Author Topic: Loop 4 speed gearbox  (Read 246 times)

Offline Mads

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Loop 4 speed gearbox
« on: March 18, 2019, 01:46:09 PM »
Good evening. A question about the four speed Loop gearbox.
I've searched but the info is scarce. Found the excellent photo stream from Antietam Classic Cycle, but I'm still a bit in the dark. Is the shimming of the output shaft done so that the standard ball bearings won't have to deal with excess axial thrust in case of heat expansion of the axle? What's the tolerances,- what do I have to "shim up to"+ gasket.
Best regards
Mads
Copenhagen, Denmark

Offline Antietam Classic Cycle

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Re: Loop 4 speed gearbox
« Reply #1 on: March 18, 2019, 03:09:48 PM »
Good evening. A question about the four speed Loop gearbox.
I've searched but the info is scarce. Found the excellent photo stream from Antietam Classic Cycle, but I'm still a bit in the dark. Is the shimming of the output shaft done so that the standard ball bearings won't have to deal with excess axial thrust in case of heat expansion of the axle? What's the tolerances,- what do I have to "shim up to"+ gasket.
Best regards
Mads
Copenhagen, Denmark

You may not need to shim the rear of the output shaft if you don't move/remove the original bearing. However, I've found that the original rear output shaft bearing is usually out of it's bore/standing proud of of the rear cover by a few thousandths - not fully inserted into it's bore or flush. I don't know if it's done this way at the factory or if the bearing moves during operation. I've seen more that a few rear covers where the bearing fits loosely - not a good thing.

If you replace that bearing and seat it fully home into the bore, then there's a good chance that you'll need to add a shim. How thick is determined by measuring how deep the bearing sits from flush in the rear cover + how deep the heavy shim/washer on the output shaft sits from flush of the gasket surface. 
« Last Edit: March 18, 2019, 03:10:18 PM by Antietam Classic Cycle »
Charlie
http://www.AntietamClassicCycle.com
'69 V700
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'76 Convert
'85 Moto Morini 350 K2


Offline Mads

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Re: Loop 4 speed gearbox
« Reply #2 on: March 25, 2019, 11:12:52 AM »
Thanks for sound advice, box is closed and going back in the frame wednesday, so let's hope I did the right thing..
A bit strange, I had to hone the standard SKF bearings .05 mm up to be able to slide the axles through, hmm
Best regards
Mads

Offline John Ulrich

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Re: Loop 4 speed gearbox
« Reply #3 on: March 25, 2019, 02:06:55 PM »
Of course shift it on the bench up and down the range before installing it. I needed to split the width of the shims between both ends of the drum for mine to properly engage.
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Offline Antietam Classic Cycle

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Re: Loop 4 speed gearbox
« Reply #4 on: March 25, 2019, 02:57:36 PM »
Hopefully you aligned everything as shown in this (upside-down) drawing:
http://thisoldtractor.com/moto_guzzi_loopframe_transmission_-_proper_shaft_alignment_for_a_4_speed_transmission.html

You basically assemble the transmission in 3rd gear. If assemble in neutral, you end up with a 2 speed - usually 1st and 2nd or 3rd and 4th, but not all four.
Charlie
http://www.AntietamClassicCycle.com
'69 V700
'69 Ambassador
'76 Convert
'85 Moto Morini 350 K2

Offline Mads

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Re: Loop 4 speed gearbox
« Reply #5 on: March 25, 2019, 10:20:36 PM »
Thanks guys, must have gotten lucky as it's still a 4speed..
Another thing, bought a new U-joint from S.Dinse and it only has one tapered end, not both ends as the original. Which way to put it or doesn't matter?
Ten days from leaving for Sardinia, in a bit of a hurry, lots of reassembling.
Best regards
Mads

Offline Antietam Classic Cycle

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Re: Loop 4 speed gearbox
« Reply #6 on: March 26, 2019, 08:17:09 AM »
Usually only one end - the tapered end - will fit into the carrier bearing.
Charlie
http://www.AntietamClassicCycle.com
'69 V700
'69 Ambassador
'76 Convert
'85 Moto Morini 350 K2

 

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