Drilled crank?

[jeepguy1948]

So, I just bought a freshly rebuilt “B” motor (with weighted crank). I was told that it had a “drilled crank” I ham some idea what that means but I know that I could learn more here. In addition, I’m wondering if it would still be a good idea to oil that center main direct or if that is taken care of by the drilled crank. BTW it is using Babbitt (which sort of disappoints me because I can’t replace the bearings myself but I doubt that they will need replaced in my lifetime LoL)

[ursus]

The B crank already has pressurized oil to the main bearings. The drilling is to allow pressurized oil to the rod bearings which, on the original crankshaft, were oiled by dippers.

[nkaminar]

The Babbett bearings can be taken up by removing shims. Usually only one or a few thousands shims at a time. This was a maintenance thing back in the day. That is one advantage of the poured Babbett bearings. If you start to hear a knocking or ticking sound, after many thousands of miles, check the bearing clearance and adjust it if necessary.

Depending on how the engine was set up during the rebuild, the bearings may be needed to be taken up after the breakin. This is usually not necessary. This was more prevalent with Model T's where the bearings were fit to the journals by scraping the bearings.

A drilled crank can be used on an engine without pressure lubrication, as long as the dippers are on the rods.

Cranks are drilled by drilling holes from the main bearings to the rod bearings. A rifle drill is used and a jig is used to make sure the drill goes though the webs and ends up at the right place on the rod journals. The holes are chamfered or the edges rounded so that they do not scrape the bearings. (Or extended drill bit, thanks John.)

[Jim Brierley]

Nothing wrong with babbitt! I've run it in my race engine for many years. The mains do hold up better than the rods, but I have turned than 6,000 RPM many times at the drags and at Bonneville. Best time on the salt was 167.45 MPH, still looking for more.

[johnneilson]

Chances are the motor has already been modified to pressurize the bearings
Stock B motors are not pressurized only have oil directed to the bearings
Get a copy of Brierley’s book the best buck for your banger

J

[johnneilson]

Sponsored Links (Register now to hide all advertisements)

Gun drill is not necessary only need extended drill bit
The distance is approximately 5 inches
I drill mine with a fixture to hold crank on proper angle in mill
J

[jeepguy1948]

I have Jim’s “Bangers an Me” book as well as one of his heads. I was not aware that he had written another book.

[BRENT in 10-uh-C]

Originally Posted by jeepguy1948

So, I just bought a freshly rebuilt “B” motor (with weighted crank). I was told that it had a “drilled crank” I ham some idea what that means but I know that I could learn more here. In addition, I’m wondering if it would still be a good idea to oil that center main direct or if that is taken care of by the drilled crank. BTW it is using Babbitt (which sort of disappoints me because I can’t replace the bearings myself but I doubt that they will need replaced in my lifetime LoL)

This is something that is often misunderstood about bearing conversions. From my experiences, probably 90+% of the time when insert shell bearing wear the alloy off of the shell, the metal bearing shell starts wearing against the crankshaft's journal pin. When this happens, at some point it generally rolls the bearing inside of the journal and cap. Unlike a cast bearing where you hear excessive clearances, most everyone says it just suddenly started rattling and then started seizing up.

Every block that has come thru here that has spun an insert bearing, it generally distorts the main cap or kills the rod. The thickness of that insert shell must go somewhere, and something has got to give!! While there are some guys that will 'butcher' it back together by polishing the journal pin and slapping a new pair of inserts in it, the proper way is to either replace the damaged main cap or re-size the existing cap. Either way, it generally takes line boring again or at least line honing again to get all mains the proper size to crush the bearings, -AND coplanar again. Most hobbyists do not have that capability, so they cannot replace the bearings themself anyway.

[johnneilson]

Brent

I think much of the insert failures are from improper initial installation/ setup

Some of the failures are a complete loss as you indicate, but even if it had been Babbitt it would have resulted in the same damage

There have been several installations that I corrected before damaging the motor
All of these issues had been with oiling schemes and insert stacking

Then of course the driver does need to pay attention to what they are doing

J

[Pete]

I have drilled a few B cranks for the full pressure mod. I did it on a Bridgeport with V blocks and tipped the head. I used a 3 flute drill. They don't wander like a standard 2 flute one.