Hi, Ken -
I had the exact same thing happen to my BJ8 engine about 7 years ago. I
heard the pieces breaking off the pistons and rattling around, but had no
idea what it was. Between the first time I heard the noise and the second
time was about 6 months. It was a loud, rattling sound like a wire coat
hanger caught in the fan, but it only lasted a split second -- just enough
to startle the crap out of me. Following the second occurrence (the engine
still seemed to be running fine), I did a compression check and found
compression way down in #4. After pulling the head, I found small pieces
missing from #2 and #3 piston edges, with one larger piece missing from #4,
just as you describe.
After removing the pistons, I found that the rings had broken up and wore a
triangle pattern (wider at the bottom) up through the remaining rings and
piston lands until the pieces broke off at the top of the piston. #4 had a
smooth score in the wall that required a sleeve to repair.
I asked on the list what could have caused it, and got the general opinion
that it was either detonation or running hot. I never heard any detonation,
and the engine continued to run about the same (well), as far as I could
tell. Before the problem, I used regular gas with a lead substitute after
leaded gas disappeared. Now, I use only premium and maybe I should be
checking my distributor advance as Dave Russell suggests. I have a Mallory
dual point with mechanical advance only. So far, so good.
Good luck!
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
-----Original Message-----
From: owner-healeys@Autox.Team.Net
[mailto:owner-healeys@Autox.Team.Net]On Behalf Of Freese, Ken
Sent: Tuesday, January 09, 2007 7:17 AM
To: healey
Subject: Pistons damaged again
I cleaned up the compression reading columns.
Ken
Saturday, I removed the head from my BJ8 to have steel valve seats
installed because of #4 exhaust valve recession and low compression. I
figured #4 was now burned enough, I should get it fixed. After putting
on the hardtop on New Years, I could hear rougher running.
Now I see that #2, 3, and 4 pistons have 1/16 to 1/8 inch notches
missing and I can see the top ring on #4. Preliminary inspection of the
notches don't show smooth melting. So, new set of problems. I figure the
causes are:
1. Swallowed debris
2. Detonation
3. Defective pistons
Incidental facts:
A - oil never filtered only changed for about the past 40000 miles due
to faulty spin on filter adapter.
B - last rebuild in 1982 and 70000 miles ago due to melted pistons
Compression 1997 Compression 2004 Compression 2007
165 130 110
155 135 90
150 145 70
150 90 70
155 130 115
175 150 145
Any thoughts on the cause until the pistons are actually out?
Ken Freese
65 BJ8
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