I have a sample here of a 1.875 valve It looks like it is slightly longer in stem length. If this is installed with new valve seats to accommodate it will it protrude enough to hit the piston with a normal 3/8 lift cam?
When you adjust the valve clearances and set the gap to the correct distance (with the cam lobe pointing 180 away from the follower then the cam will depress the valve the correct distance. If the valve stem is too long you will not be able to set the valve clearance. Do not grind the stem to make it shorter.
Pat H
Iâm talking about a thicker valve seat here to maintain valve clearance w/o playing with the stem at all. This is adding the same extra dimension of the stem to the valve seat.
âLooks to be slightly longerâ than what? It either is or isnât longer than a standard valve.
If itâs not a standard valve what is the point in using it if you are having to replace the valve seats with thicker ones?
I would have thought it would be easier to have custom shims made to accommodate the extra length if you are determined to use the longer (?) valve.
Is there an experienced opinion out there?
Thatâs pretty insulting.
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You have asked an impossible question to answer. You donât give us enough information to make an educated assessment. We donât know which pistons or compression ratio you have. We donât know how much longer the valves are over stock. Has the head been milled? Has the block been decked? What is the compressed thickness of the head gasket? It is customary to fly cut the piston tops to accommodate greater valve lift, diameter and duration. It is entirely possible to fit a S3 XJS6 4.2L (1-7/8" valve size) cylinder head to a 3.4L engine, so the valve size alone is not a deal breaker.
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There is thatâŚ
Thank you. That is the obvious answer to the question as it is asked. Yes, it does assume a std 1 7/8" valve as would be supplied by std Jaguar sources. Admittedly there are other variables to consider IF the resulting clearance would be minimal. The assumption of how much over length is a tough one so is based on a std valve. Trying to measure lengths from the 45 degree sealing surface to the nominal location of the radius in the groove for the keepers is problematic. For that reason all of these factors fall into the range of âall other things being equalâ. I do know that with higher lift cams people have at times had to make room on the pistons but I donât know how much extra lift requires this effort. I have no interest in raising the lift but would be using the usual 3/8 lift of a D spec cam on the intake with slightly longer duration. (30/60 vs 15/57).
whilst the engineering is way outside my field of knowledge, I am interested in what you are doing ie fitting 1 7/8 inch valves to an old C or B spec head? which will bring head up to D specs with a bit of porting and polishing.
I had planned to do that to an original C type head down the track. and given I have a pair of genuine original D type cams it should all work I have a lot of jaguar engine spec sheets and dyno readings etc and jaguar seemed to have some motors at 15/15, 30/30 etc
I have just had an âAâ series head rebuilt from my XK120 I have used a bloke who specializes in head and he lightly ported & polished the intake & exhaust ports.
For the valves he used a part machined valve and machined to the length he wanted to sort 3/8 lift cam and the inlet/exhaust clearances. This also included the appropriate groove for colletts.
Love to hear and see more of what you planned terry
The cam lift limitation on these engines is the diameter of the tappets. Higher lift would run the nose of the cam off of the edge of the tappet.
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