Air-cooled vs liquid-cooled.

[FilthyLuka]

The drilling of holes in fins interests me. I would've thought this would reduce heat transfer from the bore/head outwards?

hmm, im thinking the same thing.

Sure it would increase surface area exposed to air, but wont it also make hot spots on the cooling fins where there is less area for heat to be transferred?

Don't think its something i will try any time soon

[Ocean1]

The drilling of holes in fins interests me. I would've thought this would reduce heat transfer from the bore/head outwards?

hmm, im thinking the same thing.

Sure it would increase surface area exposed to air, but wont it also make hot spots on the cooling fins where there is less area for heat to be transferred?

Don't think its something i will try any time soon

Casting technology has moved on since that trick was common. The shape and number of fins used to be more basic and limited than is currently possible. And yes, there's a balance to be got between maximising cross sectional area of the fins to maximise heat transfer and actual surface area in contact with the air to dissipate it.

Still, because the power available from any given engine is ultimately limited by head and upper cylinder cooling it was worth improving that cooling. It was this fact that led Porsche to develop nikasil plated alloy cylinders, without which they would never have got the power they did from an air cooled engine.

That’s also what drove the shotgunning of bike fins. I don’t have pic’s, but the work that went into some of the more extreme examples was rather intricate, including welding in extra fins or extensions and bead blasting the lot to further increase surface area. At one stage I made several heads for a TM125 that looked more like the huge fins Maico used. It worked, but they broke a lot.

Again, if displacement isn't constrained why bother chasing hp/cc? Just make the bangs bigger, more useable and more reliable.

[Coyote]

Lmao, because that's the most reliable engine ever produced

All the issues with the XL250S/250RS motor, but twice the capacity!

It wasn't?!

I'm not sure what truely is the most reliable bike ever, I was told VFR's were and mine is making liars out of those people. I would've thought the XR500 was a pretty solid machine after all the XR rep I've heard before

[Ixion]

Maggots. They're indestructable.

[xwhatsit]

Casting technology has moved on since that trick was common. The shape and number of fins used to be more basic and limited than is currently possible.

That's interesting, I was thinking the other day that my motor has few fins, and relatively small at that, compared to many older 1960s thumpers. Leong's DRZ250 today was similar. The Honda RC166 racebikes had some serious finnage. Close together, too.

It wasn't?!

Haha, not one of the best motors they build. Top-end waaaay under-engineered, camshaft runs in the head. Rocker arms wear and the pivots they swing on mangle the rubber seals that keeps the rocker cover oil-tight. Eat pistons. Not sure if the head cracks like on the 250s, but wouldn't be surprised as it's a similar design, but with even bigger valves (even thinner bit between spark-plug and exhaust valve then). Would've run well `in the day', but longevity not good perhaps.

Maggots. They're indestructable.

Not true. Stick Guzzi tank badges on one and ride it to a Guzzi rally.

BTW: CX500 is water-cooled

[Motu]

Fins can only reach a certain size - the heat transfers from root to tip,and making them longer has diminishing returns as you can't speed up the transfer rate.If you look at bikes from the late '40's on you will see the fins got bigger and bigger,then they went to alloy heads,and the fins started bigger again.If you look at the specs of these bikes you will see the compression ratios increasing to match the increase in cooling area.....and this directly relates to fuel octane rating.As the fuels got better the engines could run higher compression ratios,meaning they ran hotter and needed more cooling.

The Honda singles weren't bullet proof - they suffered horrendous top end wear,camshafts,rockers and cyl heads.The Yamaha XT/TT 500 was a step ahead as there were practically no plain bearings in the engine - even the rocker shafts had needle rollers.The magic cure was superior oils.

[Coyote]

Haha, not one of the best motors they build. Top-end waaaay under-engineered, camshaft runs in the head. Rocker arms wear and the pivots they swing on mangle the rubber seals that keeps the rocker cover oil-tight. Eat pistons. Not sure if the head cracks like on the 250s, but wouldn't be surprised as it's a similar design, but with even bigger valves (even thinner bit between spark-plug and exhaust valve then). Would've run well `in the day', but longevity not good perhaps.

Haha, very interesting. My Dad didn't get to find that out since it got stolen. The insurance company paid him in full, but unfortunatly Honda bumped the prices up so he could only afford a new 250.

He loved that bike and the 250 was a disappointment after the 500. But he was kinda pleased to here that he may have dodged a bullet Didn't hear of any heads cracking.

[Oakie]

All very interesting stuff guys. Thanks. Now another question.
What are the implications for oil changes and type of oil used in an air-cooled vs liquid cooled engine given that there's more heat involved?
Different grade of oil?
More frequent changes?

[avgas]

I never trust those things. Look how many bikes break the speeding laws. Stands to reason some of them will break the physics laws too.

I reckon, i thought i broke them tonight in my hotel in Kyoto. Flushed the toilet and the bloody thing tried to blast me - What the fuck is a Bidet!!!! lol

[avgas]

Maggots. They're indestructable.

You must spread the love before giving more to Ixion........ but well done that man. Didn't CZ's run on maggot power - looked and sounded like it.