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3.8L Balance Shaft too tight (1998 Oldsmobile Intrigue)

Old 06-12-2019, 05:45 PM
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Default 3.8L Balance Shaft too tight (1998 Oldsmobile Intrigue)

I am rebuilding my engine. I pulled all bearings, including the rear balance shaft bushing to have the block hot tanked. I used the approved Kent Moore bearing reinstallation tool for the new rear bearing, which says that it places the bearing at the right location/depth when the tool hits the transaxle flange. It seems to indeed be a the right depth location, as upon reinstalling the balance shaft, there does not seem to be any protrusion at the other end of the balance shaft.

(For those of you who don't know, the balance shaft has a bearing sort of like a cam bearing in the back of the block bore, pressed in. In the front, the balance shaft has an integral ball-bearing that stays with and is part of the shaft when it comes out, and which gently squeezes into the front block bore. in front of the ball-bearing is a clip ring, which when hitting the front of the block bore, indicates that the balance shaft is inserted far enough into the block (slides in from front side).

If the rear bearing were too far toward the front of the block when pressed in, it would result in the balance shaft being too far forward, and the clip ring would not be able to contact the front of the block upon insertion because the bearing would prevent the shaft from sliding in deeply enough.

On my application, the shaft seems to go "thump" as the ring hits the front of the block, and it visually appears to be contacting the front of the block, indicating both:

1. The balance shaft is inserted as far as it can go into the block, and therefore is correctly installed; and
2. That necessarily, then, the rear bushing is not too far forward in the bore and is as such not preventing the balance shaft from being installed deeply enough.

The balance shaft spins freely when I rotate it by hand. So all seems fine, right?

Well, there is a metal plate called the "balance shaft retainer" that bolts onto the front face of the block and is shaped to butt up against the front of the ball bearing race on the shaft. This device acts to hold the balance shaft into the block, much like a thrust plate holds a camshaft in the block (although it is form-shaped and is not flat like the camshaft thrust plate).

When I install this, and torque the bolts to 22 ft lbs per spec, the balance shaft tightens up a lot. Such that I can barely turn it with the strength of my hand while gripping it. Seems really tight to me, perhaps way too tight. I don't remember if the factory installation was easy to turn by hand before disassembly, but that seems to be my recollection.

The next step is to install the balance shaft driven gear to the end of the balance shaft. This requires the balance shaft to be held from turning while it is tightened on. The process is to tighten the gear bolt to 16 ft lbs, and then rotate an additional 70 degrees. The shaft is snug enough when doing this, that it won't even start to turn when tightening the gear bolt at the end until the torque reaches about 10-12 ft lbs. Only then do I need to hold the balance shaft from turning.

The procedure also calls for shaft end play to be measured after the balance shaft retainer is installed. Spec is for not more than 0.028" of end play. Well, as you can imagine by the tightness of the shaft, I cannot achieve any end play by hand.

QUESTION: is this normal on a virgin install? In other words, if I get the motor running, will the tightness dissipate by high rpm friction of the shaft against the retainer, or from the inner face of the rear bearing? If this is not normal, please describe what normal would look and feel like. Is it possible that the rear bearing is actually too far forward by as little as 0.001" or so, which is not visible by the eye, but is leading to the tightness once the retainer is snugged up?

Please help. This build has already been delayed, and I am very frustrated.

Lastly, note that I have already installed the rear crankshaft seal and rear seal housing cover. This is relevant because the balance shaft bearing can no longer be accessed from the rear side of the block unless all of that work is undone. NOTE further that I may be able to move the rear bearing back a wee bit from pressing or hitting it (I have the correct Kent Moore bearing mover/remover insert) it from inside the back block wall. However, as the front ball bearing clip ring seems to be fully contacting the front of the block, moving the rear bearing may be irrelevant.

I really appreciate the help of anyone has done builds on engines with balance shafts and friction/contact retainers on the front of the block, to tell me whether the foregoing is normal, or definitely not mormal, and in either case, whether I can proceed with further assembly and installation and let it "sort itself out" by wearing the retainer metal off or whatever. NOTE: the front retainer seems to "stretch" a little just before it is fully torqued to spec, so I am hoping firm contact that makes the hand unable to rotate the balance shaft is in fact normal.

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Old 06-12-2019, 06:37 PM
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Default Solved

I used my old camshaft as a an anvil to place against the rear balance shaft bearing, and struck it good and hard with a 4 lb sledge. Nudged the bearing back about .010". Result is a free spinning balance shaft with retainer torqued to spec!

Problem solved.
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