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Burnt Out A Valve... For The Second Time This Year!


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#1 miniman86

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Posted 14 April 2019 - 12:52 PM

Hopefully someone will know...

Initially managed to burn a valve out when I went bingley hall in January. Luckily I had a brand new head on the shelf, so I proceeded to fit that and drove her home. Not used her much due to oil leaks since then. Got her back on the road last week, and yet again she's burnt a valve out! Same cylinder as before. Plug colour is biscuit colour, so I can't see that she is running too lean. But I'm worried that I'm missing something here?

Alex

#2 Daz1968

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Posted 14 April 2019 - 01:22 PM

Good chance of being incorrect distributor and curve is giving wrong advance or non working vacuum advance

#3 Steve220

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Posted 14 April 2019 - 02:11 PM

Alex, is your car leaded or unleaded?

#4 miniman86

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Posted 14 April 2019 - 02:57 PM

Originally leaded, but the head I put on at bingley hall has hardened valve seats.

#5 miniman86

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Posted 14 April 2019 - 02:58 PM

Distributor is, as far as I'm aware, the standard one on the car. I'm going to swap the head for another one, and check the vacuum advance unit is working.

Alex

#6 mini13

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Posted 14 April 2019 - 04:18 PM

Was it a new valve? What part no? What cylinder

#7 miniman86

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Posted 14 April 2019 - 04:58 PM

The head had never been run. Not sure regarding part number, was just a spare head I had that was put on to get me out of trouble. Cylinder 2, same one that went in January.

Alex

#8 Moke Spider

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Posted 14 April 2019 - 07:22 PM

I'm sure you would have checked the tappet clearances when fitted up, but when the valve is burnt, have you checked them before stripping it down?

 

As Daz suggested, if it's the wrong distributor or if it's jammed, that can lead to a burnt valve. Likewise, if the timing is too far retarded.

 

Old fuel can do it.

 

While you have hardened seats fitted (and retro-fitted) are they round and fitted properly ? If there's a crack in the casting under the seat when it gets hot (like under power) this can cause a distortion in the shape of the Insert that will not allow the valve to seat when closed and lead to burning of it.

 

Can you post a clear photo of it ?



#9 carbon

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Posted 15 April 2019 - 09:01 PM

Other reason for burning our exhaust valves is mixture too lean when under power. I managed to do this to my 998 Clubman Estate many years ago on a long motorway run. Entirely my fault, I had vizarded the HS4 to get better airflow, and had not altered the needle on misguided basis that all ran fine and the sparking plug colours were good in normal town use...



#10 viz139

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Posted 15 April 2019 - 10:50 PM

Did you do a compression test when you fitted the new head?



#11 DeadSquare

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Posted 16 April 2019 - 07:51 AM

Don't throw the burnt valve away, it is jolly useful.

 

Get someone to braze a small Tungsten Carbide tip into the burnt hole,  grind it to size,  insert it in each exhaust port and use it to cut the relief in the block for a large valve head.






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