Greg,
Piers told me about the excitement. What a shock that must have been, and at
a pretty fast part of the track, too (well before the turn-in point for turn
7, I hope? Kinda 100 mph-ish there...)
Regarding the piston scuffing issue, I'm betting you've already got inadequate
coolant flow ruled out. The two possibilities that come to mind are: 1) an
intake air leak only on #4 intake tract and 2) a bent rod.
1) Have you tried viewing temperatures at different points on the header and
surface of the engine block and head using an infrared thermometer? A look at
the exhaust header temp for each individual branch ought to tell you if one
cylinder is running leaner than the others. If all four pipes are indicating
similar temperatures I'd suspect oiling or a clearance issue.
I'm assuming you're doing plug cuts in the absence of an EGT gauge and probe
or exhaust gas analyzer. How are you performing your plug cuts? I have found
that the results are not clear if I don't put in a new plug at the very start
of a hard acceleration pull, with next to no idle time and no part-load
driving time.
2) If the connecting rod is bent, the #4 piston could be cocked (as seen from
the side of the engine). If so, the scuffing would be on a side where the
wrist pin hole is. If you're going to pull the piston and rod it's easy
enough to check the rod for trueness. Is it possible to install a rod
backwards, causing the small end to force the piston against the front or rear
of the bore? That might also exert asymmetric pressure on the big end rod
bearing -- how does the bearing look?
Is the scuffing at 90 degrees to that, on the thrust side? If so, one
possibility is lack of oil. It may be that somehow oil isn't getting thrown
up to the bottom of the piston in #4 only, causing it to run hotter. You
could bore a couple of tiny lubrication holes below the lowest movement limit
of the oil ring, where oil could get to the skirt, but not having an engine
open at the moment, I can't visualize how you might pressure-feed this.
Is the overbore you mentioned equivalent to the piston-to-cylinder wall
clearances?
Duncan
Texas
1952 Morgan Plus 4 #6 red
On Sep 11, 2012, at 10:08 AM, Robert Blake wrote:
> Pops and I had a less than excellent weekend at TWS it would true to say
that
> we were beaten by equipment, one of us physically.
>
> We just put a new engine
> in Dads #14. The second one since December. We built this one with Wiseco
> pistons, stock liners bored to 87+.005 on 1-3 and +.006 on number 4. This
> resulted in the engine lasting most of the day Friday for test and tune. On
> his last run we did a plug check. We had been trying to dial in his mixture
> all day and moving from a lean condition as evidenced by previous plug cuts
in
> the day. After adjusting the mixture, reinstalling the plugs, gapping
points,
> and rechecking timing we started the engine to hear a horrible clatter from
> within. Same clatter that dad had heard at the Mitty so we feared the
worst.
> Later that evening he and Bob Kramer confirmed that #4 piston skirt was
> scuffed again. The same thing happened on the previous engine at the Mitty.
> Oil pressure was great all day (80 psi from 3000rpm up) the water temp
never
> went above normal range.
>
> So other than lack of piston to liner clearance,
> what causes pistons skirts to scuff on the liner? Can a lean mixture on
the
> rear carb cause this without showing up as a hot running condition?
>
> On to my
> issue.
>
> My aluminum hood pins broke on the TR3 on the back straight.
> Unfortunately, the passenger hinge snapped but the drivers side did not.
The
> hood bent back and slapped my helmet pretty good (beaten by my equipment).
> Never thought of it that way before. Not pleasant. So I am in search of a
> decent bonnet. It is for a 58 TR3A. I am not too picky but proximity to TX
is
> a major consideration.
>
> Info on both issues is appreciated.
>
> Greg
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