Sprocket replaced?

[aka1004]

3 times. Last one with new main shaft and they replaced belt all three times and all the work were done under warranty. Down times? 2 weeks, 3 weeks, and 11 weeks. They even replaced rear sprocket when they replaced main shaft.

 

[SpyderWolf]

Mine was just replaced for the first time at just under 17,000 miles for a different wear issue. The splines and bolt were well intact, but the belt wore a groove in the pulley and outer flange.

 

[Freddy]

adequate torque

Red Loctite will release with the application of heat. You won't break the bolt that way.

Nothing will keep the sprocket bolt from loosening or breaking if the physical fit between the shaft splines and the sprocket develops excess clearance. The resulting movement is murder on the fastener...far worse than normal vibration. The end result is a snowball effect that can break or loosen the bolt, and destroy both the sprocket and the shaft. It is my opinion that proper shaft size, proper machining, and proper heat treatment would eliminate these failures. All the fastener torque in the world is no substitute for robust design and construction.

Hi Scotty. Just thinking out load about the opinion you expressed in ya final sentence and how it relates to your first sentence where you say 'the physical fit between the shaft splines and the sprocket develops excess clearance' - "develops" being the operative work. I suspect that the clearance between the shaft and sprocket hub at manufacture is minimal; just sufficient to permit easy slip fit. I'm of the view that excess clearance develops because of relative movement between spline and hub as a result of inadequate torque at factory and/or retorque not being done or being done after relative movement (ie wear) has started. However, I'm also of the view that the torque on the bolt should be greater than spec - I did my 30T sprocket to 110ftlb when I fitted it and again a few days ago when I had it off to inspect for wear (see 30T thread). I'm of the view that if the bolt is retorqued soon after delivery and kept that way no wear will develop.

Regarding excess clearance and relative movement, I happend to drive a 48 wheel multi-combination Kenworth truck (Volvo pictured here http://www.spyderlovers.com/forums/showthread.php?t=16907&page=5 ).

It has 10-stud alloy wheels on the drive hubs. There is about .040" clearance between the studs and the holes in the wheels. (If they were a closer fit it would be extremely difficult to get the heavy wheels on the studs by hand, as we have to do.) When all 10 wheel nuts are torqued correctly (500ftlb) there is no relative movement - to start with. The nuts must be retorqued at least 5 times (or more until no further tightening) at 100-150km intervals. The reason being that load, rotation and torque (at the hub) cause relative movement, but when the nuts are finally torqued there is no relative movement even tho there is .040" clearance, because of the clamping effect of the nuts on the hub flange.

Hence I believe that adequate torque on the sprocket retaining bolt is what's been missing, to cause these failures. Just like if the wheel nuts are not adequately torqued the wheels fall off. (And it happened last week to another driver because he had not been informed at shift change by the departing driver (not me) that he had had a flat and put the spare on. Not pleasant at 2am with 90ton under you at 95kph.)

Anyhow, that's my take on it. :thumbup:

 

[NancysToy]

The bolt is there to hold the sprocket in place from side-to-side, and not to keep it from rotating. That is the job of the splines. Rotation is the normal movement for a bolt, and only the Loctite is there to overcome that movement. Torgue forces work to hold a bolt in place along its length.

If the sprocket can move side-to-side (lengthwise on the shaft), wear will be accelerated, but this would not be the primary cause of failure. Only poor fit on the splines, incompatible metallurgy, or inadequate heat treating would cause shaft/sprocket wear under ordinary circumstances. Bearing failure which allows oblique forces to be exerted, could also cause failure. Good engineering can help overcome such possibilities.

I do not believe in torquing bolts excessively. The specs are designed to stretch the bolt a certain amount, yet not exceed its tensile strength. Overtorquing a bolt is an invitation to failure. Increasing the bolt grade allows a higher torque, but the relative strength of the mating part then must be considered. Adding extra torque to the Spyder sprocket bolt (or any other application) is just a band-aid, IMO. It will help for a while, but increases other chances for failure, while not addressing the root causes of the problem.

Thanks for your slant on this, but I'll stick with sound engineering principles as my mainstay. I sleep better that way.

 

[Freddy]

Thanks for your reply Scotty - appreciated. I guess we're approaching the root cause from different angles. I can't alter the engineering but I can alter the application of it. Experience and knowledge being critical factors. Having had a bit over 40 years in the auto repair industry is quite useful at times when working on machines of various types and sizes.

Ryde safe.

 

[NancysToy]

Thanks for your reply Scotty - appreciated. I guess we're approaching the root cause from different angles. I can't alter the engineering but I can alter the application of it. Experience and knowledge being critical factors. Having had a bit over 40 years in the auto repair industry is quite useful at times when working on machines of various types and sizes.

Ryde safe.

I understand. I use my decades of twisting wrenches and conjuring up inventive cures to advantage, too. I just don't want people to get the idea that they can readily overcome the engineering...especially with the quality of the Chinese bolts one gets these days.

 

[Freddy]

I understand. I use my decades of twisting wrenches and conjuring up inventive cures to advantage, too. I just don't want people to get the idea that they can readily overcome the engineering...especially with the quality of the Chinese bolts one gets these days.

Hey - those Chinese bolts keep me employed. That truck I was saying I drive, well - I drive it 800km per day/night carting iron ore from a mine 200km from the port from where it is exported to...... China - where they turn it into bolts and rail iron and rail wagons and steel we then buy back off em. :gaah:

Now, back on topic. If Caterpillar made metric bolts I'd use one in this application. Checking............

It looks like they do. If they're not made in China I'll buy one (or 2) - their dealership is just down the road from the trucking yard I work at.

http://www.cat.com/parts/hardware

If interested, the Spyder part number is: 2500 00250
The dimensions of the bolt are: 65x12x1.5mm

The OEM one is flanged (not just a hex head) to provide broader contact area for the hardened washer pictured above, on the broken bolt - so that's a consideration, I suppose, on whether a non OEM bolt without the flange is suitable - what do you reckon Scotty?

snip< I just don't want people to get the idea that they can readily overcome the engineering...> snip

Hey Babe - please don't report me. :chill:

(Private joke from another forum - now, what did the sage say?)

 

[NancysToy]

.....The OEM one is flanged (not just a hex head) to provide broader contact area for the hardened washer pictured above, on the broken bolt - so that's a consideration, I suppose, on whether a non OEM bolt without the flange is suitable - what do you reckon Scotty?.....

With the hardened washer, I suspect the flanged bolt is just used for ease of assembly. I doubt there is an engineering reason to double up the function.

 

[Freddy]

Yeah I was thinking along the same lines. I'll check out Cat bolts this week and report back.

 

[Freddy]

Cat bolt

Update: According to the local dealership, Caterpillar have no listing on M12x1.5 bolts.