[TR] Some interesting insight on my misfire/backfire problem, and good news

Jim Muller jimmuller at rcn.com
Tue Oct 30 18:20:13 MST 2007


On 26 Oct 2007 at 11:56, v6spitfireguy at cox.net wrote:

> the exhaust valve had basically no clearance, and the
> intake was minimal, probably around .006-8 thou.  EUEKA!!!

"EUEKA"?  Maynard G Krebs would have said "EUOPA!!!"

But all seriousness aside, this prompts a few thoughts.  On my GT6+ 
the idle smoothness and exhaust cleanliness as measured by my nose 
have always been sensitive to valve clearance.  An adjustment 
seemingly less than .001" can make a difference.  I can measure a 
valve as being too loose for the .009" feeler and too tight for the 
.011", but if I go one step further and apply careful "digital" 
judgment and tweak accordingly, the idle improves.  I don't know what 
sort of cam it has but I've never seen a car so senstive to tiny 
valve adjustment.  Could someone tell me, is this typical of the TR 
2l engine?  Or perhaps of a non-stock cam?

The second thought is that with today's engines valve adjustment is a 
disappearing art, soon to be forgotten.  We've progressed through 
30,000+ mile intervals for OHC engines for which only dealers bought 
the shim sets to no maintanence at all save oil changes.  I posted a 
few weeks ago about the 48-State Tour in a Spitfire in which the 
driver/author described all his mixture tweaking and plug swapping, 
etc., but never mentioned valve adjustments though 12,000 miles.  Do 
we just forget about them now until some email note or event reminds 
us?  (And then we feel guilty and hope we haven't burned anything for 
having run too long with one slightly overtight?)

Glad you found your problem!

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+



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