Zetec cylinder head bolts?

[tight fart]

Are they stretch bolts or can they be reused?

[E-bmw]

Does your tightening sequence say something like:

28ft lb + 90 degrees + 90 degrees?

[Mignon]

You can reuse them if you just do them up to a torque setting. Try 60-65 ft lbs.

[99hjhm]

Mignon said:

You can reuse them if you just do them up to a torque setting. Try 60-65 ft lbs.

Dave, do you work this out based on the size / thread / tensile strength of the bolt, experience or other?

[tight fart]

I’m not fitting the head myself, I asked the mechanic if I needed to get anything and he said new bolts.
I didn’t think they were stretch bolts, looks like he was right.

[Mignon]

99hjhm said:

Dave, do you work this out based on the size / thread / tensile strength of the bolt, experience or other?

All the above. All bolts have a recommended torque based on their size and material and I've routinely fitted stretch bolts at a torque setting rather than an angle method. Especially on the Peugeot 205 XU engines where so much stretch is used it can rip out the threads in the aluminium block. I also calculated the torque for a customer with a turbocharged ZVH (Zetec/CVH hybrid) with one of my big valve heads who wanted stronger bolts than the stock 10.9 grade. I suggested 12.9 grade cap head screws and 70 ft lbs I think it was and they worked fine. Never had any gasket issues with it.

Stretching any bolt past its elastic limit weakens it and I just find it a silly method from an engineering standpoint. The best bolts in the business, ARP, don't use angle tightening methods. If it's good enough for them etc......

[PeterBurgess]

ARP specify stretch measurement for rod bolts not a torque figure, which is why we use a stretch gauge for ARP rod bolts.
I attach a link to a Federal Mogul pdf partially explaining stretch bolts. I must profess I cannot see how the degrees of rotation stretches the bolt X amount when the thread could be pulling slightly, gasket compressing etc etc. I do like 'straight' head torque figures to be honest, then recheck them after say 20 minutes. In the absence of specific info we carry out tightening of bolts by the degree method if specified I have got used to measuring and trusting stretch gauge on rod bolts which was very alien to me having been brought up on torque wrench tightening.

http://www.partinfo.co.uk/files/SB2165%20-%20CYLIN...

[Mignon]

PeterBurgess said:

ARP specify stretch measurement for rod bolts not a torque figure

Yeah I was waiting for someone to say this but it's pre-elastic limit stretch not post elastic limit they use. All bolts stretch as you tighten them because they're basically springs.

[PeterBurgess]

The stretch bolts whether head or con rod are not stretched beyond elastic limit. ARP specify a max of 0.001" increase in length after use then throw them away.
Lycoming chuck all rod bolts out whether torque or stretch bolts. I suppose with your way of reusing stretch bolts for heads one should measure the free length and take note before fitting ready to check on next strip down.
https://www.lycoming.com/sites/default/files/SI145...

[Mignon]

PeterBurgess said:

The stretch bolts whether head or con rod are not stretched beyond elastic limit.

Yes, that's what I said.

[stevieturbo]

PeterBurgess said:

ARP specify stretch measurement for rod bolts not a torque figure, which is why we use a stretch gauge for ARP rod bolts.

Sometimes they do.....of course, it doesnt always mean the information they give you is correct. In fact, some recent ones I've done, have been a fking mile off and if you actually went to their quoted stretch...you'd have well and truly fked the bolts.

[PeterBurgess]

That's interesting, what were the stretches recommended and what were the bolt types?

[stevieturbo]

PeterBurgess said:

That's interesting, what were the stretches recommended and what were the bolt types?

Recently EJ25 Subaru rod bolt, 3/8" ARP2000

ARP stated 7-7.5 thou....

https://www.arp-bolts.com/kits/ARPkit-detail.php?R...

Now first off this is odd, because various other sources for rods using these same bolts might vary from around 4.5thou up to ARP's at max 7.5 thou.
That's a massive variation.
ARP state 42lbft for for this same bolt and I can say that in testing, 45lbft achieves around 4.5 to 5.0 thou of stretch.

So the mind boggles as to how much torque it might take to achieve that 7-7.5 thou but no way were we going to try and achieve it as it would probably have destroyed the bolts, and maybe taken some 60+lbtft to hit it ( and no it isnt the torque wrench )

For same 3/8" ARP2000 bolt, the likes of Oliver state 0.0050 to 0.0054" stretch although they say to use a torque+angle method, 25lb plus 42deg

Although ARP's very bizarre numbers isnt just restricted to rod bolts, as even some info supplied with head studs is just wrong, and their torques seem to vary over the years too for the same bolt.
I know of some kits supplied quoting an extremely low number with their instructions..and indeed some seem to follow this, with obvious HG problems to follow. Then those builders seem to blame all sorts, even the block !!

