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| Northstar rebuild: Will style (Page 46/119) |
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Will
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MAY 10, 10:12 PM
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I had just snugged the short block together the first time so that I could get a timely measurement of deck height. I couldn't do the final torquing and sealing because I still had to replace a couple of rod bolts. The shop overtorqued/overstretched them when checking the bearing ID. The rod bolts arrived last Friday while I was closing on the house. I installed today and put final stretch of .0055 on all rod bolts. All bolts had ARP assembly lube applied to the threads and under the heads beforehand.
The lower case half must be removed to torque rod bolts because you can't put a stretch gauge on one bolt from every rod with the case half in place.
I dug out my new in the bag case half seals. I had to look for my rear main seal for a while, but I did find it. The book calls for a dab of RTV at each end of each case seal. Two of these join the case seals to the rear main, and the other two join them to the front cover seal.
I have no idea what's wrong with the design, but apparently the only entity that can put together a Northstar without sealant between the case halves is GM's assembly line. I've heard from all directions to run a bead of Loctite 518 (same as used between the Getrag case halves) both inside AND outside the case seals... so I did. McMaster-Carr carries 50 ml tubes of the stuff for about 1/4 of what GM wants. Summit carries it for about half of what McMaster-Carr wants.
I didn't technically "need" to, but I used ARP assembly lube on the threads and under the heads of the main bolts.
The main bolts take 15 ftlbs + 65 degrees in the sequence pictured in the FSM. What GM doesn't make clear is whether they expect this to be "per bolt" or "per pass". IE, should I tighten each bolt to 15 ftlbs and then turn it 65 degrees, or should I tighten all bolts in sequence to 15 ftlbs, then turn them all 65 degrees. I chose the latter.
I'm glad I did.
Lesson learned: religiously RE-check the 15 ftlb pre-load torque for ALL main fasteners immediately prior to applying the 65 degree final load.
In following the book's sequence for the main bolts, you tighten the outer rows, then the inner rows. If you then go back over the outer rows, they will have ALL relaxed to some extent as the inner rows were tightened. If you turn the bolt next to it 65 degrees, any given bolt will also relax slightly. The last step before applying the 65 degree twist to ANY main bolt should be to re-check that it is holding 15 ftlbs.
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Scoobysruvenge
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MAY 11, 03:26 PM
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Will,
Maybe you should find a real machine shop and save yourself some money and time, because it sounds like you have had nothing but poor work done so far.....
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Will
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MAY 11, 07:27 PM
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Maybe you should find me a "real" machine shop that knows the Northstar inside and out well enough that I can turn them loose and don't need to look over their shoulders... Oh yeah, I have to be able to afford their work also.
Northstar's just a tough engine to build. I also thought it was odd that the bolts would be overtorqued, but the sheet that Eagle sent me with the replacement rod bolts listed the stretch specs for several different types of ARP bolts. The 3/8" ARP 2000 bolts in the Northstar rods get tightened to 43 ftlbs and stretch .0055. The 7/16" L-19 rod bolts used presumably in BBC rods get tightened to 78 ftlbs and stretch .0077. Many rod bolts have stretch specs between .006 and .007. It's an understandable mistake than only very specific knowledge of the application could prevent.
Got shipping confirmation on the head gaskets, so I should get them tomorrow.
Got one of the heads apart and run through the parts/dish washer. I should be able to do the other one tonight and then run them both through again with the exhaust sides down. The exhaust sides of the heads are incredibly oily thanks to the issues I had with the first build.[This message has been edited by Will (edited 05-11-2009).]
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Scoobysruvenge
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MAY 12, 08:58 AM
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Will,
It has been my experience that a good machine shop will have a proprietor that has a degree as a machinist, there is a lot more to it than learning to run a mill or a lathe, there is also a lot of metallurgy that goes along with one of these degrees. A well trained machinist should have recognized when his tools are wearing excessively for a given job, not because he’s worried about you, because he has to pay to replace that expensive tool he’s wearing out on your block.
It looks like you are trying to do a meticulous job on your engine, and I know that a precision assembly on a stock engine yields big gains in reliability as well as HP and knowing you Will, I would have thought you would have been absolutely livid after they screwed up the fist time and found someone else to do the work.
