Machining Cylinder Head Chamber Roof – DIY or Shop Tool

[William Harvey 1Participant @williamharvey1]

Posted by Nicholas Wheeler 1 on 04/07/2021 22:01:04:

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

If I don't make the pilot guide as part of the tool, what would be the best way to attach it?

[William Harvey 1Participant @williamharvey1]

So I made a start on this after work.

One problem, which I have been addressing elsewhere is the fact that the stock bar I have is too large to fit through the spindle hole in the lathe!! So after some research into using centre rests and tailstock centres, I had a go.

First off with one end of the bar secured in the chuck I drilled the opposite end with a centre drill:

Then I used a dead centre to hold it steady whilst machining a collar for the centre rest:

Then I fitted and nipped up the centre rest, removed the tail stock and faced the end:

Then I refitted the tail stock and dead centre and started to machine the end of the tool that will fit in the chuck of my lathe:

Should I be using the dead centre and the centre rest?

[not done it yetParticipant @notdoneityet]

I think this job could just be done on the mill with ‘freehand cutting using end-mills. Simply touch-off on the roof of the combustion chamber with an end-mill and, after feeding in the required depth, carefully traverse the length and breadth of the combustion chamber roof.

Milling the periphery of the chamber with a suitable bull- or ball-ended end-mill would provide a desired radius. Use of grinding/polishing tools – to obtain the required surface finish and volume balancing – would follow.

The valve seats would be ground/cut with an appropriate cutting tool, preferably, but I might grind them with my old Wolf Valve Seat Grinding kit where a pilot would be required to keep the seat concentric to the guide. I would likely use more modern abrasive cutters (or solid cutters) for a job like this. The Wolf driver operates at high speed (8000rpm – or maybe as high as 14k)

I would consider hardened exhaust valve seats a necessity for a tuned engine running on unleaded fuel.

I've only used my old kit for valves with such as 7/16” guides and up to 2 5/16” diameter valves (only unhardened seats), but I expect it would work OK. Even back in the 1930s, hardened valve seats were installed in some spark ignition engines (mostly those running on kerosene).

Edited By not done it yet on 05/07/2021 22:34:07

[Nick WheelerParticipant @nickwheeler]

Posted by William Harvey 1 on 05/07/2021 20:01:51:

If I don't make the pilot guide as part of the tool, what would be the best way to attach it?

 

Make the guide first to suit a reamer that you have. The hole it goes in and the shank are the only important diameters for size and concentricity. 

 

I have a K-series head that would benefit from this job, so I might make one of these tools to do it. It will need to be a bit smaller(K-series valves are tiny), and I think that a valve stem from a bent valve would make a good pilot.

Edited By Nicholas Wheeler 1 on 05/07/2021 22:58:15

[William Harvey 1Participant @williamharvey1]

Posted by Nicholas Wheeler 1 on 05/07/2021 22:34:16:

Posted by William Harvey 1 on 05/07/2021 20:01:51:

If I don't make the pilot guide as part of the tool, what would be the best way to attach it?

Make the guide first to suit a reamer that you have. The hole it goes in and the shank are the only important diameters for size and concentricity.

I have a K-series head that would benefit from this job, so I might make one of these tools to do it. It will need to be a bit smaller(K-series valves are tiny), and I think that a valve stem from a bent valve would make a good pilot.

Edited By Nicholas Wheeler 1 on 05/07/2021 22:58:15

Ok but how do I secure the pilot to the cutter?

[Nick WheelerParticipant @nickwheeler]

Posted by William Harvey 1 on 06/07/2021 07:36:22:

Posted by Nicholas Wheeler 1 on 05/07/2021 22:34:16:

Posted by William Harvey 1 on 05/07/2021 20:01:51:

If I don't make the pilot guide as part of the tool, what would be the best way to attach it?

Make the guide first to suit a reamer that you have. The hole it goes in and the shank are the only important diameters for size and concentricity.

I have a K-series head that would benefit from this job, so I might make one of these tools to do it. It will need to be a bit smaller(K-series valves are tiny), and I think that a valve stem from a bent valve would make a good pilot.

