Tired rod bolts - inconsistent torque development?

[Nut124]

I found one rod bolt in my Fiat twincam not developing torque as expected when adding torque in 5lbs increments. I replaced those two bolts and they felt "firmer." The replacement bolts are from a factory original block.

The book calls for 53 ft lbs. I went in 5 lbs increments from 30 to 50 then 3 lbs while watching the amount of rotation needed for the click.

How do you torque them? Pay attention to amount of turn?

Now I wonder if I should double check the three other rods or just replace the bolts? I replaced the one rod bolts w/o removing piston, but it was a bit of a hassle.

The "bad" bolt had no measureable stretch compared to other bolts. It did eventually develop the 53 lbs.

What do you think?

[Kevin Johnson]

"Whenever there is any doubt, there is no doubt."
De Niro in Ronin



Replace them all unless you like experiments.

[BillK]

I went in 5 lbs increments from 30 to 50 then 3 lbs while watching the amount of rotation needed for the click.

I never feel comfortable only going an additional 3 lbs in a step. At that point the friction just to get the bolt started again is too much to get an accurate reading. If I was torquing those bolts I would use whatever lube the manufacturer calls for and would probably torque them to 25 and then directly to 53.

[AC sports]

If your talking 1800 rod bolts your book is wrong. Or your looking at the 2000 engine rod bolt torque. They run a bigger bolt and nut.
Factory 1756cc rod nuts tighten to 36ftlb!
You have prob started pulling the heads off them at that torque value. I've seen it many times. Look around the head of the bolts and you will see.
You can upgrade the factory bolts to 351 cleveland nuts/bolts from ARP. You will need to ream the rods to 3/8' though first. Much better solution than oem.
Please ask me anything specific about this engine via pm as I'm not always online reading threads.
I know it's a bit of a learning curve when building a new type of engine...but heres some motivation for you to get it done! My street car.

[Nut124]

If your talking 1800 rod bolts your book is wrong. Or your looking at the 2000 engine rod bolt torque. They run a bigger bolt and nut.
Factory 1756cc rod nuts tighten to 36ftlb!
You have prob started pulling the heads off them at that torque value. I've seen it many times. Look around the head of the bolts and you will see.
You can upgrade the factory bolts to 351 cleveland nuts/bolts from ARP. You will need to ream the rods to 3/8' though first. Much better solution than oem.
Please ask me anything specific about this engine via pm as I'm not always online reading threads.
I know it's a bit of a learning curve when building a new type of engine...but heres some motivation for you to get it done! My street car.

AC, you are correct. I googled and found out that the torque spec in my manual is for a -79 and later M10 bolt and mine are M9. I ordered new bolts and will replace them all.

Do you use lube when tightening?

How is the bolt hole reaming done? Does it automatically require redoing the big end bore?

[AC sports]

With the oem bolts, just engine oil as lube.
The 351 cleveland ARP bolts specify 55 ftlb torque as opposed to factory 36 ftlb. I've measured the big ends after modification and torque up and contrary to popular knowledge they stayed round.

The procedure is best done on a mill. Although I got away doing it on a drill press. It's best to drill then ream. Going to 3/8 from 9mm is only 1/2 a mm but it's best to drill first.

Check your factory rods are not out of round first. They do go oval with hard use and many miles. And also make sure you buy the correct bearings for your rods. Pre 75/6 had asymmetric oil spray holes.
Later 1800 rods symmetrical.

[hoodeng]

If you torque in the sequence the manufacturer/ fastener manufacturer recommends you will get a clean feel as the wrench clicks off [or whatever yours does]. Lube threads and nut faces as they recommend, if its engine oil, its engine oil that is used in that engine unless specified otherwise [no synthetic or moly based engine oils] the aftermarket fastener manufacturer may have their own lube.

Changing fastener Ø is only performed where enough stock remains around the hole sections to retain integrity. After market fasteners are typically a much higher grade of material, but may still use stock torque settings as not to distort assemblies that are considered marginal. After market rods are not that expensive, even if you just crack test the rods and renew the fasteners you will feel more confident in your projects success.

I was wondering why you used 5lb then 3lb increments? It would take more than that just to unseat the fastener.

[Nut124]

With the oem bolts, just engine oil as lube.
The 351 cleveland ARP bolts specify 55 ftlb torque as opposed to factory 36 ftlb. I've measured the big ends after modification and torque up and contrary to popular knowledge they stayed round.

The procedure is best done on a mill. Although I got away doing it on a drill press. It's best to drill then ream. Going to 3/8 from 9mm is only 1/2 a mm but it's best to drill first.

Check your factory rods are not out of round first. They do go oval with hard use and many miles. And also make sure you buy the correct bearings for your rods. Pre 75/6 had asymmetric oil spray holes.
Later 1800 rods symmetrical.

