How to change a timing belt

[mercurymang]

'75 Merc 650 (triple)

As you may or may not know, I did quite a bit of work over the winter to my motor and it's running great now. One of the things I did not do (which I should have done) was change the timing belt. It seems to have quite a bit of play and I don't want it to snap out on the water.
My question is what it the best way to change it out. I had it on and off a couple of times over the winter but I'm not sure it's the correct way to do it. When I re-installed it, i fed it up under the stator with the flywheel off and then fit it around the timing gear on the flywheel. Then I carefully installed the flywheel with the timing belt on it. It was a little hard to get it to go on as there was barely any clearance between the belt and the end cap. As I could see it, there was no other way to do it except maybe to remove the bolts on the flywheel leaving the center portion of it attached to the crank, installing the belt, then re-attaching it.
Can anyone tell me the correct way of doing it?

 

[emckelvy]

Re: How to change a timing belt

The first way you described is the most common method for changing the belt. You could, as you stated, take apart the flywheel at the flex plate, leaving only the hub (which reveals the belt). Those are about the only 2 ways I know how to do it!

The biggest hazard with unbolting the center hub is that sometimes the flywheel bolts can be badly corroded and snap off. Not much fun drilling out Grade 8 hardened bolts & retapping! This was a big problem with the older motors that used 1/4" flywheel bolts, not so much for the 5/16", but I'll throw it out there anyway.

If your motor is pretty clean, not a lot of rust/corrosion, it'd probably unbolt OK. If you have any bolts that are really hard to break loose, you may have to carefully apply some heat then penetrant to the reluctant bolt.

First method is harder in that there's little room to move about. Plus you've got to be very careful or you'll nick/cut the belt.

If you're planning on unbolting the flywheel, be sure #1 cyl is at TDC (Top Dead Center), there's only one way to reinstall the flywheel flex plate to the center hub and be at correct TDC position. Don't move the crankshaft once the flywheel is off.

Torque 5/16" fine-threaded bolts to approx 24 ft-lb an put a drop a Loctite Red on each bolt's threads.

One last thought, these belts aren't in there extremely tight, and there's no way to adjust them. If your distributor pulley has a ton of belt-slop as you wiggle the pulley, maybe it's time to change out the belt. If the belt isn't rotted, cut or torn, it may have more life in it. But if the inner "cogs" are rotten or cracked, time to renew.

HTH & G'luck with the belt-changing..........ed