Machining Cylinder Head Chamber Roof – DIY or Shop Tool

[Nick WheelerParticipant @nickwheeler]

The maximum stick out will be entirely dependent on how rigid the toolbit is and how well it's supported in the tool. So you want the tool to be as large as will fit in the throat, and the toolbit to be as large as practical. This rigidity will be especially important If you're going to use the tool by hand rather than in a mill or sturdy drill press.

With that said, when I make mine it will be from materials that I have on hand, and using as simple processes as possible. So it will use a 3mm round toolbit in a 20mm diameter tool, because I have some and a round hole is much easier to make than a square.

[William Harvey 1Participant @williamharvey1]

Well I finally managed to dod a little bit more on this single point cutting tool. Previously I had been having immense trouble parting the tool off (subject of another thread). In the end, having sought advice, I hacked it off with a hacksaw and faced the end.

Today I popped it in the lathe and drilled a small hole with a centre drill and then drilled out the centre with a 7mm drill, going in 20mm.

This hole is where the pilot will fit to hold the tool central in the old valve guide.

Next I took an old valve and tried to part it off, it wasn't doing to bad but then just stopped cutting. Then I realised the valves are EN25, which I believe is pretty tough stuff!!.

Instead I whipped it off with a cutting disc – 2 second job!!

This is the pilot and the tool head so far.

The hold in the tool is 7mm and the valve stems are 7.08 or 9/32". I was scratching my head thinking how I would enlarge the hole in the tool maybe using a reamer (which I need to get anyway for the valve guides), but then I thought I could just stick it in the lathe and turn it down Should be Ok with a Carbide insert tool?

Here is the tool sitting in an exhaust valve throat, these are around 26mm.

The next step will be to drill a hole for the cutting bit and another for the grub screw that will hold it in place.

What I need to do now is check:

a. How to grind the cutting bit?

b. Work out the best positions for the cutting tool.

[Nick WheelerParticipant @nickwheeler]

My intention for a similar but smaller(my exhaust valves are 23mm) is for the end of the tool where the pilot is inserted to be about 5mm from the valve guide. That way, I'll be able to use a simple stop(probably a nylon collar) between them to keep the finished heights the same.

I'll be using 20mm bar for mine, and the whole tool, less the pilot, will be about 50mm long. I'll turn the chuck end first, insert it into a collet and then do the working end and pilot bore. I have a toolpost spindle, so will bore the tool hole before removing the part from the lathe. The only dimension that actually matters is the diameter of the pilot bore, and that it is concentric to the chucking diameter.

Vizard suggests roughing out the tool radius and then finish grinding(lapping is more like it) it on a suitably sized rod covered in grinding paste. That seems simple enough to do, although it won't be particularly quick. I have a couple of pieces of 4mm round carbide, so that will probably be what I use.

I might add another cross hole for  tommy bar.

Edited By Nicholas Wheeler 1 on 26/09/2021 21:36:42

[Oily RagParticipant @oilyrag]

William,

From the picture in your last post it looks like the head is in dire need of a skim to remove the bruise across the water transfer plug! Not to mention the dints across the rest of the head face.

I'm also surprised that you are not modifying to 11 stud fixing (the cores are in place in the head to allow these to be drilled thru ).

Is this an A+ head? If so, is it the 'improved water flow type' with the increased size galleries; these had a rather negative affect on water flow when combined with the blanked off rear heater feed outlet (using a sandwich plate under the thermostat housing to take off the water feed to the cabin heater ). The rear two cylinders ran considerably hotter due to the 'decreased water flow' at the rear of the engine which could result in seizure or valve problems – another Longbridge 'faux pas'!!

Also I would question your chamber capacity requirements – you stated 25 odd cc was required, have you added in the deck height and gasket capacity to the 8cc piston bowl. By my reckoning for 9.75:1 CR you will need a total chamber capacity (including piston bowl, deck height allowance and gasket ) of 36.5cc. Must admit it has been nearly 60 years since I worked on 'A' series though.

Martin

[William Harvey 1Participant @williamharvey1]

Posted by Oily Rag on 27/09/2021 22:20:22:

William,

From the picture in your last post it looks like the head is in dire need of a skim to remove the bruise across the water transfer plug! Not to mention the dints across the rest of the head face.

I'm also surprised that you are not modifying to 11 stud fixing (the cores are in place in the head to allow these to be drilled thru ).

Is this an A+ head? If so, is it the 'improved water flow type' with the increased size galleries; these had a rather negative affect on water flow when combined with the blanked off rear heater feed outlet (using a sandwich plate under the thermostat housing to take off the water feed to the cabin heater ). The rear two cylinders ran considerably hotter due to the 'decreased water flow' at the rear of the engine which could result in seizure or valve problems – another Longbridge 'faux pas'!!

