Dear Fellow Brickboarders,

May this find you well. My nephew and I recently replaced the timing belt &
tensioner / seals / water pump / harmonic balancer on his '90 760 turbo
(with B230F).

We came upon only one issue, that seems not to be addressed in the FAQs.
That issue: how to ensure that the keyway in the harmonic balancer
engages the key on the crank sprocket. Because the harmonic balancer's
keyway is "blind" - i.e., it does not run from the rear face all the way through to the front face - there is no obvious way to ensure perfect alignment of the keyway with the key, before tapping the balancer into place.

I presume the keyway is "blind" (i.e., not machined all the way from back face to front face), to keep water away from the crank sprocket.

Still, it is critically important properly to seat the balancer on the crank sprocket. This leads me to ask whether it would be feasible to drill a "sight hole" through the front face of the balancer (into the key way), through which one could check the balancer keyway-crank sprocket key alignment, before seating the balancer?

Once the balancer had been seated, the "sight hole" could be plugged with grease or even a small piece of rubber. Because this plug is close to the shaft, I do not think it would "unbalance" the balancer.

It seems clear that if the balancer is not seated into the crank sprocket key, the balancer will rotate on the crankshaft, likely scoring the crankshaft and producing many of the symptoms of a failed balancer. Moreover, if the balancer is not aligned properly, and then "seated" it could damage the crank sprocket, which I gather costs about $100 to replace.

I recognize that drilling through the balancer's face - to create a seating "sight hole" - raises the risk of water penetration and corrosion, and also the possibly (likely slight) of creating stress cracks in the balancer.

What suggestions do you have?

Yours faithfully,

spook

Hello spook,

A PO’s mechanic had smashed the key against the HB because of the problem you mentioned. The crank gear had developed a crack at the key and had to be replaced for $85. The HB did not rotate since it was torqued properly. The HB was slightly distorted but I manage to salvage it with a file.

This is a better method: I had always had to fight to get off the HB due to a build up of rust and crud. After I remove the HB, usually after a hundred hits with a chunk of wood a little twisting, and lots of PB Blaster, I’d clean the shaft and HB with emery paper or fine steel wool. Before reassembly, I applied anti-seize to the shaft. You can then really get the confirmed clunk that Don Foster speaks of. The next time the HB has to be pulled, it should be easier which, is the primary purpose of the anti-seize.
--
Tom F Back to three 940s. Mods, RainX. Lien holder on two more (the kid's). Rust in pieces, '78 245

Dear Tom,

Good p.m. and may this find you well. Good advice, whc. should be added to the FAQs.

Just heard from my nephew, who completed the job (we lacked a grommet for the pipe from waterpump to heater control valve, new alternator bushings, and a new alternator belt tensioner).

All parts went in fine. The water pump does not leak. Apparently I seated the balancer correctly. The distance from the front of the timing belt case to the front of the balancer is 2 1/8" =/- 1/32". This is the same as on my 940s, which have the factory-original balancers.

I used acetone to clean the crankshaft end, block face's water pump sealing surfaces, the wells into which the crank, cam, and intermediate seals are seated, and the timing belt tensioner stud's recess. This way, we made sure to remove all contaminants.

We lubricated the seals with an emulsion of grease and motor oil. We improvised a seating tool for the crank seal, and turned the crank bolt to press the seal into place. I will make one out of 2" diameter Schedule 40 PVC pipe: it is the perfect diameter.

How are your kids' cars doing?

Yours faithfully,

spook

I put the pulley on the crank and rotate it as I push it in. When it goes "clunk" and seats inward, I know the key has engaged the keyway.
--
Don Foster (near Cape Cod, MA)

Dear Don,

Good p.m. and may this find you well. This balancer fit the crank so snugly, that it would not rotate at all. It had to be tapped home. Is a snug fit normal?

I ask, because the crank sprocket - and the other sprockets - all slid easily into place.

I aligned the balancer using a mark I put on the timing belt case and on the balancer edge.

Would drilling a "sight hole" do any damage, so near as you can figure?

Thanks for your insights.

Yours faithfully,

spook

I would NOT drill any holes in the pulley. Doing this might introduce stress risers that could encourage it to fracture.

The pulley normally fits snug but loose enough so that you can slide it and turn it on the crank (by hand). There may be some rust or varnish (invisible) on the metal -- try scrubbing the crank and the hole in the pulley using fine steel wool and then wash it using a solvent, such as carb cleaner.

After you THOROUGHLY clean any residue from the crank, lubricate mating surfaces with engine oil and reassemble.

It's possible that one of the surfaces or edges became "dinged" and a microscopic ridge is causing inteference, hence tightness. Inspect for this.
--
Don Foster (near Cape Cod, MA)

Dear Don,

Good a.m. Thanks for these insights, whc. should be included in the FAQs. I hope you will submit them.

Yours faithfully,

spook

To the FAQ!

Jay, was the crank corroded? If so, the fit will be so snug that you'll have a tough time telling when the key is engaged. Try emery or fine sandpaper on the crank end before you replace, then some antiseize. Next time will be better.

Dear Steve,

Good a.m. and may this find you well. The crank was perfectly clean and smooth. Not a rust molecule was to be seen. Indeed, when I cleaned the area of the crank seal - with acetone - there was only a small amount of dirt/oil on the towel wipes.

In short, on a car with 167K, I'd not have been surprised by a bit of rust, but there was absolutely none.

I thought the balancer was supposed to fit snugly - in addition to being secured by the bolt - so would not have thought to apply anti-seize, which we had on hand (in addition to PB Blaster).

Perhaps in the FAQs, there should be a notation that coating the crank with anti-seize, WD-40, etc., will promote seating of the harmonic balancer.

In this case, though, I think even those compounds would not have enabled the balancer to slide easily into place.

This conclusion is what brought me to the question, about drilling a sight hole through the balancer's face, into the keyway, and the plugging it with grease or a rubber plug.

Yours faithfully,

spook