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Joined: Apr 2014
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Shade Tree Mechanic
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OP
Shade Tree Mechanic
Joined: Apr 2014
Posts: 46 |
I am wondering how bad I have screwed up. I have a 1927 motor that I was cleaning up and I ran a standard 1/2" tap into the head bolt holes to clean the threads up. Will the bolts still hold or will I have to install new threads?
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Joined: Dec 2001
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Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
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Depends on how hard it was to turn the tap. If you really got into it you may be in trouble. I would try to install the head and see if you can put 50-60 lbs on each bolt. You should be able to "feel" how it is going and see if it will accept the torque. You may have to drill and put inserts in the block.  
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: Apr 2014
Posts: 46
Shade Tree Mechanic
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OP
Shade Tree Mechanic
Joined: Apr 2014
Posts: 46 |
The tap went in freely and all that came out was some dirt. I can see the threads in the hole and they look good. At this point would you use the original head bolts or switch to modern bolts?
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Joined: Nov 2001
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ChatMaster - 15,000
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ChatMaster - 15,000
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I would use the original bolts as you can't tighten them as much before they stretch. Less tendency to over tighten in case there might be a problem. I would take it easy but don't expect a problem. 60 ft/lbs would be the max. torque with oiled threads.
How Sweet the roar of a Chevy four!
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Joined: Jan 2012
Posts: 179
Shade Tree Mechanic
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Shade Tree Mechanic
Joined: Jan 2012
Posts: 179 |
The head bolts on my '27 are 1/2"-12 threads per inch. If you used
a modern 1/2" tap it would be 13 TPI. My 6 cyl motors are 13 TPI so
I have always assumed that Chevy converted to the 13 TPI in '29 with
the new six. Looking through my Dad's old Machinerys's Handbook from
1940 I see that there was a 12 "pitch series" for S.A.E. standard screws
equivalent to the British Standard Whitworth screw thread for 1/2".
I have just run into this situation on my '27 where a previous owner
had used a modern 1/2"-13. They go in but they don't torque properly!
Did that tap damage your block??? Guess you have to place the head on and torque some bolts in.
Dan
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Joined: Sep 2008
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ChatMaster - 1,000
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ChatMaster - 1,000
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Ladies and Gents
Should I consider Lock tite on head bolts? Do you check them after reinstall to make sure they remain tight? In the past a few head bolts have loosened on my car. I did not used lock tite when I changed head.
Ken
I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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Joined: Dec 2001
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Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
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No!
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: Jan 2002
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ChatMaster - 1,500
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ChatMaster - 1,500
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No Locktite. It's normal for the old head bolts to loosen after a short while, and therefore need to be re-torqued - maybe a couple of times - after running in.
Chevy Guru
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Hi Guys, Back in 2012, I replaced my 28 Head bolts with stainless steel studs, with the normal thread going into the block, lubed with never seize, and a fine thread at the top. This allows the head to be positioned right on the first attempt, and eliminates head bolt stretch. See the link to the posting on my blog http://my28chev.blogspot.com.au/2011/10/2011-27th-october-head-studs-for-future.htmlThese studs were fitted in 2012 when I changed the head over due to a couple of burnt out exhaust valves after 39 years. See the link to my posting below, but note since then I have abandoned the after market carby and gone back to standard. http://my28chev.blogspot.com.au/2012/03/head-job-for-red-chev.htmlHave had no reason to be concerned about using studs so far, 3 years later. Cheers Ray
Some say "Street is neat". I prefer "1928 is great" I have documented my 45 years with a 1928 Chev Tourer, from 1973 to 2018, and regulary add other items that I hope are of interest to others. Your comments are most welcome.The story of the Red Chev can be viewed at http://my28chev.blogspot.com/
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Joined: Aug 2006
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Backyard Mechanic
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Backyard Mechanic
Joined: Aug 2006
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One other option is to have a machine shop install 1/2-13 helicoils in the block and use a new grade 8 bolt. You can grind and polish the bolt head to get rid of the grade marks to make it look a little more stock.
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Joined: Sep 2008
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ChatMaster - 1,000
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I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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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
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You are welcome!
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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