technical drawning of machining "water manifold" to 7a head

[Tom_]

I have a man who did this,but i dont have any numbers,dimensions where he drill.I saw the video,but he is thinking,that is only to get bigger holes Can somebody help?

[twenty valve]

I may still have the drawing at work, I will check tomorrow. I definitely have a water manifold so I'll get dimensions either way.

Bit of advise if your doing it yourself;

You really need to do this on a vertical head milling machine or a CNC mill. It's very unwise to use a twist drill as I discovered the first time (unless you have a really good jig) When you break through into the head, there is still material around a portion of the side of the hole, so it forces the drill sideways and makes an oval hole! because of this you will need a 19.7mm slot drill (these cant deflect when mounted)

You need to take the datum from the original 3 M6 holes, I used plain shank screws and clocked off them (the triangular water passage is part of the rough casting so you can't go from that).

[twenty valve]

I have a hand drawing, please let me know if you still need the info and I will do an electronic drawing and post it up

[Flat on my back]

Is that 19.7mm a deffo, I measurered mine up as 20mm but haven't had the machining done yet.

[twenty valve]

pretty sure its 19.7 or somewhere around that. Definitely wasn't 20mm, I don't have a bare head to check. If you go onto ETKA (mine doesn't work) and view the 0-ring dimensions (diameter and wall thickness) then find a website or source which tells you how much interference you should have.

It may be that the OD of the O-ring is 20mm, and you will need the corresponding hole to be a few thou smaller (i.e. around 19.7-19.8)

its ultimately dependent on the O-ring thickness. I expect you could go to a 20mm hole but you'd need an O-ring with thicker wall section that what Audi supply

[willg54]

whats more important with an oring is the gap between the inner and outer pieces. as a rule of thumb with ~1.7-2mm cross section o-rings, work with about 0.1mm radial gap. so if the water jacket is 19.7, the head needs to be 19.9mm. there is a small amount of variance in this though. dont forget lead in chamfers!!! 1mm x 20deg should do the trick!

[twenty valve]

whats more important with an oring is the gap between the inner and outer pieces.

Yes, which is called the amount of interference (a measurement of how much smaller the Internal Diameter of the hole is, in relation to the Outer Diameter of the O-ring, so it squashes the rubber and makes a seal)

And yeah you absolutely need a lead in, should be 30 degrees for O-rings not 45

[willg54]

And yeah you absolutely need a lead in, should be 30 degrees for O-rings not 45

all depends on how hard you want to push to get the oring in but i agree 45 is too much! we usually go between 20-30deg and 1 -1.5mm lead in depending on space available.

[Flat on my back]

.



I'll adjust my dwg to suit...learn summit new every day.

[martinjs]

I done a few over the years and work to 25/32. Works a treat with OE o-rings.
Thought 20mm was a bit much tbh.

[willg54]

Yes, which is called the amount of interference

this only just twigged...its not interference, technically clearance is the correct term

[Fat Audi 80]

No, It is interference if he is talking about the O-ring diameter being bigger than the hole diameter. Clearance would be if it slopped about in the hole a bit!

[twenty valve]

Yes I definately mean interferance, I'm an engineer, I know what I'm talking about and I have machined these heads before!!

Anyway.... calling the person who started the thread, do you want the drawing?

[willg54]

Clearance between the two parts, not oring! I'm an engineer too....

Sent from my HTC Desire using Tapatalk

[twenty valve]

This is pathetic and I really don't care, I'm just trying to help the person who started this thread.