I'll begin with a confession. Yesterday, I got up with a list of jobs for the day which required my urgent attention, the first of which was sifting through the emails 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 that I could get on with the job. The problem was that it was a beautiful day, contrary to expectations, 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.
It was an impressive display of stationary engines, although the show is primarily 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 15HP Tillinghast half-breed oilfield 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 rallyfields it should be an impressive debut, in the spectacular setting of the parkland at a country house. I can only hope for as good weather as we've had this weekend.
Now on with the article before I REALLY run out of time!

Having been contributing these articles to GEM for almost four years, it's quite tricky to come up with something we've not covered before, but the problem of a damaged cylinder is one that anyone who restores old iron can come across. Here's a few words of wisdom from the folks on the engine list around the world.

* Problem: You have a REALLY nice old hunk of iron with a messed up cylinder. Either it is egg shaped, or has a nasty gouge down it or someone left it sitting without the piston, etc....
My question is this, 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 a high-temperature Devcon and using 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 to bore the engine a ½" oversize and press a sleeve in. Seems like too much material removal that can contribute to weakening the cylinder in both hoop stress capacity and in longitudinal strength. While a lot more work, I 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 2 patterns for 2 different sized Hercules pistons. When done I'll be able to turn the OD of the piston to whatever diameter is needed. Rings will be easy to get.

A few people picked up on the "½" oversize" comment, which took the discussion to more specific details of measurement.

* Where are you getting sleeves with a ¼" wall? The ones we have always used usually come with a 3/32" wall, meaning that the OD of the sleeve is is 3/16" 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 F-M Jack Juniors. Otherwise, the rule of thumb for me has been that if the bore will clean up within .060", bore and resize the piston or replace it with a new oversized piston. If it takes more than .060" to clean up, sleeve it, bore the
sleeve .010" undersize and take a clean up cut on the piston to fit, clean up 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 the ½" as a rough number based on what I have seen of some
bore and sleeve jobs on large engines. Even at .060" per side that's a ?" diameter. 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 clean up borings to go before ever getting to the point where a sleeve is required. I'd be real leary of .062" thin cast iron as a sleeve!
Then there is the whole heat transfer issue 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 the "massive" boring to accomodate a sleeve, requardless of the thickness/thinness.

* We have used thin liners before, only 3/16" 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. 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 and re-used the old pistons after juggling sizes so I
could clean up the piston itself and get the ring grooves cleaned out.

* That's easy if the cylinder is really damaged. 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 with, I thought you would appreciate the wonderful quotation included in the email signature of one of the contributors to the above discussion: "If you can't make it accurate, make it adjustable!"
Take care, enjoy your engines and stay safe.


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