[nicholastanguma]

Four valve heads on an air cooled engine often have a bad habit of overheating to the point of cracking or melting (just ask Porsche and Harley-Davidson, for instance) but the Japanese have been using 4 valve heads on both their low and high performance air cooled thumpers since the 70s.  What gives, why don't these heads suffer the overheating problems usually associated with air cooling and multiple valve heads?

[Richard230]

Four valve heads on an air cooled engine often have a bad habit of overheating to the point of cracking or melting (just ask Porsche and Harley-Davidson, for instance) but the Japanese have been using 4 valve heads on both their low and high performance air cooled thumpers since the 70s.  What gives, why don't these heads suffer the overheating problems usually associated with air cooling and multiple valve heads?

Better valve and valve seat materials that were carefully selected and researched before the vehicle is sold to their customers?  And also better quality control. But I am not sure if this would still be the case if Japanese motorcycle manufacturers had not transitioned to liquid cooling for most of their current models - no thanks to the latest and constantly evolving emission regulations.

[AzCal Retred]

Maybe the decisions tend to be engineering driven vs. by marketing or sales? Look up the R&D facilities for Honda, Yamaha, Kawasaki, Suzuki and report back!   

[Arschloch]

Maybe the decisions tend to be engineering driven vs. by marketing or sales? Look up the R&D facilities for Honda, Yamaha, Kawasaki, Suzuki and report back! 

Engineering alone doesn't sell a product, however I don't want to know how many engineering heads did roll in the EU with the decision to go all electric by 2030 or so. Now I've red estimates that by 2030 about 80% of passenger cars sold will be electric.
Toyota manufacturers roundabout 10 million cars a year or so? Does it make you conclude the 80% of the 10 million are going to be replaced by electric cars? Or do they estimate the sales of ICE vehicles to drop to such levels that the current factory output of EV's will be 80% of the total sales? I suspect the later.

[AzCal Retred]

The question was why do Japanese 4-valve heads not develop cracking between the ports, not some random conceptual leap to EV marketing & sales. That's been beat to death in "E-Bike Developments".
KTM & Husqvarna don't seem to have 4-valve head cracking issues either, and I've not heard of such issues with the Royal Enfield 650 twin. Maybe those companies tend to let their Engineers do the engineering. Every discipline has it's part to play, eh?

[Arschloch]

I've not heard of those issues either, maybe a 1980ies issue?

[gizzo]

Honda XR250 RE & RF models were terrible for heads cracking between valve seats and plug hole. They'd run if you tow started but you couldn't get enough compression to kick start. We had a guy in the city we'd regularly send heads for welding. Brilliant bike otherwise though.
The models after the RF had smaller valves and zero cracking.

[Karl Fenn]

Well thankfully l have never had that issue, but now everything is moving towards electric there will be less development regarding petrol engines especially as their destiny is to become obsolute which now seems to be moving at pace.

[Richard230]

Well thankfully l have never had that issue, but now everything is moving towards electric there will be less development regarding petrol engines especially as their destiny is to become obsolute which now seems to be moving at pace.

It seems to me that what is driving petrol engine development right now is the need to meet the latest (and constantly evolving) government emission regulations.

[AzCal Retred]

Propane doesn't have emissions requirements in California, so there's always that. A sidehack could hold a 30 gallon bottle easily, the fuel is savagely detonation resistant, maybe a perfect match for a 612 kit at 12:1? You'd just need a gorilla to kick it over... 

https://www.youtube.com/watch?v=Ps2KQITVqPU

https://www.youtube.com/watch?v=DBvQmJ34mRQ

[Arschloch]

It seems to me that what is driving petrol engine development right now is the need to meet the latest (and constantly evolving) government emission regulations.

That's been the driver on the surface for a very long time. Underneath the surface it's material science, tribology and design towards ever greater variability which automatically leads to increase in efficiency and reduction of emissions. At times the technology plays catch up with the regulations though like we have seen in the recent years. New experience for me atleast since i was naive enough to believe the regulatory body would unlikely mandate something that's not market ready. 

[Richard230]

When electric vehicles have finally taken over the world, that will be the end of ever being able to smell burnt bean oil exhaust. Which generated another thought: Why hasn't someone marketed bacon grease top oil? Now that might be something that would sell like hotcakes, or at least bacon and eggs.