B18/20 Flywheel Bolts/Dowel Pins - '74-75 Metric Main Bearing Bolts/Studs

Building a pair of engines - a 67' B18 engine for road racing (most race clubs limits are only a .040" overbore) and a bored and stroked 2.2L '74 Metric B20 for a road car. Using low-mileage (less stress-cycles) 6-bolt cranks for both engines (what I have) even though an 8-bolt is better.

What is the HP/torque number at which dowel pins should be added to the crankshafts to take some of the load off of the bolts? It appears ARP no longer stocks or sells B18/20 flywheel bolts. Anyone aware of of similar high-strength 3/8"-24 bolts that can be used for this application?

The '74 B20 metric main cap bolts have covered 300K plus miles. Would like to replace the bolts with new ones or studs that can handle 200 HP for long periods of time.

Any help would be appreciated.

I ordered these last year and the P.O. scanned them as delivered, but I never got them. I ended up reusing the originals, but I'm curious to know if they work. Part # ARP 206-2802

jrv6a said:

I ordered these last year and the P.O. scanned them as delivered, but I never got them. I ended up reusing the originals, but I'm curious to know if they work. Part # ARP 206-2802

Click to expand...

Sorry you didn't get them. That part number is the same as a bolt kit BMC A-Series Kit #: 206-2802 which is for the original Austin Mini engine the largest is about 1.3L.

I noticed them when checking the ARP catalog the other day. This is the same 3/8-24 thread and is .900 long under the bolt head which should work on a Volvo. I had been thinking about calling APR and speak with a tech about them to find out if these will hold up in a larger engine with dowel pins because of the extra size and HP.

https://arp-bolts.com/kits/arpkit-detail.php?RecordID=1215

Thanks

A number of members of the Historic Volvo Racing Rally and Speed Society in a post about this have talked about having the flywheel bolts shear off and have either added two dowels pins, or changed to over-sized Dana 30 ring gear bolts. This solves the problem caused by torsional vibration affecting the crankshaft.

Tooling up the milling machine right now to be able to drill and ream two holes for pressed in heat-treated Chromoly dowel pins in the crank and this Volvo Comp Service flywheel and also a aluminum one for racing to end the problem before it gets a chance to begins. The bolts are by ARP.

Will post some photos later after finishing the project.





NOS Volvo Comp Service lightened 18lb flywheel found in its original packing.

Below 9.5lb alloy flywheel.