Lotus Elan

Chipped valve

PostPost by: mini64 » Thu Oct 27, 2016 11:12 pm

Chipped exhaust valve took me out of the races the other week. I assume I over revved him and slapped the piston with the valve but there is no evidence.
img_1843.jpg and
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PostPost by: bitsobrits » Fri Oct 28, 2016 1:10 am

Are you sure it's not just an extremely burned valve?

If a piece of the valve that large actually broke off (and presumably exited via the exhaust), you would be able to see mucho telltale marks in the piston crown and cylinder head.
Steve

Elan S1 1963-Bourne bodied
Elan S3 1967 FHC pre airflow

Formerly:
Elan S1 1964
Elan S3 1966 FHC pre airflow
Elan S3 1967 FHC airflow
Elan S4 1969 FHC
Europa S2 1970
Esprit S2 1979
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PostPost by: rgh0 » Fri Oct 28, 2016 10:33 am

Check if the valve stem or head is bent, if you hit the piston you normally put a bend in it. Been their done that :lol:

A small bend can lead to exhaust gas leakage past the valve and seat. These hot gases can rapidly burn out the valve like you appear to have.

Clean the valve and check the face of the fracture with missing bit. If its a fracture that will be obvious versus a oxidation burnt surface.

Even a small leak due to wear and without hitting the piston ( or other valve) and bending the valve can lead to a valve burning out rapidly. Lean mixtures and over advanced ignition and loose exhaust stem clearances and poor conductivity valve guides can also contribute to or cause the problem especially in a race engine with constant full throttle high rev use.

cheers
Rohan
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PostPost by: Chancer » Fri Oct 28, 2016 10:58 am

Agreed, its burned out, check the seat insert very carefully for damage or cracking.
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PostPost by: The Veg » Fri Oct 28, 2016 5:30 pm

You got off easy.

This happened to a BMW motorcycle I owned back in 2007:

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1969/70 Elan Plus 2 (not S) 50/2036
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PostPost by: mini64 » Sat Oct 29, 2016 1:15 pm

seems I had no idea what a burnt valve could look like. googled it and found many valves looking like mine. Sure enough the "fracture surface" on mine didn't look like a fracture but indeed almost like a torch cut surface!

Valve measures straight and seat looks fine. Valve seems tight in guide. I don't believe I have lean running or advanced timing issues but will recheck when all is back together. maybe it's just time for a head rebuild? Any opinions on the below cylinder head photos?

img_18591.jpg and


number four cylinder with burnt valve:
img_18641.jpg and


number 1
img_18651.jpg and


number 2
img_18661.jpg and


number 3
img_18671.jpg and
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PostPost by: Bud English » Sat Oct 29, 2016 3:13 pm

Why is the spark plug in the #3 position so recessed? Just not tightened in?
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PostPost by: mini64 » Sat Oct 29, 2016 3:25 pm

Correct-plugs loose
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PostPost by: rgh0 » Sat Oct 29, 2016 10:07 pm

It looks like something small went through the cylinder with the failed exhaust valve from the dings in the cylinder head. This may have been a bit of the failed valve or it may have been something else that caused the valve to fail.

It may have been a bit of broken ring or an electrode off a spark plug or something small that came in the inlet. Worth a look around to see if you can find where it came from.

cheers
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