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[charley fitch]

I have a TR4 engine ( 17000+ CT) that comes stock with the three valve springs on the exhaust valves.  I am interested in changing this situation to only two springs as found in the engines after 21470 CT.  It appears that the heads carry different part numbers (before and after 21470 CT). So is it possible to convert this older head to just have two exhaust springs instead of three?

I am thinking that the extra spring is not a good thing considering the extra load it puts on the cam and our poorer oil even if I add ZDDP.

Charley Fitch   

[TR3driver]

If memory serves, the head change was because the exhaust valve stem diameter changed.  The earlier exhaust valves had 3/8" diameter stems, which made them heavier than the later valves with 5/16" stems (and hence more spring pressure needed to pull them closed without valve float).

IMO the optimum conversion would be to switch to the later valves as well (the smaller stems also help improve engine breathing), which takes a special 'conversion' guide in the earlier heads.  Given the propensity of the earlier exhaust valves to burn, I wouldn't suggest lowering the spring pressure on them.  That's why the factory added that third spring.