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V2plus25

Mark VII autodrive sprocket stuck

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Upgrading from the 1050X to the 1050 Pro. Trying to swap out the old sprocket with the new one. I’ve backed off the small set screw but the sprocket still won’t budge. 

 

Reading the the troubleshooting guides it says with the set screw loosened the sprocket should be able to moved back and forth on the motor axle. That’s also the way to ensure the belt goes straight back and forth vs at an angle. 

 

Has anyone else had any luck moving or removing the sprocket? I want to make sure I’m not missing something before just pounding away with a hammer to get the sprocket to move. 

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17 hours ago, V2plus25 said:

Upgrading from the 1050X to the 1050 Pro. Trying to swap out the old sprocket with the new one. I’ve backed off the small set screw but the sprocket still won’t budge. 

 

Reading the the troubleshooting guides it says with the set screw loosened the sprocket should be able to moved back and forth on the motor axle. That’s also the way to ensure the belt goes straight back and forth vs at an angle. 

 

Has anyone else had any luck moving or removing the sprocket? I want to make sure I’m not missing something before just pounding away with a hammer to get the sprocket to move. 

 

 

You have to use a heat gun on the sprocket to get it off and the new one on. 

Edited by Thetimb

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4 hours ago, Thetimb said:

 

 

You have to use a heat gun on the sprocket to get it off and the new one on. 

 

Would a hair dryer work or does it need to get hotter?  I don't have a heat gun but guess I could go get one.

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If you have to get a heat gun I  picked up a cheapo from Harbor Freight that has worked at least twice now without burning out.... lol

I hardly ever use one but it's nice to have around when I do.

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Oh yeah true, I keep getting texts from Harbor Freight with specials.  I'll run by and check on heat guns.

 

I'd love to use a hammer and pry bar to get the sprocket loose, but I'd also like to not destroy the entire motor assembly and *gasp* have to load ammo by pulling the handle again.

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I don't understand this heat gun thing. It isn't glued on there and heat makes metal expand so how does it make any sense to make the motor rod expand inside of a metal sprocket to loosen it?

 

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Warming a nut & bolt combination with an oxyacetylene torch works wonderfully to remove frozen fasteners on heavy equipment at work. They’re both virtually identical alloys which should expand at the same rate, but it works extremely well. No matter what armchair logic might say. ;) 

 

 

Edited by MemphisMechanic

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13 hours ago, donttreadonme said:

I don't understand this heat gun thing. It isn't glued on there and heat makes metal expand so how does it make any sense to make the motor rod expand inside of a metal sprocket to loosen it?

 

 

They put it on with a heat gun. Mark7 specifically told me to use a heat gun to get it off. 

 

It works, I had to do it on mine when I converted it. 

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Used the heat gun, set it to 1000 F and went to town on the sprocket and axle.

 

Still doesn't budge!  Geez how tight did they put this thing on there.  I'll try again tomorrow after picking up a small pry bar.

 

Or get a large wooden dowel about the size of the axle.  Use the dowel as a punch on the axle and hammer away.  Sure hope that doesn't screw up the gear box though.

Edited by V2plus25

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Just a sanity check... 

 

The sprocket you are putting on has a different teeth count then the one currently installed?

 

I was in your situation, but sometime mentioned that the teeth were the same... Sure enough.. Same teeth count.

 

I converted Mark 7 X to Evolution Pro though....  

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I would love to leave the sprocket alone, but this new one is a bit larger.  It probably has something to do with upping the max RPH from 1800 to 2400 going from the X to the Pro.

Sprockets.jpg

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Sorry bud..good luck on heating and getting it off...  

 

Mark 7 assured there's no hex inside the threaded cap?

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Just an idea... never tried it before.

 

Get a can of "circuit freeze spray" from Fry's or some other source.

 

Then heat up the sprocket trying to keep heat away from the axle.

 

After it is nice and hot use the freeze spray on the axle.

 

In theory the axle should contract and the sprocket expand.

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Get a jaw puller, if heat doesn’t work. Probably get a cheap one from harbor freight, or autozone


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1 hour ago, cvincent said:

Get a jaw puller, if heat doesn’t work. Probably get a cheap one from harbor freight, or autozone


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Genius!  I never knew these existed.  It'll probably screw up the old sprocket but I don't care at this point.  Grabbing one to try out.

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Genius!  I never knew these existed.  It'll probably screw up the old sprocket but I don't care at this point.  Grabbing one to try out.



Naw it’ll be fine. I seriously doubt it’s on there “that” tight. Just watch the threads in the shaft of the mark 7, if the shaft of the puller goes inside the threaded hole it could damage them. So put a spacer or washer or something if you need to.


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52 minutes ago, cvincent said:

 


emoji1690.png
Naw it’ll be fine. I seriously doubt it’s on there “that” tight. Just watch the threads in the shaft of the mark 7, if the shaft of the puller goes inside the threaded hole it could damage them. So put a spacer or washer or something if you need to.


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Would it help to heat the sprocket up first or just start pulling on it with the jaw pullers?

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I would just try the puller first, depending on the amount of resistance you get while pulling, can dictate whether you think you should apply heat. It may take a decent amount of initial torque, then it will break free and go smooth.


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was just going to type in use a gear puller. it shouldn't damage it if you use it right. and you'll probably be surprised at how easy it makes it come off. I had the opposite problem with my old sprocket and the new one, they would slide all over the place. I had to use loctite to keep them from doing that. 

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Well thanks to everyone here for the advice.  A buddy and I finally were able to get the sprocket off and the new one put on.  Hopefully the gearbox wasn't damaged in the process because even the new sprocket had to be hammered into position (with a 2x4 in front of it to spread out the force).  I ran it at 2400 rph for a bit and everything seemed normal and sounded ok.

 

I was all excited to use the jaw puller, but all I managed to do with that is yank the front rim off of the old sprocket.  Unfortunately the gripping arms on my puller were too thick to hook all 3 on the rear of the sprocket since I opted to go with a heavier duty puller.  If I have to do this again I'll get jaw pullers with skinnier arms.

 

For future reference if anyone elects to remove their sprocket, the heat gun combined with several different sized make-shift pry bars (inexpensive set of wrenches from Walmart I had laying around) were able to finally get that stubborn sprocket off.  Heat gun set to 1300 F and then banging away on the wrenches wedged behind the sprocket finally did the trick.  The only casualties are a few bent wrenches and dinged up old sprocket.

 

Sprocket 2.jpg

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wow, I can't believe it was on like that. I'd have measured the shaft to see if it was out of spec

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Ah I don't really care.  Now that it's on it won't be coming back off unless Mark 7 comes up with a 1050 uberPro that does 3000 rph or so.  Then of course I must have it ?

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At least she’s off and mark 7 is running again!


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