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Valve Seat Height


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#1 JonnyAlpha

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Posted 21 July 2021 - 07:28 PM

I have been teaching myself (with some expert help) DIY head modding.

So far I have increased the chamber size by taking the walls out and roof down.

 

Next job, once the profile is correct, I need to make a template to apply the profile to the four chambers on the actual head. I plan to do this by making a card template with holes drilled in line with the valve stems, This can the be flipped either way up and used to scribe the outline for the chambers. 

 

At some point I will need to re-cut the valve seats. I have a Neway 46 Degree and 30 Degree Valve Seat Cutters that fit both the inlet and exhaust.

 

Question:

When cutting valve seats, how do you ensure that the face of the seat is:

 

(a) at the correct height / depth in relation to the chamber roof?

(b) the correct width?

 

Many thanks 

 

Here's the chamber I have been working on, I did a test cut of the valve seats in this chamber, but cheated and used a battery powered drill to rotate the valve cutter :-)

 

68onDos.jpg

 


Edited by JonnyAlpha, 22 July 2021 - 09:06 AM.


#2 JonnyAlpha

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Posted 22 July 2021 - 08:51 AM

Or should the valve seat be cut so that the valve sits flush with the floor?

 

EDIT

Just found this interesting article. https://mgaguru.com/...ngine/ch113.htm


Edited by JonnyAlpha, 22 July 2021 - 08:55 AM.


#3 absx2

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Posted 22 July 2021 - 06:01 PM

There are a lot of people with much greater knowledge than me that can answer this question but it seems they have not seen it yet so I`ll chuck in my humble opinion in an attempt to bump it to the top of the new posts again  :D

 

I certainly wouldn`t be sitting the valve flush with the floor as in my limited opinion a considerable amount of the valves lift will be used up just to get into the open part of the chamber.

The way I do it is to get a Vizard style reprofiled valve and cut the seat just enough to get a sensible 1.5 - 2 mm seat and that`s it. 2 mm is probably considered a bit on the wide side for performance but durability is nice.

I use a router to cut the chambers with a copy pin so everything is equal and all the seats match so the valve height is spot on.

 

That`s just me and they go well but hopefully the more knowledgeable fellows will be along soon



#4 JonnyAlpha

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Posted 22 July 2021 - 07:36 PM

A router and a copy pin? Please do enlighten me 😄

#5 absx2

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Posted 23 July 2021 - 06:35 PM

A woodworking router with a cutter similar to this

https://www.axminste...e-cutter-666043

following a Lexan ( acrylic template ) located by pins in the cylinder head stud holes and clamped.

 

Job done in a very short time and accurate, a small amount of blending close to the cylinder wall is obviously needed

The cutter lasts well and isn`t bothered by the cast iron if you take it easy but a hardened seat would kill it.

 

I don`t know how the big boys do it because they`re not replying  :ohno:  :D  



#6 JonnyAlpha

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Posted 24 July 2021 - 08:23 AM

A woodworking router with a cutter similar to this
https://www.axminste...e-cutter-666043
following a Lexan ( acrylic template ) located by pins in the cylinder head stud holes and clamped.

Job done in a very short time and accurate, a small amount of blending close to the cylinder wall is obviously needed
The cutter lasts well and isn`t bothered by the cast iron if you take it easy but a hardened seat would kill it.

I don`t know how the big boys do it because they`re not replying :ohno: :D


Whatever gets the job done I suppose 😄

I’ve got a router and using sushi a tool set to the correct depth would ensure an even chamber floor, which is very hard to achieve by hand /eye.




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