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Error Noted in Technical Manual?

From: Philip Dingle
Fromemail: Pdingle@comcast.netnospamplease
Category: Technical
Remote Name:
Date: 06 Feb 2005
Time: 20:11:52


I have noticed what appears to be a lack of correlation between the Jowett Car Club Technical Information manual, Issue 2: Dated 22/10/2001, and the "Competition Tuning Notes for the Jowett Javelin - All Models" issued by JCL. We are talking a small inconsistency, but one that deserves to be resolved nevertheless. On Page 26 of the TI manual, in the Cylinder Head sub-section, it states: "Valve seat width inlet (sic) 1/32". Exhaust 3/64"." Note that 1/32" = 0.03125" = 0.794 mm, and 3/64" = 0.0468" = 1.188 mm. If we now go to the Tuning Notes, on Page 5 under the Valves sub-heading, it states: "A seat width of 3/32" should be maintained for the Exhaust Valve and 1/16" for the Inlet Valve". Note that 3/32" = 0.0937" = 2.38 mm, and 1/16" = 0.0625" = 1.587 mm. I am prepared to accept that the recommendations for the competition engine might be different from those for the regular production engine, but a value that is double does not seem reasonable to me. Having now looked at some heads in the search for clues as to which is correct, I would say that the Tuning Notes values are correct and the values in the TI manual are questionable. There is of course an issue about how the seat width should be measured; I have taken it to mean the physical machined dimension measured at the angle of the seat (30 Inlet, 45 Exhaust), rather than the vertically projected dimension. Does anyone have any comments on this? Where did the manual seat width values originate? Is it something that should be corrected in future issues of the manual?

Last changed: November 19, 2008