1986 300, 95k miles. There is nothing wrong that I can see with my harmonic balancer, but I am planning to do some work in that vicinity (water pump) and was wondering if I should consider replacing the HB at the same time while it is convinient to do so.

I have read here that the harmonic balancer can eventually fail, giving me the impression that it is sort of a "maintenance replacement" part, kind of like a spark plug or accessory drive belt. Does that seem accurate? Or alternatively, does the HB normally last basically forever (i.e. the lifetime of an engine)?

Basically what I'm asking is if the harmonic balancer is a good thing to replace after 25 years, even if it appears to be functioning properly?

Thanks.

 

You can look it over and press on it to see if the rubber is still in good shape. If the rubber is starting to squeeze out, then it probably would be a good idea to replace it. 90% of the time, the outer ring comes loose, and slips a little bit without coming completely off. The only way you notice this is when you go to time the engine, the timing marks are way off. I haven't worked on a six, so this point might not apply, since I know some sixes were timed by a mark on the flywheel.

 

Franklin's right on about the balancer being able to slip and the timing marks not lining up.
If you want to know for sure (and an inspection reveals no rubber squirming out), pull your #1 plug and poke a longish screwdriver down the hole while cranking the engine over by hand: you'll be able, with a little practice, to tell when it's on TDC by feeling where the piston comes up. DO IT BY HAND. Then look at the HB and see if it lines up.

An alternate and more accurate way is to use a piston stop and bring the piston to the stop, put a mark on the balancer, then rotate the engine backwards and do it again. TDC is exactly between the marks.

BTW- I have almost 300 K and my HB is fine.

 

X3 on the slipping. Had a buddy with an Opel Kadet back in the late 60's. He put A/C on it and all was fine. Later he did a tuneup and it ran terribly. TERRIBLY! No one could figure out why until my Dad set the timing by ear and then we looked at the harmonic balancer. Sure enough, it had slipped and continued doing so every time the compressor came in when going down the highway. Just couldn't handle the abrupt load.

 

OK, thanks to you all for the good advice. The rubber in mine looks fine, no crumbling at all, and last time I checked timing the marks indicated perfect 10 deg BTDC with the SPOUT disconnected. So I'll just assume my harmonic balancer is not slipping (although these observations don't prove that).

To be sure, next time I'm under the hood I'm going to scribe a chalk line across the face of the HB from outer ring to inner hub - that way I can monitor it and if the chalk line ever gets separated, I'll know the outer ring is slipping.

Thanks again!