I am enjoying seeing you wrestle with this project, and I will keep tuned in.
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tjm4fun
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MAY 12, 12:15 PM
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| quote | Originally posted by Will:
...........
I didn't technically "need" to, but I used ARP assembly lube on the threads and under the heads of the main bolts.
The main bolts take 15 ftlbs + 65 degrees in the sequence pictured in the FSM. What GM doesn't make clear is whether they expect this to be "per bolt" or "per pass". IE, should I tighten each bolt to 15 ftlbs and then turn it 65 degrees, or should I tighten all bolts in sequence to 15 ftlbs, then turn them all 65 degrees. I chose the latter.
I'm glad I did.
Lesson learned: religiously RE-check the 15 ftlb pre-load torque for ALL main fasteners immediately prior to applying the 65 degree final load.
In following the book's sequence for the main bolts, you tighten the outer rows, then the inner rows. If you then go back over the outer rows, they will have ALL relaxed to some extent as the inner rows were tightened. If you turn the bolt next to it 65 degrees, any given bolt will also relax slightly. The last step before applying the 65 degree twist to ANY main bolt should be to re-check that it is holding 15 ftlbs. |
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IIRC, when doing arp fasteners, without the guage, they want you to tighten and loosen 3x, and the instructions state that for one thing it is to even out and force out excess lube. I never researched if that is a big factor tho, I just followed the instructions, as they do know what the design point is for their studs/bolts.
Sounds like you did the right thing on the mains, last motor I did that had tty bolts/studs I went round and rechecked the initial torque about 5 times, the last time I actually took a short break before going back to it and degreeing them in. That is one of the biggest issues with aluminum/alloy blocks, so your time there is well spent. Personally I don't like tty, but with the expansion factors of these materials, I understand it is the only way to maintain proper spec. besides, what's another tool in the box.... I have so many obscure ones already...
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Will
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MAY 12, 12:31 PM
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Torque + Angle is NOT Torque To Yield
15 ftlbs + 65 degrees on a 5 inch long bolt is T+A.
15 ftlbs + 120 degrees on a 1.5 inch bolt is TTY.
The first is a N* main bolt, the second is a factory N* rod bolt
Everything I've read about consistent torque of rod bolts has to do with making sure that a given torque equates to a desired stretch. If you're measuring stretch directly, it all goes out the window. The lube is only necessary to reduce friction and make it easier to pull on the wrench to get the stretch you want.
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Scoobysruvenge
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MAY 12, 03:40 PM
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Will,
I get where you are going with the rod bolt stretch measurement, but I have some questions, if you are going by stretch measurements alone then how can you properly load the bearing? What I mean is that the rod and cap need a specific torque range to ensure that the hole stays round, too much torque and the journal becomes egg shaped horizontally and not enough the journal becomes egg shaped vertically. How did you come up with the stretch measurement?
Did you buy some extra rod bolts and torque them to the desired ftlbs and measure the stretch of the bolt and then used that measurement to stretch the others to the desired measurement? Or is there an ARP chart for the bolts that you bought to convert stretch into a torque value?
The lubrication of every nut and bolt that receives a torque spec is a must, this is so critical according to multiple manuals I own that if it is forgotten that the engine component in question must be taken apart and re-assembled, they also state that torque and stretch specs should be reduced by 10% when using a mulisulfide lube and 5% for machine oil.
I will be performing similar measurements in the near future and I am curious to see how this all comes out. Keep up the Hard work..
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Scoobysruvenge
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MAY 12, 03:55 PM
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Let me clarify, is the chart an ARP chart and if it is not how reliable is it?
On the lube subject all OEM torque specs are dry specs with no lube.
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sanderson
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MAY 12, 04:56 PM
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Will
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MAY 12, 06:30 PM
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Stretch is the PRIMARY indicator of clamp load. All bolts are springs with a spring rate of Young's Modulus.
Torque is simply a WAG at bolt stretch and for torque to accurately indicate bolt stretch, a whole lot of domino(e)s have to be lined up: correct number of torque cycles, burnished threads, correct lubricant, calibrated precision torque wrench, etc. I simply bought a stretch gauge and bypassed all of that.
One thing I didn't do is mic each rod bolt for my quality records.
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