Sorry but i could not view the bolts in your link. It required me to log in/create an account.
Whatever bolt you buy do not torque it to the specs for that grade. For example, if you buy the Grade 8 bolts and torque them to Grade 8 specs I expect you will damage the threads in the block.
I would not be concerned with the new bolt being 1/8” shorter. As noted in that older post, chase the threads in the block and clean the holes very well. I spray brake cleaner in the holes, let it dry, and then blow them out with compressed air. You do not want any liquid in the holes.
Make a couple of guide pins from your old bolts. That will make sure the head gasket does not shift when you set the head on the block.
I will let a ‘32 expert jump in if my practice is not appropriate for a ‘32 engine. I do dip the head bolts completely in engine oil. Then I let them lay on a rag for quite a while so most of the oil drains away. I want just a light uniform coating of oil including under the head and along the full body.
For these bolts being oiled and threading into cast iron I would target 60 ft. Lbs as the final value. I always tighten in the sequence shown in the shop manual. I typically go in 3 steps starting at 50%, then 75%, and then 100% of that final value. Some people like to do 4 steps with the 3rd step being 90%.
Adding to Rusty's idea with the oil I put a drop of oil on the end couple of threads and another under the head just before putting them into place. That way there is no binding of the threads or head to give a false torgue reading. Tony
Awesome advice Rusty and Tony, thank you! I also read that retorquing needs to be done after warming the engine to normal. I assume this is good practice still?
A technique I learned from an old mechanic 60 years ago was to tightened each bolt using three to four cycles at each step. The cycles are tighten to the specific torque, back off, tighten again noting if the wrench moved further than last time. If it moved a noticeable amount repeat. What is happening is that the high spots on the threads both on the bolt and block are smoothed out. When re-torquing after several heat cycles I find little to no difference.
The key point in this situation is the length of thread engagement between the bolt and the hole in the block. That sure looks like more than 1/8" difference.
From a design perspective we typically wanted engagement to be 1 1/2 times the nominal thread diameter in cast iron. In this case the target is 3/4".
And now for the really stupid question. What is the reason you need to replace the original bolts?
question what is measured length of the original head bolts now ? did you mic them out ? they could be STRETCHED, i would measure to validate the Overall Length, if stretch then you for certain do NOT want to reuse them. length would be measured from underside of the head to the flat of the other end. my head bolts measure around 4.17
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When I measured the difference with tape measure it’s very close to 1/8 but not precise. The reason for changing out the bolts is I had to pull the head off due to a leaking head gasket and when cleaning up some of the bolts they looked rough. Also the previous owner had one bolt replaced that was longer and had a lock washer on it. I figured it would be best to replace all with new ones instead of trying to mess with used.
I will need to get more precise measurements on the bolts and report back.
I used my digital caliper and took some measurements. All old bolts measured longer than 4 1/8 mine or filling station. Based on the measurements a 4 1/4 bolt should fit without bottoming out. .91 vs 1.01. Doesn’t factor in any stretch? Doesn’t factor in gasket between head and block.
Mcmaster bolts measure 3.99-4
McMaster bolt sticks through head .66in
Bolt can thread in to block 1.01 in before bottoming out. Checked passenger side holes after they have been chased and cleaned.
Thanks for taking the time and making the effort to collect some real data. That really helps me when I am trying to determine next steps.
This reminds me of one of the key principles from the last manager I worked for. When he became manager of the group he stated his approach this simply. “In God we trust! The rest of you better show up with data.”
I really think you should consider going with the 4 1/4” bolts. Knowing that the 4” bolts are 4” maximum and that you only have 0.66” extending from the head I think you would be in a better situation with the longer bolts. Remember that your 0.66” does not include the thickness of the head gasket. Plus your work indicates that the threaded holes can accept the longer bolt.
Thanks for the help Rusty. I really appreciate all the insights and feedback. It looks like in 4 1/4 bolt sizes they have zinc-aluminum plated but otherwise same specs. Any issue with this bolt type, seems to have more corrosion protection. Pic attached and link if it works.
I agree with your concern about that coating on the 4 1/4” bolts. There is the potential for galvanic action between the aluminum in the coating and the cast iron of the head and block. That bond could make it really difficult to take apart.
My preference is to use a plain (no coating or plating) bolt if possible.
The “messy” alternative is what Chipper mentioned in his early post. Buy longer and cut them off. Thread a nut onto the bolt so the exposed face of the nut is 4 3/16” from the underside of the head. Clamp the bolt head and nut in a vice with the nut sticking out slightly. Use a cut-off wheel in a disc grinder to cut off the exposed thread. Turn the nut as far as you can by hand towards the head. Then round the point slightly on a grinding wheel to give you some lead threads. When you turn the nut off it will clean-up the threads.
Remember that the nut will be hot right after you finish the cut. (Don’t ask how I know.). I expect that you will sacrifice a few nuts in the process. (Pun intended.)
Also, I would not be concerned at all if you can only find Grade 5 bolts. You will be torquing the bolts to just about Grade 2 specs. The original bolts were only the equivalent of Grade 2.
Thanks, Rusty. I had to do some searching on galvanic reactions to understand more. I found the attached chart from a fastener place. Am I reading it correctly that if the fastener is aluminum in steel or cast iron it’s not likey to increase corrosion? Always learning something new. I did find some at Grainger that are black oxide, all else is similar as far as standards.
I bought some of the zinc aluminum bolts to see length and see if there was a way to remove coating. The length is perfect and only slightly longer than original bolts and the coating came off pretty easily using a wire brush on a drill. The pic attached the cleaned up bolt is on the left, bolt with coating on right. Since the length is perfect and it cleans up easily I’m inclined to go with these bolts. Either way its work with cutting the bolts or wire brushing them. Thoughts?
My first question would be...What is the Grade of the new bolt? It is a Grade 5 or Grade 8 or ? How many marks are on the head of the bolt? I would suggest that you not use a "soft" bolt as a Head Bolt.
dave
the toolman 60th Anniversary Meet Chairperson Dave VCCA # L 28873 VCCA #83 Tool Technical Advisor for 1914-1966 VCCA #83 1940 Chevrolet Technical Advisor
To be clear, since you say they are grade 8 that the bolts are steel with a zinc/aluminum coating? The wording of the question might indicate an aluminum bolt with a zinc coating, hence Dave's clarifying question. If you've decided to use these bolts and are no longer looking I'll move this thread to the Mechanical - Engine forum. There's useful info here and threads in this forum are periodically purged.
Last edited by Tiny; 01/07/2408:10 AM.
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I agree that this became a great technical discussion. Thanks for moving it!
If wire brushing removed that coating it definitely did not have good adhesion.
There is minimal risk using those bolts. The big variable that we tried to control in bolted joints was the coefficient of friction between the threads and under the bolt head. Different coatings and platings plus the presence or absence of a lubricant change that coefficient. If the coefficient is high it takes more torque to produce the same clamp load. If it is low you can overload the bolt in tension.
Just do the oil thing and tighten the bolts in stages as discussed. I do not know if the head gasket you are using requires that the head bolts be re-torqued after some use. Follow whatever instructions came with the gasket.
