B21 crank hub removal – will timing gear/belt move if center bolt is removed?

[markusknight23]

I’m working on a Volvo Penta AQ125A (same base as the Volvo B21 redblock / 240 series).

My crankshaft hub (the piece the pulley bolts to) has a broken bolt and a damaged threaded hole. As it sits now, I could reassemble it using only the remaining five bolts, but dont know if that is a good situation long term.

So I’m considering removing the hub and replacing it, which means taking out the large center crank bolt.

My main question is:

On a B21, is the crank timing gear independently retained on the crankshaft, or does removing the center bolt/hub risk the timing gear shifting or the belt losing alignment?

In other words:

Will the timing gear and belt stay in place when the hub is removed?
Or is there a risk of the gear moving or the belt slipping off?

I understand I’ll need to prevent the crank from rotating while doing this—I’m mainly trying to confirm whether removing the hub itself can disturb timing.

For context:

Engine is in a boat (AQ125A), I can’t easily pull the engine
Looking to handle this in-place as cleanly and safely as possible

Appreciate any insight, especially from anyone who’s done crank hub/pulley work on a B21/B23. AKA the AQ125.

cropped aq125 hub.jpg (27.16 KiB) Viewed 2344 times

[volvolugnut]

My Haynes Volvo 240 Series repair manual says there is an alignment pin on the end of the crankshaft to maintain timing after removing the hub. Replacing the hub with the pin alignment should restore timing mark position and allow the camshaft to be properly timed.
I suggest you find one of these old printed Haynes manuals. It will be a great help in maintaining you boat motor and 240 Volvo car.

Use an impact wrench to loosen the big nut. The crank should move little.
volvolugnut

[markusknight23]

Thank You,.

Should I be concerned about woodruff key coming out when I take off the Hub?

What is your best recommendation on immobilizing the engine turning while I work to loosen that bolt?

Ordered Haynes manual. Will be here Saturday.

[volvolugnut]

I believe it is a pin, not a key. This is according to the manual.
If you use an impact wrench, there should be no need to stop the engine from turning. The impacts will normally loosen the nut without much turning of the crank at all. If you use a manual wrench, you will really struggle to get the nut loose. If you do not have an impact wrench, this is a good time to buy or borrow one.
volvolugnut

[markusknight23]

We have one of those Black and Yellow DeWalt battery ones. I assume with the right socket it would have enough force for this.

But wont I need to immobilize the engine when I put the bolt back on and torque it to spec?

[volvolugnut]

Tightening to exact torque is tricky. Most people just hammer it good with the impact and call it good.
The manual says remove the torque converter cover at the transmission and use a large screw driver in the starter gear to hold the crank position. This sounds like a two person job to torque to specs. Maybe lock your propeller shaft on a boat?
volvolugnut

[markusknight23]

Its been suggested to take starter off and stick a wedge in there. Or flywheel lock I think.

[markusknight23]

I’m currently reassembling the pulley on a Volvo Penta AQ125 (the marine version of the B21). I need to confirm the torque specs for the small bolts (M6 or M8) located around the diameter of the pulley that secure it to the hub.

My manual lists a value of only 1–2 ft-lbs for these bolts. This feels suspiciously low for this application. While the manual also specifies a "Crankshaft Pulley" torque at the top of the page, I assume that refers to the large center bolt, not these perimeter fasteners.

Has anyone encountered this spec before? Is it possible the manual has a typo, or is there a different verified value for these specific bolts?

[volvolugnut]

My Haynes manual has the same description and torque spec. I think this is for the big nut. I would torque the several pulley bolts tight by hand to no spec.
volvolugnut