Questions & Answers

Got a question? Try to stump Mark at zimmemr@aol.com

A heated subject
Q Do air-cooled engines use different alloys in their construction than water-cooled engines? It would seem logical that certain metals (due to their ability to transfer heat) might be optimum for air-cooling and others for water-cooling.
Thanks,
Richard.
Via e-mail

A An excellent question Richard, and the short, simplistic answer is that yes, in many cases different alloys are used, but not necessarily only for the reason you suggest.

Aluminum alloys, and there are dozens of them, all have slightly different characteristics and while some are more efficient at transferring heat than others, that's not the only consideration an engineer has when he sits down to design a new engine.

For example 356.0 Aluminum is easy to cast and machine, resists corrosion well, and has a low incidence of porosity under heat and pressure. Those characteristics make it ideal for use in water-cooled cylinders and heads.

Now that's not say it can't be used in an air cooled application, it can, and in some circumstances might be. But a better choice for an air-cooled engine with its external fins might be something like 242.0 Aluminum which is a hard and tough general purpose die cast alloy that's very rugged and holds an exterior finish well, which is an important consideration on an engine that may be painted.

Obviously the topic demands a much fuller explanation than I have room for here. But the gist of it is that while air and water-cooled engines may employ different alloys in their construction, they don't necessarily have to, and when they do the choice is based on a number of different factors, other than a particular alloys ability to transfer heat.

Torque Talk
Q In the Air Force, they told us extenders could affect the torque setting ( i.e. more leverage, you had to adjust the amount of torque.) I don't recall the formula for calculating this, probably could have found it on the internet. Have you heard of this, and how important do you consider it?
JS
Via e-mail

A There are three things that you should consider:

First-extending the torque wrench's handle does not affect the torque at the bolt, although because the leverage is increased it does reduce the strain on your arm.

Second-Using a straight extension that positions the wrench directly above the socket doesn't affect the amount of torque applied either, for all of you that doubt that, I'd suggest you reread Newton's third law of motion.

Third-When the torque wrench is extended from the socket hex forward, say by using crowfoot extension or something similar the torque on the bolt is increased, though it's usually by a negligible amount unless the extension is really long and yes, in some cases the increased length is more than enough to screw up your settings.

The math here is straightforward; the actual torque applied to the fastener equals the indicated torque multiplied by the wrench's original length (socket hex to center of the handle) added to the extension length and divided by the original length or ACTUAL = INDICATED x (WRENCH LENGTH + EXT. LENGTH) / WRENCH LENGTH. Or if you're like me and easily bored by the math just go to www.belknaptools.com/extcalc.asp and use their excellent plug and play calculator.

Too young to smoke
Q I have a 2004 Harley XL1200C, which though repeatedly encouraged not to, has started smoking. It's habit seems to increase with its warmth. From a review of your past columns, I have concluded I should get a "leak down" test. What is a leak down test? How much should it cost?
Mark Travis
Via e-mail

A A leak down test is diagnostic procedure that involves pressurizing the cylinder with a specific amount of air and then measuring the percentage of air loss or leak down over a given time. It's a good indication of the top end's condition but only insofar as compression goes. In theory the oil ring could be left out of the engine and you'd still get decent leak down numbers. However a good tech can extrapolate the leak down numbers into a pretty good idea of whether or not your smoking problem is related to a worn out top end. A leak down test generally isn't to expensive, and in fact most shops don't charge for it, assuming they go on to make the repairs.

That being said, an 04 shouldn't really need a top end job unless it's got huge miles on it or has really been hammered, so before you get too carried away make certain that the engine is actually burning oil, as opposed to maybe running a tad rich due to a clogged up air filter or overly rich jetting. If you're convinced that the engine is burning oil, check the easy stuff first, make sure the oil level is correct and that the engine breather is functioning properly, before you shell out dough for a leak down test or top end job that you don't need. In any event a good shop should be able to help you pinpoint the problem with a minimum of fuss.

Spring Thing
QI enjoy reading your articles Motorcycle Cruiser and have a question. I recently purchased an '04 Shadow Sabre 1100. What do you recommend to soften up the front forks? I am thinking of trying lower weight fork oil or should I go with progressive fork springs?
DR
Via e-mail

A Reducing the fork oil viscosity will certainly soften up the front fork, but it also may make it feel mushy, and allow it to rebound too quickly. Since the bike is used and the previous owner may have made changes to the front end I'd recommend first draining and refilling the front forks with correct weight and amount of oil as specified in your manual. If the ride doesn't improve, you can try a lighter viscosity. If that doesn't do the trick, or if you just want to save yourself a few steps, by all means install a set of progressively wound fork springs, and use the spring manufactures recommendations as far as oil goes.