Short answer: no
Long answer, keep reading...
450R engines are wasted spark engines, meaning, they fire every time the piston reaches TDC, like a two stroke. That means, as long as the piston is at TDC and you line the cam marks up, you're timed properly. In a four stroke engine, the crankshaft rotates 720 degrees (twice) for every full revolution of the camshaft. There are four strokes in a four stroke engine (imagine that):
In a traditional automotive engine, like a 350 SB Chevrolet, you can install the cam "180" out because the distributor only causes the ignition for an individual cylinder to fire every 720 degrees of crankshaft rotation. That means, if the cam is 180 out you'll be firing between the intake and exhaust strokes instead of between the compression and power strokes. Then, when the compression and power strokes come around, nothing happens. With an unburned charge floating around still, when the intake and exhaust strokes come around and the plug does fire, there will likely be fire blown through both the carb and exhaust -- here are some diagrams on what happens on a traditional 350 SB Chevy engine:
This is what happens in a correctly timed conventional V8 engine:
Here is what happens with the cam 180 degrees out in a conventional V8 engine:
On a 450R engine - the ignition fires every 360 crank degrees (i.e. wasted spark -- because one spark event is wasted & doesn't actually light a charge). So, if the cam is 180 degrees out (compared to what it was to begin with) and the stroke pairs are reversed, the ignition still fires at the right (and wrong) time - just like it did before the cam was moved 180 degrees. The engine still fires and nothing has really changed.
Here is what happens with a 450R engine as it comes from the factory:
Here is what happens if you took that engine and rotated the cam 180 degrees and reinstalled it:
The cam's orientation always determines:
In a distributor engine, these events have to be coordinated with the ignition, since it only fires once for all four strokes. In a wasted spark engine, it does not have to be coordinated with the ignition since the plug fires every TDC event regardless.
If you have the crank timing mark lined up, the piston is at top dead center, give or take a few degrees. There is no way possible to have the mark 180 degrees off and not notice it. As far as putting in the cam 180* off, it doesn't matter. Say you are putting the cam in 180 degrees off; ok, instead of setting the motor up at TDC of the compression stroke, you set it up at TDC overlap stroke. All you did was make it harder to install because you are fighting the valve springs. The cam will still be in the overlap stroke every odd time the crank is at TDC and on compression stroke every even time the crank is at TDC. Or if you want to think of it like this: the cam will be on the compression stroke every odd TDC and the overlap stroke every even TDC and vice versa. The whole myth of the 180 degrees off thing came from multiple cylinder motors that have a cam driven distributor. The cam couldn't be set 180 degrees off, but the distributor could be set 180 degrees off, in which case, the spark would only occur at TDC overlap. Thus the motor would not run. But on our machines, the spark is timed to the crank. So, every 12-36 degrees before TDC the spark will occur. It occurs once at 12-36 degrees before the TDC compression stroke and once 12-36 degrees before the TDC overlap stroke.
Since a 360 degree rotation of the crank only represents one TDC event, all the mark on the flywheel tells you is if the piston is at TDC - the transition between the compression stroke and power stroke is SOLELY determined by cam position in these engines since the ignition fires on every TDC event. There is no way to get ignition timing 180 degrees out and there is no way to determine which TDC event was the original one that the bike actually lit the fire on when first assembled at the factory - nor does it matter. All you have to do is put the engine on TDC, set the cam timing marks properly (which includes installing the cam in the proper orientation - but even if you managed to install lobes down, as long as the marks line up it's fine) and you're done - the engine is properly timed at that point.
Many of the pictures below show the engine removed from the frame and some of the pictures show the engine with the cam carrier assembly, cylinder head, cam chain guide, and internal cam chain tensioner (black) removed. You do NOT need to remove the engine from the frame, or remove any of the aforementioned parts from the engine to replace only the timing chain.
Purchase a new timing chain, Honda part number: 14401-HP1-671 for the 04/05 model (not shown) and the correct flywheel puller (M28 x 1.0) with crankshaft protector.
Read the disclaimer, required tools, notes, and checklist sections of the valve adjustment how-to. Also complete steps 1 through 7 of the valve adjustment how-to in order to remove the required parts from the quad and set the engine to top dead center with the valve cover removed. Although optional, this may be a good time to incorporate checking and adjusting the valve clearances (steps 8 through 11) into the remaining steps of this how-to.
Drain the engine side oil by removing the drain plug on the underside of the engine.
Trace the wiring from the top of the stator cover back to under the right side of the hood/right front fender plastics and unplug the three stator connectors from the wiring harness. Remove the oil cooler line from the stator cover and then remove the top/middle two bolts from the stator cover that hold the clutch cable bracket onto the engine. Remove the clutch cable from the clutch arm and move the clutch cable out of the way. Finally, remove the stator cover itself (left side engine cover) by removing the remaining seven bolts.
