Reusing TTY head bolts

[M4ncyy]

Where I live, there's no replacement bolts available (at least for quite some time) and I need to bolt the head back on, I understand they are TTY and are not to be reused, however, I realy cannot find new ones. Can I re-use them using the same torque specs and then once I find new ones, just take em out and replace them one by one?
Should I get 12,9 grade hex bolts and torque them using the old method then replace them as soon as I get torx ones?

[moroza]

I don't know the answer, but I have an idea of how to find it. Most bolts get tightened to less than their elastic limit. TTY bolts exceed this limit as well as the lower yield stress point. If the ultimate stress point D has been reached or exceeded, then they can never clamp as hard as new ones, and should not be considered reliable if used. If instead they've been tightened to somewhere between C and D, then they can clamp as hard, and (in theory) could be reused. The answer could be found by measurement and analysis of the used bolts, to see where on the curve they are. I'd talk to a physics teacher or a mechanical engineer...

https://www.physicsforums.com/attachments/ttttttt-jpg.232149/

[danespann]

In the turbo LS world, people re-use TTY headbolts all the time.
I think the general consensus is around 55 ft/lb on those when re-used.
And that's around what they tighten to with the TTY on new bolts if you have a digital wrench that logs the max torque that was hit.
The TTY procedure only works once, so after that it's just torqued like any normal bolt.

[johan750]

Question to me would be how much would I regret it if I had to do the whole repair again...

[M4ncyy]

In the turbo LS world, people re-use TTY headbolts all the time.
I think the general consensus is around 55 ft/lb on those when re-used.
And that's around what they tighten to with the TTY on new bolts if you have a digital wrench that logs the max torque that was hit.
The TTY procedure only works once, so after that it's just torqued like any normal bolt.
So, what you're saying is I should first tighten to 22 ft/lb then to 55 AND NOT DO 90+90 degrees?


Question to me would be how much would I regret it if I had to do the whole repair again...

Well, it's not a matter of anything other than I simply cannot find new bolts in this place :( There's only used ones avaiable. I have to place an order but that would take weeks to arrive and I need to car operational right now. I already placed the order and I will swap the bolts as soon as they arrive


I don't know the answer, but I have an idea of how to find it. Most bolts get tightened to less than their elastic limit. TTY bolts exceed this limit as well as the lower yield stress point. If the ultimate stress point D has been reached or exceeded, then they can never clamp as hard as new ones, and should not be considered reliable if used. If instead they've been tightened to somewhere between C and D, then they can clamp as hard, and (in theory) could be reused. The answer could be found by measurement and analysis of the used bolts, to see where on the curve they are. I'd talk to a physics teacher or a mechanical engineer...

https://www.physicsforums.com/attachments/ttttttt-jpg.232149/

Would you happen to know the stretch limit on M20 head bolts? I could messure them, maybeeee they were still withing specs

[Simmo2222]

General consensus is not to reuse. You are certainly going away from the standard torque process (angular displacement) as you can't recreate that without new bolts. So you will need to figure out what's a reasonable torque to achieve to hold your head on but not over stress the old bolts which could be operating at the limit. A guestimate of 55 ft/lb seems a little light in comparison with the standard torque for metric bolts but, I guess, you would rather leave it loose than risk snapping one in situ. If you get it wrong, you will have premature gasket failure which could warp your head while stranding you somewhere awkward. You will then have to replace the head gasket as well as the bolts (I can't believe head gasket sets are that much more plentiful or cheap if you are struggling with head bolts). Personally, I wouldn't do it.

If you are really desperate - How about replacing them with generic (high tensile) bolts, or studs and nuts that might be available locally? You could then be a bit more certain about the torque you are applying and that they are consistent in each case. Clamping force required is ultimately a function of the gasket composition but getting the bolts consistently tight across the head will be half the battle in reliably keeping the head on.

https://www.engineeringtoolbox.com/metric-bolts-maximum-torque-d_2054.html

[ross1]

A fellow near me does a good business(or did when more of these were still on the road) repairing Cadillac Northstar engines which are notorious for failed head gaskets.
I've discussed his procedure with him and he claims to re-use the original TTY bolts. His tightening process is a simple torque spec which he understandably won't reveal.
I'm sure he does a careful inspection and probably measurement as well.
I'd speculate that he asks these bolts yield just a bit further which doesn't mean they'll fail.
Me? Not knowing how much is too much will always err on the cautious side and replace them. They usually aren't very expensive.
Also, I'm unsure if "yield" means exceeding the elastic limit or plastic limit. I have been under the impression it is only the former.

[demetk]

On my m30's with normal hex bolts I simply use this torque process with oiled bolts and never had a problem.

1st 26-32 ft/lb
2nd 49-52
3rd 56-59
4th 56-59

If I was in a bind and needed to put my car in service I would choose one of these options.

Option 1 would be to get regular hex bolts that can be reused in the future if needed.
Option 2 would be so see if you can get 60 ft/lbs with your existing bolts and have good compression and no leaks.

Wish you luck with your car.

[M4ncyy]

On my m30's with normal hex bolts I simply use this torque process with oiled bolts and never had a problem.1st 26-32 ft/lb2nd 49-523rd 56-594th 56-59If I was in a bind and needed to put my car in service I would choose one of these options.Option 1 would be to get regular hex bolts that can be reused in the future if needed.Option 2 would be so see if you can get 60 ft/lbs with your existing bolts and have good compression and no leaks.Wish you luck with your car.I spoke with a trusted mechanic, he said I better replace them anyway, but he inspected the bolts and found 3 of them to be deformed, so at least I gotta replace those, he said we'd find out if they can be torqued or break and he said he recommands 50-60 ft/lb final toruqe after chasing the threads and lightly oil them. But he said all this with the existing torx bolts. He said he never had a problem using this method. It appears to be consistent with your recommandations. So thanks you so much, I'm gonna try to see if I can get my existing torx ones to 60ft/lbs
I can find regular hex bolts tho but since I am gettign new torx bolts anyway I'm gonna see if I can re-use this ones first.