Doing the annual valve adjustmant check in prep for the new
autocross season and found exhaust cam is retarded about 2-3
degrees. Must be fault of ham fisted mechanic who ajdusted them
the last time (me).
Could this contribute to engine overheating? What other effects
could it have? Several years ago I recall someone one telling me
that advancing stock cams a few degrees could provide modest
performance improvement but I don’t recall details or disadvantages.
In reply to a message from Ponyman sent Thu 3 May 2012:
Nick
Retarded cam timing can most certainly cause overheating.
A 4 degree cam advance can improve your low end torque. This
would give your a little better performance for autocross,
but may result in a little loss in top end speed.
IIRC, set your engine to 8 degrees BTDC, and then zero up
the cams. It will only be a few clicks on each cam sprocket.
Since the cams turn at half the distance of the crank, when
you set the crank at 8 degrees, the cams will have been set
at 4 degrees.
Personally, I don’t know if it’s worth it for what you’re
going to get. I do more highway driving than I do autocross,
so I keep my cams at zero degrees.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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In reply to a message from Ponyman sent Thu 3 May 2012:
Thanks for the input - will set it to rights and see what happens.
Probably not bother with advancing them, as that means fiddling
with two cams not one.
Nick–
The original message included these comments:
Doing the annual valve adjustmant check in prep for the new
autocross season and found exhaust cam is retarded about 2-3
degrees. Must be fault of ham fisted mechanic who ajdusted them
In reply to a message from Ponyman sent Sat 5 May 2012:
Are we talking 2-3* at the cam…or the crank? 2 or 3* at the cam
is not too worrisome, but you may as well reset it. However, while
you are in there, take special notice of the intake cam’s position
since the intake valve closing event is the most important aspect
of valve timing events. We are lucky with our XK engines since we
can alter the lobe separation angle to whatever we desire…unlike
single cam engines which must have the exhaust advanced(or
retarded) along with the intake. Think about leaving the exhaust
at 2 crank degrees retarded while advancing the intake 2*…a
subtle change that you just might feel out on the track at lower
revs. I don’t remember if that small of a change can be achieved
though…it would depend on how much chain stretch you are working
with.–
Lee140FHC
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In reply to a message from Lee140FHC sent Wed 9 May 2012:
If you want to alter the timing of one cam just a little,
then its possible to do so by undoing the front bolts,
altering the fine-toothed serrated adjuster by one or two teeth.
Use locking clamps to grip the rough part of the cam to turn
it a little to line up the bolt holes.
Cant remember the tooth count–
The original message included these comments:
Are we talking 2-3* at the cam…or the crank? 2 or 3* at the cam
is not too worrisome, but you may as well reset it. However, while
In reply to a message from ex jag sent Wed 16 May 2012:
I have now to set them up with zero degrees, but with error on the
side of a little advanced.
Hope to get it on road this weekend to see what happens
Nick–
The original message included these comments:
In reply to a message from Lee140FHC sent Wed 9 May 2012:
4 degrees at the cam, which would be 8 degrees at the crank.
Not worth the hassle though.
Joel