True Valve Diameter & Throating

[mack124]

Hello Guy,

I¢ž¢ve just been down to the machine shop to have the valves and the seats prepared for my Fiat TC head. When I asked them to grind the seats out to true valve diameter they looked at me like I had two heads and advised against it. So if I could clarify a few details with you it would be great.

1: When you say "grind the seats out to true valve diameter" does that mean if my valves are 42mm then I take the outer edge of the 45 deg angle all the way to 42 mm? The OD of the insert is 43 mm so the 45 deg angle should come to 0.5 mm on either side of the insert. The lapped part of the valve (Contact area) should the come right to the outer edge of the valve?

2: Throat the seat out so that there is 1.5 - 2 mm lapped area (contact area) on the valve.

3: The machine shop doesn't have a 70 deg throating tool BUT does have a 60 deg. If they use the 60 deg tool and I very carefully open out and blend the lower half of the throat, will this give me the desired effect?

I know you have answered these questions in various forms before and I was sure I had a grasp on your answers but because someone else is doing the machining I'm just ensuring I've got the details 100% correct.

Thank you once again for your invaluable advice.

Regards Gill

[Guy Croft]

The response from your firm is not uncommon unfortunately and is perhaps more a statement of their being unable - rather than unwilling - to do it, and perhaps a bit nervous too. There is a marked difference in approach between my techniques (for getting more power) and the mainstream overhaul people. A firm taking on my kind of stuff needs a real 'can-do' attitude.

You are quite correct in your understanding of what to do. I advise you do not go to that firm, but buy some Neway cutters (see links) and do it yourself. The only thing you'll need them to do then is the regrinding of the valves and the post-lap 30 deg back grind.

GC

[mack124]

Thanks Guy,

Getting the cutters and doing it myself was exactly the conclusion I came to last night when I couldn't sleep. So thank you for the confirmation

I'll be able to do the 131 1585 OHV head myself when I get the cutters.
I'll let you know how I go and send some photos.

Regards
Gill

[TC1780]

Guy,
What cutters do you use for the TC 8v heads? Neway 271 & 234?
Which is the proper pilot to use?

Karl P.

[Guy Croft]

This is what you need for the 8V TC Fiat and many other units in valve range ex 30-40, inlet 40-46mm. You can adjust the blade cutting radius with a small Allen key.

For old guides you need the expanding pilot (left) and new ones the solid pilot. The solid pilot is a fine taper and gives much better concentricity. it is vital to check valve-seat seal by means of 'Engineers' Blue' before lapping. Much depends on the valve guide condition and I have always had most problems with the expanding pilot.

You can rotate the cutters with a 6 point deep-drive 13mm socket but be careful not to 'lean' the cutter over as you rotate it. Neway also offer a little hand driver which is quite good.

The tungsten carbide cutters will do dozens of heads before they blunt. If working with non OE nickel-steel seats use a cutting lubricant or the cutters will tear the seat. I still use Neway for roughing out and development work.

Hope this helps,

GC

[Walezy]

Will those cutters be suitable for 16v heads or will I need smaller dimensions?

[Guy Croft]

Hi Tomasz

for 16v (Lancia and many others) you need:

- inlet cutter 220 (20 x 45 deg)
- ex 268 (single 45 deg)
- both throats 222 (70 deg)

You need 7mm pilot too of course.

I don't know of a cutter small enough to do top cut on the ex seats, sorry.

I can photograph - but later on.

GC

[Walezy]

Thank you, I will look for those cutters.