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Joined: Aug 2012
Posts: 13
Grease Monkey
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OP
Grease Monkey
Joined: Aug 2012
Posts: 13 |
I need your collective help. I have stripped the threads in the block of a head bolt of the ’28 engine I’m building. The block was rusty, chemically de-rusted, and the ½-12 tap sold by The Filling Station to clean the threads passed easily down and up. New head bolts were used and failure occurred before 50 foot pounds was achieved.
What is the fix? I like to install a HeliCoil but which one? What are the threads of the head bolts, UNC, BSW or something else? From my experience with British cars UNC is 5 degrees different in tooth angle and not compatible with BSW. Has anyone installed the more common ½ - 13 HeliCoil and found a new bolt? Your thoughts are appreciated.
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Joined: May 2002
Posts: 6,149 Likes: 42
ChatMaster - 6,000
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ChatMaster - 6,000
Joined: May 2002
Posts: 6,149 Likes: 42 |
The best and easiest helicoil to use is the original thread size and type. UNC and BSW may have the same thread count but as you mentioned the angle and depth are different.
If 1 stripped out the others could well be in similar condition. A friend works for company that builds Military specification equipment, part of the specs is that all threaded holes in alloy must have helicoils fitted as part of original assembley.
Tony
1938 1/2 ton Hope to drive it before I retire
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Joined: Aug 2012
Posts: 13
Grease Monkey
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OP
Grease Monkey
Joined: Aug 2012
Posts: 13 |
Thanks Tony, I will do all 8 when I find the thread, tools and inserts.
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Joined: Dec 2001
Posts: 10,379 Likes: 1
Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
Joined: Dec 2001
Posts: 10,379 Likes: 1 |
My recommendation is to purchase a new set of headbolts, unless you already have them. Take a sample to a good parts house and consult with them for the approiate Heli-Coil kit. The recommendation to "kit" all 8 holes is expensive, however will be the correct choice in the long run. I have used many of the "kits" with complete satisfaction. Good luck on your project!  
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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Joined: Aug 2012
Posts: 13
Grease Monkey
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OP
Grease Monkey
Joined: Aug 2012
Posts: 13 |
Thanks Ray for your thoughts and sharing your success with kits. I've underlying health issues that cause me to do everything 'distance' and Monday will try and set up a drop off and pick up to get the correct tools.
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Joined: Aug 2012
Posts: 13
Grease Monkey
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OP
Grease Monkey
Joined: Aug 2012
Posts: 13 |
Approach taken and why.
Taking the head off after stripping the threads in the block of a head bolt I found a ”˜divot’ almost circular and .17” deep around the stripped thread whole. I also discovered the new head bolt had gone into the block only .4 inches.
Not having any past success with welding cast iron I was unwilling to put in a ½-12 Helicoil and use the new head bolt as they would only have 2.76 threads engaged. Agreeing with advice and noticing the threads in the rest of the holes were in poor shape I decided to treat all 8 holes the same.
Not finding longer bolts in ½-12, and the high cost of the tap and installation tool I decided to abandon that thread.
Placing ¾ inch long ½-13 Heilcoils near the bottom of the holes and using 3 inch studs in the intake side and 7 (6 might be better) inch studs in the exhaust side the and nuts torqued to 60 ft-lb seems to have worked.
Thank to those who shared their thoughts.
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