Exhaust valves

[mu0u207b]

What does a pitted and burnt exhaust valve look like and how bad would the pitting need to be for it to be unusuable. Does anyone know how many miles an average hardened exhaust valve should last. Mine has done about 20-30000 miles and looks quite worn since fitting an unleaded head 4 years ago.

[Cam]

What does a pitted and burnt exhaust valve look like

Well, you can see the pits and marks. Sometimes they have bits missing too, like a V chipped out is common.

how bad would the pitting need to be for it to be unusuable

If the pitting is severe enough to prevent a gas tight seal then it's unuseable as it won't do it's job and you will loose compression.

how many miles an average hardened exhaust valve should last.

They CAN last the life of the engine.......

Mine has done about 20-30000 miles and looks quite worn since fitting an unleaded head 4 years ago.

That does not sound too good. What fuel/additives have you been using? If you have been using standard 95 octane unleaded then I'm not surprised at the damage.

[mu0u207b]

Ive been using standard unleaded petrol from the pump. I assumed it being an unleaded head with hardened valves and seats that no additive was required. Should i use the additive every few fillups.

[Cam]

Personally I would use the additive all the time as it's healthier for the engine. It will run cooler, have more power, be less prone to pinking and will protect the valves from burning. Castrol Valvemaster Plus is a good additive which a lot of us on here use.

[Alec]

Hello Mu,

Our traveller runs an unleaded head and is fuelled with standard unleaded fuel, and I wouldn't consider using an additive. (Sorry Cam)
What do you mean by quite worn?, is there an unbroken dark ring all around the seat , on both the valve head and the cylinder head seat? Clean all the carbon off the valves and the head and just look closely at the seats. A quick check, assuming you don't have any engineers blue is to put a few pencil lines across the valve seat, put it back in the head, without springs and spin it. Remove the valve and see the 'witness' of how the valve is fitting.

Alec

[Cam]

I wouldn't consider using an additive.

Just out of interest, why is that then, Alec?

[mu0u207b]

The valves are definitely worn. There is clear pitting which is quite deep. At a rough estimate, about 0.3-0.5mm deep, which explains poor performance and the head having large carbon build-up. Im wondering whether other people have experienced bad wearing on the exhaust valve that are meant to be hardened for unleaded. The seats themselves look fine albeit a bit of carbon and burning. Im thinking since i do alot of motorway driving that its best to put some additive in now and then, just to keep things happy.

[MikeNash]

Coo! Alec! You're brave! Hope you've got a tin hat! Can I stand behind you?
I also have a standard cylinder head and use unleaded fuel without an additive. After almost 30,000 miles I've no trouble. And the head hasn't been off since about 1965! True!
Watch out! Into the trench! Mr Cam and Ray O'Fleam have taken off the safety catches and are taking aim! Mike N.

[les]

I'll hazard a guess that your mixture is wrong, unusual to get excesive carbon buildup with modern fuels, I also don't use an additive, I'm thinking the hardened seats with valves puts the engine on equal par with a modern one as far as fuel requirement goes. So far so good.

[MikeNash]

I agree with Les. I take great care (that is check it every 3-5000 miles) that the ignition is timed properly using a strobe, and check the mixture using a colortune plug (you know, the type you can see the colour of the flame thro'). Weak mixture and retarded spark are exhaust valve killers. Regards, Mike N.

[Vernon]

Alec said

Our traveller runs an unleaded head

Mike said

I also have a standard cylinder head

You're confusing me!

[Alec]

Hello all,
yes, it has an unleaded head so I don't see the point in spending extra for an additive, there is no pinking, which was one reason given. I do use Millers VSP with an octane booster on my Triumph, which has a standard head and 9.5:1 compression.
One point that valves don't like is the clearances being too tight, that will not do the seats any good whatsoever.
Mu, I don't know what is cheaper, new valves or have the seats ground, I suspect the former and you can be sure then of actually getting unleaded valves. Is it possible that leaded valves were fitted? and I don't know how you can identify a used valve. (Perhaps a metallurgist could tell me what sort of sparks to look for). I still see that using an additive is not required, but also be sure that you are not running too weak a mixture. (if inside the exhaust pipe is very white then you are.)

Alec

[rayofleamington]

MikenAsh,
Cheers for ne name change Mr.Ash

As for unleaded fuel (95 octane) it is not perfect for the engine, but I also don't use an octane booster additive if the head has hardened seats. You have to be careful with the timing to avoid pinking and therefore don't go very advanced.

For the original issue mentioned - there's been a lot of very good advice given.
As mentioned - heavily retarded timing can kill exhaust valves. I ran one to a rally with very retarded timing (I hadn't had time to service it as the MOT jobs got in the way) and the engine boiled off all its water!! - The problem is that heavily retarded timing means that the fuel hasn't fully burnt when it leaves the cylinder, and passes a huge amount of heat to the head. Not enough tappet clearance will also cause speedy valve damage as there will be more leakage.

Pitting of valves is fairly normal and used to occur even in the days of higher octane leaded fuel. As a rule of thumb you can remove up to 0.5mm if you use a lot of valve grinding paste but if you don't want sore hands and you don't want to spends hours grinding the valves by hand then a replacement valve would be a better solution.

As mentioned in another post above - if there isn't a path across the valve then it is less of a problem. If the pits join up so the valve won't seal then it will cause a burn path and the valve could get damaged (once the exploding gasses can leak they burn a channel which gets rapidly bigger until you vave a big V in the valve).

So timing too retarded can cause problems (too advanced will also be bad)
Mixture too weak will cause hot running which reduces valve life
Mixture too rich will cause deposits which can cause overheating... which reduces valve life.
Also the carbon deposits may be from poorly piston rings (or poor valve stem seals )

[Kevin]

I also have a standard cylinder head and use unleaded fuel without an additive. After almost 30,000 miles I've no trouble.

We also have a branch member who has done the same Mike, as his engine has now done 140,000 he thought that he would chance it and do the whole engine when it became an issue rather than just replace the head and he has used on a few Minors on Tour trips as well.

[MikeNash]

Re Alec's point that a weak mixture can give a white inside to the end of the exhaust pipe, I think that stopped when lead went out. You look around, and ALL exhausts are now black inside. I suppose it was the lead that gave it the grey/white if insufficient carbon was present.

Like Kevin's mate running unconverted on straight unleaded petrol, I've been expecting my motor to die and then I'd have to do the big job, but its still got 150 psi when hot on each cylinder, so it soldiers on.
The nub of our and muOu207b's (cor! couldn't you choose a better handle than that?) problems is that the Minors are propelled by a heat engine and like all heat engines they run best with the greatest temperature drop in their working stroke but unfortunately its excessive heat that kills them. And the Achilles heel of the IC engine is usually the exhaust valve. Has anybody got a source of better material than standard for these valves? Regards, Mike N.