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head bolt stretch

mr.belvedere

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Jul 20, 2008
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Location
eagle mills, new york
Hey guys. Anyone have a 440 block on the shelf they could give me some head bolt hole depths on? Bolting on some new 440Source stealth heads today, and 3 or 4 of the short head bolts have actually stretched on me before they reached the instructed torque of 70 lb.ft. I'm using 30 weight oil, and 3 step torquing procedure as instructed by 440source. Even using their 12 point head bolt set. Stopped when I thought I was pulling the threads out of the block. Holes were thread chased and cleaned before assembly. Super pissed. Everything brand new and clean. WTF? Read maybe I used too much oil on the bolt head/washer? some say to scuff one side of the washer with 60 or 80 grit emery for some bite? This is a friends motor, but this will be on my dime. Another set of bolts and gaskets already ordered, just dont want to go thru this again. Budget is tight on this car. Put together 3 other B/RB engines in the past. Nothing like this before, but this is the 1st set of aluminum heads I've installed. Not an idiot, just missing something. Any help or advice is greatly appreciated. Thanks guys.
 
Without knowing what kind of torque you have, a torque wrench problem? Borrow one to check against yours.
 
The general torque spec's for cast iron is less than in steel, but you should
check the depth of the tapped holes with a bottom tap and see if your bolts
are too short! If they are, you might have in-fact pulled the threads. In that
case you'll have to Heli-Coil the affected holes. Bummer!
 
Correct or not, I'm not sure, but I've always heard that torque settings are for dry (unlubed) threads.
 
At 70 ftlbs there shouldn't be any observed/measured bolt stretch. If those bolts actually stretched at that torque I'd throw them in the scrap bin! I'd use either ARP or stock head bolts. JMO 440'
 
If you're pulling treads out or stretching 7/16" bolts at 70lbs there is an issue. I always oil stock threaded fasteners. Assuming the Source heads are the same cross section thickness you should have zero issue with a stock bolt as the tread engagement would be factory depth. What type of tap did you chase the holes with? Did it seem to remove metal? Have you tested your wrench? Do you have a "good feel" for what 70/ft feels like? Are you sure the bolt stretched? Lets see a picture.
Doug
 
That thing about the washers sliding is right on. I have had it happen to me but no damage I was using a stud but I knew they had over torqued. But I was unsure the reason the nut just "slipped'' around - luckily for me no harm done.
I now sand the washers and no lube under them. On head bolts light hydraulic oil - one drip on the threads one under the head. None on the washer.
If those bolts got to the "plastic" stage they are no good now.
Faulty fasteners could also be your problem.
1.5 times the thread diameter is a good rule of thumb for thread engagement.
 
Very good info. I had always thought you shouldn't lube washers, and had typically just put a drop of 30 wt engine oil on the threads of the bolt. Didn't realize the engine oil could change things that appreciably.

Thanks for the info! Was going to be bolting down a set of heads soon, using a new set of 440 Source bolts.
 
If you're pulling treads out or stretching 7/16" bolts at 70lbs there is an issue. I always oil stock threaded fasteners. Assuming the Source heads are the same cross section thickness you should have zero issue with a stock bolt as the tread engagement would be factory depth. What type of tap did you chase the holes with? Did it seem to remove metal? Have you tested your wrench? Do you have a "good feel" for what 70/ft feels like? Are you sure the bolt stretched? Lets see a picture.
Doug
Definitely have a good feel for the torque, thats precisely why I stopped. Felt wrong. You know, like your hot cousin? Used a bottoming tap. Didn't feel like it was cutting new threads. Used a thread chaser to just to see how it felt. All Snap-on. I also took one of the longer bolts that didn't give me any issues, and with a little oil, ran it in by hand in all 34 holes with no resistance. The same bolt every, hole. The deck was cut minimally just to get it straight. Still even some evidence of minor pitting around the water jackets, so I know the didn't go nuts. Here's some pics. Maybe I'm confusing stretching with twisting. Honestly at this point, I'm thinking my torque wrench is wonky, or I went crazy with oiling the threads and I hydro-locked them. There was oil on the head gaskets when I pulled it back down. I think I was in a rush, and thought I was doing the right thing.

20201227_164349.jpg 20201227_164422.jpg
 
Definitely have a good feel for the torque, thats precisely why I stopped. Felt wrong. You know, like your hot cousin? Used a bottoming tap. Didn't feel like it was cutting new threads. Used a thread chaser to just to see how it felt. All Snap-on. I also took one of the longer bolts that didn't give me any issues, and with a little oil, ran it in by hand in all 34 holes with no resistance. The same bolt every, hole. The deck was cut minimally just to get it straight. Still even some evidence of minor pitting around the water jackets, so I know the didn't go nuts. Here's some pics. Maybe I'm confusing stretching with twisting. Honestly at this point, I'm thinking my torque wrench is wonky, or I went crazy with oiling the threads and I hydro-locked them. There was oil on the head gaskets when I pulled it back down. I think I was in a rush, and thought I was doing the right thing.

View attachment 1046311 View attachment 1046312

Is that bolt hourglass shaped or just an optical illusion?! I would send those back and get ARP. Worth the money imho.
 
Yep, I'm seeing it also.
My brother gives me a bad time but I still use a old sk beam torque wrench.
 
Good catch on the feel. I've had bolts do what you have illustrated. I wouldn't trust those bolts. China? Light coat of oil on the threads with oil under the head. Makes sense not to oil the washer but I've done it for years. Torque to spec. Let it set 1/2 hour. Crack each bolt loose and retorque. Most every case the wrench will rotate further. Done the this way for over 30 years of motor building. Never an issue.
Doug
 
Good catch on the feel. I've had bolts do what you have illustrated. I wouldn't trust those bolts. China? Light coat of oil on the threads with oil under the head. Makes sense not to oil the washer but I've done it for years. Torque to spec. Let it set 1/2 hour. Crack each bolt loose and retorque. Most every case the wrench will rotate further. Done the this way for over 30 years of motor building. Never an issue.
Doug

Well I started again from scratch. Everything checked out mechanically, so I am blaming human error(me) for the bolts stretching. Got a new set of bolts and head gaskets in FEDEX this morning from 440Source and went to town. Chased and blew out holes again. Sanded the head side of the washers with some 80grit, drop of 30w on the threads, and in between the bolt head and the top of the washer. 40,55,70lbft. Both heads pulled down nice. Man was I relieved! A repeat of that bullshit, and I was taking the bridge. So next question, do I leave them alone? Click up to 71 and hit them again? Back them off and re-torque?
 
I always crack them loose. Learned this long ago. I believe when I worked for Dave Koffel. The bolts always turn a bit further. Many high end rod manufacturers tell you to torque their bolts up 3 times. Good practice. No need to go 3 steps on retorque question. Just pop them loose one at a time and pull to spec.
Doug
 
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