Exotic/Rare Bikes

[Rockburner]

Late response due to being wiped out with covid

Was the oval piston really that innovative? As I remember it they wanted to build a V8 because it's the optimum config for a 4T but the regs in racing limited them to 4 pots so the just merged cylinders to make a v4. Technically difficult yes but based in Honda's obsession with 4T engines its not exactly without precedent it's just making a V8 fit the regs at the time.
It didn't work because the NR500 was no match for 2 strokes and it was never likely to catch on commercially

From what I remember - the main issues were things like piston-rings.

Bit of a bitch to bore and hone anything which is not a circle too. Machining the bores might be OK, but can you imagine honing them? There are plenty of more mundane reasons you'd want to make a (slightly) non circular bore though so the knowledge would have been useful to Honda either way.

VW actually made oval piston diesel engines too, but never put them on sale. Their idea was to "squash" the whole engine up axially so you could fit the capacity of a big engine into the length of a small one.

I'd assume the Wankel rotary had similar issues - the 'chamber' isn't circular either.

[Yorick]

Late response due to being wiped out with covid

Was the oval piston really that innovative? As I remember it they wanted to build a V8 because it's the optimum config for a 4T but the regs in racing limited them to 4 pots so the just merged cylinders to make a v4. Technically difficult yes but based in Honda's obsession with 4T engines its not exactly without precedent it's just making a V8 fit the regs at the time.
It didn't work because the NR500 was no match for 2 strokes and it was never likely to catch on commercially

They wanted 8 valves per cylinder. Sort of merging 2 cylinders.
The hardest part was getting the rings to seal properly.

[Le_Fromage_Grande]

Honda wanted a 4 cylinder engine that worked like an 8 cylinder engine to fit the rules
Yamaha have made 7 and 9 valve per cylinder engines with round pistons.

[Mr. Dazzle]

Companies seem to flit back and forth between 2, 3, 4, 5 etc. valves. VW and Ferrari both also had a long period of making 5v heads, but they've both knocked it on the head (if you'll excuse the pun ) now too AFAIK. Mercedes messed with and sold loads of 3v heads in the 90s/00s.

Kinda tells you what you need to know really, it's a big fat "depends" as to whether it's worth it. At least as far as "normal" engines go, the NR is a very special case.

[Skub]

Somewhere along the line didnt Yamaha admit the gains from extra valves were marginal or have I imagined that?

Yeah,they dropped the 5 valve heads some time ago.

[mangocrazy]

Somewhere along the line didnt Yamaha admit the gains from extra valves were marginal or have I imagined that?

What engines were the 7 & 9 in? I'm only aware of 5 in bikes and race cars (but I haven't kept up with engine development since the end of the 90s)

I think Yamaha persevered with 5v heads for rather longer than they should have. For a while they ran 5V heads in the F1 engines they built for various teams but quietly went back to 4V heads later in the program while still publicly maintaining they were 5V units.

Never really saw the point of 5V heads meself. A marginal increase in valve area offset by significantly more complexity. Pretty sure that most high performance motors these days are 4V.

[Mr. Dazzle]

Never really saw the point of 5V heads meself. A marginal increase in valve area offset by significantly more complexity. Pretty sure that most high performance motors these days are 4V.

I'm guessing you're a huge fan of the VTEC Honda bikes then

Now there is pointless. Works well on cars, so they port across all the BAD bits of it for bikes

[Mr. Dazzle]

Thats exactly what's good about it a car, my wife's old Civic had a reasonably 2 litre like bottom end but then a manic top end. Still one of the best engines I've ever used.

[mangocrazy]

Never really saw the point of 5V heads meself. A marginal increase in valve area offset by significantly more complexity. Pretty sure that most high performance motors these days are 4V.

I'm guessing you're a huge fan of the VTEC Honda bikes then

Now there is pointless. Works well on cars, so they port across all the BAD bits of it for bikes

Hah! One of my least favourite gizmos. Honda basically took away the VFR's USP of gear driven cams, just so they could fit a bastardised version of VTEC that no-one had asked for. I've never ridden one, but most people are not impressed by the step when VTEC kicks in. Then they compounded the error a few years later with the 1200, by going to a SOHC layout (but marketing it as 'Unicam')...

