My Tractor Forum banner

new spindles - old pulley problem. (Pics & CAD drawings !)

1951 Views 8 Replies 3 Participants Last post by  aeroguy

a) After several months, rain is once again falling here on California's Central Coast.
b) Suddenly I seem compelled to make my first post on MTF.

Hey, it's probably just one of those 'strange coincidence' things, right? :D

Anyway, some while back, I acquired my first "fixer" and promptly dove in to the deep end of the MTF pool in my quest for total lawn tractor enlightenment. Wow! What an amazing storehouse of knowlege and experience. Thank-you, thank-you! Found lots of great info; made some significant repairs; and even stared down perhaps the most terrifying thing ever to haunt MTF - yes I'm talking about that icon of pure villainy and voodoo... the Variator. :eek: On the brighter side, I also made a new "best friend" down the street - a very friendly, retired gentleman who has four different welders in his shop, knows how to use them all, and enjoys helping people out with a project now and then. (seriously, how perfect is that!)

Well then the first part of that 'coincidence thing' occurred, and I suddenly felt "inspired" to finish rebuilding and installing the deck. That's where I ran into a little glitch. Fortunately for me, even with the massive sleep deprivation caused by spending waaay too much time on the forum, I still managed to remember MTF's MOST important lesson on problem solving:

You Want Pictures! :sidelaugh

So, in a blatant and slavish attempt to curry favor and get responses to my questions, here are some pics. :D (with my questions accompanying the last image.)

First two are just after getting 'it' home - an MTD 600 series w/ B&S 12hp IC. Needed battery and ignition work at minimum. Not too bad from a rust standpoint, compared to places where you guys have *real* weather. Had been stored in a garage for the past 4 years or so as well. (clearly not very well maintained before that though.)

Dump Cart. Also got a complete Grass Collector attachment. (no pic for that)

Here's a shot after some minor disassembly and a lot of pressure washing.

begin next phase of disassembly and cleaning

example of "not well maintained" (before and after)

Ok, on to my fit questions. The spindles and bearings on the deck were pretty far gone, so I went with the low-cost replacements from mowtownusa after noting favorable reviews. (we get virtually no rain for more than half the year, so use will be fairly light.) Using the "Deck G for 600 Series Lawn Tractors" manual, I ordered replacements for spindle assembly - part# 717-0906.

Here's a model I made to show the (blade)spindle (with pulley) design used on my deck.

The replacement spindles seemed to be identical to the originals when I compared them, so I figured I was good to go. Well, after resuming work on the deck last week, the spindle plates fit the deck perfectly and the blades installed with no problem - I had to buy one new coupler, and both the old and new coupler made a nice snug fit - tapped on with small hammer and wood block (blade side) - on the new spindles. So far, so good. (blade end not shown in the model)

The pulley side however, is a different story. Both pulleys seem to fit a bit loose where the toothed(?) sections of pulley and spindle interlock - they definitely interlock, but the fit is certainly not snug. But worse than that is that the pulley sleeves bottom out against the spindle bearing before the shoulder sections of shaft and sleeve make contact. Which means if I tighten down the pulley, it binds against the bearing. After doing some measuring, it seems like the mismatch is only about 0.1" or so, but more than enough to be a problem. (Unfortunately, I tossed the old spindles a while back, so I can't do any precise measurement and fit comparisons at this point. Doh! :00000061:)


a) do pulleys typically fit a bit looser than blade couplers, but are fine once they're tightened down? (assuming they're not pressing on the bearing.) I presume they would be well aligned with the spindle shaft once the internal shoulder is firmly seated on the shaft.

b) if yes for 'a', can I just grind an 1/8" off of each sleeve and install the pulleys? (balance shouldn't be a concern with such a small diameter involved.)

I'm assuming that with two bearings pressed on those spindle shafts, that moving each of them 'just a bit' isn't happening without a serious press and other jigs to do it properly. There *is* about 3/16 of shaft length exposed on the blade side, if it could be done.

c) pulleys should fit snug, just like the blade couplers; order new ones from same source with expectation that they should fit properly or allow a return.

- or -

d) Newbie Alert! 'Your view of the forest is blocked by the trees, Grasshopper.' :D

1 - 9 of 9 Posts
Re: new spindles - old pulleys. Fit problem?

I think I would use some locktight....
Re: new spindles - old pulleys. Fit problem?

It would seem odd to have the bearings on the spindle shaft not resting against a shoulder on that shaft on the opposite side of the pulley. If there was no shoulder then there would be nothing preventing the spindle from creeping up while in use.

I suspect that the pulleys are meant to rest (tightly) against the inner race of the bearings.

With respect to the "shoulder?" in your diagram, I believe that is required for the machining process which puts the splines (teeth) on the spindle shaft. If there was no indentation there, then the broach which creates those splines would not be able to clear the chips off at the end of the cut. A more careful examination of the spindle should reveal that the OD of the splined area is the same as the area past that "shoulder".

When I refer to a "broach", think of a metal tube with teeth on the inside that would be pushed down over the end of the spindle with great force to cut the splines. I suppose it might also be possible to knurl those splines if they're small enough, but clearance on both ends of the splines would still be beneficial.
Re: new spindles - old pulleys. Fit problem?

thanks Chagrin -

(sorry, my ability to reply was delayed by some weird "server is redirecting the request for this address in a way that will never complete" error that kept me from connecting with any part of the MTF site. Thanks to Google I found out that I had to delete all cookies associated with MTF. Go figure.)