Edited By Nicholas Wheeler 1 on 05/07/2021 22:58:15

Ok but how do I secure the pilot to the cutter?

Loctite.

[noel shelleyParticipant @noelshelley55608]

Pilot = old valve stem ! Fix is as above ! BUT as NDIY has said do the job on a mill, round nose cotter Etc. I feel you are trying to achieve a degree of accuracy that is not needed and in combustion space balancing UNLESS you can macine every space to a hight tolerance to get ballance will in balancing alter that shape. The shape needs to be right ish but it's the chamber volume that needs to be right ! I have a little used B & D valve seet cutter/facer, PM me. Good Luck, Noel.

[William Harvey 1Participant @williamharvey1]

Posted by noel shelley on 06/07/2021 11:31:02:

Pilot = old valve stem ! Fix is as above ! BUT as NDIY has said do the job on a mill, round nose cotter Etc. I feel you are trying to achieve a degree of accuracy that is not needed and in combustion space balancing UNLESS you can macine every space to a hight tolerance to get ballance will in balancing alter that shape. The shape needs to be right ish but it's the chamber volume that needs to be right ! I have a little used B & D valve seet cutter/facer, PM me. Good Luck, Noel.

The reason I am doing this on a lathe is (a) to learn how to machine on a lathe and (b) because I don't have a mill.

So bore a hole the same dia as an old valve stem and loctite it in place?

[Nick WheelerParticipant @nickwheeler]

Posted by William Harvey 1 on 06/07/2021 13:25:57:

Posted by noel shelley on 06/07/2021 11:31:02:

Pilot = old valve stem ! Fix is as above ! BUT as NDIY has said do the job on a mill, round nose cotter Etc. I feel you are trying to achieve a degree of accuracy that is not needed and in combustion space balancing UNLESS you can macine every space to a hight tolerance to get ballance will in balancing alter that shape. The shape needs to be right ish but it's the chamber volume that needs to be right ! I have a little used B & D valve seet cutter/facer, PM me. Good Luck, Noel.

The reason I am doing this on a lathe is (a) to learn how to machine on a lathe and (b) because I don't have a mill.

So bore a hole the same dia as an old valve stem and loctite it in place?

Yes. Think how much easier that is than reducing a 25mm to 9/32" over a 70mm length. Not only do you save work, time and material but you get a better result.

Another thing; why is the tool so big? The tool head only needs to be long enough to hold the cutting tool. I spent a few minutes guesstimating for my head, which use a 23mm diameter valve, and think this

will need to be slightly smaller diameter to fit inside the valve seat once I actually get the head apart.

[William Harvey 1Participant @williamharvey1]

Posted by not done it yet on 05/07/2021 22:31:58:

I think this job could just be done on the mill with ‘freehand cutting using end-mills. Simply touch-off on the roof of the combustion chamber with an end-mill and, after feeding in the required depth, carefully traverse the length and breadth of the combustion chamber roof.

Milling the periphery of the chamber with a suitable bull- or ball-ended end-mill would provide a desired radius. Use of grinding/polishing tools – to obtain the required surface finish and volume balancing – would follow.

The valve seats would be ground/cut with an appropriate cutting tool, preferably, but I might grind them with my old Wolf Valve Seat Grinding kit where a pilot would be required to keep the seat concentric to the guide. I would likely use more modern abrasive cutters (or solid cutters) for a job like this. The Wolf driver operates at high speed (8000rpm – or maybe as high as 14k)

I would consider hardened exhaust valve seats a necessity for a tuned engine running on unleaded fuel.

I've only used my old kit for valves with such as 7/16” guides and up to 2 5/16” diameter valves (only unhardened seats), but I expect it would work OK. Even back in the 1930s, hardened valve seats were installed in some spark ignition engines (mostly those running on kerosene).

