As far as I know this is an issue that affects all C-Series machine engines using the 5J-5794 Bolt on the rocker shaft (4 bolts per shaft) - the lower of the 2 bolts in the photo. That Part No. has been replaced by 356-5212 (the upper in the photo). Engine models affected are C-15, C-18, C-27, & C-32. On-highway engines may also be affected but I have no concrete nformation either way. We've seen 2 failure modes, the head breaking off as shown in the photo, and the bolt breaking at the shank/thread interface. Fortunately we got away with it both times without any major damage, although the 1st failure did also break a rocker shaft. After the first occurence we started a programme to replace all the former bolts with the new ones as each machine came through the PM Bay. This was the 3rd last engine that needed doing (the other 2 are both very low hours we were not worried about those) and it was due for PM next week - bugger. The engine had 9000 hours. The new bolt seems to have a much better thread quality, a larger washer built into the head (some applications apparently used a loose washer previously - throw that away with the new bolt), and no major diameter change between the threaded portion and the shank as well as moving that transition point closer to the head of the bolt. Note to Moderators: I'm really not sure where this thread belongs, but certainly it needs to be in a section where folks will see it. Feel free to move it as you see fit.
Was a problem on the C32, Cat invented a few different procedures to tighten them down. I never had one fail on any of the 26 C32's in the fleet, Only the Odd injector bolt snapping. Made in China hold down clamp side loading the bolt. Wonder how many other "Made in China" parts are holding the engines together?
Dreaded double post .............
The new tightening procedure applies to all C-series engines AFAIK, but even with that procedure the occasional bolt still broke. For anyone who's interested the sequence is as per the diagram below and the procedure is tighten bolts 1-4 in sequence to 55Nm (41 ft.lb.), tighten them a 2nd time in the same sequence to the same torque, lastly tighten in sequence a further 60 degrees. I worry about when things like rear axle housing castings on 789's are marked "Made in China" quite frankly ............
Av used the above procedure on C32's and I dont like it. Seems to me like the bolt is just a fraction away from snapping BUT, It works. The C11 Dont / Didnt have a Procedure or even a torque Value for the rocker shaft bolts. It isnt an OHC design like the C32. Just button them down to standard Cat Torque.
Apologies. The procedure applies to C-15, C-18, C-27, & C-32 engines.
the new bolt almost looks like a stretch bolt, the shank might be slightly softer than the original bolt too
I was surprised that the D&A procedure for tearing down the engine (or this part of it at least) didn't call for junking the bolts when you remove them and installing new ones. For torque-turn fasteners that would make sense if a bit expensive.
I have seen this on On-highway C-15's. I found it while replacing a valve cover gasket actually. Not sure how long it had been broke but the damage hadn't made it any further than the broken bolt thankfully.
I replaced an injector on a c-11 and also had trouble finding torque specs for rocker shaft bolts. I called my local cat service rep and he also could not find torque specs, so he talked to his tech's and they said to torque to 65 FT-LBS + or - 15 ( I torqued it to @70 LBS ). I came to this site to get help and did not get it which prompted me to find the right solution and return to post an answer to help other techs.
So what is correct procedure talked with cat dealer they said standard torque (around 80 ft lbs) or is it the torque turn method seems to me cat forgot to put it in the book so it is up in the air flip a coin on which way you want to do it. lol
Exactly what engine model are you working on..?
Rocker shaft bolt torque Cat c-11 , I've worked on many engines since and 80 ft lbs has been working so far, I figured the engine brake torque is 80 ft lbs and tighten down over the rocker shaft bolt-studs anyway. Thank you for replying
The engine is a c15 mxs17331
Yep happens with the on highway motors all the damn time... broken rockers are also not far behind
If your setup is the one with the 3 long unequally spaced studs on the rocker shaft then correct torque and tightening sequence is as follows. Why the Cat dealer couldn't tell you that I have no idea, it's straight out of the manual: - 1. The tightening sequence is first the centre stud, 2nd the outer stud furthest away from the centre, 3rd the outer stud closest to the centre - as per the diagram below. 2. Tighten the 3 studs in order to 50Nm (37ft.lb.). 3. Tighten the 3 studs in the same order an additional 45 degrees.
It is on 05 379
Thanks
A C18 that broke the bolts and then the shaft and ran for quite some time like that too I believe