Honda Oval Piston - article from back in the day.
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Oh Moto Guzzi had plenty of success with the V8 alright, but all the manufacturers agreed to step out of motorcycle racing. and they all did...except for MV Augusta, who cleaned up for many years. Honda just didn't want to build a 2 stroke, but finally had to.
My photo - I saw Sammy Miller ride this at Pukekohe.
My photo - I saw Sammy Miller ride this at Pukekohe.
When Honda decides to make it, it wins. Greatest car company ever IMHO. They strive so much.
I rode an NR750 back in the day. Interesting bike that Honda built I think mainly so they could say they did. The NR750 mirrors made it onto the mainstream CBR1100XX, which I owned in later years. Hated the brakes on that bike.
They had to ban everything Moto Guzzi brought to motorcycle racing - like the V8, and the dustbin fairing. It was all getting out of hand and the average rider couldn't buy a bike and ride at championship level with factories having stuff like that. But that's what happened anyway. No chance of going down to the Honda shop and entering the race at Jerez next weekend.
The NR500 was Honda's attempt to make a 'V8' to get around the FIM rules of 4 cylinders max by going with the oval pistons. ie, two pistons "Siamese" together with 2 connecting rods. Pretty unique engine design for sure.
From memory and my late 80s early 90s Car & Driver subscription days, I remember reading about Honda in Formula One Racing and the talk of oval piston & 8 valves per cylinder engines...that never made it to the circuit IIRC. This is when Honda was at the top of their game and way ahead of the competition in racing and in the motorcycle & automobile marketplace.
I believe the oval piston put out a lot of power, but ring sealing was problematic.
Originally Posted By: Inspecktor
I believe the oval piston put out a lot of power, but ring sealing was problematic.
On moving surfaces, separated by seals, the minimum seal length is the best...round pistons have the shortest length for any given volume.
Asides, the long straight seal in itself is a hard ask, and then transitioning it to a half round at the end is not good.
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
I believe the oval piston put out a lot of power, but ring sealing was problematic.
On moving surfaces, separated by seals, the minimum seal length is the best...round pistons have the shortest length for any given volume.
Asides, the long straight seal in itself is a hard ask, and then transitioning it to a half round at the end is not good.
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Originally Posted By: Shannow
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
Originally Posted By: ZeeOSix
Originally Posted By: Shannow
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
They did?
The proportion of RX-7 and RX-8 cars that got warranty engines doesn't gibe with this.
There were good reasons that manufacturers with far greater engineering resources than Mazda, like GM and DB played with this engine back in the seventies and ultimately walked away from it.
Originally Posted By: Shannow
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
They did?
The proportion of RX-7 and RX-8 cars that got warranty engines doesn't gibe with this.
There were good reasons that manufacturers with far greater engineering resources than Mazda, like GM and DB played with this engine back in the seventies and ultimately walked away from it.
Originally Posted By: fdcg27
Originally Posted By: ZeeOSix
Originally Posted By: Shannow
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
They did?
The proportion of RX-7 and RX-8 cars that got warranty engines doesn't gibe with this.
There were good reasons that manufacturers with far greater engineering resources than Mazda, like GM and DB played with this engine back in the seventies and ultimately walked away from it.
Where there warranty issues due to rotor seals, or something else. I've seen 1978 RX-7s with 200K miles on the engine without any problems. The RX-2, 4 & 4 blew rotor seals and burned lots of oil as a result ... RX-7s didn't blow rotor seals (usually tip seals) unless they were boosted pushing huge amounts of boost pressure and weren't tuned right for massive boost.
I owned two RX-7s (1988 & 1995 twin-turbo) and drove them hard ... they never had any engine problems.
Lots of talk in the link below about rotor seal issues on the early engines, and how Mazda was always changing rotor seal design as they developed the Wankel throughout the years. Mazda was smart enough to figure it out ... GM and others weren't.
https://en.wikipedia.org/wiki/Mazda_Wankel_engine
Originally Posted By: ZeeOSix
Originally Posted By: Shannow
Felix Wankel's major efforts were in the field of sealing systems, which were forced upon him by his novel engine design which had huge lengths of sealing area for a given unit of swept volume.