Edited By not done it yet on 05/07/2021 22:34:07

I don't have a milling machine

[noel shelleyParticipant @noelshelley55608]

Hi William, Having some experience of both A and B engines please tell us what you have been advised to do and more importantly what it is you aim to achieve ? What vehicle is the engine to be used in? Vizard and others wrote for guys with basic gear, does your A series modder have full workshop equipment ? DECK HEIGHT .0045 " ? To increase the depth of the combustion chamber why not use a depth gauge mike working from the head face ? Mounted points and flap wheels in a die grinder should do all you need. When you have the shape Etc right then balance for volume. I fear your lack of experience could result to a bad headache !

And just in passing, the BMC 1800 S (landcrab) the inlet valves were SO big they had to recess the cylinder bore, as the lift took the valve down into the bore ! Good luck, Noel.

PS whilst I understand your wish to practice I think this is not a good place to start. N

[William Harvey 1Participant @williamharvey1]

Posted by Nicholas Wheeler 1 on 06/07/2021 14:04:52:

Posted by William Harvey 1 on 06/07/2021 13:25:57:

Posted by noel shelley on 06/07/2021 11:31:02:

Pilot = old valve stem ! Fix is as above ! BUT as NDIY has said do the job on a mill, round nose cotter Etc. I feel you are trying to achieve a degree of accuracy that is not needed and in combustion space balancing UNLESS you can macine every space to a hight tolerance to get ballance will in balancing alter that shape. The shape needs to be right ish but it's the chamber volume that needs to be right ! I have a little used B & D valve seet cutter/facer, PM me. Good Luck, Noel.

The reason I am doing this on a lathe is (a) to learn how to machine on a lathe and (b) because I don't have a mill.

So bore a hole the same dia as an old valve stem and loctite it in place?

Yes. Think how much easier that is than reducing a 25mm to 9/32" over a 70mm length. Not only do you save work, time and material but you get a better result.

Another thing; why is the tool so big? The tool head only needs to be long enough to hold the cutting tool. I spent a few minutes guesstimating for my head, which use a 23mm diameter valve, and think this

will need to be slightly smaller diameter to fit inside the valve seat once I actually get the head apart.

Nice drawing, what did you used to draw it?

I am considering your idea of using the stem from an old valve, but need to check a few things.

The valve throats on and A Series 12G940 head are around 26mm (Exhaust) and 31 – 32mm (Inlet).

So with this in mined, the diameter of the tool needs to be small enough to fit into a 26mm valve, but the cutting bit needs to be able to stick out far enough to cut a recess of around 3 – 5mm (Not su re how much) around the top edge of a 32mm valve throat?

Let's say we 2mm clearance between the tool and the valve throat sides. The tool needs to have a diameter of 24mm.

We want a recess with a 5mm diameter.

With a tool head of 24mm, on a valve throat of 32mm, the end of the cutting bit needs to protrude 8mm?

Drilling a 7mm hole into the base of the tool head to fix a valve stem into the base of the tool will impede the hole for the tool bit, unless the hole for the tool bit is drilled far enough up the tool head? If it is will this be an issue?

[Nick WheelerParticipant @nickwheeler]

William,

that's Fusion360; the toolbit, pilot and tool body are separate components. I've turned on visibility of the revolved sketch for the toolbody so the dimensions are visible. I've stated on other threads that I don't think 2D drawings are required for lots of parts if a 3D model is available, and this is a good example.

Those are good questions, which is why that model is a guess. The body needs to fit inside the valve seat, but it can't go too deep because of the valve guide. Juggling the depths of the pilot and bit holder bores is necessary. I need to remove a valve and take some measurements, and combine those with the stock I have on hand.

I'm doing this for the original use of Vizard's tool; to get most of a 3 angle valve seat on the cheap. Like Noel, I think you're complicating what you want to achieve. Sheet metal templates and hand grinding of the combustion chambers is the traditional way of doing that job, and I think CNC is the only realistic way to avoid it.

[William Harvey 1Participant @williamharvey1]

Posted by Nicholas Wheeler 1 on 06/07/2021 15:22:59:

William,

that's Fusion360; the toolbit, pilot and tool body are separate components. I've turned on visibility of the revolved sketch for the toolbody so the dimensions are visible. I've stated on other threads that I don't think 2D drawings are required for lots of parts if a 3D model is available, and this is a good example.

