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Bosch 3 gear aluminum cross drive magneto

Posted: Mon Oct 12, 2020 9:35 pm
by Michael Peternell
I'm asking about the gear noise. The first one I purchased center gear was really worn/ sharp. Replaced it with a very good one. Less noise, but still some.
Pumped it full of grease helped a bunch. Still a bit of noise. I have nothing to compare it to. Any insight would be appreciated!

Re: Bosch 3 gear aluminum cross drive magneto

Posted: Tue Oct 13, 2020 11:32 am
by Mark Gregush
I think you are asking about this type esp. when you talk about the middle gear;
http://www.mtfca.com/discus/messages/33 ... 1373403034
A cross drive has the magneto mounted at a right angle to the motor on the left side.
Is the noise at idle or speed? Could be a number of things; like crankshaft gear to cam gear, other teeth worn, shaft for middle gear allowing it to move around etc.
If it is the type shown in the link, counting the cam gear and main drive gear as on, there are 4 points starting at the crank gear that could be loose, teeth not making good contact.
If it is a cross drive, could be also all the teeth are worn or maybe the shaft is loose in the holes it rides in, or thrust is worn allowing the shaft to move in and out. The cross drive would only have two gears, the one on the magneto drive shaft and the one on cam shaft.
Kinda hard to diagnose a noise that we can't hear from a distance.

Re: Bosch 3 gear aluminum cross drive magneto

Posted: Tue Oct 13, 2020 12:51 pm
by big2bird
Keep in mind straight cut gears are far noisier then helical gears, which are always meshed.

Re: Bosch 3 gear aluminum cross drive magneto

Posted: Tue Oct 13, 2020 12:59 pm
by Kevin Pharis
Hey Michael, my dad ran one on his speedster for a bit... don’t remember noticing the gear noise🤔

The idler and the driven gears ride in bushings, and so will affect the gear mesh as the bushings wear. Also the drive gear is mounted to the camshaft, and may not locate well when mounted to the timing cover. Try to adjust backlash between the drive and idler gears by sliding the aluminum housing around. Gears too tight make just as much noise as gears too loose...