The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - PROJECT: How would a Chevrolet dealer build a shop truck in the early 1970s?

**mattfranklin** · 09-05-2015, 02:00 AM

Where did that rod noise come from???

SHORT ANSWER: A 0.010 under crank with STD rod bearings makes a lot of noise.

LONGER ANSWER:

EXPLORING
Pulled the pan and had a chance to check the crank bearings. Yikes! There was movement I could feel and hear as I rattled the big ends back and forth. Of course there was the side clearance which is ok, but also a clink-clunk in the direction of rotation. I've not done a lot of engines, but I don't remember any healthy engines doing that. I pulled off one of the caps that was among the loosest offenders and convenient to reach: #4 cylinder. With the #4 piston and rod fully out I could measure the crank and look at the bearings.

MISMATCH!
Look at the pics and you'll see micrometer reading and a picture of the rod bearings. The later small blocks had a 2.10 rod journal diameter. Micrometer reading looked like .012 less (25 minus the 13 reading on the scale = 12) than 2.10. To me that feels like a 0.010 bearing might fit that with a nice 2 thou clearance. Note that "STD" stamped on the rod bearing! No wonder it made those rod noises even with 15W-40 oil! I'm guessing the rest are in about the same state.

09-05-2015, 02:00 AM	#48
mattfranklin Senior Member Join Date: Dec 2011 Location: Moraga, CA Posts: 804	Re: PROJECT: How would a Chevrolet dealer build a shop truck in the early 1970s? Where did that rod noise come from??? SHORT ANSWER: A 0.010 under crank with STD rod bearings makes a lot of noise. LONGER ANSWER: EXPLORING Pulled the pan and had a chance to check the crank bearings. Yikes! There was movement I could feel and hear as I rattled the big ends back and forth. Of course there was the side clearance which is ok, but also a clink-clunk in the direction of rotation. I've not done a lot of engines, but I don't remember any healthy engines doing that. I pulled off one of the caps that was among the loosest offenders and convenient to reach: #4 cylinder. With the #4 piston and rod fully out I could measure the crank and look at the bearings. MISMATCH! Look at the pics and you'll see micrometer reading and a picture of the rod bearings. The later small blocks had a 2.10 rod journal diameter. Micrometer reading looked like .012 less (25 minus the 13 reading on the scale = 12) than 2.10. To me that feels like a 0.010 bearing might fit that with a nice 2 thou clearance. Note that "STD" stamped on the rod bearing! No wonder it made those rod noises even with 15W-40 oil! I'm guessing the rest are in about the same state. Attached Images __________________ (Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1 http://67-72chevytrucks.com/vboard/s...d.php?t=567340 Last edited by mattfranklin; 11-05-2016 at 10:21 AM.