Those are good questions, which is why that model is a guess. The body needs to fit inside the valve seat, but it can't go too deep because of the valve guide. Juggling the depths of the pilot and bit holder bores is necessary. I need to remove a valve and take some measurements, and combine those with the stock I have on hand.

I'm doing this for the original use of Vizard's tool; to get most of a 3 angle valve seat on the cheap. Like Noel, I think you're complicating what you want to achieve. Sheet metal templates and hand grinding of the combustion chambers is the traditional way of doing that job, and I think CNC is the only realistic way to avoid it.

If only I had a sheet metal template

All I have managed to get is a photo of a modified chamber with a ruler next to it, but will be trying to use that to make a template.

I have been grinding out a chamber on my test head, using advice from a renowned expert. First step was to take the roof down to the already machined recess around the valve seat. Once re-measured, as I needed a little more capacity, I was advised to get the recess around the valves taken down again by a set amount by a machine shop. They did this on one chamber only (the chamber I was starting out on). Once this was done I went back in with the grinder.

Here's a pic of the chamber I have been working on, I even did the valve seats with a second hand set of Neway valve seat cutters (only have a 45 degree cutter though).

I am now trying to make this tool so I can do the other three myself.

Let me know how you get on with the dimensions?

[William Harvey 1Participant @williamharvey1]

Here's a model of the tool using TinkerCAD, I can print this out and see what it looks like?

The holes for the tool bit are 7.94mm and I put one 6mm hole for a grub screw, but I'll probably need two?

There is a 7mm hole in the base for the pilot (old Valve Stem).

[William Harvey 1Participant @williamharvey1]

And for this tool I'll need some cylindrical cutting bits. Iv'e never ground a tool bit before so looked up some YouTube videos. Most cover rectangular tools (obviously) like BlondiHacks Grinding Lathe Tools but then I found this one using old drill bits (got plenty of those).

But grinding the bit for this job should be pretty simple, I guess I simply grind a flat edge along one side, then adjacent to that grind a clearance angle. Then as Stueee mentioned earlier in this thread I rotate the tool so that the rake angle of the cutting edge is zero or negative.

What diameter should the cutting bit be?

[nigel jones 5Participant @nigeljones5]

William, if your not intending to go for bigger valves then you are over thinking this. The modded chamber in the above photo has beed achieved using a high speed die grinder, ive done dozens of them and thats what they all look like. If all you are modding is the chambre you wont see much gain – the inlet throat is a nightmare design and requires extensive work. Get yourself the DV bible and all will be revealed. I can only assume you are turbocharging it as thats the only reason to open just the chamber and have such a low cr. Please do tell us what its for (sorry if you already have and ive missed it). Nostalgic stuff this is !

[William Harvey 1Participant @williamharvey1]

Posted by fizzy on 06/07/2021 20:59:00:

William, if your not intending to go for bigger valves then you are over thinking this. The modded chamber in the above photo has beed achieved using a high speed die grinder, ive done dozens of them and thats what they all look like. If all you are modding is the chambre you wont see much gain – the inlet throat is a nightmare design and requires extensive work. Get yourself the DV bible and all will be revealed. I can only assume you are turbocharging it as thats the only reason to open just the chamber and have such a low cr. Please do tell us what its for (sorry if you already have and ive missed it). Nostalgic stuff this is !

People can we focus on the questions on how rather than the whys 🤣😂

I have my reasons for doing this and have explained parts in the various posts. The Mini technical stuff is / has all been dealt with on Mini specific forums. The questions on here are ref machining and making this tool.

For information and nostalgia, I am using Hepolite P21253 pistons which have a an 8cc dish. To achieve the CR of 9.75:1 for modern fuel I need to increase the chamber size. I was advised to simply have the piston dishes enlarged but at the time I was also advised that this could be achieved when the head was done. I was having the head Stage 2 modded but since COVID etc the prices and waiting time ma have rocketed, so I opted to DIY.

That’s my head in the pic above and the chamber has been re-shaped to a specific specification.

