Thursday, 5 July 2012

Bores

    When you own an engine of more than a couple of decades age, you are not merely its owner but its custodian. You feel its every ache and pain, you know it intimately from crankshaft to valve spring, and its every revolution comes with a frisson of worry that something in its running might be inexorably destroying it.
    I own more than one machine with a geriatric motor. The Wreck and the motorcycle have 89 years on the road between them, one has an engine made of soft and easily worn cast iron while the other has a highly stressed engine made from Japanese alloy with a cam chain tensioner inexplicably made from metal with wear properties similar to chocolate.
    In the season when the roads are not covered with salt, my engines worry me. Because I use them, and the worry comes from the thought that each mile might be their last. The number of ways in which a geriatric engine can expire are many.
    Which brings me to the subject of this post. The Wreck's engine is weighing heavily on my mind at the moment. With its new radiator it's now happily hanging on to all its coolant, but I'm acutely aware that previously it had overheated a few times.
    You're probably familiar with the basic layout of an engine. A piston is moved up and down a cylinder by the petrol being ignited above it and the crankshaft below it. The piston is made of aluminium and in the case of the Wreck the cylinder is made of cast iron. The seal between piston and cylinder is made by hardened steel piston rings.
    Nowadays, engines are pretty reliable. Advanced metalurgy means the cylinders are much stronger, and synthetic lubricants mean that engine wear has been reduced to a shadow of its former self. But back when they made the Wreck they hadn't perfected those materials, so the Wreck's engine just has cast iron bores and good old-fashioned multigrade oil. So Wreck engines wear pretty quickly at the best of times, and overheating accelerates that wear.
    Years ago I had an Austin engine that I thought I'd done pretty well to get to a hundred thousand miles without a rebuild. When I removed the cylinder head and inspected the cylinders, their bores were so worn you could feel the point at the end of their travel with your fingernail, the pistons were slapping around in the bores held only by carbon deposits from burnt oil. Funnily enough there is an upside to an engine like that, they may be about to expire but in that state they can have a little bit extra power because the wear gives them extra capacity. Stories are legion in kit car racing circles of races won by cars sporting hundred thousand mile engines from family cars against competition with expensive hand-built race engines.
    But the Wreck has a much lower mileage engine than that. What scares me isn't simple wear like the Austin engine, but that I might have damaged a piston ring. If the wear is uniform you simply have the bore honed out to a new size and fit larger pistons, but if you've broken a ring there is always the worry that it will have scored a groove in the bore that simple honing can't remove. So your engine becomes scrap.
    As you might imagine, the supply of 50-year-old replacement Wreck engines is meagre. So I'll be nervously testing the compression on the Wreck engine, and if it becomes necessary, lifting the cylinder had to inspect its bores. Not something I fancy, the nuts and bolts holding the exhaust manifold are notorious for seizing up and I don't want to end up with a broken stud to complicate my reassembly.
     So there you go, my bores are worrying me. I never want to see another car again.

6 comments:

  1. I no longer wish to break a fingernail or get dirty grease under it except in the case of a dire emergency, seized studs are only going to give suddenly and have you remove the skin on for knuckles! All badges of honour down the pub for blokes...

    Endoscope is what you need to find and poke it down the plug holes, check the gaps while you are at it...

    My old wreck was passed on to someone who had the money and patience to cosset her and forgive her for any skinned knuckles incurred. Mine was also a triumph of engineering, I shall send you a snap.

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  2. Jenny, the simple answer is to buy a few more vintage cars. One goes wrong, drive the other .

    Also the sheer multitude of problems faced by having near double digit ol' wrecks is that soon or later you reach that zen state of how to stop worrying and love the grease under ones nails.

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  3. Back in the day of my old Singer, I went to the trouble of buying a spare engine, rebuilt it at leisure, fitted it and then set about the original, that had the added complication of alli head and cast iron block, separating the two became such a complicated job that the rest seemed easy.

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  4. Morning all,
    It's a long time since I rebuilt an engine myself. Silly really, that one was an Austin A series and the scrapyards were full of them at the time. Wreck engines by contrast are getting rather rare now.
    Owning many Wrecks? I've been there. And while it was fun, I learned that you can spread it all a little thinly.
    I haven't had a chance to look at the Wreck yet. It was running very well when I bought it home last week though so maybe it's not as bad as I worried. I hadn't thought of an endoscope, I may know someone who can help.

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  5. Can you use a heavier weight oil?

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  6. It's not so much a heavier weight as superior lubricating properties at higher temperatures that make modern synthetic oils attractive. And I am told that the tolerances in newer engines are different because of the better oils, and an older engine may even require the old-style oils for that reason.

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