Topic: Camshafts: 180 degrees out or not?

[fmctm1sw]

I was going to reply to a 650 post with this but didin't want to add any confusion.  After I wrote it all, I thought the 650 may be different (electronic ignition).  Maybe I'll research it.  Here's what I was thinking: 

I will contend that it makes no difference if the camshaft is 180 out (on these Honda fours) or not.  Here’s why:  We know the 4 cycle engine consists of a compression, power, exhaust, and intake cycle.  From taking enough of these engines apart, I know that cylinders 1/4 are 180 degrees apart from 2/3.  So if 1/4 are on an intake cycle, 2/3 are on exhaust.  The layout is thus:

1/4 C -> P -> E -> I
2/3 I ->  C -> P ->E

If you rotate the camshaft exactly 180 degrees, you simply flip what 1/4 was doing with what 2/3 was doing.  There would be no colliding of pistons and valves.  But how would the ignition timing work then?  Wouldn’t the plugs be trying to fire at the top of the exhaust stroke?  Yes, they would and they do anyway.  These are wasted spark ignitions.  The camshaft turns 1/2 turn for every revolution of the crankshaft.  Therefore, the 1/4 "F" and 2/3 "F" timing marks are hit twice per each revolution of the camshaft and are 180 degrees apart.  Depending on the position of the camshaft, the “wasted” spark could be the “effective” spark or vice versa.

Based on my own personal observations...  When I was putting my 550 top end together, the manual I have stated to “line up slot in the camshaft with the top of the cylinder head.”  But it did not say which way the slot should be pointing (toward the front or toward the back of the motor).  After some thought, I went back and looked at the manual and there was a photo that showed the slot toward the front.  I took my top end apart and shifted mine 180 degrees (I did slot to back).  It had no effect.

[Bailgang]

During my years playing with cars I too was confused about the 180 deg off myth and the only way I can figure how it got started was guys using double roller timing chains that had crank gears that give you multiple cam timing options. Most had 3 key ways to choose from (some even more), 1 for retarding the cam timing, 1 for straight up and another for advancing cam timing. A mechanic is always initially taught lining cam and crank gear dot to dot and that's all well and good with a standard timing chain but this isn't always so when using a double roller timing chain.

Most wannabe gear heads don't take the time to notice that each of those key ways has a different mark, say for instance 1 key way slot will have a triangle above it, the other a dot and the last 1 a square and don't realize that if you choose the key way that has a triangle stamped above it then they better find the tooth on the crank gear that has a triangle stamped on it as well and use that triangle to line up to the dot on the cam gear and of course if you were to choose the key way with the square then you better find the tooth that has a square on it as well. Unfortunately the dot to dot teaching is drilled into their heads and they choose the tooth that has the dot on it to line up with the dot on the cam gear regardless of what key way slot they chose.

I've already pulled apart 1 small block Chevy where the owner did this, sure enough he had the the cam and crank gear dot to dot however he tried to be fancy and used 1 of the other key ways that didn't correspond to the "dot" which put his cam timing a mile off, 16 bent valves and 8 chewed up pistons

[lucky]

The way you can tell is to line up the crank on TDC as if you were going to time the engine.

The no.#1 cylinder should have both cam lobes pointing down on approx 45 angles.
If they point upwards then the cam is in upside down.

I used to work at a dealership and had to fix this problem a couple times.
The owner of the motorcycle would just say it needed a tune up but when trying to get the timing marks lined up to install new points nothing would work.

[fmctm1sw]

Here's the thread that started me thinking:  http://forums.sohc4.net/index.php?topic=107242.0 

[lucky]

Here's the thread that started me thinking:  http://forums.sohc4.net/index.php?topic=107242.0

It is astounding how people just guess what clearances should be.
I always just go look them up.

[dave500]

with cars you can get the distributor 180 out,,so the valve timing is wrong with the spark timing.

[dave500]

google up how the holden v8 camshaft is timed,anyone from america would just line up the dots as you are taught,when ever you dissemble an un familiar engine work out what the timing marks are.

[bryanj]

On the Honda fours the ignition timing is on the crank not the cam and is a "Wasted Spark" system so it matters not a stuff which of 1 & 4 is on the on compression, I.E timing notch on cam can face either way.