Honda 450 Cam Timing

In order to avoid damage to the valve train and pistons, it’s critical to know where the valves andpistons are relative to each other and to the four “cycles”. The following diagram shows these relationships - it’s read from right to left, as it would appearfrom the left side of the engine, where the entire procedure is performed.

Begin by removing the cam chain tensioner itself. Attach wires to the ends of the cam chain ifyou haven’t done so already.And it’s always prudent to buy several cam chain “master” links, in case you mess up and have tostart over.

Step one is to make sure the crankshaft is turned to align the “LT” mark on the alternator rotorwith the index mark. The cam timing was designed by Honda to (thankfully) be performed NOTon the top of the compression stroke - as we all know, it’s very difficult to keep the crankshaft inplace at the top of the compression stroke, it always tries to “run by”. This is a result of thetension of any torsion bars that are being compressed, as well as the fact that the crankshaft rod is

actually mounted slightly off-center to the piston - this also tends to keep the crank moving atTDC. So the actual cam timing is performed at TDC (Left) at the top of the exhaust stroke (justprior to beginning the intake stroke). By this means, the crank will remain relatively stable andthe entire procedure can be accomplished quickly by one person.

To insert into the head and allow the bearings/covers to go on, the cam lobes must be turnedtowards their loosest points. You will not see the timing marks on either cam in this position.Once this is done and the covers are in place, the cams must be manually turned to align thetiming marks with the indicator marks on the inside of the right side covers. Most folks use ascrewdriver or tire iron to accomplish this, engaging the teeth of the cam sprocket and leveringagainst the bottom of the cam opening. As indicated in the photo, the presence of gouges at the bottom center of the cam openings is aclear indicator that your engine has been through this procedure before.

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To align the exhaust cam mark, the cam must be rotated clockwise (as viewed from the left sideof the engine) almost 180 degrees. This will require some force, as you’ll be fighting the pressureof the torsion bar, opening the right exhaust valve.The intake cam will also need to be rotated, but only slightly, relative to the exhaust cam.

The cams may have several marks each which could be confused for the timing marks.You will recognize the proper cam marks when the cam lobes appear to be “pointing” to thefollowing “clock” positions when they’re in the proper places (as viewed from the left side of theengine)- Left Exhaust - 3:00 (valve closed)Right Exhaust - 5:30 (and almost completely open valve)Left Intake -8:30 (valve closed)Right Intake - 12:00 (valve getting tighter, but still closed)

Once you think you have them in place, thread the cam chain through, make sure it’s engaged onthe teeth of the cam sprockets, check all your marks, then rivet the new “master link” in place.Generally this is done on the intake side, but that’s not carved in stone.

Very CAREFULLY turn the engine through a few revolutions, watching the valves and pistonsto make sure there is no contact. You can see the pistons approach the top of their stroke throughthe empty spark plug holes, and you can see the valves open and close by watching the cam lobesthemselves (as well as looking into the exhaust/intake ports).These valves can be bent very easily, so be careful and make sure you get it right. Do not attempt to rotate the engine until you have riveted the master link - if it happens to fallapart , you’ll have to start all over and tear down the whole engine to retrieve the pieces.

If everything is ok, you’ll hear the familiar “whoosh” of compression as the pistons reach the topof compression stroke - first at TDC left, then 180 degrees later at TDC right.

Re-install the cam chain tensioner, adjust the tappets to a nice snug 0.002", and you’re on theroad.