Timing belt idiocy - could use some help

[rmconner80]

Trying to replace the cam belt on my 944S.

The problem: the teeth don't line up between the cam gear and the crank gear. In other words, when I get the belt on the crank gear and run it up to the cam gear and pull it taught, the belt teeth meet the gear teeth instead of mating into the gear.

If you line them up to mate, then you have too much slack in the belt span, and you also can't complete the rest of the belt circuit - not slack on the other side of the gears.

When I pulled the old belt, it was really tight in the span between the two gears.

Flywheel lock is in. I thought I had it at TDC, but I now believe I am just shy of TDC. I'm trying to figure out the next step here without loosing timing / making this worse.

It seems that the crank needs to move a bit more clockwise, and the cam gear half as much more clockwise?

This is probably the fourth time doing the cam / balance belt. I do them every 3 or 4 years. I've never had this problem.

Anybody have any ideas?

[v2rocket_aka944]

if the crank is firmly, definitely at TDC, you can use a big wrench and grab the big hex on the cam gear and rotate it clockwise the half a tooth or so necessary to "hook the teeth".

once the belt is on the gear, use the wrench to back the gear up until it lines up on its TDC mark again...adjust tensioning as normal.

[dgcantrell]

Installing the belt so that there is no slack (extra teeth) between the pulleys takes a little finesse and practice. When I do mine, I'll time everything, slip the belts on and tension the belts (not to spec but tighten them to where they aren't flopping around). Remove the crank lock and turn the engine over by hand two complete revolutions at the crank. Put it back on TDC and lock it. Removing the spark plugs makes turning the engine over much easier. Check ALL of the timing marks to see if they are aligned. Even if you're off a tooth or three, turning it over by hand slowly with a rachet will not damage anything. But remember if you encounter ANY hard stops while turning it STOP immediately. If all your marks line up after the two rotations, tension your belts and torque down the tensioner pulleys. If not, make you adjustments and get everything back in time. DO NOT fire the engine up until you can rotate the engine over by hand and all the timing marks stay aligned. By the time I'm ready to fire one up, I've probably turned it over by hand at least 2 or 3 more complete cycles to absolutely sure everything is right. Too much fubar potential to rush it.

[rmconner80]

Ok thank you for the advice. I'll give it a shot by turning the cam gear the half a tooth worth to get the belt on. Then tension / rotate. I always rotate the crank / cam a number of times too.... I do this to observe timing but also to triple check measured tension of the belt (arnworx tool)

What happens if I spin the engine and timing marks don't align when I get back to TDC? I assume I'll need to align the cam marks, remove the belt, and then spin the crank slightly more or less than 2x more rotations required to get to TDC on the flywheel. Then install the belt again. Is that correct? This seems daunting, and I wonder: what am I missing?

[v2rocket_aka944]

Don't remove the belt before spinning the engine around...if something isn't lined up, line it up...

[dgcantrell]

As long as it's just a couple or three teeth or less off a the cam, simply locking the crank at TDC, removing the belt enough to readjust the cam to where it's right, and slip the belt back on, it's fine. As long as you're turning the engine over by hand and it is NOT hitting any hard stops, you know the valves are not being touched by the piston. Even if you loose total track, all you need to do is bring the crank back to TDC and the take it about a quarter turn past that to move any and all pistons down in the bore an inch or two. Then you can turn the cam as degrees as you wish to get it back on the mark. When the cam is back in time, then turn the crank BACK that quarter turn you just did to TDC again. Again, as long as you're doing this by hand and not hitting any hard stops, you're fine.