Service

SERVICE

The Iceman rideth

Paul Dean

As a Massachusetts resident, I like to start riding as early as possible in the year, and ride as long as possible into the winter. This forces me to ride when the mercury dips to some very low levels. The temperature gauge on my 1992 Kawasaki ZX-6 tends to stay way down in the lower ranges and doesn’t seem to increase much during my short rides to and from work every day. To boost my engine temperature, I mask the radiator with cardboard so only just enough air cools the engine, but it does run hot enough to kick on the fan. I am wondering if this practice is an okay thing to do. Will I cause engine damage or should I even be worrying about this? Jim Gosselin

Northbridge, Massachusetts

First, the basics. Liquid-cooled engines are equipped with thermostats for two reasons: 1) to help the engine warm up more quickly; 2) to prevent the engine from operating at too low a

temperature. Thermostats come in different ratings that determine the temperature at which they allow coolant to flow from the source of the heat (the engine) into the cooling device (the radiator). A thermostat of any giv-

en rating is chosen by a bike’s manufacturer because it regulates the minimum temperature at which the engine will operate acceptably.

Now, let’s establish need. If your ZX-6’s cooling system is still stock, it > is fitted with a thermostat that opens when the coolant temperature reaches approximately 180 degrees Fahrenheit. If the temperature drops below 180, the thermostat closes, which then causes the temperature to rise, which in turn causes the thermostat to open, and so on and so forth. The engine therefore can’t run any cooler than 180 degrees once the bike has been ridden long enough for the thermostat to open. And since the bike’s manufacturer has determined that 180 degrees is an acceptable operating temperature, there’s no real need to put cardboard in front of the radiator. The temperature gauge on a frigid day may have a significantly lower reading than it does on a hot day, but that doesn’t mean there ’s a problem; it only means the engine is running cooler.

Then there ’s the matter of warm-up time. For the most part, putting cardboard in front of the radiator does not help an engine reach operating temperature any more quickly, because coolant cannot circulate through the radiator until the thermostat opens. So, the only good reason for blocking off part of your radiator would be if the engine needs to run hotter than 180 degrees to carbúrete properly.

If that’s the case with your ZX-6, partially obstructing the radiator will do no harm, so long as you don’t allow the engine to get too hot. The fact that the fan comes on while you ’re riding in very cold weather indicates that you have too much cardboard blocking the radiator.

Even if you use a smaller amount of radiator blockage, be careful to keep a close eye on the temperature gauge during high-load, high-rpm situations in which increased engine heat is generated—things like climbing a long, steep upgrade at high speed or with a heavy load, or blasting along a backroad at full-throttle, race-like speeds and engine rpm. Under these kinds of circumstances, the engine could overheat and suffer serious damage if you didn’t happen to notice the rise in temperature until it was too late.

Building a Smoothster

I am converting a 1995 XLH Sportster 883 to a 1200. I intend to use a Wiseco 883-to-1200 overbore kit. Other than the obvious cylinder-boring requirements, are there any other changes or pitfalls (such as heads, valves, intake, exhaust, etc.) I should make or avoid? My goal at this point is to end up with the same level of performance as a stock XLH 1200.

Robert B. Marquis Romulus, Michigan

You have chosen well: The Wiseco kit in question makes for a very nice conversion-much more so, in fact, than installing original-equipment 1200 Sportster pistons in an 883. The stock 1200 pistons are noticeably heavier than their 883 equivalents; consequently, even though the crankshafts and connecting rods in both engines are the same pieces, the factory uses a different balance factor on the 1200 than the 883. So, if you put stock 1200 pistons in an 883, the converted engine will vibrate more than a stock 1200.

On the other hand, the pistons in the Wiseco 1200 kit are about the same weight as the 883 pistons, which means the stock 883 balance factor is virtually spot-on. Indeed, some people who have installed Wiseco 1200 kits in 883s insist that their engines vibrate noticeably less than stock 1200s.

One thing you should check closely, though, is the compression ratio. Any time you increase the swept volume of a cylinder (a fancy term for the cylinder’s displacement) without proportionately increasing the volume of the combustion chamber, the compression ratio will also increase. To compensate, the Wiseco 1200 pistons use a dished-out crown that effectively increases total combustion-chamber volume so the compression ratio doesn’t soar way up into the detonation zone.

I know some engine builders who have checked the actual compression ratio after installing one of these Wiseco kits, however, and they report that the compression ratio ends up being a little too high for their liking, somewhere in the area of 9.75:1 to 10.0:1; much better is to keep it down in the 9.0:1 to 9.25:1 range. That prevents detonation and precludes the need always to use and find gasoline of the highest possible octane rating.

Checking the compression ratiousing a procedure called “cc-ing ” the engine-is not something the average person can do or should even attempt. Contact a reputable engine builder in your area and talk to him about having this service performed on your 883 ’s top end. E3