TTY and Plastigauge. What do you do?

Normally I have the machine shop check clearances. This time I'm building a motor that is using a factory new block so the only outside work needed was balancing the rotating assembly.

This leaves me with the task of checking bearing clearance. It was fairly easy with the rods but the mains use tty bolts so I can't completely torque them. This leaves the bearing crush and measurements in question.

First I torqued them to 30 ft lbs which is where they normally are prior to adding 90 degrees. At that point the clearance was right at a little under .003".

Keeping an eye on wrench deflection I continually added 5 ft lbs at a time and rechecked clearance. The last check was done with 65 ft lbs and came out between .0015 and .002 for all the mains.

At 65 ft lbs the wrench had deflected about 20 degrees and there was no sign of the bolts hitting the plastic state. I've torqued enough tty hardware to know when they are stretching as designed. IIRC the bolts are engineered to start the yield process at 66 ft lbs. I think the bolts were taken as far as they safely could be taken without entering the plastic state.

I'm wondering if any engine builders have done any type of sacrificial testing to determine how much if any the clearance changes with torque increases? I'm fairly certain it won't change much from here. Anywhere between .001 - .002" is fine and I know it's less than .002" right now. A guess would be that they are from .0019 - .0017 right now. The plastigauge calibration doesn't really show a more detailed scale than .0015 and .002".

So the question is will the clearance change much going from 65 ft lbs to 30 ft lbs + 90 degrees? If so how significant would it be?

I will still be able to check torque to turn after installation of the crank so if it needs more than max or is in the higher end I should know that something is up.

If my stuff were ready to be assembled I could answer your question in about 10 minutes, I have new factory studs along with ARP's that I am using. It wouldn't be much to have my in the factory bolts and check, problem is I don't have my crank back yet , from when I was building the smaller race motors and using ARP bolts, I rarely saw a change in clearance after reaching the purposed limit before it started to stretch. If it's the same here, well I guess were all wondering.

Could you not substitute a non tty grade 8 or higher bolt and simulate the torque? Forgive my engine building ignorance if that is a stupid question.

What would I torque it to? The factory hardware is torqued to 30 ft lbs plus 90 degrees.

I'm pretty sure the tty bolts were taken almost to the point of stretching. Still, I wonder just how close it was? After the crank is installed I'll see what the torque ends up at with 90 degrees.

SNKPWR said:

Could you not substitute a non tty grade 8 or higher bolt and simulate the torque? Forgive my engine building ignorance if that is a stupid question.

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SNKPWR said:

Could you not substitute a non tty grade 8 or higher bolt and simulate the torque? Forgive my engine building ignorance if that is a stupid question.

Click to expand...

even though a grade 8 is 160,000 psi iirc, it wouldn't be ideal to substitute one another with something this precise when you're talking about .0001"'s. There are different clamping loads and different amounts of stretch in each bolt, example: when using your normal factory tty connecting rod bolt you could have the rods machined for your build etc, but if you for say order ARP bolts they would have to go back to the machine shop due to the extra clamping force resulting in a smaller clearance. In my opinion it's just not worth the risk of assuming it's okay with a different bolt that you most commonly would never use in the bottom end in the first place.. hope this helps!

for every certain degree its like 15 ft lb torque or so dont remember the math on it

As I was installing the main caps torque values were adjusted until it was determined that the torque value is between 70 and 73 ft lbs with my torque wrench.

That should be useful knowledge for anyone who is checking clearances with plastigauge and tty hardware. 60 ft lbs will yield a tighter indicated clearance than 30 ft lbs and still not render the tty main bolts unuseable.

Glad you tried this before me! Thanks! I will need it for sure.
Keep updated please!
Why not sacrifying 2 bolts? (At least for 1 main)

BruceH said:

As I was installing the main caps torque values were adjusted until it was determined that the torque value is between 70 and 73 ft lbs with my torque wrench.

That should be useful knowledge for anyone who is checking clearances with plastigauge and tty hardware. 60 ft lbs will yield a tighter indicated clearance than 30 ft lbs and still not render the tty main bolts unuseable.

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Would need 6 to do one main, I think.

I'm using boss rods and can't even find the torque spec anywhere. I'm hoping Ford will help me out. The regular 5.0 numbers are out there, but the fasteners on the stock rods do not resemble those on the new ones.

I came across this forum, and although I don't mess with Ford's, the older SBC and Chevy LS engines all use TTY bolts from the factory. Again, I'm not sure how Ford does it, but the GM TTY bolts are *not* stretched during the torque process. (All bolts stretch, but the amount of stretch is what is important. Under normal installation torque, for all purposes in this discussion, they are not stretched). The design of TTY bolts are in the event of failure, unlike other hardened bolts, the TTY bolts will stretch instead of breaking, causing a much more catastrophic failure. I've done tons of stock engines by reusing the TTY bolts and had 0 issues with them spinning bearings or blowing head gaskets. As for studs, if you use plastigauge as a torque measurement, you don't "need" to have the block machined. However you can't follow the bolt manufacturers torque recommendations either. You have to test and see what torque works for your application. Or have the block machined and follow the "ARP" torque specs. Now, back to TTY. Since they shouldn't significantly stretch under normal circumstances especially during installation you should be fine torquing them all the way down and checking plastigauge. And although technically they do stretch a little, the holding pressure is not designed based on the length of the bolt, but by the torque pressure itself. So once the bolt is undone the plastigauge removed, and the bolt retorqued to the "same specs" the bearing clearance will be the same. The reason we check clearances on every rod and main, is because of machining tolerances having such variation on a very small scale and because the metallurgy of each in particular bolt varies to a minute amount based on cooling and heat treating and there can be small differences.
Those of you putting back together stock motors should have no fear of using TTY bolts to plastigauge and for final installation.
Those of you building high performance engines should not be using TTY bolts in the first place and studs made from companies like ARP are designed to be reused and therefore this discussion shouldn't even exist for you.

Perfectly happy with ARP studs and rod bolts pulled up to ARP recommendation.