Rod cap torque? November 19, 2007, 12:01:18 AM Is the torque for the connecting rod bolts really only 19-24 ft lbs?--------------------------------This weekend I lapped in some low mileage GT40 heads form a 93 Cobra and built up the fresh longblock which is to wait for powdercoating of a few parts before bolting on the oil pan and intake. I want to verify this though as it seems kinda low for the connecting rods. They're new Scat I-beams with ARP bolts.On a related note, I didn't realize until this weekend that the heads and intake I got from a guy also came with NEW ARP head studs and what appears to be brand new sparkplugs. All in baggies, I never took much of a look at them and thought they were just bolts and used sparkplugs. $500 well spent for 35k mileage heads, port matched intake to heads, gasket matched upper to lower, and new ARP studs. All I was told when I bought them was they were low mileage, nothing about port matching or studs. Its been a pretty good weekend :D Pistons and rods weigh in at 768.5 grams within I think it was like .002 grams of each other after the balancing. Standard 30/10/10 rebuild with 7.4cc dish pistons, 62cc gt40 heads with stock 1.7 RR, HO cam, cobra intake, Scat 4340 rods with ARP bolts. Should be right at 9:1 compression and will get 6psi added next year.As for , it currently sits as below: Quote Selected
Rod cap torque? Reply #1 – November 19, 2007, 03:39:47 AM QuoteIs the torque for the connecting rod bolts really only 19-24 ft lbs?That's what Autozone and Haynes say for the 5.0 Quote Selected
Rod cap torque? Reply #4 – November 19, 2007, 05:40:47 PM Actually, it depends on the diameter of the bolts. If those are 5/16" bolts, then 19-24 is plenty to stretch them, if they are larger diameter then you will need to apply more torque to properly stretch them. ARP should provide torque specs for their bolts though - look it up, call ARP or do a search on a site like Hardcore50.com. Quote Selected
Rod cap torque? Reply #5 – November 20, 2007, 02:25:44 AM Fair enough, just making sure. Using 3/8" bolts, they're supposed to be 28 ft lbs I believe - still not a lot.Are there any things I may overlook when rebuilding the motor? Simple things such as sealing the lower head bolts as they protrude into the water jacket. Any certain bolts that would be best to loctite? Everything's on right as far as I know - caps/bearings are all in the correct place/direction and the connecting rods are all facing the right direction with the beveled edges facing the crank and not the opposite rod; stamps on the rods are all facing the oil pan. So far all clearances are within specs with plastigage.Its really the small things that'll get you.On another note, the spark plugs face different directions when installed into the heads? This doesn't seem right... Quote Selected
Rod cap torque? Reply #6 – November 20, 2007, 10:41:53 AM Do you have assembly lube on the bearings? Has the engine been primed with oil? If so, you should be able to rotate the crank with with out much effort. What were your clearances on the main and rod bearings? 0.0015 - 0.002" is a good range for street engines.Don't forget to loctite the cam bolt, many forget this. Quote Selected
Rod cap torque? Reply #7 – November 20, 2007, 12:32:26 PM Quote from: Seek;188713Fair enough, just making sure. Using 3/8" bolts, they're supposed to be 28 ft lbs I believe - still not a lot.The optimum bolt torque leaves the bolt stressed at 75-90% of its proof load. The proof load is the highest load the bolt can take without permanently deforming.You can measure this directly using a dial gauge to see how much the bolt stretches. Since strain and stress are related, you can use this relationship to find out how much strain (change in bolt length) is needed to properly load the bolt. Using a torque wrench throws a proverbial wrench into the equation. You aren't directly measure bolt stretch, but rather trying to guess what the friction is and applying proper torque to overcome it. As you tighten the fastener, the thread-to-thread interface generates friction. Adding oil or anti seize to the fastener can change the coefficient of friction and change the actual proof load generated by a certain torque applied by the torque wrench. Thread pitch also plays into the formula. Finer pitch causes more friction.Also, the proof load is dependent on the strength of the fastener material. A grade 8 bolt will require a higher load than a grade 5 bolt.All of these variables play into the torque required to reach a certain proof load.In this page, you can see how thread pitch, friction, and strength all play into the proper torque needed to properly tighten a certain fastener. Quote Selected
Rod cap torque? Reply #8 – November 20, 2007, 01:19:47 PM Someone had to take it to the ultimate level of detail!The pro's measure the stretch directly as they cannot afford to have the variables involved in torquing lead to a broken rod bolt. Quote Selected
Rod cap torque? Reply #9 – November 20, 2007, 07:02:05 PM Quote from: 88BlueBird;188733Do you have assembly lube on the bearings? Has the engine been primed with oil? If so, you should be able to rotate the crank with with out much effort. What were your clearances on the main and rod bearings? 0.0015 - 0.002" is a good range for street engines.Don't forget to loctite the cam bolt, many forget this.Yes on the assembly lube, haven't bolted everything together to load up with engine oil all over other than the cylinder walls and such. The crank rotates beautifully as it sits. I don't remember clearances (this is being built 150 miles away) but they were within tolerances. The machine shop seems to think a 3/8" ARP bolt should be much higher than 28 ft lbs but the counter guy was going to talk with the machinists on that.edit:Talked with SCAT, 50 ft lbs on the rod bolts - sound much better. Quote Selected
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