[Healeys] Strange Engine Situation

[Alan Seigrist]

Ray -

I don't know if you ever quite got a full answer on this.  A few thoughts:

1) Pistons made back in the day weren't made as well as they are now.  As a
result replacement pistons now rarely if ever fail, whereas in the 60's it
was quite common for pistons to "collapse" or lose rings and what not.  This
is partly because the small high revving / high heat engines in modern cars
have forced manufacturers to drastically improve the material and casting
methods, of which get carried over into our repro parts.  The problem with
your piston is probably just because the piston was made in the 'olden' days
with old gravity castings.  Ask any LBC repair shop now how many "collapsed"
pistons they've replaced recently, probably zero wheras in the 60s it was a
common occurance.

2) Losing the top edge of the piston can be caused by a couple things.
First if you are running a lower octane fuel and getting lots of "pinging",
this will damage the piston top and the top compression ring of the piston
because continuous cumbustion times will overheat the piston and the ring.
This is probably what happened with your car, with the pinging weakening the
compression ring over time and destroying the top of the piston.  Also, once
the ring is compromised it can crack, which when it does it can rattle and
then many times "score" the cylinder wall, and if this ring fragment digs in
far enough it'll rip off the top edge of your piston and get ejected out of
exhaust.  There are probably rusty ring fragments and piston pieces in your
muffler somewhere.

Your friends PO probably put cheap gas in his car and that just destroyed
the pistons over time....

Alan

'52 A90
'53 BN1
'59 Jag Mk IX
'64 BJ8


On Sun, Jan 3, 2010 at 9:06 AM, Ray Carbone <racarbon at verizon.net> wrote:

> A while back I was visiting a friend who was beginning a BJ8 engine
> rebuild.
> It seems he had owned the car since 1983 and always had problems setting
> the
> idle, however, driving above 1200 RPMs and the car pull strong.  After
> pulling
> the head and delivering it to the machine shop, he began to clean the
> pistons
> when he noticed some gaps around the edges.  After pulling the pistons, he
> found 4 with missing top rings, broken top edge sections and no debris or
> cylinder scoring.