The standard valves in A14 are 37/30, what do you think about 35 outlet and 42 inlet valves, is it bossiple to fit those?
Those 42/35 valves are from BMW 316 75-79

In finland we don

Yes, stock A14 is 37 mm intake and 30 mm exhaust (A12 valves are 35 and 29)

There have been rumors in this club before of using 42 and 35 from L-series engine, but no confirming details.

The famous a13 race engine head uses 40mm inlet valves and 35mm exhaust valves.

I'm using 38mm inlet and 33mm exhausts.
I was going to go bigger but I didn't want the valves too close together. Also I had to notch the block so the inlet valve didn't hit it anyway. So I didn't want to go any bigger.
Mine are L series valves.
I tried to fit big L series ones but I also found the head wouldn't take it . The inserts were too large in diameter and cut too far into the water jacket. I had to try 7 different heads before I found one that wouldn't leak. So I erred on the side of caution with the last one.
If you have a good head guy I'm sure you could fit bigger than I did though.
I've changed engine builders 3 times so far and am yet to fire the engine up.Everytime someone else tears ther engine down to check it we find more dodgey work.

L16 valves are the go

im using aftermarket valves (shin-ichi) 39mm inlet - 35mm exhaust. The only thing needs to be done is to have them stortened, new collet groove and use lash caps.

ive had great success with using k-liners on the exhaust guides as well as they are self lubricating. From memory, they are made from a bronze type composite. Helps increase the life of the valve stem / guide.

So if I am using L-series valve 33/38, do I have to install larger inserts (I hope that

The inserts are valve seats. All alumuminum heads have valve seat inserts. Cast iron heads usually don't. For inserts, the head is heated to 175C, the seat is put in, then the head cools down and the seat won't pop out. The seat doesn't usually ever need replacing in a street engine. Even if a valve burns, they can just be resurfaced.

yeah but what i think the flying finn and myself now wants to know is if you put bigger valves in a head do you have to change to bigger seats?

yeah, I know you were asking that. Sorry I don't know the answer, I was just adding what I know thinking somebody in the club might find it informative. Dattoman_1000 mentioned fitting larger seats, maybe he can answer that part of the question, when are bigger seats required?

Benny said that to fit 39mm inlet and 35mm exhaust: "The only thing needs to be done is to have them stortened, new collet groove and use lash caps." I notice fitting new seats wasn't listed.

I'll second Benny on those bronze-type valve guides. It's not unusual for the A-series valve guides to wear, causing oil burning, even though the rings are still fine. The bronze guides will fix this, plus last longer. Or a new set of umbrella valve seals might take care of it.

I would assume that you must change the seats to match the valve size, other wise the valve opening would not change.
Speaking of valves and guides... I once had my head rebuilt and I intalled the old rocker arms with out checking the tips for wear. Some of the rocker tips/pads had grooves worn in them and they wouldn't slide across the top of the valve stems. They would actually grab the valve and push it over as I turned the engine by hand. At the time i had no idea anything was wrong. A couple of days later, my engine started burning oil and smoking bad. I found 4 of the 8 valve guides had broken.
New bronze guides and good rocker arms have lasted for about 8 years and counting.