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360 vs 180 engine

This is a discussion on 360 vs 180 engine within the Technical forums, part of the Caferacer.net Forums category; On a twin if the pistons go up and down the same time is that a 180 or 360 engine? Champ...

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    360 vs 180 engine

    On a twin if the pistons go up and down the same time is that a 180 or 360 engine?

    Champ

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    Moderator imslow's Avatar
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    depends


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    Moderator joe c's Avatar
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    i thought it was a 360 like 95% of the time, only unless its a twingle.

    jc






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    Moderator jbranson's Avatar
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    It's almost always a 360.
    But yeah...like both of them dudes say....almost.

    360 means that each cylinder fires 360 degrees of rotation from the previous cylinder. Technically all you'd have to do to make them both fire at the same time would be to re-grind the camshaft. Assuming it was a four stroke.
    JohnnyB


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    Moderator joe c's Avatar
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    if they both go up and down at the same time, its a 360. (triumphs and early type1 only honda twins i think right?) I could have that all backwards though. at least i was told that the type1 hondas were 360 cranks. i have yet to actually look to see on the 2 i have still together.

    if one goes, then the other, its a 180. so each cyl would fire at 180°. if they both go up and down, they still fire at 180° right?? or youd have like a kawa/duc big bang motor. so does it relate to cam timing, or crank config? i always thought crank figuration. since you can vary cam timing and valve overlap.

    you could also just wire the ig to fire both sides, but youd have the cam timing all out of whack. itd be interesting to hear a twin with the correct timing on one cyl, then the 180° out on the other. triples is where it gets real weird. and v-twins. im sure the v5's of gp have some really weird crank configurations if you looked at it from a classic point of view.

    j








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    Senior Member Judeyramone's Avatar
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    I concur, re: Triumph twins. Anyway, that's how it was explained to me by engineer/mechanic pal-o-mine, years ago rebuilding top end on my Bonneville.

    Didn't know any Honda twins were 360, tho. I've got several 350 motors & watching the pistons, I always figured 180, which I assumed would run a bit smoother than the Triumph. However, I just picked up a '68/69 type-1 motor, which I've heard has a slightly hotter cam (is this true?). It has "Type-1" stamped into the points cover. If it's a 360 degree crank, does that mean it's going to sound more Triumph-y? That would be sweet.


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    Senior Member mikeo's Avatar
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    I think the only Honda bigger twins that were 360 crank are the 305's designated as "CP". These were the police specials. Joe, I think you have one. But I think all of the 350's were 180 cranks (I could be wrong but I wouldn't bet on it).

    BTW I rode the Triumph to work today. Its going to get up to 75 by mid day. It hasn't rained in 50 some odd days. I don't even really have any rain gear out here.

    Mike O.


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    Moderator jbranson's Avatar
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    All Honda 160's, 175's, and CB200 are 360 degree engines. Both pistons go up and down at the same time. However they alternate firing. Left side goes to TDC (compression)..fires....crank rotates one time...right side is at TDC (compression)...fires....crank rotates one time...left side is at TDC (compression).. fires.....etc.

    Don't confuse "firing" with ignition....these bikes can use a one dual outlet coil because you can send spark to both cylinders at the same time...only one is at TDC on the compression stroke...so only one fires. A 360 degree twin has combustion every rotation of the crank...that's why they sound like two strokes at 12,000 rpm.

    I call these engines "360 Engines" instead of 360 degree cranks...because...with the SAME crank and a different cam you could combust both cylinders at the same time if you wanted....which would be either a 0 degree engine or a 720 degree engine.

    Probably the safest way to discuss it is to talk about crankshaft offset....how many degrees one crank journal is offset from the other....if they are on opposite sides of the crank....a 180 degree. If they are on the same side....0 degree or 360 degree....depending on the camshaft.

    Can get real complex with more than two cylinders.

    JohnnyB


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    Senior Member Geeto67's Avatar
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    the honda dream 305 is a 360 degree motor. The superhawk and 305 scrambler are 180 degree engines. I always thought that was really funny because externally the engines look the same.


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    Moderator jbranson's Avatar
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    That is kind of curious, wonder why they did it. I've talked to people who have pressed apart 175 cranks and put them back together as a 180 and then had a new cam ground up. They could never find a definative answer on the dyno as to what made more power. Seemingly not enough difference to matter. I prefer the 360 degree on a small bike because it make the ignition system much simplier and lighter.
    JohnnyB


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