Tech Questions & Answers

Got a question? Try to stump Mark at

Valve Vacillation
Oh Great and powerful Swami of all Scooterdom. Wise One from the oily workbench. I have traveled far through treacherous lands to ask this question. (Actually, it was about fifteen feet to the computer, but I did trip over a cat toy). Why does the Yamaha V Star 1300 need to have the valves checked or adjusted every 4000 miles, while the V Star 950 only needs it every 16000. Please cast your glow of enlightenment upon us.
Ron Rickers
Elk River MN

An excellent question Rickers. Unfortunately, despite that impressive build up, without direct access to Yamaha's engineering staff all I can provide is a semi-educated guess. Valve inspection intervals are dependent on many factors, including cam design; radical cams tend to be hard on the valves so they require more frequent adjustment. The quality of material used for the valves and valve seats matters too. Things like the valve's size and weight, the type of adjusters chosen and even the compression ratio of the engine all play some role in the process. Furthermore, there's a fair amount of field testing that goes into decisions like this. When the reborn Triumph Bonnevilles were first released, valve inspection intervals were scheduled every 6,000 miles. Reports from the field led Triumph to reevaluate the intervals, so they were extended, first to 8,000 miles, and eventually to 12,000. As to why there is such a huge disparity between the 1300 Star and the 950, I can't say, but Yamaha must feel it's necessary, as the need for the more frequent adjustment puts the bike at some maintenance disadvantage compared to its competitors.

Wet or Dry?
I have a '97 Honda Shadow Spirit 1100 and I'm starting to think about my next bike. I like the idea of an engine being liquid-cooled and wonder if you could shed some light on the differences between air-cooled vs. liquid-cooled engines. Should this even be a concern?
Charlie Haase
Redding, CA

Because water is a great noise damper, liquid-cooled engines tend to be mechanically quieter than their air-cooled counterparts and because the coolant can be routed to places where it's needed most (for instance around the exhaust valve pockets), it does enjoy some advantages over an air-cooled engine. Furthermore, because the temperature of the coolant is thermostatically controlled, the temperatures tend to remain more consistent, especially when circumstances, such as being stuck in traffic, prevent the free flow of air over the bike's fins. On the downside, liquid-cooled engines are more costly to build and maintain simply because they employ more parts, and the coolant requires the occasional change.

Most modern air-cooled engines also employ some sort of oil cooler to aid the transfer of heat, are cheaper to build, require less maintenance and have the right "look." Furthermore, they work exceedingly well, which is why they continue to be popular. Bottom line; while liquid-cooled engines do enjoy some technical advantages over their air-cooled counterparts, the air-cooled engine has been around for a very long time, and it's been developed to a very high degree, so I wouldn't pick one bike over another based solely on its cooling medium.

You're going how high?
If you lived in an area where you rode frequently in altitudes from 0 to 8,000 ft., would you prefer NA or injection? Since I am in the market for new wheels, just thought I would seek the opinion of a pro.
Via email

By NA I assume you mean normally aspirated, which is inaccurate, as all current EFI systems are normally aspirated. So I'll assume you really mean carburetor-equipped. The short answer is that while modern Constant Vacuum-style carburetors deal well with changes in altitude, the latest generation of fuel-injected bikes work even better, so if it were my dough, and I were riding under those conditions I'd definitely be looking for something with nozzles and a computer.

Where'd they go?
I'm mystified as to the oil capacity guidelines in my manual. It gives a dry fill capacity of 4.5 liters, but the oil and filter change capacity is 3.8 liters. I know I go by the 3.8 figure to change the oil but I'm wondering what a dry fill is and where does the extra .7 liters go in a dry fill. Is it the same place where my missing socks in the dryer go?
Via e-mail

I'll have to ask my better half where the socks go, but as far as your oil fill goes it's no mystery. When an engine is assembled for first time or after a rebuild, it'll always take a few extra ounces of oil to bring the level up to the "Full Mark." This is because most motorcycle engines, and particularly those built with their clutch and transmission within the same set of crankcases, have lots of little nooks and crannies where oil can hide. Some of them have intentionally designed reservoirs used to lubricate things like cam lobes, or splash oil onto a gear to cool it. Some are just the result of the casting/machining process and are nothing more than spots that trap oil.

In any event, when the oil is changed, some of the old oil remains behind so it adds to the total, hence the need to reduce the amount it takes to fill the sump. When the engine is rebuilt the old stuff gets washed out of all the hidey holes. As they become refilled, the oil level drops slightly, so on the first fill a few extra ounces is required to bring the level to the full mark.

Tech Questions & Answers - Shop Talk