Crimsonknight3 Posted December 28, 2017 Share Posted December 28, 2017 Hiya, I have a gearbox missing plastic or actual bearings for the gears. I measured the holes to find and buy new bearings and my callipers measure between 7.1 and 7.2mm for the various holes, however everywhere I look I can only find bearings at whole numbers... e.g 7, 8 or 9 mm od. So the question is, if it measures 7.2mm is a 7mm bearing the right choice? Link to comment Share on other sites More sharing options...
Davegolf Posted December 28, 2017 Share Posted December 28, 2017 Most likely the bearings should be 7mm. You could be reading over because either the old bearings spun in the casing effectively wearing the hole out bigger or you're your pulling the calipers too hard. You can also test for fit with a 7mm drill bit. Order 7s and see what the fit is like, never bad practice to use high strength bearing loctite to bond them into place. Link to comment Share on other sites More sharing options...
Hangtight Posted December 28, 2017 Share Posted December 28, 2017 The better quality the gearbox, the closer to x.0mm the holes will measure. 0.2mm over isn't uncommon. Buy the 7mm (SHS enhanced are good) and epoxy them in. Link to comment Share on other sites More sharing options...
Crimsonknight3 Posted December 28, 2017 Author Share Posted December 28, 2017 Thanks for the help guys, going to order the shs ones next week and get a bit of loctite and see how it goes Nice to know i'm not totally useless at googling haha Link to comment Share on other sites More sharing options...
Hangtight Posted December 28, 2017 Share Posted December 28, 2017 Use epoxy rather than Loctite bearing fit. If you ever need to get them out again then you can soften the epoxy by putting the cases in the oven at 180° or soaking them in acetone. The bearing lock is pretty much impermeable to solvents and doesn't let go until a temperature fairly close to the melting point of the pot metal the gearbox is made from. And epoxy is cheaper... Link to comment Share on other sites More sharing options...
Crimsonknight3 Posted December 28, 2017 Author Share Posted December 28, 2017 3 hours ago, Hangtight said: Use epoxy rather than Loctite bearing fit. If you ever need to get them out again then you can soften the epoxy by putting the cases in the oven at 180° or soaking them in acetone. The bearing lock is pretty much impermeable to solvents and doesn't let go until a temperature fairly close to the melting point of the pot metal the gearbox is made from. And epoxy is cheaper... Would aridite be overkill? lol Link to comment Share on other sites More sharing options...
Davegolf Posted December 28, 2017 Share Posted December 28, 2017 You can release bearing stud lock AKA Loctite 270 with a hot air gun, which isn't capable of melting metal. I will say that if you've got a big gap to fill epoxy is better for that. Link to comment Share on other sites More sharing options...
Crimsonknight3 Posted December 28, 2017 Author Share Posted December 28, 2017 11 minutes ago, Davegolf said: You can release bearing stud lock AKA Loctite 270 with a hot air gun, which isn't capable of melting metal. I will say that if you've got a big gap to fill epoxy is better for that. My main worry is that anything TOO permanent means that if there is a .2mm gap and the bearing ends up off centre then releasing the bearing will be a nightmare. Link to comment Share on other sites More sharing options...
Davegolf Posted December 28, 2017 Share Posted December 28, 2017 I can see your point, the good thing with loctite is that it doesn't cure until it is under pressure, if your gearbox shell was a bit iffy and there was a potential to be off centre or out of square then fitting the new bearings a pair at a time with the related gear and bolting the 2 shell halves together and left to cure would be ideal. In an ideal world though and if I was doing a build and the shell was worn I'd start with a new shell. On high end builds I check alignment of the shell bearing bores with a precision dowel pin Link to comment Share on other sites More sharing options...
Crimsonknight3 Posted December 28, 2017 Author Share Posted December 28, 2017 Well someone off the forum offered to send me another metal shell for free, but while I am waiting for that, I wanted to get at least 1 gun working so I can go to a few games in January lol I'm only just shy of having enough parts to make 3 working guns now haha Only 2 of the holes appear to be worn out to .2mm the other 3 holes still have their original plastic bushings press fit EXTREMELY tightly. Taking the bushing out of one of the tight holes and trying to press it into the 2 larger holes, the bushing just falls out. So luckily the size issue on only 2 holes on one side of the clam shell. I might loctite both of the large holes with bearings, and put all 3 gears in and then close it up like you suggested. That will do me fine for a month or two while I wait for the other shell. Its either that or using my plastic gearbox with which has literally NO bushing or bearings at all (the holes for gear shafts are just holes in the gearbox shell) for a month or two haha Link to comment Share on other sites More sharing options...
Hangtight Posted December 28, 2017 Share Posted December 28, 2017 I use the 2500psi Devcon epoxy, but only because I use it for everything. And as for getting bushings out again, I stick the tip of my soldering iron in the hole and heat them up that way. I've had cases warp heating them to the point where the Loctite gives up. Link to comment Share on other sites More sharing options...
Davegolf Posted December 28, 2017 Share Posted December 28, 2017 I admit loctite have a massive range and there are some serious concoctions available ranging from mild thread lock to full on metal adhesive Link to comment Share on other sites More sharing options...
Hangtight Posted December 28, 2017 Share Posted December 28, 2017 It might be because I used the bearing lock stuff we use to stick the bearings into the gearbox on the drag bike... Proper job! Link to comment Share on other sites More sharing options...
Crimsonknight3 Posted December 29, 2017 Author Share Posted December 29, 2017 2 hours ago, Hangtight said: It might be because I used the bearing lock stuff we use to stick the bearings into the gearbox on the drag bike... Proper job! "proper job" my late grandad's favourite saying! >.< I think what I could do is use something like blu tac to position it if it's too loose, make sure its centred, then with the blu tac in place, apply glue one side and once dried glue the other side. Would have to be thin to seep it, but would make sure it stays centred Link to comment Share on other sites More sharing options...
Hangtight Posted December 29, 2017 Share Posted December 29, 2017 Find a fairly strong spring that will push the bushings firmly against the inside of the gearbox halves when they're screwed together. Then use the shank of an appropriately sized drill bit to hold the bushings in line with the spring between them and the gearbox screwed closed as the epoxy sets. As a bonus you can eyeball the protruding drill bit for square to the case. Link to comment Share on other sites More sharing options...
ak2m4 Posted December 29, 2017 Share Posted December 29, 2017 I've got a set of barely used 7mm bearings you can have for free, offered these to a mate but he's not got back to me so assuming he doesn't need them. give me a shout Link to comment Share on other sites More sharing options...
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