GS850...how concerned should I be of overheating it in traffic?

[tkent02]

Exactly. Singles have inherently better airflow; a BMW twin is two singles from an airflow POV. The nikasil cylinder is another advantage that atv's are going to. Suzuki's SCEM is an example. Barely moving is a whole lot better than stopped. How hot it is doesn't matter so much because the air next to the metal gets hot fast even on a cool day. You can't get rid of the heat without getting rid of the air.

Just curious how nikasil helps the rings... Does the whole cylinder stay cooler for some reason?

[John Park]

Just curious how nikasil helps the rings... Does the whole cylinder stay cooler for some reason?

Liner less aluminum cylinders are the next step up from steel sleeved aluminum which is a step above cast steel. The heat sink effect goes directly to the cylinder surface - minus a few thou of silicon carbide and nickel. You also aren't trusting the conductivity between the liner and the finned casting, which is a bit variable. The outer fin temperature wouldn't necessarily be much cooler, but the gradient up to the cylinder wall would be less steep. IOW, the heat transfers a lot more efficiently.

The big problem with nikasil is that it can be susceptible to corrosion from sulfur in the fuel. That's pretty much gone in the US, but in Mexico you could smell the sulphur stink from the 82 octane regular.

I'm a bit wary of reasons for the rings getting hot enough to lose their spring. In my theory of things, the rings cool out the ring lands, which means the pistons would have to get pretty close to melting. There's more surface area that way than out the faces. But they're getting hot through contact with the cylinder wall, so it's maybe pretty much a factor of cylinder temperature.

I'm in favour of blipping the throttle every half minute of so just to throw some different oil at the cylinder walls and piston; not much extra heat and some fresh liquid. The plain bearing motors have a bit of an advantage in that they have a spray jet on the rod that shoots oil at the piston, but then have - except for the 2 valve twins - rather poor head finning.

I remember taking apart a tired Honda 305 and things looked pretty usable except that the rings were slack. A customer picked up the cylinder block from the bench and when he turned it over the liners fell on the floor. I think the liners expanded so much they stretched the block. Metallurgy got better after about 1970 but there's still a limit.

[bobgroger]

The BMW 4.0 V8 motors had Nikasil cylinders at the exact time sulfur reached its peak. It was a very expensive problem. Porsche used the same alloy, no problems, maybe Porsche owners didn't buy regular at the KwickyMart. http://www.bimmerforums.com/forum/sh...Nikasil-recall.

Then again, remember the Chevy Vega with hypereutectic silicon infused cylinders? Very rare to get 40k out of one. Sulfur was removed from US fuel around 2000 so if they survived they are still good

[John Park]

The BMW 4.0 V8 motors had Nikasil cylinders at the exact time sulfur reached its peak. It was a very expensive problem. Porsche used the same alloy, no problems, maybe Porsche owners didn't buy regular at the KwickyMart. http://www.bimmerforums.com/forum/sh...Nikasil-recall.

Then again, remember the Chevy Vega with hypereutectic silicon infused cylinders? Very rare to get 40k out of one. Sulfur was removed from US fuel around 2000 so if they survived they are still good

The Porsche was air cooled and didn't have the same acid buildup in the oil due to higher oil temps, or so I've read. Moto Guzzi has used it for ages, and the Porsche cylinders were supposedly made in their facility. Jaguar had so much trouble they went back to liners. Most dirt bike motors are small oil capacity [ read marginal] and rarely have any condensation buildup to worry about. Doesn't seem to be a problem and the ring/cylinder longevity appears to be excellent.

[Chaz]

Interesting thread. I hadn't heard of sulfur being a problem with the nikasil cylinders before (admittedly hadn't looked into it).