Author Topic: Swing Arm Widths  (Read 1185 times)

Offline Groover

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Swing Arm Widths
« on: July 16, 2019, 09:38:15 AM »
Are the swingarms from the mid 70's tonti interchangeable with the newer models? I know there are the three lengths, but are the witdhs the same? Meaning, if I put say a T3 swingarm on a say a 98 EV (examples), would the shocks be vertically lined up, or will the shocks be spaced out wider on top in this case and narrower at the bottom when looking at the bike from the rear? like this \ 0 /
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Offline Groover

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Re: Swing Arm Widths
« Reply #1 on: July 17, 2019, 09:14:20 AM »
Don't know buddy, you ask dumb questions..
1981 Moto Guzzi V1000G5
1987 Moto Guzzi LM1000SE, a
1987 Moto Guzzi LM1000SE, b
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oldbike54

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Re: Swing Arm Widths
« Reply #2 on: July 17, 2019, 09:19:59 AM »
  :laugh:

 There are some variations , I think the later EV's have a slightly wider swingarm . The experts will weigh in shortly .

 Dusty

Offline s1120

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Re: Swing Arm Widths
« Reply #3 on: July 17, 2019, 09:41:17 AM »
  :laugh:

 There are some variations , I think the later EV's have a slightly wider swingarm . The experts will weigh in shortly .

 Dusty

When they changed from the Jackal to the Stone they were made wider for a bigger tire. Im assuming the EV's also changed at this time. Where the width increase was in the arm?. that I don't know.. might just be a bigger dimple in the drive shaft tube.
Paul B

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Re: Swing Arm Widths
« Reply #3 on: July 17, 2019, 09:41:17 AM »

Offline Groover

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Re: Swing Arm Widths
« Reply #4 on: July 17, 2019, 09:45:56 AM »
Thanks guys, wondering if the frames on the EV, Jackal, etc are wider up where the shocks mount, or if they are the same width as say a T3. The later swingarms have bigger tube structure with the dimple for the wider tire, but the left side of the swingarm (brake side) also comes out a bit in a curve on the later models, vs the older short swingarms are straight, I guess that's what's confusing me.. does that curve mean wider frame above?
« Last Edit: July 17, 2019, 10:00:20 AM by Groover »
1981 Moto Guzzi V1000G5
1987 Moto Guzzi LM1000SE, a
1987 Moto Guzzi LM1000SE, b
1980 Piaggio Vespa P200E
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Offline Tom H

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Re: Swing Arm Widths
« Reply #5 on: July 19, 2019, 12:36:46 PM »
Go to Greg Benders site thisoldtractor and look at the section with repair manuals. Many of the manuals have the frame dimensions and the swing arm dimensions.

I took a quick look yesterday at some manuals and from what I could tell the rear frame rails under the seat were about the same between a T and my EVT.

Tom
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Offline 5154guzzi

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Re: Swing Arm Widths
« Reply #6 on: July 19, 2019, 12:53:47 PM »
The swingarms are all the same width at the pivot point, so yes, they are interchangeable.  I believe the newer frames are wider, as are the shock mounts, not but much though and doable. The latest 03/04 style Tonti swingarm uses a different pivot pin ( different diameter threads and it`s not a direct swap without changing out bearings and modifying the pin length.  The pin length is too long from an early tonti due to the shallower swingarm bearing recess on the right side of the swingarm.  Recently modified pins to mount an 04 swingarm to fit my t3 type chassis to run a wider tire and rim.  Also mounted the long Cal 3 / Jackal style swingarm to a Lemans 1000 , that was a more direct swap with the same bearings and pivot pin.

  With either of these conversions, the shock will lay down at a much lower angle, dropping the rear height as well as changing the spring rate action.

Offline Groover

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Re: Swing Arm Widths
« Reply #7 on: July 19, 2019, 12:59:09 PM »
Great answers, that last one by 5154 was exactly what I needed to know. Thanks again to all, and have a great weekend!
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1987 Moto Guzzi LM1000SE, b
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Offline Groover

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Re: Swing Arm Widths
« Reply #8 on: July 22, 2019, 01:12:13 PM »
The swingarms are all the same width at the pivot point, so yes, they are interchangeable.  I believe the newer frames are wider, as are the shock mounts, not but much though and doable. The latest 03/04 style Tonti swingarm uses a different pivot pin ( different diameter threads and it`s not a direct swap without changing out bearings and modifying the pin length.  The pin length is too long from an early tonti due to the shallower swingarm bearing recess on the right side of the swingarm.  Recently modified pins to mount an 04 swingarm to fit my t3 type chassis to run a wider tire and rim.  Also mounted the long Cal 3 / Jackal style swingarm to a Lemans 1000 , that was a more direct swap with the same bearings and pivot pin.