Break the two cam sprocket bolts loose, but don't remove them yet. When breaking the cam sprocket bolts loose, you will need to keep the cam sprocket from turning. Hold the bolt inside the crankshaft check hole on the right side of the engine (8mm allen) to keep the engine from turning over. It's generally much easier to break each cam sprocket bolt loose when its at the bottom, away from the top frame rail. To accomplish this - turn the engine over via the aforementioned 8mm crank nut on the right side of the engine; but be sure to return the engine to the top dead center position before removing the cam sprocket (step 9).
*Note:
If you have a slotted or adjustable cam gear, make sure the gear and cam flange are both scribed so you can set the cam timing back accurately.
Remove the flywheel nut (and washer) with an impact gun. If an impact is not available, you may need to hold the bolt inside the crankshaft check hole on the right side of the engine (8mm allen) while removing the flywheel nut.
Install the crank protector onto the end of the crank to protect it from the puller. Install the flywheel puller onto the flywheel (over the protector) and then screw the puller shaft into the puller snugging it against the crank protector. While holding the bolt inside the crankshaft check hole on the right side of the engine (8mm allen) tighten the puller shaft until the flywheel comes loose from the crank. Pay close attention that you do not lose the key between the flywheel and the crankshaft.
Next, remove the cam chain tensioner by slowly backing out the two bolts (alternating) that hold the tensioner to the cylinder. The external tensioner assembly is spring loaded, so proceed slowly with this step. Another method for removing the tensioner is to remove the center bolt from the tensioner and insert a small flat screw driver into the hole in the tensioner. Turn the screw driver clock wise several rotations until it stops - this retracts the internal arm and relieves all of the tension. While still holding the screw driver, you can then remove the two bolts holding the external tensioner assembly to the cylinder.
*Note:
The pictures below show a manual cam chain tensioner rather than a stock auto-tensioner.
Remove the two cam sprocket bolts completely and pull the cam sprocket off of the cam flange. Remove the cam sprocket from inside of the timing chain and set it aside. Allow the timing chain to "fall" down inside of the head/cylinder and remove it from the engine.
Remove the lower metal timing chain guide plate (at the bottom of the chain by the crank). Remove the cam chain by pulling it off of the crank and out of the bottom of the engine.
Reverse all of the previous steps to install a new timing chain and reassemble your engine/quad. It is recommended to complete reassembly in the following order to more easily set the cam timing correctly: Install the new timing chain and re-install the cam guide plate. Use a magnet or other means of fishing and holding the cam chain up through the cylinder and head to the cam tower area. Install the flywheel back onto the crank and ensure the key that goes between the flywheel and crank is in the correct orientation. Torque spec for the flywheel nut is: 54 lb-ft. Re-install the stator cover at this time and then remove the flywheel check hole cap at the top/center of the stator cover to help in setting the cam timing accurately.
Ensure the cam lobes are still facing back and slightly up. Now put the handle-end of a ratchet through the end of the cam chain and hold it level with some tension on it while rotating the engine over (using the allen bolt inside the right side crank check hole) until the slot inside the flywheel check hole is exactly aligned with the "T" mark on the flywheel.
*Note:
There are two marks on the flywheel - one is labeled "T" and the other is labeled "F". Use only the "T" mark for setting the cam timing.
While still holding some tension on the cam chain, remove the handle-end of the ratchet and slip the cam sprocket into the new cam chain in an orientation that will closely allow the bolt holes in the cam sprocket to align with the mounting holes in the cam flange and slide the sprocket onto the cam flange. Losely install one of the cam sprocket bolts to hold the sprocket in place on the cam flange. Set the cam timing accurately by ensuring all of the remaining timing marks line up at top dead center (flywheel/check hole marks are aligned). The cam lobes should be facing back and slightly up. The marks on the right side outer case's crankshaft hole and internal gear, as well as the cam sprocket and and cam tower assembly should both align when the cam timing is properly set (site each of the pairs of marks with your eyes level to the marks). You may need to pull the cam sprocket back off of the cam flange and out from the cam chain to rotate it one way or the other in order to get the timing set correctly.
*Note:
The pictures below show a slotted cam gear and a cam with a welded flange and scribe marks; your engine may not have these.
Once the timing is properly set, and before installing both cam sprocket bolts, it is recommended to snug the single cam sprocket bolt down, re-install the cam chain tensioner and check all of the timing marks again to make sure they all still line up. Take your time with this step, it is very easy to install set the timing one tooth advanced or one tooth retarded. Before permanently re-installing the cam sprocket bolts, clean the old loc-tite off the bolt threads, re-apply red loc-tite to the threads, and torque them to 14 lb-ft. Allow the loc-tite to set at least 20 minutes to before starting the quad. Continue reassembly of the quad by reversing the remaining steps from this article and steps 1 through 7 of the valve adjustment article. Torque spec for the valve cover bolts is 7 lb-ft. Don't forget to plug the stator's electrical connections back into the wiring harness and don't forget to refill the engine with oil.