300TD Engine Balance
 

I hope some one can answer this. The Harmonic Balancer on my 79 300TD came loose. I've ordered the lost retaining hardware, but since it free wheeled on the crank shaft, I don't know where it was originally positioned (radially). The MB parts dept in Knoxville tells me it doesn't matter, which makes no sense.

Is the balancer self positioning? How can that be? Help.

I just bought this car and I love it! 1st Benz. Quirky, but lots of charm, classy, but best of all, my wife hates it.

Well, speaking generically it could make sense,, and there is another tidbit of information , from Larry Bible,that the 240 four cylinder flywheel can be used on the 300 five cylinder... to me that means that the engine is internally balanced.. and the flywheel is balanced by itself..not a situation like many engines which require help from the flywheel to make them smooth... So your harmonic balancer may serve only to dampen vibrations ..,just acting as a cushion effect to keep them from hanging around.... and as a weight on the other end of the crankshaft to offset the weight of the flywheel or torque converter on the other end...
Does it have a key slot in it..? that is one way of attaching which would indicate only one way it can be attached...

There is no key way on the shaft, which is what I expected to find, and the lack of which adds to my confusion. However, the purpose of the balancer may very well be as you have said. The balancer appears to be uniform and not counter balanced or weighted more on one side. I have not attempted to verify this by suspending it or anything.

Thanks for the reply. Perhaps some one out there knows all about these things.

The harmonic balancer is dynamically balanced to the engine it is assembled on. The MB engine manual shows the way to balance a replacement HB to the old one using a special tool. The flywheel is indexed to a particular position on the crankshaft. From looking at several of these it looks like maybe both the HB and the flywheel are balanced (the partial drill holes in both) and they do this to help balance the engine at both ends (like they balance your tires by putting wheel weights on the inside and outside of the wheel - nutating forces are minimized).

The HB is positioned so that the HB TDC mark is indexed to cylinder #1 TDC compression stroke using the pointer mounted on the engine block. The HB is mounted to the crankshaft and indexed/positioned using two dowel pins that are a bit difficult to position correctly. I wrote up a very good procedure to install the HB - look up my old posts to find it (when I get a moment I'll look to give you the date and which forum to look in). I just rebuilt my 300D's engine and used the same procedure to mount the HB - then I checked my work by verifying the HB TDC, the pointer, and #1 piston were correctly positioned using the MB procedure and a dial gauge. The positioning/alignment was perfect.

Are you sure the HB is the problem and not the vibration dampner?

This would be a good time to replace the front crank seal (check to see if the front crankshaft spacer has grooves caused by the crank seal and, if so, replace it too - I've got a spacer with some serious grooves caused by the seal and leaked oil like crazy) and check the timing chain guides/timing chain gear for wear and replace if needed.

Good Luck!
Tom

The crank, harmonic balancer, and flywheel are balanced separately on the 616/617 and later engines.

Please note that this IS NOT TRUE OF EALIER ENGINES!! Rotating the HB on a 615 can make it hop up and down on the engine mounts, ditto for rotating the flywheel, and the bolts are symetric!

The position of the balancer won't matter on a 617 -- there are two small keys that position it -- see Larry Bible's postings on re-installing the HB.

On ealier engines the three parts MUST be balanced together -- big pain in the butt if you have to replace a part, as it must be adjusted to match any imbalance in the original!

Peter

Peter's imformation is not supported by the specifications provided in the official M-B service manuals (both print and CD).

The M-B manuals state that on all 617 engines: "Engine 617 is balanced as a whole, i.e the entire engine is balanced on a balancing machine." Balancing the entire engine as a whole is for all 617 engines 1975-1985, 617.910 (non-turbo) to 617.952 (turbo). There is no info about balancing the 615 or 616 engines as a whole, only the individual components, and then assembling them to the engine.

M-B goes on about engine balancing as whole: Since this balancing operation cannot be executed in a repair shop it is necessary to note the following rules and measures:

replacement crankshafts do not come with flywheels, balance plates, pulleys, and vibration dampners - take the old parts from the old crank. Replacement cranks are balanced at zero;

when replacing the crank make sure the mark on the flange of the old crank is matched to the same mark on the new crank as it relates to the flywheel;

flywheel and balance plate (harmonic balancer) must be adjusted/matched to the balance of the old parts using the M-B special tool and the procedure outlined in the shop manual (several pages of info);

new connecting rods must be the same weight category as the old rods (there are 5 weight categories for rods);

the vibration dampner (not the balance plate/harmonic balancer) must not be balanced and is not indexed to a specific position when installed on the harmonic balancer;

partial engines (short blocks) are balanced as whole assemblies.

On all 615, 616, and 617 engines the balance plate/harmonic balancer and the flywheel must be matched balance-wise to the old components when replacing. All flywheels are indexed to the crankshaft and must be positioned in the same place when replacing with either a new or the old one. The harmonic balancer/balance plate has the timing marks on it and if it is installed 180 degrees out of position it will not only make the engine un-balanced, it will also be hard to make key adjustments/measurements that require indexing the engine to specific positions in degrees.

The method I use to install the haramonic balancer/balance plate is a good procedure. The harmonic balancer/balance plate is positioned/indexed with two dowel pins. The vibration dampner is bolted to the harmonic balancer/balance plate using 6, 8mm bolts (the belt pulley also bolts to the HB using the same bolts as the vibration dampner).

I just rebuilt a 300D engine and followed the above M-B guidelines to ensure my engine remained balanced. I swaped my old engine with a Euro 300D engine (this is the engine I rebuilt) and swaped many parts (including the belt pulley, vibration dampner, flex disc on the trans., and other parts not related to the engine's balance). I even balanced the old flex disc to the replacement one using a tool that I had already owned. The result - a very smooth, well balanced engine, in fact smoother than the old engine.

'Nuff Said!
Tom

TOM,
this mysterious tool you mention in the last paragraph... will you be bringing it to the shindig..?
Are you balancing these things statically or dynamically ?
thanks, Greg

My information is from an MB factory trained Master Mechanic (Dusseldorf 1972), for what it's worth.

Doesn't hurt to balance everything, anyway.
Peter

Guys, thanks for the information. I think I'm hearing two different schools of thought. As I feared, this may not be cheap. I sure don't want to rebuild this engine, as it seems fine otherwise, not consuming or leaking oil, and ran fine until the balancer came off.

I have a local independant Benz mechanic, who while being cheaper than the dealer, obviously doesn't work for free.