Camshaft piston rod issues
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Cross-Country
Joined: Nov 2020
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Camshaft piston rod issues
I’ve been rebuilding my ’53 Ford 239 Flathead V8. I had to replace the center main bearing cap and so had to find a machine shop that could align as well as bore the crankshaft. They bored the cylinders to .030, the rods to .020 and the main bearings to .010.
I installed the pistons but only tightened the rod caps firmly. I was able to turn the crankshaft. But when I tighten two rod caps to spec (45 to 50 ft/lbs), I am unable to turn the crankshaft. It doesn’t appear the rods were machined at all, only cleaned.
The machine shop is closed on weekends.
Recommendations?
Thank you.
I installed the pistons but only tightened the rod caps firmly. I was able to turn the crankshaft. But when I tighten two rod caps to spec (45 to 50 ft/lbs), I am unable to turn the crankshaft. It doesn’t appear the rods were machined at all, only cleaned.
The machine shop is closed on weekends.
Recommendations?
Thank you.
Fleet Owner
Joined: Jul 2004
Posts: 27,305
Likes: 1,063
From: NM
Are the main bearing caps tightened to spec? Align-boring the mains is very tricky because of the dovetails in the block and caps, I'm surprised you could find a shop to do that.
Since it binds up when the rod caps are torqued, I'd assume the machining was not done correctly on the rod journals. You might try doing two other journals/caps, see if it is a uniform problem. Otherwise I think you'll have to wait til the shop can weigh in. Likely have to take the block and rods back to them to mike everything.
Since it binds up when the rod caps are torqued, I'd assume the machining was not done correctly on the rod journals. You might try doing two other journals/caps, see if it is a uniform problem. Otherwise I think you'll have to wait til the shop can weigh in. Likely have to take the block and rods back to them to mike everything.
Fleet Mechanic
Joined: Apr 2012
Posts: 1,275
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They wouldn't have bored the crankshaft, they would have turned it to a under size, boring the cyl's .030 would be ok, and turning the rod throws to .020, and the mains to .010, is ok. But if you.re saying they bored the rods to .020, and they needed that much to be round, they should've been replaced, you might check the rod inserts for the size, they might have given you the wrong ones.
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Cross-Country
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Thank you. I discovered my 'rookie' mistake. The book I've been using instructed to "install the bearing shells with the seam at the bottom." My bearings were to be installed in the rod and rod caps with the notch matched to the notch.
Mountain Pass
Joined: Nov 2015
Posts: 221
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From: Clarkdale, AZ
You may want to use plastigauge to verify clearances on all mains. I also check one rod. This is a little more work but worth it to me to verify the machining.
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Fleet Owner
Joined: Jul 2004
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From: NM
I'd assume since you torqued the rod caps down, that the tangs were squashed flat? If so the tangs need to be reworked so they prevent the bearing shells from spinning. Or get replacements. Careful work with a punch with the shell inserted into the rod or cap may work.
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I was thinking that, too, about the bearing shell tangs, that they may be damaged, or even the shells themselves deformed just enough to be an issue from the improper installation. Personally, I don't think I'd risk running them and just replace them for peace of mind. For as expensive as it would be to redo it later, the cost of a new set of rod bearings now is pretty cheap insurance. Imho.
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