I got a set of once torqued factory bolts from an 1800 that has not been taken apart. They look and measure good.

I checked a few over torqued bolts. They have visible stretch in the thread below the nut or in the waisted shank. The stretch makes it so threads do not mesh when putting against the thread of a good bolt. Bolt length had increased about 0.3mm or more. One bolt had the waisted shank stretched to the point where diameter was down from 8.35 to 8.20mm.

I did order 2 pcs of the 351C bolt just to check but I will likely just install these good OEM bolts correctly.

I could have purchased custom US made rods for $800 but passed because of cost. They would have had ARP bolts.

[Nut124]

If you torque in the sequence the manufacturer/ fastener manufacturer recommends you will get a clean feel as the wrench clicks off [or whatever yours does]. Lube threads and nut faces as they recommend, if its engine oil, its engine oil that is used in that engine unless specified otherwise [no synthetic or moly based engine oils] the aftermarket fastener manufacturer may have their own lube.

Changing fastener Ø is only performed where enough stock remains around the hole sections to retain integrity. After market fasteners are typically a much higher grade of material, but may still use stock torque settings as not to distort assemblies that are considered marginal. After market rods are not that expensive, even if you just crack test the rods and renew the fasteners you will feel more confident in your projects success.

I was wondering why you used 5lb then 3lb increments? It would take more than that just to unseat the fastener.

I started at 25lbs, then went 5lbs at a time up to 50. Then 3 for 53 final. The problem was that the 53 spec is for a later, beefier bolt. The spec for the smaller bolt was missing in my shop manual.

[Truckedup]

I don't know if drilling rod holes to fit new bolts without resizing the rods is a good idea...

[Nut124]

I'm starting to think these bolts are a lot more resilient than I thought.

I did some testing with my most severely stretched rod bolt. This bolt has thinning of OD at the waisted shank (8.17mm vs 8.33mm) and stretched threads below the nut. Permanent stretch is approx 0.015, or more.

I Torqued it to 10lbs, measured length, then 15 and measured, no change. Then 100% of spec, 38lbs. Torque stretch was about 5 thou. Then torqued to 45lbs, or almost 120% of spec. Torque stretch now measured about 6 thou. This was previously torqued to 54lbs, which did deform it.

But it is still acting like a good bolt from what I can observe.

Thoughts?

If anything, perhaps this makes me feel better about using good used bolts when new are not available.

[hoodeng]

Those small increments in torque value gain would still muddy the feel.

I use a digital wrench which clearly shows a break free torque value rise before smoothly going to the next higher value.

This is not to sound as a nag, but I have seen guys use wrenches in a nervous manner for lack of a better description,, they slowly creep up on the wrenches leverage then are uncertain or even shakey as they get to the click off. A bit of confidence in the use of this tool will make it as accurate as it can be, even standing [or positioning] in a manner of control over the tool is necessary, knowing what fasteners are going to feel and behave like is also necessary,, as the old boss used to say "don't practice on the finished product".

Get some old rods and mount them in a vice, practice different lower torque values and how they feel, then have a crack at torque to yield and you will get a confidence of what fasteners feel like when put through their paces.All serviceable fasteners feel clean and concise when behaving in their designed manner.

Replace your rod bolts with new at least. If you can see any damage of any type on a fastener in this application warrants immediate replacement. Previously used bolts have no provenance.

Cheers.

[DJ58]

I would think the bolts are probably around 5/16 they normally tq to 35lbs. 3/8 50lbs say for ARP.
Not sure on bolt size for Fiat. But like most are saying 5lb increments is way to close. for 50lbs I'd go 20 then right to 50. For 35lbs probably 15lbs then right to 35lbs.

Dan
S.W. Mi

[BCjohnny]

Specifics aside, some really good advice in this thread, not limited to :

I never feel comfortable only going an additional 3 lbs in a step. At that point the friction just to get the bolt started again is too much to get an accurate reading. If I was torquing those bolts I would use whatever lube the manufacturer calls for and would probably torque them to 25 and then directly to 53

...... but I have seen guys use wrenches in a nervous manner for lack of a better description,, they slowly creep up on the wrenches leverage then are uncertain or even shakey as they get to the click off. A bit of confidence in the use of this tool will make it as accurate as it can be, even standing [or positioning] in a manner of control over the tool is necessary, knowing what fasteners are going to feel and behave like is also necessary ......

[My highlights]

Apart from being a fundamentally better method, I can't help thinking that after years of getting the blame for sloppy repair techniques, most OEs have gone over to angle tightening critical fasteners at least in part to help negate this

[pdq67]

Please school, me??

What is this 1800 you talk about and then a 351C is talked about?

351 Cleveland Ford engine?

Thanks,

pdq67