[PeterBurgess]

I know the 206-2002 5/16 rod bolts we use in the track day B engines changed from 38lbs/ft to 35 lbs/ft a few years ago, stretch is .0065-.0070 with the 35lbs/ft. Std rod bolts are 34lbs/ft oiled.
I thought it would be worth having a little experiment to see if the assembly lube was any different to engine oil in terms of stretch at a specific torque.
I put a pair of new ARP rod bolts in a new rod, the bolt threads and nuts were cleaned with choke cleaner. One side I tested with oil then cleaned them and tried ARP lube. The other side I tested with ARP lube then engine oil.
Results @ 35lbs/ft
First bolt Oil first .0055( and a bit) ARP lube .0065
Second bolt ARP lube first 0.00625 Oil .0055

Looks like it pays to use the ARP lube which, to be honest, I didn't think would make any difference!

The MGB ARP head studs say 45 lbs/ft with ARP lube. Standard is 50lbs/ft with oil. We have always used 54lbs/ft on std or ARP head studs with oil. On race Cometic gaskets we use oil and torque to 70lbs/ft to keep the head down especially on longer distance 45 mins to 90 min races.

[stevieturbo]

I've never used anything other than ARP lube, so cant comment as to what other lubes might do.

But no way is that stretch info correct, although I never did email them about it.

Edited by stevieturbo on Thursday 18th October 22:13

[Kccv23highliftcam]

Bolt stretching gawd I hate bolt stretching...

[99hjhm]

PeterBurgess said:

I know the 206-2002 5/16 rod bolts we use in the track day B engines changed from 38lbs/ft to 35 lbs/ft a few years ago, stretch is .0065-.0070 with the 35lbs/ft. Std rod bolts are 34lbs/ft oiled.
I thought it would be worth having a little experiment to see if the assembly lube was any different to engine oil in terms of stretch at a specific torque.
I put a pair of new ARP rod bolts in a new rod, the bolt threads and nuts were cleaned with choke cleaner. One side I tested with oil then cleaned them and tried ARP lube. The other side I tested with ARP lube then engine oil.
Results @ 35lbs/ft
First bolt Oil first .0055( and a bit) ARP lube .0065
Second bolt ARP lube first 0.00625 Oil .0055

Looks like it pays to use the ARP lube which, to be honest, I didn't think would make any difference!

The MGB ARP head studs say 45 lbs/ft with ARP lube. Standard is 50lbs/ft with oil. We have always used 54lbs/ft on std or ARP head studs with oil. On race Cometic gaskets we use oil and torque to 70lbs/ft to keep the head down especially on longer distance 45 mins to 90 min races.

70lbs.ft seems a hell of a lot on 3/8" MGB stud. No issues with cracking the blocks open on the cam side not much material there?

[stevieturbo]

99hjhm said:

70lbs.ft seems a hell of a lot on 3/8" MGB stud. No issues with cracking the blocks open on the cam side not much material there?

Depends on stud material, and if using oil the torque target would be higher than the specified ARP lube anyway

For a 625 fastener in 3/8", torque would generally be around 60lbft with ARP lube, so 70lbft with oil isnt necessarily that high. Of course those targets could be below target stretch anyway.

[Mignon]

PeterBurgess said:

Std rod bolts are 34lbs/ft oiled.

That's fookin high for a 5/16" bolt. Way more than 8.8 grade. The grade 10.9 metric 8 mm CVH big end bolts were mid 20s ft lbs. A grade 12.9 caphead screw takes about the same torque as the MGB bolt.

[PeterBurgess]

We have been running the 70 lbs/ft 3/8ths studs on the Cometic gaskets for three plus years on the competition engines. No signs of threads pulling at all. One problem the B has is cracking to the sides of the thread holes on the four studs on the cam shaft side of the block. The cracks tend to go into the holes drilled for pushrods, we have seen no cracking either.

Dave, I didn't write the workshop manual on the rod bolts, I don't know what the bolt material is but they have been OK at the stated 34lbs/ft oiled for the 33 years I have been building B series engines. As I mentioned above the ARP 5/16ths were 38 lbs/ft with ARP lube then reduced to 35 lbs/ft with ARP lube. It may be the rods were starting to deform at the 38lbs/ft Arp lube. I have mentioned before about seeing rod deformation with the newest ARP rod bolts with greater stretch requirements on Cossie rods. The answer I am told is to contact the rod manufacturer for suitability before upgrading the rod bolts to the higher spec ARP ones.