  With either of these conversions, the shock will lay down at a much lower angle, dropping the rear height as well as changing the spring rate action.

I have a follow-up question in regards to the jackal swingarm on the LeMans 1000. Is this for a custom job, or is the rest of the Le Mans the same, except for the swing arm swap? How does it ride, and how does it look (assuming the bike/fender/tail is stock otherwise)
1981 Moto Guzzi V1000G5
1987 Moto Guzzi LM1000SE, a
1987 Moto Guzzi LM1000SE, b
1980 Piaggio Vespa P200E
1980 Piaggio Vespa P125X
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1980 Vespa SI Moped
http://scooteropolis.com/

Offline jcd06

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Re: Swing Arm Widths
« Reply #9 on: November 23, 2021, 02:55:18 PM »
The swingarms are all the same width at the pivot point, so yes, they are interchangeable.  I believe the newer frames are wider, as are the shock mounts, not but much though and doable. The latest 03/04 style Tonti swingarm uses a different pivot pin...
I'm looking into swingarms because I want a wider rear tire for my T3 with sidecar.
What are these 03/04 style swingarms refering to, 2003 and 2004, or something else?
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Online TOMB

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Re: Swing Arm Widths
« Reply #10 on: November 23, 2021, 03:20:12 PM »
What everybody else has said however don't overlook the pivot point to the center of the axle especially on the right side the rear end length might be different maybe spacers Etc just an after thought

The lenght of the swing arm on a T3 convert G5 Etc is different than what's on a cal 11 and newer right side swing arm is longer where the one on the t3 to has a shorter right side piece but it's longer overall on both sides and may work out just they careful measurements from the pivot point to the axle and the rear end you're going to use
T3 wheelbase is approximately 58 in Cal 11 and  newer the wheelbase is approximately 60-in apparently it's done all in the length of the swing arm and it may also be harder to put the bike up on the center stand however if you have a sidecar you shouldn't have a problem

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« Last Edit: November 23, 2021, 03:23:49 PM by TOMB »
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Offline rodekyll

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Re: Swing Arm Widths
« Reply #11 on: November 23, 2021, 04:44:56 PM »
The late model swing arms are "doglegged" for the tire width consideration.  They have a "dogbone" driveshaft, where the cardan joint is elongated.  Some of the longer swing arms have the crossbrace in a different position.  This can interfere with the centerstand and crossover pipe (colostomy bag) on some models. 

Here's a possibly incomplete list.  There may be some direct interchange with the kindred loop and early tonti stuff.  Maybe someone will discuss some of the differences.  For example, the drum and disc brake shorties may be a difficult interchange.  The longer arms may need different shock absorbers.  The later arms are 3" longer than the older ones.  This makes the fender placement problematic.  Etc.

SHORT ARM variations
drum brake loop
disk brake loop
drum brake early Tonti
Disk brake early Tonti

LONG ARM variations
CalIII straight swing arm
EV dogleg

Offline Frenchfrog

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Re: Swing Arm Widths
« Reply #12 on: November 23, 2021, 04:49:04 PM »
There are medium lengths too ...Guzziology has the full SP on this. The width at the pivot point remains the same as far as I remember.

Offline rodekyll

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Re: Swing Arm Widths
« Reply #13 on: November 23, 2021, 04:52:11 PM »
I slept through the 80s.  I don't know about the medium length stuff.

Offline guzzisteve

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Re: Swing Arm Widths
« Reply #14 on: November 23, 2021, 05:12:16 PM »
If you keep currant fender/shock set up the LM4/5 has the widest clearance for rim width. Think about shock angle if using longer.
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Offline moto-uno

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Re: Swing Arm Widths
« Reply #15 on: November 23, 2021, 09:33:48 PM »
  I installed a Jackel swingarm on my Le Mans 2 a few years ago . First off it 's more than 2" longer , which is
what I wanted , because I was stretching the seating space . I made rear fender struts to relocate the seat and fender
and to move the shocks back so they maintained the same angle ( and ride height as the Le Mans ) . The wider swingarm and
rim allowed a 130 rear tire . You'll also need the original drive shaft for which ever swingarm you chose . The
handling was not as good as the original . I made a longer brake hose also , the pivot points were the same . Peter

Offline John Croucher

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Re: Swing Arm Widths
« Reply #16 on: November 23, 2021, 11:39:55 PM »
This Old Tractor site has many resources. Including drawings with dimensions.  A good resource when interchanging parts. 

