Re: Help on a Chevy 350 rebuild

Each rod has a chamfer machined into 1 side where it meets the radius on the outer edge of the rod journal, place 2 rods together in your hand with the chamfers opposite each other.....this is how they bolt to the crank. you must also make sure that the piston that is attached to a particular rod is facing the correct direction (note direction of arrow of top of piston). hope this helps.........

Thanks for the help. It did make sense. But I have a new problem. After assembling, I noticed the crank plus pistons turned over pretty darn hard. I started loostening rod bolts and discovered most of the drag was from the

1-2 pistons. I also noticed there is maybe zero clearance between the big ends of the rods when fitted to the crank. I measured a couple of the other sets and got between 10 and 13 thousands. What should the clearance be? Can't find that spec anywhere. I may have to disassemble and return to the machine shop. If they have to grind clearance, does my balancing job need to be redone? Any comments would be appreciated. The crank was ground to 10 under and I did get the correct bearings. Plastigage told me so.

Unless you machine all 4 rod journals the balance work will be for naught. When assembling a short block you should install the crank assy. , torque the main caps and check for binding, then install 1 set of rods/pistons and rotate the crank again. Are the piston rings file-fit or pre-gapped.....are you sure the rods for 1 & 2 are installed on the journal with the chamfers facing away from each other. It sounds more like operator error if only 1 set of rods is binding. Bearing to journal clearance is measured in ten-thousandths of a inch..... Example:(.0008-.00010") .010"-.013" bearing to journal clearance will have ZERO oil pressure at idle.

The clearance I was referring to the connecting rod endplay (side clearance). Best numbers I can find say 0.006 to 0.017 inch. I was using a feeler guage for this. The rod bearing clearance is within spec and I used plastigage for that measurment. Pistons move up and down without much drag until I torque the 1&2 rod bolts down. Then it binds up. I will recheck those bearings to be sure nothing got in between the bearing and cap or anywhere else but the fact remains I cannot get a feeler guage in between the rod caps so zero clearance on the endplay. I think he made a mistake on the crank machine work. Any other possibilities? Thanks

Nothing i can think of w/o being there.......... Take the whole assy back to the machine shop and measure

Rod end play shouldn't be affected by any crank grinding since it is based on two items that cannot get thicker. The rod faces cannot get thicker and the crank throws cannot either. BUT the problem could be that the fillet grind at the root of the throw could be ground wrong. If it was ground with a racing style fillet it could be to large to fit in the chamfer that street bearings have. That would make the bearings tight. One way to discover the problem would be to use a marker and draw lines straight across the journal and then bolt the rods on, then turn the crank ONCE. Now pull the rod caps and see where the marker is removed from. If it is at the edge of the bearing then the fillet MAY have been ground to large OR you have a rod/bearing in backwards OR on the wrong throw.

350 rod side clearance for STREET engines runs about .006-.010 with anything higher getting close to the limits, Bearings should run .0008 -.0015 any looser and your getting close to limits again.

Good info Steve... but I'm stumped as to why only 1 set of rods is troubled.

Could be the guy grinding the crank didn't set the wheel up on the last pass. I had one that they must have rushed the polish on. The 3/4 journal looked like it was polished with 80 grit... Took it back in and asked them who was the guy who forgot his glasses.

I've also had bearings that were missing the chamfer on the edge as well.

Steve Williams

bearing

rod/bearing

balancing

included

numbers.

I finally disassembled it and took crank and rod/piston back to the machine shop, different machinist. After his first look at it, he thought something looked funky. I'll let you know what he found. Thanks for all the help.

Just FYI, the latest on my crankshaft is that the second machinist told me that the crank was the "worst job of grinding a crankshaft he has ever seen. Absolutely no excuse for this poor quality of work." He also said my rods were improperly resized and the same comment, the "worst". Five of the eight were not bored correctly and would have fit too tight. Three were OK. I guess I did start out saying I was not a mechanic, but I guess I need to get some measuring tools and learn how to use them. It is sad that you trust them with your parts and pay them good money and get crap work. I suppose a good mechanic would not trust the work and check it out everytime. But I have never had any problems before. I talked to the Manager of the NAPA machine shop responsible for the work and he claims that at the time I brought in the crank, they were between machinists and they were farming out the work to other local shops. He did offer to make it good. I had half a notion to ask for a refund and go elsewhere, but now that I have their attention, I hope they will be more careful. And of course, I will have it measured right before my very eyes to let them know I am now paying attention. So what about the plastigage? Either it does not tell the whole story or I don't know the proper way to use it. Thanks for the comments. You did convince me to have it checked out and we did find a problem.

Plastigauge has it's place as a test item but it is no substitute for a good set of micrometers. However if you are only building one engine they are expensive. Crank grinding is not a real hard job BUT you have to know what your doing and have a reliable machine. The guy who does my work has been using the same machine for a LONG time. he makes sure it is maintained very well. I trust his work completely, AND I still check every journal twice....

If they admitted that another shop did the work but they will make it good then I would have it done and let them foot the bill. I would also ask the new guy to show you the measurements for the journals after he is done. Since he will probably have to turn it down to the next undersize so you will also need another set of bearings. He should be able to save the rods.