valve stuff

[sdp]

I've been playing around with my old cylinder head, having a go at grinding out the inlet ports n that, got nothing better to do really.

Anyways, some questions:

1) I've read that there's no point in having the inlet port flowing 5,000,000cfm if the valve area if averaging 50cfm. What can be done with a bench drill and a dremel in this area? Or is this where a cam with more lift should come in?

2) The ch I replaced it with (12g206 cooper) has double valve springs; are these a good thing or a bad thing? I know they'll help at high revs (I think) but otherwise won't they be wasting horseys - I mean it takes more effort to open em right?

[Jiff Lemon]

The best bit of advice I can give is get hold of Dave Vizzards guid to tuning A series engines - Has PLENTY of pictures showing what needs to be done and to where.

[sdp]

Yeah I got that it's good but he goes on about cutting 3-angle or 30degree seats and modifying the exhaust valves but it looks complicated and it doesn't say how you do it.

It doesn't say anything about valve springs either..

[Zak33]

well.......to get a better flow AROUND the valve is one way.

If the valves are really high quality, and hard, you put them in a bench drill, or a lath.....you then use a sharp tool to gently take the stem width down....to narrow it...BEHIND/ABOVE the valve head....

you dont do it on the entire shaft, cos it must still fit into the head and slide up and down with the valve stem oil seals...

BUT the bit that the air flows AROUND can be made thinner.

WARNING.....valve heads snap off if its too thin


NEXT...the shape of the area directly in the head where the valve sits...each can be a different size and shape...but ultimately you want no big lumps in the way, UNLESS they create swirl on the way in...the exhaust should be smooth and gently curved...no jags or evil corners.

The SHAPE on the cylinder head combustion area is also changeable...but that Vizzard book does a good decription IIRC.

Dremmel.....? hmmm......thats a perfect tool for the exhaust manifold if its cast iron.

Valve springs....only need to be stronger IF the duration of the cam leaves the valves open for so long, that crossover is a problem (ie both valves wide open together ) AND if the piston is on its way up while the valve is shutting.

Note: At high revs the vavle is often still open while the piston is on its way up...but not too high, or it'll push out the air before it gets a chance to squeeze it.

[Zak33]

3 degree valve seats.....also known as Triple Angle Valves....

instead of the valve seating in just one angle, you can get a much better fit, and hence higher compression, AND get a bigger valve, with more vertical seats, IF you have the edges of the valve at three different angles.

Its an engineers job....not a dremmel job

AS IS the valve stem narrowing I mentioned above

[IainB]

3 degree valve seats.....also known as Triple Angle Valves....

instead of the valve seating in just one angle, you can get a much better fit, and hence higher compression, AND get a bigger valve, with more vertical seats, IF you have the edges of the valve at three different angles.

Its an engineers job....not a dremmel job

AS IS the valve stem narrowing I mentioned above

Im going to have to disagree with your there (for the first time!)
The 3 angle seats I have seen have all been on the seat only (cant remember the cutting angles of the top of my head) - the valve only sits on the first cut, the 2nd and 3rd are to allow airflow an easier passage out - as in not so much of a sharp angle to navigate.
The valves I have are waisted direct from the manufacturer - but only appear to have one face cut (and the engine builders I go to havent offered to 3 angle the valves either)
but - I could be totally wrong
As Zak mentioned though - this is machine shops only - not something that you could attempt with a dremel

[sdp]

Cheers, I'll leave it alone then, but I'll have a look for some aftermarket valves.

The Vizard book does have a bit about valve springs, my mistake, - it's in the camshaft section, it's got a complicated table but apparently you just buy a cam kit and use the springs that come with that

[IainB]

Cheers, I'll leave it alone then, but I'll have a look for some aftermarket valves.

The Vizard book does have a bit about valve springs, my mistake, - it's in the camshaft section, it's got a complicated table but apparently you just buy a cam kit and use the springs that come with that

Hi mate - thats probably your best bet - a cam kit usually works out cheaper as well (matched cam, followers, springs, cam lube and anything else you need). If such a thing exists for the A series - look for waisted valves - its what has been described below.
If you are changing the cam - make sure you dot go too radical - the thought of a cam that makes HUGE power sounds like a good idea - BUT - it might not work until the revs hit say 4500 and will be a pig to drive on the road.
Try to match the cam to what you want from the car, im guessing its mainly road use? Also remember that a nice lumpy cam is going to need to breathe on both the inlet and exhaust side - so you 'could' be looking at a carb/manifold, exhaust change and cylinder head work to get the best benifits.
(speaking from experience here - im looking down the barrel of a set of £2k heads to match what I want from my engine!!)

[sdp]

Is that 2k each?

I've been looking at the sw5 which is like the 997 cooper profile but I need to find out stuff about the oil pump and whether it'd be an engine-in or engine-out job.

Cheers,

[IainB]

Is that 2k each?

I've been looking at the sw5 which is like the 997 cooper profile but I need to find out stuff about the oil pump and whether it'd be an engine-in or engine-out job.

Cheers,

2k for the pair - but sill a LOT of money to find, just for a set of heads
from what I remember Im 99% sure a cam change is an engine out on them - unless a hole is made in the wing, and the cam withdrawn through that? Could be totally wrong on that front though!

[Zak33]

the triple angle valve seats do sit better....I promise. The flowing is better as well, BUT the 3 angles all seat into the head..not just one. Well, least, thats what I've seen.

I didnt ever think about it before I was shown but some of the compression on quick engines is lost up through the valve seats...kinda squeezes round them.

It was ALL THEORY tho

[sdp]

from what I remember Im 99% sure a cam change is an engine out on them - unless a hole is made in the wing, and the cam withdrawn through that? Could be totally wrong on that front though!

On the 998cc's it can be done but only if it has a slot or peg drive oil pump. If it has a spider drive and you try to do it in-situ the oil pump falls into the gearbox - which cant be fun to fix. For 1275's it's definately an engine out job because you cant get to the tappets.

I've got the MOT to pay and I've just killed god knows how much computer hardware so it'll be a while yet..

Talking of silly priced cylinder heads, you seen these 16v crossflow babies?

[IainB]

Talking of silly priced cylinder heads, you seen these 16v crossflow babies?

Rah - thats expensive, probably due to the limited production run, one off tooling etc. When I had my old Rover V8 a decent set of heads were circa £3k (actually made in wales) - the ones im looking at are off the shelf mass produced - as the engine I have is still big in the USA. But - if I wanted to go for full race heads - money goes totally through the roof. Luckily for what im doing, they arent needed.... yet

Zak - will have a look into 3 angle on the valves, could be interesting, popping up to Northampton next week to look at another block and discuss some machining requirements

[sdp]

Anyone know what 'triple collet grooves' means?

http://www.minispares.com/web/Item/C.../InvDetail.cfm

[Zak33]

well a Collet is something that expands inside a hole.

So I guess its a seal of somesort for the valve stem....looking into it now for ya...

[Zak33]

think I;m wrong tho

Is it the groove round the TOP of the valve stem that holds it in position ?