If you change to a shorter swingarm you will need to move the top shock mount forward. There is a boss welded in the frame that can be drilled through and tappeded.  I did this on my bike when I changed to a Magni swingarm.

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Re: Swing Arm Widths
« Reply #17 on: November 24, 2021, 05:02:40 AM »
The swingarms are all the same width at the pivot point, so yes, they are interchangeable.  I believe the newer frames are wider, as are the shock mounts, not but much though and doable. The latest 03/04 style Tonti swingarm uses a different pivot pin ( different diameter threads and it`s not a direct swap without changing out bearings and modifying the pin length.  The pin length is too long from an early tonti due to the shallower swingarm bearing recess on the right side of the swingarm.  Recently modified pins to mount an 04 swingarm to fit my t3 type chassis to run a wider tire and rim.  Also mounted the long Cal 3 / Jackal style swingarm to a Lemans 1000 , that was a more direct swap with the same bearings and pivot pin.

  With either of these conversions, the shock will lay down at a much lower angle, dropping the rear height as well as changing the spring rate action.

what 5154 said, and please for gods sake do not try and move an upper shock mount. Buy a shock of the proper length to give you the geometry you want.
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Offline Alfetta

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Re: Swing Arm Widths
« Reply #18 on: November 24, 2021, 09:25:34 AM »
what 5154 said, and please for gods sake do not try and move an upper shock mount. Buy a shock of the proper length to give you the geometry you want.

i recall back-in-the day...  i would cut off the top shock or sometimes the lower mount on the old dirt bike. It was a trend back in the early 70's. had to have the "lay-down" shocks !  Id did make landing jumps a bit softer, unless you blew through the travel !    good times !
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Offline jcd06

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Re: Swing Arm Widths
« Reply #19 on: December 02, 2021, 02:25:26 AM »
Thanks to all for the replies.
It was nice to practice some English as well  :laugh:

I would prefer to keep the same arm length, given the consequences for the various mounting points and stuff around.
Iíll check out Guzziology once I got my copy back from my friend.
So far Iíve checked Gregís sources and indeed the factory manuals pretty well show the dimensions of the swingarms.

At first glance I canít find an arm with the same length that has a recess for the tire.
Using an angle grinder to take a bite out of the T3 swingarm and weld a sheet onto the hole would work but will to a certain extend weaken the construction.
Later swingarms with recess have larger diameter legs.
I have no clue about the wall thickness of the tubes for the different swingarm types.

The current tire is a Michelin Collection X 125/80 15 but thatís a summer tire, and I would like to have a winter tire.
Unfortunately they donít exist with these dimensions.
I can have 135/70 15 but at the moment there is barely 8 mm between the current tire and the right leg of the swingarm.
With the 135 wide tires the rubber would be very close to the shaft tunnel (3 mm in theory).

The best trade-off seems the LM1000 swingarm.
It has a recess, larger diameter legs and fits my T3 frame, at least on paper.
Disadvantages are it is 20 mm longer and the left doglegged side might complicate the upper shock attachment.
A LM1000 swingarm is on its way to me and I will test-mount it in an empty frame I have laying around.
I will post the result of my findings.




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Offline Frenchfrog

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Re: Swing Arm Widths
« Reply #20 on: December 02, 2021, 04:00:06 AM »
Notching the short swingarm used to be commonly done back in the 80's . If it's done competently there should be zero loss of strength.

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Re: Swing Arm Widths
« Reply #21 on: December 02, 2021, 02:44:12 PM »
LM IV swing arm is a good choice. The only thing you will have to do is stack shock eyelet washers on the inside up top. Better hope your shocks have a narrow enough eyelet (in and out, ID must be right of course). I have done the LM IV swinger on an old short swing arm frame with many different shock brands, ohlins, koni, marz, works. Some of the long konis for LM IVs have the shock eyelet welded offset. Eyeball the shock and using washers or reversal of the shock (if eyelet offset), get the shock most close to vertical that you can. It will be good enough.
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