Mazda perfected the Wankel. They had a few issues in the early days with rotor seals in the RX-2, RX-3, RX-4 ... but by the time the RX-7 came out in 1978 they had it all solved.
They did?
The proportion of RX-7 and RX-8 cars that got warranty engines doesn't gibe with this.
There were good reasons that manufacturers with far greater engineering resources than Mazda, like GM and DB played with this engine back in the seventies and ultimately walked away from it.
Where there warranty issues due to rotor seals, or something else. I've seen 1978 RX-7s with 200K miles on the engine without any problems. The RX-2, 4 & 4 blew rotor seals and burned lots of oil as a result ... RX-7s didn't blow rotor seals (usually tip seals) unless they were boosted pushing huge amounts of boost pressure and weren't tuned right for massive boost.
I owned two RX-7s (1988 & 1995 twin-turbo) and drove them hard ... they never had any engine problems.
Lots of talk in the link below about rotor seal issues on the early engines, and how Mazda was always changing rotor seal design as they developed the Wankel throughout the years. Mazda was smart enough to figure it out ... GM and others weren't.
https://en.wikipedia.org/wiki/Mazda_Wankel_engine
How many miles did you put on these Mazdas?
These engines were famous for failing around 100K.
I've never heard of a Mazda Wankel making it to 200K in miles, maybe kilometers.
I have seen RX-7s with coolant black from failed seals allowing engine oil to leak into it.
Guy at work has a 120K RX-8. It's on its second engine, of course.
Are these old girls really that much better than I've seen them to be over the years?
Please tell me that they are, since these are really smooth engines and I'd love to own one as my next daily driver warm weather toy.
I've driven Mazda Wankels and they are incredibly smooth, like no reciprocating piston engine.
These engines were famous for failing around 100K.
I've never heard of a Mazda Wankel making it to 200K in miles, maybe kilometers.
I have seen RX-7s with coolant black from failed seals allowing engine oil to leak into it.
Guy at work has a 120K RX-8. It's on its second engine, of course.
Are these old girls really that much better than I've seen them to be over the years?
Please tell me that they are, since these are really smooth engines and I'd love to own one as my next daily driver warm weather toy.
I've driven Mazda Wankels and they are incredibly smooth, like no reciprocating piston engine.
I think a lot of the RX-7s that had early engine failure are either heavily modified and/or not maintained very well. Lots of guys heavily modify the rotary engine, and if not done right they won't live very long.
Here's a thread that shows many have tons of miles on them, and I'd bet most are in stock or near stock form and well maintained.
https://www.rx7club.com/2nd-generation-non-technical-pictures-198/high-mileage-fcs-991905/
Here's a thread that shows many have tons of miles on them, and I'd bet most are in stock or near stock form and well maintained.
https://www.rx7club.com/2nd-generation-non-technical-pictures-198/high-mileage-fcs-991905/
Had a 1980 RX7 that was dead reliable that I ran hard for 150K miles. It didn't even burn oil. My neighbor (a notorious early adopter) had the first Mazda in town and a REPU and both gave him fits. The 12A in the RX7 had a good reputation, I believe. But it didn't make much power and it didn't get good fuel economy for its size. But it was dead reliable, and easily modified. And they are now cheap as chips.
Originally Posted By: Shannow
Asides, the long straight seal in itself is a hard ask, and then transitioning it to a half round at the end is not good.
What's interesting is, the production NR750 that Honda built after the racebikes didn't have the long straight sides, they were instead slightly curved so that the pistons were slightly elliptical. Maybe that made ring sealing somewhat easier?
Imagine being that engineer at Honda who asked 'guys, do cylinders really need to be round?'
Thanks for the scans.
Asides, the long straight seal in itself is a hard ask, and then transitioning it to a half round at the end is not good.
What's interesting is, the production NR750 that Honda built after the racebikes didn't have the long straight sides, they were instead slightly curved so that the pistons were slightly elliptical. Maybe that made ring sealing somewhat easier?
Imagine being that engineer at Honda who asked 'guys, do cylinders really need to be round?'
Thanks for the scans.
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