Also I would question your chamber capacity requirements – you stated 25 odd cc was required, have you added in the deck height and gasket capacity to the 8cc piston bowl. By my reckoning for 9.75:1 CR you will need a total chamber capacity (including piston bowl, deck height allowance and gasket ) of 36.5cc. Must admit it has been nearly 60 years since I worked on 'A' series though.

Martin

Martin – this is a head I bought for £15 postage as a scrap head, completely rusted up until I cleaned it.

It may actually go again once I have finished with it though.

I hadn't considered doing an 11 stud conversion – what are the benefits?

With regards to the CR calculations see below copied from a post of mine on the Mini Forums:

My engine details:

Block is 1310 (1275 + 0.040&rdquo

BK450 Gasket

Pistons Hepolite P21253 +40 Pistons

Average Deck Height is 0.0045"

And these are my calculations:

Initial calculations for a standard 1275 head with 21.4cc chambers:

A = 0.45cc (Average Piston Crown to Deck Height = 0.0045&rdquo

B = 8.3cc (P21253)

C = 21.4cc (Standard 1275 Head)

D = 4cc (BK450 Head Gasket)

E = 0.75cc (Ring Landing Volume)

SV = Swept Volume 327.5cc (1310cc / 4)

UV = 34.9cc Unswept Volume (A+B+C+D+E)

CR = SV+UV / UV

CR = 327.5 + 34.9 / 34.9

Current CR = 10.38:1

Calculations for target CR of 9.75:1

To calculate how much you need the chambers to be (UV) for a given CR

UV = SV / (CR-1)

UV = 327.5 / (9.75 – 1)

UV = 327.5 / 8.75

UV = 37.428

A+B+D+E = 13.5cc

UV = UV – 13.5

UV = 37.428 – 13.5

UV = 23.929cc

So my target chamber volume = 23.929cc

[William Harvey 1Participant @williamharvey1]

So back to tool making.

Based on some recommendations earlier in this thread, I bought a piece of 100mm x 5/16 round HSS tool blank to make the cutting bit (could maybe get three bits out of this, but need to check length requirements).

And I bought 6mm grub screws.

To fit the tool bit II should be able to get away with an 8mm hole.

Question: For strength, how far from the base of the cutting head should the tool bit sit?

[William Harvey 1Participant @williamharvey1]

I had about an hour yesterday to do some work on this and used this by taking some measurements to confirm the tool bit location.

To get help with an answer on the specifics of grinding a round tool bit as opposed to a square one, posted up another thread on grinding the tool bit, but it also included some other info, so I'll link it here in case anyone happens to be following this and needs it.

Grinding a round tool bit

Part of this task involved prepping the tool head for drilling. To mark where the holes need to be for the tool bit and it's securing grub screw, I blued up the base.

Next I marked the centre line, using a recently purchased centre finder.

I then marked up another line at 90 degrees to the first:

My second scribe line was a little off, not sure what too I could have used to ensure the second line was at 90 degrees to the first?

I then had to transfer these lines up the side of the tool bit. I did this using this protractor, but could have just used a square.

I then did some quick maths to work out where to mark the centre line of the tool bit and the securing screw.

The tool bit is 8mm and I was not sure whether I should leave 10mm or 5mm below the bottom of the tool bit (hence the additional post to ask the question).

It turns out 5mm would be enough, so the centre line at 9mm will suffice.

I then had to pack up

Next job, drilling and tapping.

[William Harvey 1Participant @williamharvey1]

So, managed a little bit after work today.

Popped the tool head in the vice and drilled a pilot hole all he way through with a 4mm drill bit.

Then in with an 8mm drill bit.

Quite a bit of chatter using the 8mm drill bit? Should I not have done the pilot hole?

The 5/16" tool bit slides through nicely, with a slight amount of play.

Next job will be to drill the grub 6mm screw tap hole and then grind the tool bit.

[William Harvey 1Participant @williamharvey1]

Another little bit tonight (but rushed).

Drilled the 5mm hole for the 6mm Grub Screw, then tapped it.

Hole ended up being not quite perpendicular to the first

Then inserted the grub screw and checked the tightness on the tool bit:

All I need to do now is turn down and fit the pilot and grind the tool bit.

[William Harvey 1Participant @williamharvey1]

So, pilot has been turned down and glued in place and I have ground the tool bit. Need to adjust the length of the tool bit, it needs to be able to cut recess with an OD between 31.7mm – 38.2mm.

