Valve Springs

Greg Fripp writes:
After the recent flurry of interest in valve springs, below is a partially complete list of interest to 1275 users in particular.

The different valve lift heights listed should be checked carefully, bearing in mind that original cam lift and rocker variation play a significant part in spring compression pressures.

At stock fitted height of 1.390":


Model	Std Metro A+	1300MG Metro	Dual 'S'	Isky Orange
Free length, in	1.925	2.050	-	1.675
O/side dia, in	1.15	1.15	-	-
Rating, lbs	75	80	75/140	60
Compressed std	1.050
Compressed full lift lbs	115	135@0.4lift	-	180@0.4lift
Max safe lift, in	0.335	0.4	0.4	0.47
Lbs@max lift	-	135	150-155	~200
RPM limit	~5500	6000	7500	8500
Application	YUK!	Mild road	Hot road	Race

Std BL cam lift is 0.335"

Most perf cams are 0.36-0.40" with 1.25 ratio (std) rockers. 1.5 ratio rockers increase lift on a performance cam from 0.395 to 0.475" lift.

Warning: there are several points to consider - max valve lift/ rocker ratio, shimmed or not, etc...you need to know what you are using and have, as well as what you want. There are also other valve spring choices available.

Its a complex subject (which I'm digging up more about every time) and you need to read 'How to power tune the BMC/Rover 1275 series engine' by Des Hammill and perhaps also Vizard to find out more. The figures above are quoted from the Hammill book, which is a recommended read.

Greg

Mini-List International, February 1999