[Healeys] To fit or not to fit - that is the question: apologies to Hamlet

[kags at shaw.ca]

Mirek:

 

My experience: When my BJ8 engine was rebuilt the first time in 1985 (at
approx. 140k miles, 40k or so by me), 5 ring pistons were used (.030 over).
I vaguely remember being told at the time that the factory used these
pistons in their truck and marine engines - something about reduced piston
slap for less wear, and maybe a bit more friction, but nothing really
important in a stock big Healey engine for the street.  In any case, that
was what was available at the time, so that's what went in.

 

Fast forward another approx. 140k miles to the recent second total rebuild,
this time all miles driven by me, and with really good hobby car maintenance
by me - a bit of overkill if anything.  The engine was in really good shape
when taken apart - didn't really need to be done quite yet, but we were
doing a total ground up resto on the car, so now was the time.  ( I just
might be the only big Healey owner that has run an entire rebuild cycle with
5 - ring pistons and then had the engine apart again and had a look).

 

New 5 - ring pistons were chosen - again all we could get in .040 over - and
again, the engine was done to stock specs - ignition, cam, carbs etc. all as
original.  After some 'sorting', the engine has now approx. 15k miles on the
new rebuild, and is running beautifully - excellent power for a stock spec
engine.  Approaching 300k miles. Amazing!

 

As an aside, at the first rebuild in 1985, 12 hardened valve seat inserts
were installed in the head - 2 adjacent ports had cracks, and at the time
the world was faced with the unleaded fuel changeover.  At this recent
rebuild, the head barely needed work, a valve grind and not much else after
being run exclusively on unleaded fuel for that entire rebuild cycle.  (
didn't even have hardened exhaust valves - couldn't find any at the time).
Sintered bronze guides too - we didn't know any better!  They must have been
fitted right, they were left as is at the 2nd rebuild.  Normal o-ring valve
stem seals were used again - no unusual oil consumption at this time. 

 

Based on my experience, unless you are modifying the engine for more power
and therefore might not want the slight extra friction, I would install the
rings.  There is no question that the piston skirt is better supported with
the extra ring below the pin, and the groove is already there - also, there
is the possibility that there could be a down side in the long term from
running with the groove empty.  I doubt that anyone has enough mileage on
such a rebuild to say for certain that it will be trouble free.

 

Hope my experience helps with your decision.

 

Earl Kagna

Victoria BC

BJ8, BT7 tri-carb

 

     

 

 

From: Healeys <healeys-bounces at autox.team.net> On Behalf Of m.g.sharp--- via
Healeys
Sent: Friday, April 16, 2021 10:35 AM
To: healeys at autox.team.net
Subject: [Healeys] To fit or not to fit - that is the question: apologies to
Hamlet

 

Hi all,

 

More on the rebuild of my BT7 engine.  A number of years ago I purchased
+0.030" AE pistons in anticipation of this rebuild.  The AE pistons have 5
rings: 3 compression and one oil control above the wrist pin and one oil
control lower on the skirt, below the gudgeon pin.  The pistons that came
out, which were the originals, had the conventional 3 compression rings and
one oil control ring.

 

I am wondering about that second oil control ring below the gudgeon pin and
whether I should fit it or not.   I am not building a performance engine,
just want the highest quality job possible.  The original pistons functioned
fine and I never had oil consumption issues in the 110,000 miles I put on
them.  This engine had a bit of piston slap, which was typical of them.  I
wondered if the extra ring lower on the skirt was to address this.  Perhaps
it was a complaint from Austin Westminster owners wanting quieter engines?
Was the 5th ring for another application?  I also wonder whether wiping the
oil off the bores by the lower control ring is a good thing or whether it is
better to have some cylinder wall lubrication from oil splashing onto the
cylinder walls.

 

I have searched for a service sheet on these pistons (thanks Scott!!) but
found nothing.  I also searched the List Archives, and there are a few older
postings that suggest fitting all 5 rings, but no reasons why.

 

I doubt we can really know what is going on in there as the dynamics are
complex, but I would be interested in any experience anyone has had with the
5-ring pistons.  Theoretical discussion is always welcome!

 

Best, Mirek

 

 



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