July issue of ATV-Action: "We might even see something as wild as an eight-valve, twin sparkplug, oval piston 440cc single. The design allows a motor to breath like a twin, while retaining some of the simplicity, narrowness and power characteristics of a single". There is a picture of some engine parts, so at least a prototype must exist.

What do you think??? Trouble is, engines usually spend at least 5 years in a dirt bike, before we ever see them in a quad!!

 

You mean like a Honda Hemi?

 

Honda has had the oval piston in a racing superbike a few years back, so they know it works.

 

Sounds like ATV Action had some page space to fill... Pretty wild speculation that Honda would bother with that setup - the superbike that had that configuration was insanely expensive and cutting edge - Honda knows the bulk of the quad market won't support cutting edge performance (and more importantly the maintenance it requires).

If they come out with a new quad in September, it will likely be a CRF based engine that has been detuned to the point that it will survive the average quad rider's maintenance schedule...

 

I think the concept of the oval piston is to reduce surface area, and therefore friction. That configuration gives you the most bore area, for the least amount of metal going up and down in the cylinder. I don't see why maintenance would be any different than a round cylinder.

What worries me about the CRF and YFZ 450 is their "mini skirt" pistons. Here we are reducing friction by shortening the skirt on the piston. From the pictures I have seen, the YZ piston is wafer thin.

 

I'd rather replace 10 short skirt pistons than try to find one machine shop to bore or hone an oval cylinder - or heck, replace one oval piston - $$$$. It will never happen - not in a quad...

The jist of my message was that if Honda were to go the Oval piston route, they would not waste their time with a low performance engine (hence the term "Cutting Edge"). This would mean increased maintenance. The "maintenance" time would increase 10 fold when you had to find machine shops, parts, aftermarket support, etc etc etc. for this engine. Again, it will never happen - the magazine had page space to fill and one of the editors went "Hey guys, remember that $50,000 oval piston Honda NR750 superbike engine? Let's stir the pot, we've got nothing else!"..

Honda's more likely to install a small block chevrolet in a quad than a NR750 based engine.

 

The NSR bike was a short production run, only to be able to race that design in Grand Prix bikes.

During WW2, Honda made all the piston rings for the Japanese "Zero" figters (aircraft). There is SERIOUS technology involved in getting an oval-shaped piston to seal properly in the bore, as 1986atc250r implies. Honda mostly built this motor as a display of their technical prowess - they were able to make an oval-shaped piston seal up enough to make a small production run. I believe they bought all the NSRs back from their original owners a few years ago - as is usually the case with short-run machines. They can't support them with OEM parts, so they buy the bikes back frmo the original owners, or tell them "good luck" maintaining a bike with no available OEM parts to keep it running.

I wouldn't expcet to see oval piston technology ever - fuel cells would take over long before techniques for mating oval pistons to oval cylinder bores would become mainstream.

 

A CNC machine shouldn't have any trouble with an oval bore. The ring problem makes some sense though.