TO CHAMFER OR NOT TO CHAMFER CRANKSHAFT

chamfering the oil galley holes in the crank is a good idea to help eliminate stress risers in the crank. just be very careful if you do the job yourself as you dont want to damage the crank journals.

SCHOONER said:

Hi Rbohm

Can you tell just what is the BEST way to approach chamfering the oil holes please?

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most machinists use an abrasive ball, rather small in size.

SCHOONER said:

What should I watch out for when chamfering?

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you need a steady hand to avoid scratching the journal, and you dont want to over chamfer the opening.

SCHOONER said:

And finally, have you ever done this work on your crankshaft?

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i have never done it, yet, but i have seen it done and i can tell you that patience along with a steady hand is required to do the job right.

SCHOONER said:

THANK YOU GUY

GOD BLESS

Schooner

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anytime.

It's also a good idea to chamfer the oil holes before the crank is ground or polished.

If the crank is already prepped, try using a couple layers of duct tape on the journal to protect it.

I meant more to protect it in case the bit tries to wander off. I would use the ball if it is a larger diameter than the hole, something like twice the diameter, to get it started. Lay the dremel down on it's side at about a 45 degree angle to the hole. You basically want to chamfer the edges of the hole, not make a cup out of it. Then change over to a straight bit and lay it over to about 15-20 degrees to the hole perpendicular to the journal and lengthen it about 3/16" either side of the hole, but no wider. Taper the depth from the outside end from nothing to about 1/16" deep at the edge of the hole. You'll then need a small abrasive bit to ease the edges and then use some emory cloth to polish it out a bit. you don't want the scratch the journal surface, only the hole and 'troughs' you made. This is why this is best done before the crank is prepped to go in.

Personally, for your build (thinking it's a cruiser and not a street/strip warrior) I wouldn't bother. If you're not making over 300hp, I don't think it's needed.

Chamfering the holes at the front and rear of the valley are good. If the block hasn't been cleaned or hot tanked and you want to do more you can clean up all the casting flash on the outside and inside of the block taking care to steer clear of any machined surfaces. I had a 289 block that the whole outside had been ground clean of any casting sand marks. It wasn't perfectly smooth, but with a little more care it could have been and would have looked like a mirror painted black.

all you want to do is break up the sharp edge, and leave a small chamfer on the oil passage opening. a small ball and a little grinding on the edge will do nicely. if the ball is large enough you can just sit it down in the opening, otherwise work the ball around the edge carefully.

Look for bit that is made of I think called Cratex. It's like an ink pen eraser. There different grits. I use them on guns. They can remove metal with out the danger of stones. The fine grits will put a mirror polish on. Still use the tape on the journals. You can find these at some hardware stores or Brownell's web site if you strike out localy. A little slower, not much, but you have way more control and almost totaly eliminate a damaged crank.