345 PTO replace
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Thread: 345 PTO replace

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    345 PTO replace

    My PTO went bad on my '96 345. It worked fine the last mowing a week before. Started it up and I noticed the deck belt was slowly turning and the long spring assist arm was hammering the deck along with a lot of other noise. Shut her down with-in a minute. Removed deck and found the PTO bolt very loose and the bottom bearing seal fell off. Got the PTO assembly off the crankshaft with the help of Kroil and a large puller. Inspecting further I see that the M10x 1.5 thread at the bottom of the crank is battered- the bolt (neither the original or a new one) won't pick up a thread until .71 deep from the crank end. Looking closer I find that the original bolt was shortened - manual depicts a 90 mm length, my bolt is 83 mm. The one previous owner was a JD dealer who used it at his home-but you can see that it was cut. I've scanned the net for similar problems and in a quandary as to a long lasting fix. Already got a new JD PTO as the old one looked poor. I also repaired the bottom of the threads with epoxy ( applied release agent to unused bolt and applied epoxy to threads and threaded onto crank). My next step is to install the PTO using a new 90 mm bolt of same spec as original (12.3 hardness). I got conflicting torque values-my manual says 60 ft lbs, another owner with same problem was told 45 ft lbs by dealer. I wanted to use blue locktite but after reading others experiences that will be a hindrance if the bolt should break off in the crank. IMO the design is asking an awful lot from a single bolt with little lateral support. Any advice?
    Thinking further about the design, although the cupped washer was installed according to the manual (concave side towards the PTO) my engineering intuition tells me it would be better served the opposite -to allow the bolt to center-up with the lower bearing to give the bolt more lateral support. IMO the washer is much too thick to expect it to compress to allow constant tension on the bolt to prevent it from loosening.
    Last edited by lhsmith; 06-30-2018 at 07:54 PM.

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    Fozsey's Avatar
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    Quote Originally Posted by lhsmith View Post
    My PTO went bad on my '96 345. It worked fine the last mowing a week before. Started it up and I noticed the deck belt was slowly turning and the long spring assist arm was hammering the deck along with a lot of other noise. Shut her down with-in a minute. Removed deck and found the PTO bolt very loose and the bottom bearing seal fell off. Got the PTO assembly off the crankshaft with the help of Kroil and a large puller. Inspecting further I see that the M10x 1.5 thread at the bottom of the crank is battered- the bolt (neither the original or a new one) won't pick up a thread until .71 deep from the crank end. Looking closer I find that the original bolt was shortened - manual depicts a 90 mm length, my bolt is 83 mm. The one previous owner was a JD dealer who used it at his home-but you can see that it was cut. I've scanned the net for similar problems and in a quandary as to a long lasting fix. Already got a new JD PTO as the old one looked poor. I also repaired the bottom of the threads with epoxy ( applied release agent to unused bolt and applied epoxy to threads and threaded onto crank). My next step is to install the PTO using a new 90 mm bolt of same spec as original (12.3 hardness). I got conflicting torque values-my manual says 60 ft lbs, another owner with same problem was told 45 ft lbs by dealer. I wanted to use blue locktite but after reading others experiences that will be a hindrance if the bolt should break off in the crank. IMO the design is asking an awful lot from a single bolt with little lateral support. Any advice?

    I would put everything back to factory specs and use Rocksett as opposed to locktite if you are concerned about getting it back off. I use Rocksett on gas blocks on rifle barrels. Heating it will release it to be removed.
    Attached Thumbnails Attached Thumbnails p_100010681_1.jpg  
    Last edited by Fozsey; 06-30-2018 at 08:03 PM.
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    I misspoke in the original post- my manual confirms 45 in. lbs. for bolt torque.

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    That puny little bolt and a crankshaft too short to reach through the lower bearing just doesn't sit right with me either. When the bolt is torqued with a conventional torque wrench, the bolt head will more likely than not be off center when seated. So spin that baby up to 3600 RPM, then remove the load several thousand times, and it can bend or stretch enough to loosen ever so slightly. Then one day it is loose enough to back out completely. That's just a theory on my part, but could be correct.

    On a couple that I have worked on, I made a washer with a pilot that was a slip fit to the inner bearing race. The flange was just slightly smaller than the inner race. The clearance hole for the bolt of plus .010 (.25mm) seemed good. Then a conventional lock washer and OEM bolt.

    Some of the new OEM bolts that I have purchased seemed to have a thread locker already on the thread, though sparingly. I look for something else if the original bolt does not thread in at least 1 1/2 times the diameter. 2 times the diameter feels even better if the crank will allow. I realize not everyone has the means to do this, but the factory does, and should have done it instead of saving a few pennys.

    BTW, I'm sure inch pounds was a misprint for you. 45ft. lbs. right?

    tommyhawk
    Last edited by tommyhawk; 07-01-2018 at 12:11 PM. Reason: More info. Corrected description.
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    Quote Originally Posted by tommyhawk View Post
    That puny little bolt and a crankshaft too short to reach through the lower bearing just doesn't sit right with me either. When the bolt is torqued with a conventional torque wrench, the bolt head will more likely than not be off center when seated. So spin that baby up to 3600 RPM, then remove the load several thousand times, and it can bend or stretch enough to loosen ever so slightly. Then one day it is loose enough to back out completely. That's just a theory on my part, but could be correct.

    On a couple that I have worked on, I made a washer with a pilot that was a slip fit to the inner bearing race. The flange was just slightly smaller than the outer race. A slight relief in the face of the flange to clear the inner race diameter, if I remember correctly. The clearance hole for the bolt of plus .010 (.25mm) seemed good. Then a conventional lock washer and OEM bolt.

    Some of the new OEM bolts that I have purchased seemed to have a thread locker already on the thread, though sparingly. I look for something else if the original bolt does not thread in at least 1 1/2 times the diameter. 2 times the diameter feels even better if the crank will allow. I realize not everyone has the means to do this, but the factory does, and should have done it instead of saving a few pennys.

    BTW, I'm sure inch pounds was a misprint for you. 45ft. lbs. right?

    tommyhawk
    Yes, ft.lbs. To clarify your fix, you forgo the original cupped washer and in it's place used the custom washer as detailed in your post? With a 90 mm bolt I will had at least 5 full threads of engagement. The epoxy took care of the bolt slop and lack of threads at the crank end that was there when I started. I have a few buddies with mills and lathes who could fix me up with a better designed washer like yours. Thanks.

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    Yes, but the cupped washer could be used in place of the lock washer if the bolt engagement is still sufficient. I need to point out a big mistake on the origional description of the washer. It must locate on the inner race, not the outer race as originally stated. Think I got that edited OK. Boy, that was dumb, and I thought I had proof read it to make sense!

    I gotta do better.

    tommyhawk

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    I recently had the PTO bolt broke off in crankshaft. I figured out guy before, supposedly a lawn mower mechanic, had too short of bolt by 10mm. I would say buy factory bolt with cupped spring washer, torque to 45ft/lbs, so you have correct tension on it. Iyou use impact or get too tight you may have premature failure of bearings.

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