Five Valve Head

I i'm looking for a history lession. Did Yamaha start with four or five valve heads?

What years were what?

Yes i'm referring to the YZF450

Thanks

All YZF's and WRF's except the new WR250R and WR250X have always been 5 valve. Up until the last year or so, so were the R-1 and R-6 sport bikes. The design debuted in 1984 with the Genesis engine, used in the FZ750 4 cyl.

Thanks

Gray- Did Yamaha use Ti valves in the street bikes? or was the 01 YZF the first for Ti?

Gray- Did Yamaha use Ti valves in the street bikes? or was the 01 YZF the first for Ti?

I know the later 5-valve R1's used the exact same valves as the YZ250F. I'm not sure how long before that Yamaha was using titanium valves though.

The R1 and R6 had them for several years. Currently, both have gone back to 4 valve configurations, but they are still running Ti valves. Without looking, I'd guess that Ti valves were first used by Yamaha in '01, when they showed up in the YZF's, but I could be wrong about that.

why are they going back to 4 valves?

The most obvious reason would be simplicity and reduced expense of manufacture. The intake ports on the sport bikes enter the head at different angles than the MX'ers, but if it can be correlated at all, the 4 valve head on the CRF is much easier to get big power and flow out of than the YZF head.

if it can be correlated at all, the 4 valve head on the CRF is much easier to get big power and flow out of than the YZF head.

Any particular reason for that? Something about airflow being better with 4 than 5 valves? I've got no idea about the dynamics of engine airflow, so it would be good to know.

I know the later 5-valve R1's used the exact same valves as the YZ250F. I'm not sure how long before that Yamaha was using titanium valves though.

Interesting KJ... Boy that would be expensive to replace all the valves on an R1, wouldn't it?... lol.

Without looking, I'd guess that Ti valves were first used by Yamaha in '01, when they showed up in the YZF's, but I could be wrong about that.

I'm guessing Yamaha was the first manufacture to use Ti valves in anything with 2 wheels?

Any particular reason for that? Something about airflow being better with 4 than 5 valves? I've got no idea about the dynamics of engine airflow, so it would be good to know.

Here's my educated guess:

Using 3 intake valves is an advantage and disadvantage. If you take the circumference of the valves and multiply it by the valve lift, you can achieve the same value with three small intake valves as two larger exhaust valves. This number is the area that air can flow through when the valve is open. If you can flow the same amount of air with smaller valves then it is a good thing since smaller valves weigh less, and can change directioin easier. However, there are downsides. One being now you have an extra valve spring sucking power out of the engine. It takes power to compress the extra spring, it is only a small amount, but it is there. The bigger problem is with air flow itself. When air flows over a surface it creates what is called a boundary layer. The air directly in contact with the surface does not move, and the air just above that drags on the still air. As you move away from the surface the speed of the air increases back to normal. When you split the intake into two ports, there are two "pipe" walls to cause this drag (basically) on the air. When you split the intake into three ports you now have three pipes, and thus it becomes harder to make up for the boundary layer effects.

I'm sure there are other factors that go into it, these are just some things that come to my mind.

Interesting KJ... Boy that would be expensive to replace all the valves on an R1, wouldn't it?... lol.

Yeah, you're not kidding. Maybe that's why Yamaha got titanium valves right to start with. When I discovered that they were the same part number I priced up valves for an R1 right away hoping they would be listed as cheaper than a 250F. My hope was that they would feel bad for an R1 owner that needs to replace valves and so they would sell them for a little less. I was wrong, they are the same price :)

I remember when the first 5 valve Yamaha was introduced. The 1985 FZ 750 was the bike we all saved for. I dont imagine them ever thinking that technology would make it to the dirt bike side of things.

I remember when the first 5 valve Yamaha was introduced. The 1985 FZ 750 was the bike we all saved for. I dont imagine them ever thinking that technology would make it to the dirt bike side of things.

I was 6 when that came out. :)

The FZ was called a Fazer wasn't it?

I was 6 when that came out. :)

The FZ was called a Fazer wasn't it?

Not sure abotu the "Fazer" name. I sort of remember that coming later. It was cool reading abotu the "revolutionary" yz 400 in 98 with the 5 valve head. As cool as the bike was, it looked a LOT like that original 1985 head.

It would have been THE bike. Suzuki stopped that because they decided to drop kick about 150 lbs of weight from the streetbikes and called them GSXR's.

Interesting KJ... Boy that would be expensive to replace all the valves on an R1, wouldn't it?... lol.
Can you imagine? $80 x 12 + $90 x 8 ? Do the math.
Any particular reason for that? Something about airflow being better with 4 than 5 valves? I've got no idea about the dynamics of engine airflow, so it would be good to know.
I think so. The triple branched intake port presents some very different and complex conditions as far as airflow is concerned. The heads are tricky to work with.

http://www.thumpertalk.com/forum/showthread.php?t=741883

Can you imagine? $80 x 12 + $90 x 8 ? Do the math.

Ouch... If you needed valves, it would be best just to trade it in....

All the comment about the yz's 5 valve engine and know one has mention the awesome reliability, I owned A 2000 yz426 that never had one engine problem or needed a valve adjustment sold it in 2008.Now I have a newer yz450 and love it.

ya my bike have over 120 and valves never moved.

All the comment about the yz's 5 valve engine and know one has mention the awesome reliability, I owned A 2000 yz426 that never had one engine problem or needed a valve adjustment sold it in 2008.Now I have a newer yz450 and love it.

That's because there is no need to mention their reliability, everyone here already knows about it. As said before, the R1 used the same exact valves as the YZ250F for years, and how many of those do you see needing new valves...

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