[William Harvey 1Participant @williamharvey1]

Incidentally what RPM should I be using with this tool on a cast iron cylinder head?
Cutting OD of 31 – 38mm

[William Harvey 1Participant @williamharvey1]

Well here are the results:

Due to the restricted space in the lathe, the tool bit had to be inserted and then positioned in place by moving the cross slide and vertical milling slide towards the chuck and then lining everything up.

First I did the exhaust valve area:

And then the Inlet valve area:

Here are both valve seat areas referenced:

On the lathe I found 50RPM for the exhaust and 80RPM for the inlets to be about right for cutting. I also tried negative and 0% rake on the tool bit, but found 0% rake to work best.

The target depth was 0.359" and amazingly I managed to get them both at 0.355".

This reference cut will now act as a guide on which to grind the chamber roof.

For all intents and purposes, this is a test head, sold to me as scrap, however the more work I do on it the better its looking

[William Harvey 1Participant @williamharvey1]

Oh I did have a bit of a problem during the last cut that the pilot came out of the tool head

Super glue didn't seem to hold it.

But thanks to everyone on these forums for their help. It's been a long haul and everything has been a new learning experience. I have never:

• Made a tool on a lathe
• Ground an HSS cutting bit from scratch
• Used a lathe for milling
• Used a vertical milling slide
• Machined a cylinder head

So all in all a very happy chap.

Just four more valve seat areas to go and I do need to modify the clamping arrangement as this was only held with two studs in the vertical slide.

[Dave HalfordParticipant @davehalford22513]

Don't forget that as that head stands the head gasket will blow between bores 2 and 3

Edited By Dave Halford on 18/10/2021 11:09:22

[not done it yetParticipant @notdoneityet]

Posted by Dave Halford on 18/10/2021 11:03:26:

Don't forget that as that head stands the head gasket will blow between bores 2 and 3

Edited By Dave Halford on 18/10/2021 11:09:22

Dave,

Nothing that a surface grinder could not fix.🙂 But it may need rather more taking off at the middle or ends.

JasonB would likely fly-cut it, but I wouldnt.

[William Harvey 1Participant @williamharvey1]

Posted by Dave Halford on 18/10/2021 11:03:26:

Don't forget that as that head stands the head gasket will blow between bores 2 and 3

Edited By Dave Halford on 18/10/2021 11:09:22

Sorry, could you expand?

Do you mean because it's not been skimmed?

As I said this is a test head, it was sold to me a scrap and completely rusted up. I cleaned it with a citric acid solution, with a view to just practicing on it. It cleaned up really well though.

[Tim StevensParticipant @timstevens64731]

When surface grinding, or fly-cutting a head to restore a flat surface, it is (of course*) necessary to keep all four chambers the same volume. It can be tempting to take a bit more off one end to rectify damage, but you don't want an engine with four different compression ratios, only to be rectified by a head gasket tapered in its length. No, I don't know where you'd get one, either.

* I say of course to pacify the purists, but my explanation is not for them. They know it all already.

Cheers, Tim

[Oily RagParticipant @oilyrag]

That cylinder head in the JA Productions video picture posted above looks uncannily like the one you are machining! How much did you get paid for / did you pay for the rust removal?

[William Harvey 1Participant @williamharvey1]

Posted by Tim Stevens on 18/10/2021 11:42:33:

When surface grinding, or fly-cutting a head to restore a flat surface, it is (of course*) necessary to keep all four chambers the same volume. It can be tempting to take a bit more off one end to rectify damage, but you don't want an engine with four different compression ratios, only to be rectified by a head gasket tapered in its length. No, I don't know where you'd get one, either.

* I say of course to pacify the purists, but my explanation is not for them. They know it all already.

Cheers, Tim

Tim, absolutely. Iv'e been doing tonnes of research. From old skool reading, like Vizards Ywllow Bible, How to Modify Your Mini and Modifying Cylinder Heads to getting up to date info on modern chamber profiles for modern day fuel. If the chambers are unequal, you could end up with three equal and well performing cylinders messed up by one that is not, at worst case detonation!!

[William Harvey 1Participant @williamharvey1]

Posted by Oily Rag on 18/10/2021 14:25:08:

That cylinder head in the JA Productions video picture posted above looks uncannily like the one you are machining! How much did you get paid for / did you pay for the rust removal?

Because that's me in the video – oops – given away my true identity!!!

I paid postage on the cylinder head – £15. No cracks, apart from around the Rocker Post Stud Holes, which can be fixed.

Citric Acid Crystals from eBay about £14 for 5Kg, mix is around 125g per Litre of water?

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