Re: liners over piston rings

[JHertzman@xxxxxxx]

The recent discussions of pulling liners off over pistons and then replacing
them has been interesting. A point has been mentioned (by Colin, I think) of
the difficulty of getting the liner back over the piston rings-

Alfa Romeos used removable cylinder heads as early as the RL of 1922, the
capolavoro of the geometra Merosi, but continued to use non-removable heads
(and thus pistons inserted from the bottom of the cylinders) on most but not
all of the higher performance cars at least through the 159 Alfetta and the
160 flat-12 prototype of 1952. The standard 1500, 1750, 1900, 2300 and 2500
Jano engines all had removable heads but most of the higher-performance
hemispherical-head twin cams from the 1914 Grand Prix through the 1923 G.P.R.
(P1), P2, 1500TF, 1750TF, P3, 8C 2900, Tipo C 8 and 12 cylinder GP cars, 158,
159, and the Tipo 316 (a three-liter V-16 with two crankshafts, essentially
two 158 engines on a common crankcase) and the 512 (another flat 12) all had
fixed heads. The 8C 2300 and 2600 Monzas were I believe the only exception to
the parade. I don't know the normal assembly sequence; no doubt they could
have been assembled in the shop inserting one piston at a time before
assembling the rods to the crank, but my understanding is that with these (as
with Bugattis, which were also normally fixed heads) it was not unusual to
lower the block over the pistons and onto the crankcase.

I have noticed that on the section drawings of most (but not all) of these,
and also of many of the separate-head, separate block engines such as the 1750
and the Monza the lower end of the cylinder is appreciably chamfered, which
undoubtedly would help somewhat with the getting-over-the-rings problem. 

The biggest objection I have heard to pulling and replacing liners in a V-6
with the lower end together is the difficulty of keeping everything sanitary
if there is any trace of scale or other debris in the water-jacket.
Compressing the rings may be tricky but should be doable. I would certainly
prefer the standard assembly sequence, out of the car, but if I absolutely had
to do a liner replacement from the top I might at least be curious about the
possibilities of the chamfered entry. 

The great merit of the fixed-head design was, of course, a definitive end to
head-gasket problems. It also generally allowed larger valves and better
coolant circulation passages, but made valve seat work a bit more difficult,
particularly on the smaller bores, like the 54mm of the Tipo 512. (Perhaps
their mechanics have small hands?)

John H. 

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