Please could I have some advice as I'm getting a little fed up with top-end rebuilds!!
I have a Dominator 99 fitted with an early SS cam. The cylinder head has the larger inlet ports and in the process of rebuilding it I now have 5/16 valve stems in oversize valve guides. The valve guide tops are 1/2 inch (12.7mm) in diameter.
The problem I have is the valve seals lasting less than 50 miles, splitting and falling off. Although the seals fit over the guides, I have a feeling that the valve guide tops are too broad being around 2.5mm larger than the internal diameter of the seals. This stretches them and leads to them splitting.
The seals are new, without springs, sold as suitable for the 5/16 valve stem and are from a reputable Norton supplier.
The questions I have are
1) Are there seals available for a 5/16 stem and a 1/2 guide?
2) Are there "softer, higher quality" seals available?
3) Or will I have to remove the valve guides, take them down to a standard diameter top and if so, what diameter should that be?
Many thanks,
Derek
I think I now know what is…
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I think I now know what is going on.
Dominators did not have oil seals until the mid-60s. Commandos did have seals.
The valve guides I have are for a Dominator and do not have the recessed ring on the guide that takes the flange on the oil seal on a Commando.
I have been trying to fit a seal where it doesn't fit. I will now stop trying to do this!
BW,
Derek