How often can I use the same Head Bolts? On my 351c? Closed chambered heads.
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It depends what bolts you have. If they are modern replacement and Torque to Yield then the correct answer is they are single use as they are torqued beyond their spring back point and permanently stretched the first time you use them.
OEM bolts should be okay for reuse, but give them a thorough inspection, paying particular attention to any distress in the threads near where they would tighten in the block.
you want my honest opinion ? Once used ... REPLACE ... you'll be sorry if you don't
How much do the screws cost and how much does a new head gasket, head refacing and labor cost to replace it? You have your answer!
Appreciate the reply
There is no limit on the original Ford head bolts. If in doubt go to the ARP head bolts but it isn't really necessary.
On condition of being certain that during the 50 years of life of the car, no mechanic has tightened these screws with his biceps as any measuring instrument and has not exceeded their elastic limit.
A set of screws costs less than $100.
A couple of years ago I reinstalled the heads on my Euro Pantera with a new set of ARP head bolts after they had a valve job and the bolts worked great. After that I had to pull the heads two more times to fix some problems. During the last reinstall I could tell that the bolts are pretty much done and will get a new set of bolts if I have to pull the heads again.
@stevebuchanan posted:..... During the last reinstall I could tell that the bolts are pretty much done and will get a new set of bolts if I have to pull the heads again.
was Your indication they were "done", increased head rotation to reach set torque? or necking at the top threaded section?
I have done more then a few rebuilds in my time. The bolts that I have had the least issues with are the original equipment Ford supplied bolts.
If someone is in the situation of tearing down a lot, it is just logical to predict that something is going to get to the point that it should be considered worn out?
The flanged grade 8 head bolts that Ford originally used are at a level of, or better then the ARP's.
The amount of torque applied is not to a point where you need to measure bolt stretch. Much of that is going to be absorbed in the compression of the head gaskets used.
If you get to the point of stretching the bolts, then you had better start looking at stretching the block. For even a serious vintage road racer, that simply isn't a necessary consideration.
At this point, this discussion is simply an over reaction to "a little knowledge is dangerous".
The only way to be certain that a screw has not exceeded its elastic limit is to measure it as precisely as possible with a micrometer when it is new with an accuracy of a few hundredths of a mm, carefully note this length and check when it is dismantled again the length has not increased? Everything else is just speculation that has no place in a technical discussion.
Now, as almost no one does this (personally I only do it for connecting rod and crankshaft bearing screws), especially on a 50 years old car, I no longer take the risk of refitting screws which I don't know life to save less than $100. I did this on the first engines I rebuilt a long time ago when I was young, inexperienced and had little money........ until I destroyed an engine because of a screw that broke.
I am of course only talking about the main engine screws which support significant forces, not the screws which hold the oil pan or the cylinder head covers or.....
But everyone does as they want their knowledge, their experience and their means.