RTH head bolts (1 Viewer)

[60 toy ota]

Hello All,

re-assembling a 1fz right now and have had 4 headbolts that yielded early. For refreshers, the FSM calls for 29 fl.lbs for the first pass, 90 degrees for the 2nd, and another 90 for the 3rd. All headbolts are brand new from mr. T. These 3 of these yielded during the 2nd pass, one towards the end of the 3rd, and the rest have been fully torqued in the proper sequence.

I bought 4 new Toyota bolts, and my method has been to replace each one at a time, making sure to blow out the hole, thoroughly oiling the threads then taking off excess oil so as to not cause compression below the bolt.

This has only worked for one bolt though. Aside from the fact that the bolts are 22 a piece, I'm concerned that it isn't the bolts that are yielding but the female threads in the block. It felt like the kind of yield that headbolts normally have, but on the other hand, the aluminum block may be inferior to the steel bolt, and the engine has already been rebuilt once in it's lifetime.
Is my concern for the threads valid?
Is there any other reason these bolts could be yielding so early...like one as early as 29ft.lbs+50degrees?

wanting to get this done asap, thanks for any help
Drew

 

[tominboise]

By yielding early, what do you mean? The bolt spins without getting tight? When I torqued my head bolts., they all got tight and none stretched or refused to tighten to where I couldn't go any further.

 

[60 toy ota]

Stretched. Went suddenly from regular, proportionate resistance to "giving way", similar to the feeling you get the instant before you shear a bolt head

 

[tominboise]

The block is cast iron, so I doubt you are pulling the threads. But maybe you are. Did you clean the holes and chase the threads with the correct tap? I have my old head bolts somewhere if you need some. Might be worth measuring your old ones and using 4 that are within spec.

 

[60 toy ota]

The block was sent to a shop to be machined, other than what they may have done we did not clean or chase the holes...didn't see the need for that coming but I guess that would have been smart. It feels smooth though. I'll try and find a way to chase it with the head on, and maybe even consider shortening one of the (within spec) bolts by a thread or 2 and see if That makes a difference. Thoughts?

 

[Gabriel 71]

You Need the ever elusive 1.25 m11 thread chaser. I don't want to start a rumor but I hear they are made of pure Unicorn horn.Nah but I did have fun tracking 1 down for my build Jegs I think had them but pricey

 

[Malleus]

It's the oil you put on the threads. The torque values are for dry, clean threads, male and female. When you tighten the bolts, you're driving the oil to the bottom of the hole and the pressure will cause it to climb back up. This results in all the oil being trapped in a couple of threads. This isn't my opinion, it's engineering practice. FWIW, when I worked in industry, I held an SAE member card.

I doubt the bolts yielded, but the only way to know for sure is to put a strain gauge on them, prior to tightening them (too late now). That's why Toyota (and most everyone else) uses the "turn of the nut" method. It's been proven accurate enough in lab tests, many times over.

However, you're there and I'm not. If you have any doubt, replace them. It's cheaper than a head gasket repair. Immediately prior to installation, clean the threads with mineral spirits, and vacuum all you can get out. Blow dry the holes with warm air to encourage the spirits to vaporize. If you do it now, and replace the bolts more than a couple of hours later, rust will start to form on the threads and you'll have the same problem, for different reasons, all over again.

Also, FWIW, if you do replace the headbolts, and this happens again, you need to have someone inspect the block.

 

[Dave 2000]

If you do 'pull' a thread, don't have a meltdown, A helicoil insert will see you right.

I fitted them to MOD stuff as a matter of course when bolting to aluminium.

Regards

Dave

 

[ppc]

Interesting reading on lubrication and installing ARP fasteners

ARP | Official Website | ARP Ultra-Torque