Hello again all..

My 300D has always had (since I've had it) a slight "wobble"
in the crankshaft pulley, thus the belts wobble some too.
This seems to be getting worse now. Should I be worried? What's causing it, worn bushings/seal? I wouldn't think the shaft is warped. Belts are all fine. I'm planning another 1200 mi trip this weekend. Thanks
Phil
300D
260,000 mi

Take a look at this.....

Failed 123 Diesel Harmonic Balancers

might be your problem.

Ernie

I own a 1977 300D. The belt pulley on my 617 engine is bolted to the harmonic balancer with 6 bolts with a 5mm hexagon head (could be 6mm, I'll check and post an update if they are 6mm). If these 6 bolts are loose it could cause the belt pulley to wobble. These bolts are recessed in the center of the belt pulley and an allen wrench can be fit either be feeling along the inside of the belt pulley to find them or use a mirror to see them. The belt pulley bolts should be torqued to 26 ft. lbs. (a good effort if you cannot fit a torque wrench into the area or do not own one - but, you do not need to use a cheater bar - just a fair amount of force to tighten them enough, the crankshaft may turn a little when tightening the pulley bolts unless you are on the compression stroke of one of the cylinders). You should loosen the belts to correctly tighten the belt pulley (but, you do not need to remove them). I used an allen wrench that is in a socket that fits onto a 3/8" ratchet, but the job may possibly be done with a regular allen wrench.

There is a slim chance the belt pulley has been damaged and is coming apart. I say slim chance because the belt pulley is cast in one piece - but it could be cracked, for example, and you would need to remove the pulley to inspect it for damage.

The other suggestion about the harmonic balancer bolt needing tightening is also a possibility. If this is the case, then you should be able to see the harmonic balancer and another plate that is attached to the balancer wobbling in addition to the belt pulley. The harmonic balancer bolt is torqued to 200-250 ft. lbs. (I used a 4 foot cheater bar to loosen mine). The balancer bolt has a 27mm hexagon head and has normal right hand threads (not reverse threads) and is tightened in a clockwise direction or loosened in a counter-clockwise direction as you look at the bolt from the front of the engine.

Hope this helps.
Tom!!

Pardon my ignorance, but what does a harmonic balancer do?

John

The belt pulley bolts on my 1977 300D with the 617 engine have 6mm allen head bolts (not 5mm as I thought). However, I would check the size of your belt pulley bolts to make sure what size they are.

The harmonic balancer is used to balance the engine when it is operating. This is needed because the manufacturing process creates the same part that have different weights (pistons, rods, flywheels, crankshaft, etc.). After these parts are made (typically only the pistons and rods) they are weighed and grouped with those with the same weight (or very close, like 1-2 grams or less - some members may know the specs for this). Meaning, your engine will not have pistons or rods with different weights (or the difference will be very small). After the engine is assembled at the factory it is rotated/spun, the out-of-balance condition is found, and the harmonic balancer for that particular engine is adjusted to balance the engine (dynamic balancing - like when they spin balance the tires on your car; a 1 ounce out of balance condition on a tire equals about 28 pounds out-of-balance condition at 60 mph). This is why you MUST mark the harmonic balancer/belt pulley/degree marked balancer to show their relationship to the crankshaft BEFORE removing them (flywheel also if you are removing it) - otherwise the engine will be out-of-balance when these parts are re-installed (unless you get lucky and by chance re-install them in the correct position). Without dynamic balancing the engine would vibrate a lot and probably damage itself eventually (and probably damage the transmission and drive train as well) - much less cause a lot of vibration in the car chassis (mirrors would not have clear images, seats vibrating, etc.).

When an engine is "blueprinted" these parts (usually only the pistons and rods) are weighed and material removed so that all of them weigh the same (usually the heavier parts are made lighter to match the weight of the lightest part since you should not add weight, or if you have access to an inventory then parts with the exact same weight may be found and/or very close in weight so that a minimal amount of weight needs to be removed). This is done to aid performance and allow an engine to run at higher RPM's without damage caused by an out-of-balance condition (this can be done even on a non-high performance/stock engine to achieve a better dynamic balance condition, but most people will not go to this trouble because of the extra time and cost). A harmonic balancer is still needed even if the parts are all made to weigh the same, however.

Hope this helps!!
Tom