Unicam??

[KXMike]

I was looking at a honda crf250r and was wondering why they have a unicam. i know what a unicam is it has one cam but what are the benefits of this from dual overhead cams like on a yamaha or kawasaki? thanks

[skipn8r]

I don't know all the benefits, but I'll guess at a couple:

1) Reduced rotational mass. Reducing engine rotational mass reduces the gyroscopic effect of the engine. The gyroscopic effect basically resists turning and makes handling more difficult. A Unicam engine has a shorter cam chain (significant rotational mass) and only one rotating camshaft. There is the reciprocating mass of the exhaust rocker arm, but that won't affect handling like the rotational mass.

2) Reduced engine weight. I haven't weighed the two (I should next time I'm in there), but the rocker arm seems lighter than the camshaft to me, so the overall engine weight could be less with the Unicam. This will reduce overall engine weight, lower the bike center of gravity and improve handling.

[monkeymotocross]

it just it good

[JGlaze]

It keeps a lower center of gravity.

[NE14MX]

Also cheaper to replace and easier to assemble the top end, smaller head (weight), allows for steeper included valve angle by allowing valves to be closer together (I think this allows a straighter path for the fuel air mixture into the cylinder though I'm no expert)

[a_gunslinger]

.... Reduced rotational mass. Reducing engine rotational mass reduces the gyroscopic effect of the engine. The gyroscopic effect basically resists turning and makes handling more difficult. A Unicam engine has a shorter cam chain (significant rotational mass) and only one rotating camshaft. There is the reciprocating mass of the exhaust rocker arm, but that won't affect handling like the rotational mass.

skipn8r

I love it when you talk like that..... gyroscopic

[redrider144]

skipn8r is right of course.....

I'll add to his list a more compact head

[Grog]

less moving parts

[Honda0001]

To save space in the valve train & easier valve clearance adjustment on exhaust valves...

[skipn8r]

I love it when you talk like that.....

Somehow, I feel like I should hide this comment from my wife .

[a_gunslinger]

Somehow, I feel like I should hide this comment from my wife .

Maybe not.... have you spoken like that to her? She might let you play with her ratchets...

[The Storm]

I would think that the less unicam would have less overall inertia, moving parts, and weight, which would make it easier for the bike to handle higher RPM's.

[KXMike]

so is the unicam the reason why the crf250r are not as reliable valve wise?

[novaman64]

No...... combo of valves, seets and springs. I think majority of the prob is the seets though.

[monkeymotocross]

there is no PROBLEMS!(knock on wood)

[batilzown]

another advantage ova the dual is that the valves on the uni are slanted more then what can be done on a dual. It creats better flow and mo power

[crf-f crf-r trx cbr]

thats what makes hondas so much better-dont u know that?

[xXHondaOwnsXx]

I don't know all the benefits, but I'll guess at a couple:

1) Reduced rotational mass. Reducing engine rotational mass reduces the gyroscopic effect of the engine. The gyroscopic effect basically resists turning and makes handling more difficult. A Unicam engine has a shorter cam chain (significant rotational mass) and only one rotating camshaft. There is the reciprocating mass of the exhaust rocker arm, but that won't affect handling like the rotational mass.

2) Reduced engine weight. I haven't weighed the two (I should next time I'm in there), but the rocker arm seems lighter than the camshaft to me, so the overall engine weight could be less with the Unicam. This will reduce overall engine weight, lower the bike center of gravity and improve handling.

I totally agree with you. Also a smaller cam chain saves weight too.

so is the unicam the reason why the crf250r are not as reliable valve wise?

No, some of the Honda's have valve problems because of the soft valve seats and the coating on the valves. I don't get why everyone is giving them such a bad name. Don't ride on the rev limiter and keep your engine clean, your valves should last a long time.

Read this, it will tell you about all the advantages of the unicam.

http://www.honda.ca/MotorcycleEng/Technical/FlashTech.htm

[skipn8r]

Read this, it will tell you about all the advantages of the unicam.

http://www.honda.ca/MotorcycleEng/Technical/FlashTech.htm

That's a cool link!!