I’ll begin with a confession. The other day, I got up with a
list of jobs for the day that required my urgent attention, the
first of which was sifting through e-mails to the Stationary Engine
Mailing List to find a suitable subject for GEM -and
getting the article mostly, if not completely, written.
I had the house to myself, no children to feed or chase away
from the computer so I could get on with the job. The problem was
it was a beautiful day. Contrary to expectations it was warm and
sunny with a pleasant breeze, and the rest of the family had gone
to the first big show of the year. I did try to get on with the
article, honestly, but unfortunately the weather won out and I
raced off to join them, leaving myself a lot less time to get the
job done.
The show had an impressive display of stationary engines (even
though this particular show is primarily about historic transport)
and, even more impressively, most of the engines were running most
of the time.
There was an undisputed rumor going up and down the line that
the next show, at the end of the month, will be the rally debut for
Tillie, the 15 HP Tillinghast half-breed oil field engine, last
seen in public at Portland in 2001. As she’s probably the only
half-breed in England, and about twice the horsepower of the
average engine seen on our rally fields, it should be an impressive
debut, especially given the spectacular setting of parkland at a
country house. I can only hope for weather as good as we had this
weekend.
I’ve been contributing these articles to GEM for
almost four years, and it’s tricky coming up with something we
haven’t covered before. But the problem of a damaged cylinder
is one that anyone who restores old iron can, and probably will,
come across, so herewith are a few words of wisdom from the folks
on the engine list around the world. Our thread started with the
following question:
Problem: You have a really nice old hunk of iron with a messed
up cylinder. Either it is egg shaped, has a nasty gouge down it or
someone left it sitting without the piston, etc. My question is,
what would you do to get it running again?
I’d bore it and flame weld the piston to fit, especially if
it’s a big one as the piston probably won’t be too round,
either. Alternatively, bore it again or sleeve it back to original
size.
I think the answer depends on how badly it’s messed up and
how fat your wallet is. Lightly damaged, you might get by with a
rigid power hone and oversize rings. Maybe you will need to build
up the piston with flame spray.
A local score (like that done by the end of a loose wristpin)
might be repairable using high-temperature Devcon-type material and
a piston ring as a scraper. And of course, the last resort is to
bore and sleeve.
I for one am not in favor of the all too popular trend of boring
an engine a 1/2-inch oversize and pressing a sleeve in. It just
seems like too much material removal, which can contribute to
weakening of the cylinder in both hoop stress capacity and in
longitudinal strength. While a lot more work, 1 am in favor of
boring the cylinder only as much as is needed to correct wear, out
of roundness, and pitting, and then making a new piston to match
the oversized bore.
Currently, I am making two patterns for two different sized
Hercules pistons. When I’m done I’ll be able to turn the
outside diameter of the piston to whatever diameter is needed.
Rings will be easy to get.
A few people picked up on the ‘oversize’
comment, which took the discussion to more specific details of
measurement.
Where are you getting sleeves with a 1/2-inch wall? The ones we
have always used usually come with a 3/32-inch wall, meaning that
the outside diameter of the sleeve is 3/16-inch larger than the
bore. There are times when removing this much material is
unacceptable, like in an 8-cycle Aeromotor, some headless Wittes
and some Fairbanks-Morse Jack Juniors. Otherwise, the rule of thumb
for me has been that if the bore will cleanup within 0.060-inch,
bore and resize the piston or replace it with a new, oversized
piston. If it takes more than 0.060-inch sleeve it, bore the sleeve
0.010-inch undersize, take a cleanup cut on the piston to fit,
cleanup the ring lands and re-ring it.
As always, there are no hard and fast rules – each case should
be considered on its own merits. I spend more time staring at the
pieces and considering what might go wrong than I do making the
repairs. For me, that is the fun part.
I picked 1/2-inch as a rough number based on what I have seen of
some bore and sleeve jobs on large engines. Even at 0.060-inch per
side that’s an 1/8-inch. My point is that it seems better to
bore just enough to clean up and make an oversized piston.
There are lots of increments of cleanup borings to go before
ever getting to the point where a sleeve is required. I’d be
real leery of 0.062-inch thin cast iron as a sleeve! There is also
the whole heat transfer issue of relying on the contact pressure to
assure decent heat transfer.
I’m probably guilty of being the typical engineer and
overanalyzing the situation, but it seems to me that the better
practice is to just bore and fit an oversize piston. I suspect that
boring and making a new piston with new rings will be about the
same cost as boring, buying the sleeve, installing the sleeve,
boring the sleeve, turning the piston (because you know it is out
of round too), and buying rings.
Who knows. Though … I’m getting ready to go down that path
once the Hercules patterns for the pistons are done. I’ll keep
track of the costs and report back. One thing is for sure, I’ll
never be worried about a sliding sleeve, poor heat transfer or
seeing the shoulder at the back of the cylinder where the sleeve
ends.
Bottom line is that I prefer the small incremental borings,
preserving wall thickness before resorting to a ‘massive’
boring to accommodate a sleeve, regardless of
thickness/thinness.
We have used thin liners (only 3/16-inch or less thick) to bring
an engine back to standard bore to re-use the old pistons.
On the Rolls Royce Silver Ghost engine overhaul we used Bedford
(GM company in the UK) truck liners, which were really thin. They
were pressed in place and then bored out to size. It worked really
well, and only a small amount of the block was taken out to start
with.
In that case we bought new aluminum pistons, but I have used the
same technique on other engines, reusing the old pistons after
juggling sizes and cleaning up the piston itself – and getting the
ring grooves cleaned out.
If there was enough meat left in the cylinder, I’d have it
bored then have the piston built up to fit. Easiest all-around
repair, although it is a little pricey.
Has anyone ever considered machining the piston round, measuring
where the ring grooves are, and then using Loc-tite to fit a cast
iron sleeve onto the piston, then re-machining the ring grooves?
I’d probably leave the sleeve off the top of the piston.
If it’s a good engine and you are really keen to restore it,
I would recommend cylinder boring and a new bushing to fit the
piston.
In this particular instance, the engine owner decided to
take a middle line from the advice offered:
I agree that boring and sleeving would seem to weaken that old
cast iron way too much. I am going to try to get the piston
sprayed, and then go from there.
To finish, I thought you all might appreciate a
wonderful quotation included in the e-mail signature of one of the
contributors to the above discussion: ‘If you can’t make it
accurate, make it adjustable!’
Engine enthusiast Helen French lives in Leicester, England.
Contact her via e-mail at: Helen @insulate.co.uk You can join the
Stationary Engine List on the Internet at: www.atis.net
