow. **LINK**

[William Harvey 1Participant @williamharvey1]

Posted by not done it yet on 02/07/2021 12:18:54:

It would be of interest to know:

What head you are modding.

Hardened seats?

Increased valve sizes.

Target head volume (plus volume over the pistons, if dished.

Anything else that might be relevant, like increased cam lift, are you cutting pockets in the deck, etc.

Hi,

This is a 12G940 BMC A Series Head, non hardened valve seats.
Valves will be Metro which I believe are 35.6mm Inlet, 29.2mm Exhaust.

Target head volume is I believe 25.3cc (but I’d need to recheck my notes) Piston dish is 8cc, Deck Height is averaged at 0.0045”. Rockers will be zero tolerance 1.3:1. No pockets required as this Amis a 1275 A +. Pistons are Nural Hepolite P21253 +40.

[not done it yetParticipant @notdoneityet]

Thanks.

[William Harvey 1Participant @williamharvey1]

So, taking this further I have started to make the required tool.

Here is a pic of my rough size calculations:

A couple of the dimensions are missing and I could do with some help with some of the others.

1. What length and diameter should I make the shank to snuggly and safely fit in the 3 Jaw Chuck on the lathe?

2. If I use a 5/16" cutting bit will length 'c' 35mm be OK?

3. The smallest valve throat is 26mm (not the inlet as in the pic, its the exhaust) so I need a diameter for the tool head that will need to be small enough to fit in the throat, but big enough to hold the tool bit secure, so what size should I choose?

I cut a piece of the bar I have, took me ages using a hacksaw, went through two blades!!

Next problem, I wend to put it in the lathe to face off the ends and realised that the diameter of the bar is too big to slide up through the head stock to reduce the stick out!! So how on earth do you face off bar that exceeds the minimum stick out? This bar is 160mm?

[noel shelleyParticipant @noelshelley55608]

IF I understand this right you are trying to remove part of the valve guide support to open up the throat or portway ? Had you considered a mag drill and rotabroach, it may need several sizes ? Noel.

[William Harvey 1Participant @williamharvey1]

Posted by noel shelley on 04/07/2021 21:11:17:

IF I understand this right you are trying to remove part of the valve guide support to open up the throat or portway ? Had you considered a mag drill and rotabroach, it may need several sizes ? Noel.

No I am trying to make a tool to cut a recess in the valve seat area similar to the process of cutting a recess to fit a hardened valve seats. What I am doing is cutting a recess around the valve seat area to act as a reference for grinding the entire chamber roof to the same depth.

[Nick WheelerParticipant @nickwheeler]

I would turn the shank first. That only needs to be reduced enough so that it is round, and fits in the chuck. Turn all the other diameters with the part made tool in the chuck. None of those sizes need to be particularly precise.

There's no reason for the pilot diameter to be made as part of the tool body. Making it a separate, inserted part is easier, quicker, cheaper and can be easily replaced if you manage to bend it.

As it's a fancy fly cutter, the tool hole doesn't need to go all the way through so the pilot can be seated deeper. And use a round tool so you don't need to make a square hole…

As you need the tool to cut a 26mm diameter, Starting with some 25/22/20mm stock would be sensible.

Edited By Nicholas Wheeler 1 on 04/07/2021 22:02:41

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