Bob
These compression ratio figures are those stated in the Hepolite piston
catalogue and must make some assumption about the volume of the cylinder
head.
Perhaps the BMC/DHMCo made their own measurements or calculations and
came out at a slightly different figure. Alternatively they could have
switched to using 12623 at a later date and not bothered to change the
publicity documentation?
However using C.R. to define a piston is somewhat hit and miss and a
safer way, other than using a part number, is the bowl depth
measurement. This is the measurement from a line across the top of the
piston to the centre of the bowl.
For interest Hepolite bowl depth measurements are as follows
12572 0.562"
14296 0.499" (Measured)
12623 0.422"
For what it is worth the bowl capacity of 14296 is measured at around 28
cc.
Regards
>OK, now I'm confused.
>
>Have always read/heard/etc. that the high compression pistons fitted to
>100Ms at the factory were 8.1:1 CR. Have never heard anything about 8.6:1
>CR pistons coming from Austin or DMHMCo.
>
>bs
>
>--------------------------------
>Bob Spidell - San Jose, CA
>
>
>
>We don't often see technical tips but here is one that perhaps only a
>few people are aware of.
>
>I am in the process of reconditioning my BN1 Le Mans engine and decided
>to keep the original pistons and just fit new rings. It is believed that
>these pistons were fitted when the car was quite young at the Donald
>Healey Motor Company.
>
>I had great difficulty finding replacement rings and had after much
>searching to give up and have the compression ring grooves widened.
>
>Most owners will know of Standard and so called Le Mans pistons with
>Hepolite Number 12572 (C.R. 7.5 to 1) and 12623 (C.R. 8.6 to 1)
>respectively. These have 3/32" wide compression rings.
>
>However mine are Hepolite 14296 with a stated C.R. of 8.1 to 1. These
>appear in catalogues up until the early 1960s but then disappear.
>
>The problem is that the compression rings fitted to these pistons are
>NARROWER at 0.070" wide.
>
>So if you have these early pistons and need to re-ring them, be warned.
>
>Regards
--
John Harper
_______________________________________________
Healeys@autox.team.net
Donate: http://www.team.net/donate.html
Suggested annual donation $12.75
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
|