Go BottomJD 790 Air Filter
 | DougB
Join Date: Posts: 1 
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2001-10-24 32648
Hello all, I just finished the 50 hr. maintenance... here's a word of when checking or changing the air filter on a JD 790. There is a plastic wing nut that holds the primary air filter in place. I dont' know how the nut was tightened down the way it was but there was no way it was coming off by hand. The concave top to the filter made it tough to grab the nut with a pair of pliers or vice grips. I used a pair of pliers when SNAP - one dog ear of the nut broke off... I figured I'd be very careful with the SNAP ... second one. Could not get a grip on the remains with pliers/ vise grips so I had to break off the remains with an old chisel. JD dealer could not tell me what the thread size was but he could order me a new nut for $8.90 (plus $4.19 for a die to chase the threads). When I got the new wing nut there was a plastic tag with "7/16 - 20, please remember to clean any burred threads" note attached to it. Only one other issue with the package I bought, JD 790 and Woods 5' XT-160 brush cutter, ... the vent plug on the Woods is VERY soft aluminum. Went to check the oil level in the gear box and stripped out the bolt when I put it back in. Its been a month and Woods still hasn't shipped my dealer a new part.
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| Glen Schattner
Join Date: Posts: 1
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2001-10-25 32659
Doug,
I have the same tractor and had the same problem.....the lads on the assembly floor must be using air wrenches to tighten those wing nuts.
The solution is to ..a) either buy another one,,as you did...but I had a heck of time getting it off the second time as well...for whatever reason....or
b) replace plastic wing nut with steel one or use nylox bolt and you can use socket set to remove it next time.....
Problem is partly due to engine vibration,,,you have to crank it on a little bit or you will loose same in short while. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-10-25 32661
Couple of surprising things here, or maybe I just surprise easily. First is that would have guessed that JD engines are still Yanmar, made in Japan (substantially assembled in N.A.), and everything would be metric. Second is that 7/16" seems a very large shaft for an air cleaner mount. By comparison, the shear pin on my post-hold auger is 5/16". I imagine a shear pin has to withstand more force than an air cleaner mount. ....
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| DougB
Join Date: Posts: 1
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2001-10-25 32665
Glenn... Kind of glad to hear that I'm not the only one to run into that problem. Turned a 20 minute task into a 1/2 day run-around. I now have a spare metal nut with a 3/4" fender washer and a 7/16" rubber grommet. If, more like when, the nut cracks, I'll put the grommet/ washer/ nut combo on - for the price of $ 2.17.
Tom... I was sure that the bolt would be either 10mm or 12mm since Yanmar does make the motor (11mm is kind of hard to find around here) so I had run back and forth to the local hardware store. You're right the shaft that the primary and secondary air filter hangs off is pretty large. I guess that due to the fact the filters are mounted sideways ?!?
Other then that one SNAFU, everything else on the JD seems to be pretty solid, well built and easy to get at. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-10-26 32669
Wish I had my old bolt data book handy, because 7/16th - 20 sure sounds like an inches nut at 20 threads per inch. 20tpi may be the NC standard for 7/16" bolts but I can't remember. I do know that some metric bolts and inches nuts are close enough that the starter threads go together easily. The nut only starts being difficult to turn when it's more than half-threaded onto the bolt. It would be easy enough to keep turning a plastic nut. Anyway, why I'm still hacking away on the subject is that if somebody forced a plastic inches nut onto a metric bolt, it sure would be hard to take off. However, it's difficult to imagine how that would happen, since I believe the part marked 7/16 - 20 came from a dealer. ....
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| DougB
Join Date: Posts: 1
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2001-10-26 32675
Tom,
The nut came in a little plastic John Deere baggie - I'm still surpised that a non-metric nut is on the motor. For grins - let me know if you track down your bolt data book and find anything out.
Thanks, DougB
....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2001-10-26 32678
We discussed some of the odd sized bolts on the 750 on the posting before. As the main castings on the 790 are the same I would assume that it has some of the same oddities.
With some bolts there was nothing that felt proper and my box has all the 32 froationals. It crossed my mind that some may be Whitworth. With the age of the original castings I guess this is possible but?
The 750 had a nut verus the wing nut on the air filter. It was difficult to remove in the airbox can due to the depth in the can and the dimple in the end of the filter. I think I bought a deep socket and then ended up using an adjustable wrench using just the tips. I am not sure it is the same style. ....
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| DougB
Join Date: Posts: 1
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2001-10-26 32680
Peters...
Sounds very similar, there is the outer primary air filter then an inner secondary air filter. The secondary air filter has the same wing nut, which fortunately was not anywhere near as tight as the primary.
Thanks, Doug ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-10-27 32684
My old bolt books seem to be beyond the pale, but I found something in a web search. Twenty threads per inch is a standard for 7/16th hex-bolts, but it more likely is the fine (NF) rather than the course (NC) standard. That seems to fit my memory better as well. This probably doesn't help get the air filter on and off, but it sure does seem a curious nut to find in this application. Peters: I remember seeing some deep sockets where there was a split up one side and an allen screw across the split. I never was sure of the intended use of these things, but I always thought the allen screw was for making small adjustments to the socket size. Could be that such things might work for the odd sized bolt heads on that sometimes end up on tractors. Wouldn’t help mismatched threads or the sloppy manufacture of much of the current hardware that’s around today though. ....
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| Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2001-10-27 32689
Futile logic - I bought the deep socket thinking it was metric, but naturally it did not fit. In the location you could not get a wrench or normal socket on it to check. Then ended up using the tips of the adjustable wrench.
Peters ....
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| Bob L.
Join Date: Posts: 1
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2002-02-04 35288
I believe that a solution is something that I ran across. The thread size is 7/16 x 20 - which is the same as a lug nut for a car. Try a chrome plated acorn style that is "open" to allow the bolt to go all the way through. The acorn nut is easy to get on and off and sticks out far enough to get a wrench on if need be. The way the nut is flared also allows a great seal on the filter with no additional washer needed. Bob L. ....
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| H. PETERSON
Join Date: Jul 2003 Posts: 7 COXSACKIE,NY
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2002-09-14 42390
My 2002 790 does not have wingnuts securing the primary or secondary air filters. The air filters have a built in silicone gaskets that push on and are locked in place by the top housing. It appears that JD has been reading these posts!!!! ....
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