M43 valves in M20 head

[Bullhead]

I will use 285/285 cam. So you say I could maybe even not shorten the valves, but just space the valve springs?

He is saying if you get a reground cam where it's base diameter is smaller than stock would compensate for the taller valve tip. This theory is sound if everything is in spec. You just don't want to have to shim everything all weird to achieve the desired tension. I would talk to the people you are getting the cam from and tell them your valves are 2-3mm taller and see what they say. If they are decent machinists they will grind the camshaft to where it will fit those tolerances and you won't have to worry about tip height. But you will still need to shim your springs up to keep the correct spring rate on your rockers. I agree some mild steel zinc coated or stainless steel washers would work fine.

[abit]

I will use 285/285 cam. So you say I could maybe even not shorten the valves, but just space the valve springs?

[e21jps]

one advantage i can see is the fact you could run a fairly large profile reground cam with a reduced base circle and still get the eccentrics to be in range! The geometry would be quite good infact

ps but you MUST shim the springs back up to the original install height, mild steel washer works fine

[Bullhead]

I started thinking on this as well. The longer valve would put more pressure on the camshaft via the rocker arm possibly keeping the valve open. I don't think just a spacer under the spring would solve the problem, yes it would keep the spring tension the same but it wouldn't help the fact the rocker arm was being depressed a few mm further.

[digger]

is the valve tip properly hardened? you wouldnt want to expose a softer part of the valve which i have heard about on other engines.

people machine down valves all the time though

[abit]

Thank you all for participating in this discussion, me like

Just throw more boost at it....it'll push air in quicker.....

yeah right :D

ive wondered what affect the longer valve has on the resulting valve motion but never investigated, similarly will it tend to wear out the guides a bit more because the eccentric is not in the optimal location and causes higher lateral forces on the stem?

...mmm but valve top will be shortened about 1mm, so at the end It would be almost the same length as stock and all rocker movement will stay like original :)

[digger]

whoop.... that's a whole 'nother can of worms, thanks. At the core though it still introduces more problems than it fixes.

ive wondered what affect the longer valve has on the resulting valve motion but never investigated, similarly will it tend to wear out the guides a bit more because the eccentric is not in the optimal location and causes higher lateral forces on the stem?

[IronFreak]

Just throw more boost at it....it'll push air in quicker.....

[SkiFree]

The M43 valve is longer than the M20 valve.

whoop.... that's a whole 'nother can of worms, thanks. At the core though it still introduces more problems than it fixes.

[digger]

seems like there are easier alternatives.

[LJ851]

Let me explain a bit more why I'm not a proponent of this attempt.

1) The better profile of the valve is also found on any decent stock-replacement valves. Case in point, the SS IE valves (which cost the same as std. replacement valves).



2) The "weight savings of 13grams" is largely because of the valves height difference. Which means by adding in something to make up the gap between the spring/eccentric you have to add the piece's weight as well (given the height difference this would need to be thicker than a lash cap or over-sized eccentric). This could very likely could end up ADDING to the overall weight negating your primary reason for doing this. Not to mention you're needlessly adding one more component under pressure invariably increasing the assemblies chance that something goes wrong.

3) If you don't add something in to compensate the height difference then you're increasing the installed height pressure which is generally the OPPOSITE of what you want out of a stiffer valve spring (the installed-height pressure will increase with stiffer springs, but ideally at a much slower rate in comparison to the compressed-height pressure). In short, this means NEEDLESSLY adding pressure on the cam lobe, wearing it out noticeably quicker.

With all due respect to your tinkering (which is awesome), this particular instance is like taking a sledge hammer to set a dislocated joint. You're going to do more harm than good.

The M43 valve is longer than the M20 valve.

[SkiFree]

Let me explain a bit more why I'm not a proponent of this attempt.

1) The better profile of the valve is also found on any decent stock-replacement valves. Case in point, the SS IE valves (which cost the same as std. replacement valves).



2) The "weight savings of 13grams" is largely because of the valves height difference. Which means by adding in something to make up the gap between the spring/eccentric you have to add the piece's weight as well (given the height difference this would need to be thicker than a lash cap or over-sized eccentric). This could very likely could end up ADDING to the overall weight negating your primary reason for doing this. Not to mention you're needlessly adding one more component under pressure invariably increasing the assemblies chance that something goes wrong.

3) If you don't add something in to compensate the height difference then you're increasing the installed height pressure which is generally the OPPOSITE of what you want out of a stiffer valve spring (the installed-height pressure will increase with stiffer springs, but ideally at a much slower rate in comparison to the compressed-height pressure). In short, this means NEEDLESSLY adding pressure on the cam lobe, wearing it out noticeably quicker.

With all due respect to your tinkering (which is awesome), this particular instance is like taking a sledge hammer to set a dislocated joint. You're going to do more harm than good.

[abit]

mmm, yeah, I thought about that too, that soft spacer can be wearing out in short time

so, I should take some stainless steel spacers and make them polished finish - slippery, so valves would keep rotating on high rpms and so on?
....and hope that these spacers won't make grits in my oiling system :D

[IronFreak]

I think 7000rpms would create some serious havoc on soft metals, why most you your valve train is hardened.

[Ether-D]

I really like any idea that takes parts off other, less desirable cars, and makes em fit our cars.

I'd say definitely space the springs to keep the tension the same. It seems easy enough. Nobody likes broken rockers.