Timing Belt Tensioner Pivot Bolt-snapped

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njoconnor
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Timing Belt Tensioner Pivot Bolt-snapped

Post by njoconnor » Mon Sep 16, 2019 2:54 pm

Per prior thread, got the crank pulley off w/o issue. Slowly and carefully replaced the crank gear, the tensioner, and today, got the new belt on and rotated twice without anything hitting/knocking/slipping. Yay me.

While tightening the belt tensioner pivot bolt to 33ft/lbs (per Haynes and the handy "guide to belt changing"), I heard a snap, instead of the quiet click of my torque wrench (3/8 drive, btw). Here's what I see:
Screenshot_2019-09-16-13-27-52.jpg
Screenshot_2019-09-16-13-27-52.jpg (280.35 KiB) Viewed 675 times
One can see the shiny part where the bolt/stud broke in circle 1. I suspect I'm in for a treat getting the broken piece out.

My bigger question: the larger spring blot under circle 2 (bolt not seen) will obviously need to come out so I can access the broken pivot bolt. As I loosen and remove that spring bolt, any precautions on removal in regards to a flying spring and or other objects?

Working on locating a replacement bolt now. Leads appreciated.....

Neil
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
71 Fiat 124 Coupe (long ago and far away...and very much missed!)
Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
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miker
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by miker » Mon Sep 16, 2019 3:17 pm

MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
njoconnor
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by njoconnor » Mon Sep 16, 2019 3:38 pm

Grazie, Mike!

Went back pout and found very little tension on that spring...wonder why..... :oops:

Pic of the bolt below. I think I'm needing the local Fiat guru (Patrick Slattery) to extract the broken bolt end.

Thanks again, all...

Neil
20190916_142920.jpg
20190916_142920.jpg (948.78 KiB) Viewed 669 times
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
71 Fiat 124 Coupe (long ago and far away...and very much missed!)
Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
spider2081
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by spider2081 » Mon Sep 16, 2019 5:31 pm

While tightening the belt tensioner pivot bolt to 33ft/lbs
I looked in the Fiat Service manual and it states Tensioner nut. I think they are talking about the # 10 stud that the tensioner bearing is held in place with. I also think the threaded portion of the bolt you had break is #8. Other bolts this size would be torqued to 14 ft lbs in the Fiat Manual.

Not sure if I am correct in this thinking maybe someone with more engine experience could comment
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by fp55scca » Mon Sep 16, 2019 6:07 pm

spider2081 wrote:
Mon Sep 16, 2019 5:31 pm
I looked in the Fiat Service manual and it states Tensioner nut. I think they are talking about the # 10 stud that the tensioner bearing is held in place with. I also think the threaded portion of the bolt you had break is #8. Other bolts this size would be torqued to 14 ft lbs in the Fiat Manual.
----------------------------------------------------------
--Neil, I concur with what Dave is saying here. Appears you have applied the torque value for the timing belt idler (a 10mm stud) to the spring lever support bolt (an 8mm x 1.25 thread pitch bolt). If you can't readily find a replacement for this bolt, an 8mm bolt with a locking nut on the shaft will do in the interim. I know this because I snapped the same bolt about 40 years ago, not using a torque wrench, but just being heavy handed. The bolt you broke does not really need a torque value, just snug, as it is only a support for tension spring.

--Take care when using a torque wrench on 8mm and 6mm bolts on your Fiat, particularly if the bolt or stud is threaded into aluminum. Remember that a torque value is designed to provide a "clamping" force, but your torque wrench measures "resistance". Where a torque value is critical, like head bolts, this is why it's necessary to clean, chase and oil the threads.
Jim Scurria
Norfolk, VA

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1971 Spider - SCCA FP-24
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1981 Fiat Spider Ratrod
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18Fiatsandcounting
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by 18Fiatsandcounting » Mon Sep 16, 2019 6:12 pm

Man, that's definitely one bolt that I would hate to break... At any rate, I read through my various manuals, and my thinking is essentially the same as Dave and Jim above, that is, 33 ft lbs for the nut that secures the belt tensioner/pulley to its stud, and around 15 ft lbs (but not more than 20) for the (broken) post that the tensioner spring pushes against.

-Bryan
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by njoconnor » Mon Sep 16, 2019 7:41 pm

Yup to all. Off line response said the same thingS: I simply misread the torque values. Lesson learned.

Anyway, gave our local guru a call. Even though he was in Oregon, Patrick answered, and said he didn't think it would be a problem since the at bolt is a comparatively losse fit. He encouraged me to take the whole tension assembly off, and see if I could slowly ease it out with a pick. Turns out about 1/8 in was sticking out of the block, and I was able to turn it out with fingers. Whew!

Replacement part is on the way, and I'm filing Jiim's alternate suggestion away in case of need. Thanks again, everyone, for the syggestions, info, and support. Hopefully next post is a "job done" post.

Neil
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
71 Fiat 124 Coupe (long ago and far away...and very much missed!)
Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
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18Fiatsandcounting
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by 18Fiatsandcounting » Mon Sep 16, 2019 8:18 pm

njoconnor wrote:
Mon Sep 16, 2019 7:41 pm
Turns out about 1/8 in was sticking out of the block, and I was able to turn it out with fingers. Whew!
Whew is right, and my heart rate just went down when I heard how easy you got it out. Congrats! But that kinda begs the question: If the remainder of the bolt was that easy to remove, why did it snap in the first place?

-Bryan
njoconnor
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by njoconnor » Tue Sep 17, 2019 7:22 am

Good question. Thinking back on it, I needed quite a bit of push too loosen it originally. Wondering if the PO's mechanic cranked it on, caused a partial failure, and I finished the job 8 years later. It also cracked mid thread, when I would have thought it would crack at the hex head.

Another Fiat Imponderable, I suppose....

Neil
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
71 Fiat 124 Coupe (long ago and far away...and very much missed!)
Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
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18Fiatsandcounting
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Re: Timing Belt Tensioner Pivot Bolt-snapped

Post by 18Fiatsandcounting » Tue Sep 17, 2019 11:21 am

My guess is that the bolt post was previously damaged, perhaps from overtightening and corrosion, but managed to "hang in there" until you worked on it, when it finally called it quits. With the grease/oil on the bolt, I don't see any corrosion in the pictures you posted, but you never know what lies beneath. Maybe the previous "mechanic" felt the bolt starting to shear off and stopped tightening before it failed completely?

Anyway, good news on being able to get it out without some extreme measure like having to pull the engine out.

-Bryan
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