Helicoil for head bolts
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=205481
Printed Date: 21 Feb 2025 at 6:43am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Helicoil for head bolts
Posted By: WF owner
Subject: Helicoil for head bolts
Date Posted: 16 Feb 2025 at 3:15pm
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I am putting together a WC engine that has been changed to a 4.5" stroke crankshaft. Two of the head bolts (for the 3" head) are (what I would describe as) "sloppy". When they are threaded in finger tight, they have a little side-to-side movement. I planned to install heli-coil's today during the worst snowstorm we have had in many years (high winds and 18+ inches of snow expected), but I only had 3/4" long (1/2"x13) inserts. There is enough room for a 1" insert. Should I wait and get inserts that are 1" long or do you think the 3/4" are sufficient?
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Replies:
Posted By: ekjdm14
Date Posted: 16 Feb 2025 at 3:24pm
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I would say 3/4" should give sufficient engagement of the threads, but then I guess there's the possibility of the inserts "walking" down the hole as you torque the bolts & resulting in less engagement. If it was me, I'd probably leave the "sloppy" threads be as long as they'll torque down since they'd "probably" be fine also, but as you're aiming to do it the right way then I'd suggest waiting on the 1" inserts.
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Posted By: Alvin M
Date Posted: 16 Feb 2025 at 3:39pm
| I put studs in with red loctite and fine thread at the top to get more torque |
Posted By: Ed (Ont)
Date Posted: 16 Feb 2025 at 3:45pm
Tough question. Helicoils work well. But do you have to have it all the way down is hard to answer. Maybe a machinist would be able to help you. Threads all the way should be better. 
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Posted By: ekjdm14
Date Posted: 16 Feb 2025 at 3:57pm
Actually now I think more on it, the issue of the inserts "walking" may not be as serious as I feared. It was based on the way they screw in easier and tighten up if you tried to back them out, but then they're driven from the inside end anyhow & the torque applied from tightening bolts/studs would be applied from the outer end. We're due to collect a flywheel from our machinist tomorrow so will pose the question to him if I remember.
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Ed (Ont) wrote:Posted By: steve(ill)
Date Posted: 16 Feb 2025 at 4:00pm
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when you screwing into STEEL, you try to get 1 diameter of engagement ( 1/2 inch bolt gets 1/2 inch thick nuts / threads)... when you doing Cast Iron it is 1.5 MINIMUM up to 2 Recommended ..... so for a 1/2 inch bolt, 3/4 thread is the MINUIMUM and 1 inch would be the Recommended depth.. GOOGLE reference.. The minimum thread engagement for cast iron should be 1.5 to 2 times the base diameter of the bolt or screw. ------------- Like them all, but love the "B"s. |
Posted By: DrAllis
Date Posted: 16 Feb 2025 at 5:53pm
| If you decide to helicoil, you'd better try to go with the 1 inch version if you can. If 1 inch is too long, install it and cut it off flush at the blocks deck surface. Remember, you have ONE SHOT at this or the block is JUNK for trying anything else. I had one of my puller blocks with a helicoil repair dead center on the carburetor side for decades and never had a problem. I also used an A-C head stud that was red loctited, so it was never disassembled once the repair was made. I always torque the fine thread nut on a 1/2" stud at 75 - 80 ft lbs and 90 to 95 ft lbs on grade 8 1/2" head bolts |
Posted By: HudCo
Date Posted: 16 Feb 2025 at 9:44pm
| make sure you get hardend nuts grade 8 nuts |