TTY head bolts?

I understand why some people think that the 17mm head bolts used on some 1500 engines are TTY. The Fiat workshop manual specifies that the torque turn method is used to tighten them.

But even though the Fiat workshop manual is very comprehensive it does not specify that those 17mm head bolts are TTY, or that they shouldn't be re-used.

Does anyone have any information, other than the torque turn method is specified in the workshop manual, that definitively specifies that the 17mm head bolts that Fiat used in the 1500 engines are indeed TTY?

If they are TTY - fine - everyone should know that. But if they are not, everyone should know that too.

double post?

I've never seen actual Fiat literature that says they should be discarded after a single use, but I have read in Fiat literature that they can be used again once or twice, after a thorough inspection to determine suitability.

I just translated the German workshop manual (1987 vintage) using Google translate and here is what it tells me.

"bei den mit der dichtung astadur verwendeten zylinderkopfschrauben handelt es sich um schrauben mit vorbestimmter streckgrenze. nach viermaliger verwendung sind diese schrauben zu erneuern"

"in the cylinder head bolts astadur used with the seal is screwed with a predetermined yield strength . after quadruple use are screw them to renew"

obviously Google's translation is a bit rough... but the meaning is obvious ....

"predetermined yield strength" (to me this means torque to yield)

and "after quadruple use ...renew" meaning you can get a few more uses after the factory... but their life is definitely finite.

And "predetermined yield strength" and 'Astadur' (head gasket composition) are the two components that provide the total TTY system... it NOT just the BOLTS.

SteveC

Hi Steve,

Would it be correct to assume the Uno Turbo head bolts (14 bolt) are the same as the X1/9 head bolts? On that same note while I'm asking, how about valve springs?! I would imagine these are all carry over?

Thanks in advance!

AFAIK Myron yes those parts carry over, for certain though the exhaust valves are a different material... and later engines used a three groove collet system.

I don't have a series 1 UnoT manual (my Dad does though), but would like to get my hands on one.

SteveC

Thanks Steve!

I have an early (86'ish) Mk1 engine and you're right, the exhaust valves are indeed different. Those I will reuse, but figured I'd put in new springs.

I have a set of new head bolts from some guys in the UK, but of course - the box says something completely different (Peugeot application or something like that.. arghh...) Last thing I want to do is blow a gasket


Cheers!

Most certainly are TTY from the factory...

Pull one out and look at it closely. The bolt tapers down to 9mm diameter directly under the head, then enlarges to become M10 thread:

TTY:



Compared to a straight 10mm bolt:

Straight Torque:



Given that nominal 80% yield on an M10 / R10 bolt is under 60 Ft-lbs, and the TTY process applies over 100ft-lbs, I am leery of using them over. That said, I >have< used them over, but when you perform the factory manual process of 40ft-lbs, then 90 degrees, then 90 degrees, the last 90 degree turn really makes you wonder if you're going to break them or pull the threads out of the block.

In true FIAT fashion, the only outlier here are 1980 FI engines. They have 10mm holes in the block, but 12mm holes in the head. They used a special shouldered bolt like this and they were a straight torque process.



-M

Interesting Matt! Thanks for the info and pictures.

BTW: I believe I have an injected engine with M12 studs/bolts in my pile of used parts - which makes me wonder if they did a changeover to M10 bolts, had M12 FI heads left over and then had those bolts made up to work with that combination - but then again, I'm just speculating.

Also nice meeting you and your son at FFO!

Translation

Steve, Thank you for digging into this. Yes, I agree that it seems the term "predetermined yield strength" could indicate TTY. (although all bolts have a "predetermined yield strength")

Funny, if they are indeed TTY they shouldn't be reused - ever. They were torqued to the point of yield when they were installed and have been stretched past their ability to "spring back" to their old shape (length).

ARP recommends torqueing their studs several times to get the studs threads "accustomed" to the threads of the nut before the final torque is applied. It sort of "laps them in". Makes sense. But then they tell you that you shouldn't torque them more than 5 times. And those studs are def not TTY. All bolts have a limited life.

Bottom line - it never hurts to replace old bolts with new - known to be good - bolts! You certainly can't go wrong if you never reuse the 17mm head bolts. Who sells them?

So, Matt you recommend changing over to regular head bolts on the late model TTY 14-bolt heads if the head is removed?

We use straight torque...

...for simplicity sake, and because I cannot find a source for the correct TTY bolts, except the rare occasion when we find OE NOS from old dealer inventory.

-M

M10 head bolts

I wasn't aware that current replacement M10 head bolts are not TTY.
I just checked the ones I bought and they sure aren't, so thanks for that info.

Now here is my concern.
Originally our engines had M12 non-TTY head bolts and studs. These give a certain clamping load when torqued to spec.
Then, a change to TTY bolts was made, allowing for a reduction to M10 with (I assume) the same clamping load because of the TTY (TTY results in higher and more consistend clamping force).
Now, if I install M10 non-TTY bolts, won't I have a significantly lower clamping force than both the M12 and M10 TTY bolts?

Also, what torque should I use for the non-TTY M10 bolts?

That's why the M10 ARP stud setup is best for a high performance engine, they will easily handle 70lb/ft of torque and provide the same clamping force as the M12 factory setup.

More work to get it 'right' for sure with the stepped inserts and pad machining to go the ARP option with both M12 an M10 versions, but easier than replacing head gaskets.

SteveC

Hi Steve,

is there more info on the "pad machining" and the stepped washers?
I don't quite understand what they are for.

I read this thread: http://xwebforums.com/forum/index.php?posts/208182#post208182/
Is there more info in other threads on this?

Also, has anyone installed the complete "set" of ARP head M10 studs and used the aircraft wrench to retorque successfully?