[Mr. Dazzle]

My Dad has had a few VFRs I've ridden and I've done many miles on my old RC36. IME I can best describe the VTEC as meh/pointless. Honestly can't see why Honda did it.

In the Type R cars it's great. There's a definite transition between driving to the shop and "wahhheey! We're off!". My wife's old Type R "on cam" was like a proper little touring car engine. But one which idles at 800rpm and can drive down the high street quietly.

That just didn't come across in the bike at all, like I said I don't really know why they bothered.

[mangocrazy]

I've had 3 VFRs and just love the gear driven cam motor. My first RC24 was bought as something to get me through a 90 mile daily commute from Stafford to Solihull and have fun on at the weekends. I put 80k miles on it in 5 years (no big deal for a car, I know) and the motor still felt like brand new when I traded it in - for an RC36!

[Mr. Dazzle]

I only got ride of mine because my wife inherited a load of bikes and I didn't have space. It's the BMW 3 series of bikes (got one of them too) uncannily brilliant at everything. And people think they're boring because of it

[mangocrazy]

Yeah, agreed. One of my mates who had poo-pooed the VFR when I bought it, rode it after his TZR expired and a bunch of us were going for a ride out in Wales. He loved it and couldn't stop rabbiting on about how good it was... I took mine on track days and 2-up to the south of France and it managed both with aplomb.

[Bigyin]

I saw an NR750 a few years ago at Ludgershall bike night. Us oldies were drooling over it. The kids had no idea

I was allowed access a few years back to a blokes collection of exotic/rare modern bikes he was either keeping as a pension fund or drip feeding onto the market while prices keep high.

He had 3 NR750's i saw and a further couple in another warehouse in Holland. At the time the going rate here was about 70 grand for one of them and he actively seeks them out in Japan to buy when they come up

[Horse]

Mr Google strikes again. Now he's an expert on oval pistons. Well. In the last 5 minutes.

Pssst. Yozzer. You do realise, don't you, that they weren't 'oval'.

And I know that without the aid of Google

[Mr. Dazzle]

Here you go...VW engine with oval pistons, from some time in the late 80s/early 90s. Completely different reason to Honda, the idea is to fit a bigger engine in a smaller engine bay. I guess in the end they just invested in turbos and injection etc.

I remember talking to one of the old boys about this back when I worked 'in engines' proper. That conversation would have been in about 2007 with someone who was about 50-60 at the time...so he'd seen a few things.

I'd lay a pound to a pinch of shit that other manufacturers have at least thought about it. You'd pretty much have to, what if Honda actually pulled it off and fucked off into the distance? As I've been trying to say, this is how OEMs think and work.

[Cousin Jack]

In theory VTEC should be good for bike lots of valve opening at high revs but only open 2 at low revs to keep it tractable

I've always wondered if they're as bad as people crack on or if the people who give them a bad rep don't actually own one

I did 36k miles on one, and I loved it. I imagine it is possible that the VTEC might upset the bike on a racetrack, but on the road it was never a problem and often a positive help. If I had a dream bike it would be a VFR but lighter and with modern fancy bits like cornering ABS.

[mangocrazy]

Here you go...VW engine with oval pistons, from some time in the late 80s/early 90s. Completely different reason to Honda, the idea is to fit a bigger engine in a smaller engine bay. I guess in the end they just invested in turbos and injection etc.

I remember talking to one of the old boys about this back when I worked 'in engines' proper. That conversation would have been in about 2007 with someone who was about 50-60 at the time...so he'd seen a few things.

I'd lay a pound to a pinch of shit that other manufacturers have at least thought about it. You'd pretty much have to, what if Honda actually pulled it off and fucked off into the distance? As I've been trying to say, this is how OEMs think and work.

I see that there are cutouts for 4 valves on the pistons - did VW ever play around with 6 valves, seeing as they had some extra real estate available in the head?

[Mr. Dazzle]

Dunno...this is something I talked about years ago and found a pic of

I know old race cars have used 6 and 7 valve heads as the Cheese says. I would not be at all surprised to learn that Rolls-Royce or someone like that did some weird 13 valve engine or something in 1939. All of the really mad stuff you associate with motorsport has usually been tried in aero engines before WW2.

[JackyJoll]

Four valves per cylinder was popular in the 1920s because they had metallurgy limitations and the smaller valves were more resilient.