[Healeys] Healey 100 4 cyl (A90 actually but same) Engine Bore Q

Alan Seigrist healey.nut at gmail.com
Sat Dec 22 06:00:01 MST 2007

Hi All -

 My mechanic has got my engine apart.  If you recall the engine had a bent
push rod, and we just decided to get the head off and check stuff while we
were at it.

We pulled the pistons to check the bore and all looks pretty good except #4
had a broken compression ring (no scoring on the cylinder).  The cylinder
bores all look very good with no scratches or scoring.  The bore
measurements appear pretty much standard except for #4 which is about 15
thou over.  See the table below.  The Standard bore measurment for the motor
is 3.4375".   All the pistons weigh and measure well so I will reuse them.

My question is with #4 a little over, can I just hone the cylinders and buy
a set of standard rings and put them on?  I also assume I want to hone the

The compression on this engine is only 6.9:1 (standard for the A90) and I
really don't want to bother replacing a bunch of stuff.  The old lady just
toodles about town so a very soft rebuild is all that is necessary.

I don't want to rebore the cylinders as it will be a huge pain for me to
pull the block, and even bigger pain for me to find someone in Hong Kong
that can bore the motor properly.

Standard rings ok??

 Austin A 90 Atlantic Bore and Piston size


*Bore (inches)*

*Piston (inches)*

*Piston markings (identifiable)*

*Weights**Piston w conrod complete*



3.426 at wrist (gudgeon pin)3.418 at top

DT 808  15, w V3 in centre

1.925 kg
4 lbs 4 ozs



3.429 at wrist
3.416 at top

DT 808  15 w T 11 in centre

1.935 kg
4 lbs 4.5 ozs



3.426 at wrist
3.410 at top

DT 808  15 w T 11 in centre

1.925 kg
4 lbs 4 ozs



3.428 at wrist
3.413 at top

DT 808  15 w (T) 11 in centre
T not identifiable (assumed)

1.925 kg
4 lbs 4 ozs

*The piston of cylinder 4 had a broken top ring but the piston is not
damaged and there is no significant marking on the cylinder bore.

Standard bore is 3.4375"

Thank You!!!


 '52 A90
'53 BN1
'64 BJ8

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