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Hi,

last year I bought an old TR4A engine and today I had a closer look on the cylinder head.

I had not so many cylinder heads in my hands but I wonder about the exhaust valves of cylinder 2 and 3.

Have they been running too hot?

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Closer look on the exhaust valve from cylinder #2

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After cleaning wit a brass brush

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What could have been the reason? No valve clearance? Mixture too lean? Others?

Ciao, Marco

Edited by Z320
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That valve has not been seating so on the power stroke super heated mixture is being forced around the valve. This has cut the V into the valve and also taken some metal from he head around the valve. You can see the melting in the crack. There are signs of micro welds so it may be caused by heavy load for a long time on unleaded fuel. Or it could simply be a worn valve which started to leak due to age. Of course it could also be zero clearance on a tappet, or even carbon buildup or a bent valve preventing full closure, hard to diagnose remotely. My best theory would be heavy loading on unleaded fuel for many years.

No signs there of mixture problems but I think head gasket was leaking between 2 and 3.

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Could it be that the engine has been running on unleaded fuel without hardenened seats? Perhaps compounded by running lean or with incorrect timing raising combustion temps?

Either way the head needs a refurbisment with new valves and hardened exhaust valve seats so what caused it is in many ways of academic interest only.

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Years ago I had a valve go like that in the days when 4 Star petrol was freely available, it was on a Triumph 2000, all the other valves and seats were perfect, we re-ground the seat and put in a new exhaust valve and the engine carried on as if nothing had happened, we came to the conclusion that it was a metallurgy problem with the individual valve. 

Cheers Rob 

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On 10/4/2021 at 3:55 PM, Rob Salisbury said:

Years ago I had a valve go like that in the days when 4 Star petrol was freely available, it was on a Triumph 2000, all the other valves and seats were perfect, we re-ground the seat and put in a new exhaust valve and the engine carried on as if nothing had happened, we came to the conclusion that it was a metallurgy problem with the individual valve. 

Cheers Rob 

+1

I have an identical TR4A tulip shape exhaust valve I took from my cyl head back in the 1970’s.  pre unleaded malarkey.  Burnt in exactly the same v groove.  I too fitted a new valve after a recut of the seat with a hand reseat tool and plonked the head back on my car.  I sharpened the stem of the burnt valve and used it as a punch.  I will dig in the drawer, it must be some where.

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I had one that looked like that on one of my Imp engines, and I have another in the garage that I think came from my 1600 Mk 1 Escort. Both date from the 70s/80s, so not caused by unleaded.

Pete

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Hi and thank you all for your answers,

I will take all valves out next weekend to compare them and have a look on all seats.

Ciao, Marco

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We used to get that back in the 70`s when racing Jaguars and we used to run them on 5star!

Stuart.

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Short question (I really don’t know and can't expain myself):

if unleaded fuel would be a problem with not hardened seats - why is the valve damaged while the seat looks OK?

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Because the seat can get rid of the excess heat by conduction to the cooled head but the valve cannot do it anything like as easily. 

Edited by RobH
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Posted (edited)

Yes, this is clear,

but how does this answer fit to my question "unleaded fuel / not hardened seats / damages valve"?

 

Edited by Z320
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Hi Marco,

the valves lead a very hard life.

As Rob states - the valve can not get rid of the heat as easily as the seat in the head.

Using unleaded fuel also presents essentially clean seats on both the valve and the head. With leaded fuel there is a layer of 'lead' deposited on the seats.

When the valve strikes the valve seat in the head is can not stick as the lead deposit will be pulled away.

With no lead in place the valve can actually weld it self to the head seat and when they pull apart metal can be torn off one or other of the seats.

Because of the valve temp it is easier for the valve to lose metal.  (Galling)

This metal removal will obviously weaken the valve seat.

 

Roger

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Posted (edited)

I found that on a German webside (my own translation):

"For the use of unleaded fuel engines need hardened valves (in my opinion this is always the case) and valve seats.

Otherwise the valves dig in themselves in their seats, causing a reduction of the valve clearance.

This causes a valve overheating up to a rip off of the valve stem."

.....

I found the valve damaged, but the seat not damaged....?

I suppose in my case this has nothing to do with leaded or not leaded fuel.

 

Edited by Z320
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Hi,

the seat of exhaust valve of cylinder 2 looks OK, perhaps a bit "dull", I make a tool to prepare it.

The head seal is 100% OK and between cylinder 2 and 3 is coolant, I guess the head seal never can blow through here.

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After some cleaning, all other valves are OK, the seat of exhaust valve of cylinder 3 looks "worse" ( a bit "dull").

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I have already heard about coolant leaks below the spark plug.

A look on the coolant channel below the spark plug explains why, the cast is about only 3 mm "solid"?

Ciao, Marco

Edited by Z320
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