My `72 Spitfire (1300cc) makes a tapping/knocking noise that sounds
like one worn out big-end bearing. I initially thought it was an out-of
adjustment valve, but a valve adjustment did not make the noise go
away. I isolated the noise to the #4 cylinder by shorting out one
spark plug at a time until the noise went away.
Anyway, last week I took off the oil pan to have a look at the #4
piston and connecting rod. I could not detect any play in the
big-end bearing by wiggling the connecting rod on the crankshaft.
I took off the bearing cap, and removed the cylinder head, and
took out the piston and rod. There were no broken rings, the
gudgeon pin had no apparent looseness, and the cylinder bore
had no detectable ridge or scoring (I was able to get the piston
out the top without reaming the ridge and only gently tapping it.)
Well anyway, I ask you all, where could this noise be coming from???
I noticed that the big-end bearing shells were worn enough to
expose the copper-colored underlayer. How much wear does this
correspond to? Enough to make a clearly audible knocking?
Alas, I did not get a chance to look at the other cylinders'
big end bearings yet for a comparison.
Obviously, I am confused. Without a known good or known bad
engine to compare things to, I can't gauge the significange
of what I am seeing. Any general advice on what tends to wear
out in Spitfire engines would be appreciated.
P.S. The compression is excellent (over spec on all cylinders)
and hte engine does not appear to burn oil under any circumstances.
I remain, etc.,
Doug Braun Intel Corp CAD
408 765-4279
dbraun@scdt.intel.com
or maybe:
/ decwrl \
| hplabs |
-| oliveb |- !intelca!mipos3!cadev6!dbraun
| amd |
\ qantel /
|