The valves I am fitting are as big as you can get without going for full race valves.
I will be modding the short side radius of the valve throats and cleaning up the ports and areas around the valve guide bosses. I will not be reducing the valve guide bosses as it reduced valve guide / valve stem life. The engine and gearbox are built (by me) AC RS Cam (similar to a Kent MD256 but with slightly longer duration. Good for Tq from 1000 – 6500RPM around 85lb/ft With a HIF 44 (or a Weber 45 as I am fitting) power curved electronic ignition and this slightly modded head, It should increase to about 90 lb/ft Torque / BHP. Not bad on a engine that was around 75 stock and going in a 998 that was about 35 – 40BHP out of the factory 😂😅🤣

[not done it yetParticipant @notdoneityet]

BTW, don’t forget the typical 3cc increase, in combustion chamber volume, due to the head gasket thickness….

[Nick WheelerParticipant @nickwheeler]

It seems a lot of work to lower the compression ratio, especially for such a mild camshaft, when a 3D mapped ignition system would solve the problem. And provide several other benefits like better starting, throttle response, fuel economy and remove the Mini's wet weather weakness. When you factor in the time and effort saved, it's probably more cost effective too.

Edited By Nicholas Wheeler 1 on 07/07/2021 11:34:35

[William Harvey 1Participant @williamharvey1]

Posted by Nicholas Wheeler 1 on 07/07/2021 11:32:12:

It seems a lot of work to lower the compression ratio, especially for such a mild camshaft, when a 3D mapped ignition system would solve the problem. And provide several other benefits like better starting, throttle response, fuel economy and remove the Mini's wet weather weakness. When you factor in the time and effort saved, it's probably more cost effective too.

Edited By Nicholas Wheeler 1 on 07/07/2021 11:34:35

Like this?

My understanding is that adjusting the ignition to offset an incorrect Compression Ratio, is false economy? Anyway lets stick to the machining question please

So can we look back through this thread and help me with the machining questions.

[William Harvey 1Participant @williamharvey1]

Posted by not done it yet on 06/07/2021 22:26:09:

BTW, don’t forget the typical 3cc increase, in combustion chamber volume, due to the head gasket thickness….

Isn't it more like 3.8cc and then there's the ring landing to add as well

[Nick WheelerParticipant @nickwheeler]

Posted by William Harvey 1 on 07/07/2021 19:16:15:

Posted by Nicholas Wheeler 1 on 07/07/2021 11:32:12:

It seems a lot of work to lower the compression ratio, especially for such a mild camshaft, when a 3D mapped ignition system would solve the problem. And provide several other benefits like better starting, throttle response, fuel economy and remove the Mini's wet weather weakness. When you factor in the time and effort saved, it's probably more cost effective too.

Edited By Nicholas Wheeler 1 on 07/07/2021 11:34:35

Like this?

My understanding is that adjusting the ignition to offset an incorrect Compression Ratio, is false economy? Anyway lets stick to the machining question please

So can we look back through this thread and help me with the machining questions.

It's more a matter of having an effective ignition system rather than it sort of works that a distributor provides.

Everything I've seen and tried for performance cams is that getting the compression ratio right is important, but the usual problem is that it isn't high enough. And you're using a very mild cam.

Back to the machining:

if the photo you showed is your head, then the finished chamber(and ports) is your template. You reproduce it three more times by whatever means you find easiest; thick cardboard, sheet metal, depth gauge, casting a urethane master, whatever. Making them all the same is what matters. This is tedious, time consuming and reasonably skilled hand work which is why it costs so much for an effective modified head.

[William Harvey 1Participant @williamharvey1]

So I bought the Modifying Cylinder Head book by DV and it compliments his yellow Bible, but there is a lot of info on other heads that is not needed.
Anyway here is a better image of the valve cutting tool

mentioned in the book.

[William Harvey 1Participant @williamharvey1]

I know I won’t be using this tool to cut valve seats so the setting size is not crucial but it would be helpful to be able to work out the setting size formula as it might help me get the best diameter for the tool head and maximum permissible stick out for the cutter?

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