ET: Engine (Twin) hard valve seats

timetraveller

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It is a figure I have 'known' for about fifty years and I think that I got it from the original Service Sheets. If I have got that wrong then I apologise and perhaps someone who has access to the original figure could either confirm or correct it. :confused:
 
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timetraveller

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Thanks Bill, so my remembered figure was not too far out which raises an interesting point. Vincents were not originally known for having valve seats fall out but one of the local owners bought a new cylinder head a few years ago and had the inlet valve seat fall out within very few miles. This was replaced and then it happened again. A few years later the exhaust seat fell out. We wondered at the time whether the aluminium for the cylinder heads was not being heat treated properly. Valve seat materials have had to change a lot since the introduction of lead free seats and I am no longer sure what the expansion coefficients of modern seat materials are. Perhaps Vic, or someone else, with access to modern material specifications would like to comment about what the interference fit should be with modern materials.
 

vibrac

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I think that a few latter (60-70) IOM efforts had seats drop out (Slater?) so it may have been prevalent under hard conditions back then.
 

greg brillus

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Heating the cylinder head is an issue as well........aluminium heated to 200 degrees Celsius will anneal the metal which turns it into expensive Plasticine.......... I think some of the earlier Godden heads suffered valve seat failures.
 

Peter Holmes

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Surely this information and expertise should be readily available, after all it does not just apply to Vincent cylinder heads, Rolls Royce Merlin Engines were thrashing around our skies 80 years ago, heat treatment of Aluminium and valve seat shrink fits should be a well known science by now , or is the complication simply the reduction or withdrawal of tetraethyl lead being the culprit in this phenomenon.
 

timetraveller

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The incident I referred to was only about five years ago so not just early Godden heads. Note that the bike referred to is a Comet and only used locally and sedately. No racing, thrashing or other abuse. I was subjected to some criticism for mentioning the incident in MPH but my feeling was that if the seat had fallen out while the rider was in heavy traffic, and the engine had locked solid, he could have ended up under a 40 tonne lorry.
I do remember the problems that Slater had with his IOM efforts. Terry Prince must have got the combination of materials right as his heads tend to be used in anger and do not have this problem.
 

macvette

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Surely this information and expertise should be readily available, after all it does not just apply to Vincent cylinder heads, Rolls Royce Merlin Engines were thrashing around our skies 80 years ago, heat treatment of Aluminium and valve seat shrink fits should be a well known science by now , or is the complication simply the reduction or withdrawal of tetraethyl lead being the culprit in this phenomenon.
Maughans fitted unleaded seats in my heads so they must know
 
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