Anyway, my reference to the 'shoulder' was because, if I understand correctly, a small shoulder at the bottom of the pulley's splines is supposed to meet a corresponding shoulder at the base of the spindle's splined section, and restrict any further movement down the shaft. This allows for a washer and nut (on the end of the spindle shaft) to tighten the pulley onto the shaft *without* forcing it against the bearing. A bearing wouldn't last very long with any sort of side load like that.

I'm assuming that if the pulley is sized correctly for the spindle, the design is supposed to leave just a slight gap between the bottom of the pulley sleeve and the bearing. (not sure if 'sleeve' is the right term for that portion of a pulley, so feel free to correct me there.)

You're probably right about the bearings having their own shoulders to restrict their movement. Perhaps someone who has seen one in parts will let us know. (And shed some light on what a "proper fit" for a pulley is, as well.)

Re: new spindles - old pulleys. Fit problem?

If you measured the outer diameter of the splined area and compared it to the thicker part (below the shoulder) of the spindle, how much difference in size is there? Per your rendering it appears to be less than ~1/8" difference?
Re: new spindles - old pulleys. Fit problem?

Chagrin -

It's not a diameter thing. (well ok, the 'not a snug fit' part is, but that's minor compared to the main problem.) Here's another view that should help.

Despite what I described as a 'less than snug' fit with the splines, there is *plenty* of overlap where the shoulders should seat against each other. They just don't make contact before the pulley hits the bearing. So it's a *length* (mismatch) issue between pulley and spindle shaft. From measuring, my estimate was that the pulley sleeve only needed to be ~0.1" shorter. That's why my idea was to just grind a bit off the end of each sleeve.

To clarify a bit more on the 'fit' part - if "wood block, hammer and a bit of force required" represented 100% overlap (or interface) between the splined sections, then I'd call my fit a 95% (as a description, not actual measurement). As I'm sure you know, it doesn't take much at all for something like that to feel loose, but it's not like I have splines that are barely overlapping. (That's also why I said there should be plenty of contact for the shoulders - IF they get there.)

Maybe I'll just go ahead with my "mod" and see if it works. I just figured I'd check to see if anyone else had encounterd this, or see if I was completely missing a different solution.

What I'm trying to say, Gary, is that I think the existence of that shoulder is merely incidental and only due to a requirement in broaching the splines on the spindle. I believe that the pulley *should* rest firmly against the inner race of that top bearing and would advise against grinding the extra length off.

Finally found a picture that should explain why:

I understand the spindle is different than yours, but the principle is the same. Notice how the top radial bearing (4) is pressed against by the pulley due to the spacer (5). This is the same situation you are in, except the spacer is part of the pulley.

Why is it done this way? Because the spindle needs to be able to handle the thrust force (along the axis of the spindle) against it, and radial bearings are weak in that respect. Notice how the spindle (3) traps the lower bearing against the spacers (6), the upper bearing, the spacer (5), and the pulley. They're all squeezed together tightly so thrust forces on the spindle are shared equally by the two radial bearings.
Ahhh... now I understand *your* point, which makes perfect sense as long as the bearing's inner race is supported on the opposite side.

Only one (BIG!) problem here. Apparently, mine isn't. When I start to tighten down the nut and lockwasher, if I spin the blade I can feel the bearing friction increase noticeably **before I even fully compress the lockwasher!** (I'm using the nut and lockwasher that came off the old spindle, and they match the description in the 'Deck G' manual. The lockwasher is *quite* stout; about 5/32 thick.) I didn't continue on to anything near normal torque, as I had the distinct impression I'd really be binding up the bearing and probably causing damage.

I did check again just now, and the pulley cleanly contacts the innner race without pressing against any other portion of the bearing, so there doesn't seem to be any mis-alignment issue.

It seems to me that if the thrust forces along the spindle axis were all that significant during operation, then tapered roller bearings would be necessary in these spindles. Given the amount of force (typically) needed to press these bearings onto a shaft, along with the other flange (the gold portion in my model) that also appears to be pressed onto the bearing, I would think that would be sufficient to keep the bearings in place. But then, I'm not a machinist or a bearing expert, so what do I know?

Aaaaarrrgghh! Someone here has to have a clear answer on this. Maybe tomorrow I'll see if I can contact the place where I bought the spindles, and get them to put one of their replacement pulleys on the same spindle and see if it reaches the bearing.

Ok, I have to stop now and go write on the blackboard 1,000 times: "Never toss the old part, until the new part is installed. Never toss...." :banghead3 :D

Your efforts to help are much appreciated.

Ok, I held off another day on grinding down the ends of my pulleys. In the meantime, I discovered this:

On two different websites, my replacement spindle is listed as 5.5" in height (i.e. shaft length); and the matching pulley (sleeve length) at 2.065 . My pulleys measured right on the money, so I pulled one of the replacement spindles from my deck and very carefully measured the shaft length... at 5.41". Gee, what a coincidence that I estimated I'd need to grind off about 0.1" to keep the sleeve from pressing on the bearing. (yes, the *effective* length of the pulley is really determined by where the shaft and pulley splined sections meet -or in this case, don't meet- but at least the pulley matches its stated dimension.)

Maybe someone with a 600 series MTD (or clone), or a Simplicity or Snapper that uses this same spindle could lower their deck and check to see if a piece of paper or thin piece of metal can slide between the upper spindle bearing and the bottom of the pulley (sleeve portion). Or someone who just knows could say, "The sleeve should not (or should) contact the bearing."

Yeah, it seems logical and like it's a simple fix, but since I can't "put the genie back in the bottle" if I grind them down...

Anyone? Anyone? Bueller? Anyone? :00000062:
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.