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Acceptable valve spring length
Posted: Fri Oct 24, 2008 6:09 pm
by MarkyB
Is there a figure for this?
I've looked through various manuals etc. and haven't found one although I thought such a number should exist.
I'm rebuilding a head and got to wondering as they are probably 40 years old.
It is probably academic as I'm not very prone to thrashing my Minor.
Posted: Fri Oct 24, 2008 6:38 pm
by polo2k
there is a measurement in the "rebuilding the head" section of the ringbound maunal. Its in the garage though so I cant check. as a last resort just make surer there is still about 3/8" minimum (from memory) of compression once all the collets are in and the top plate too and the rockaer os away from the top of the valve stem.
Posted: Sat Oct 25, 2008 8:47 am
by MarkyB
I've had another look in the BMC workshop manual and still can't find it.
The measurement I'm thinking of is the free (uncompressed) length of the spring compared to a new one.
Maybe it isn't an issue with the A series and I've seen spring length checks on motor bike engines.
Posted: Sat Oct 25, 2008 11:55 am
by polo2k
its definatly in there somewhere because I remember spending ages looking for it. from memory it is quoted in the text below a pic on the left hand side of a left hand page (possibly bottom half) Ive got to grab some stuff from the garage in a bit so ill grab a manual
Posted: Sat Oct 25, 2008 12:02 pm
by bmcecosse
If you are not looking for maximum revs -just use the springs as they are. If you line them up side by side - as long as they are all similar length, they will be fine. Obviously if one or two are noticeably shorter they should be changed. Note that 1275 springs are much longer than 948/1098 springs - and must NOT be fitted to these engines !