Comet 108EXP Cam Arm Search

[Mark633CSi]

Hello, I have been searching high and low for what appears to be, discontinued cam arms for the Comet 108EXP. I have a 102C on my '81 Liquifire and am going to replace it with the 108 however, from the countless hours of research I have done, it would appear that the purple spring with C-2 arms is what's needed for the late model 108EXP's. The problem is, I can't find a listing for C-2 arms. Anywhere. Does anyone have a lead on them and if I'm incorrect on weights and spring choice, let me know too.

Thanks!
Mark

[nick80lf]

I'm by no means a clutching expert but I do have a 108 EXP on an 80 liquifire. In all honesty, I wouldn't do it again. For me the biggest issue is that I live in Ohio and the snow doesn't last enough to fiddle around with the setup.

I can share a few things that have tripped me up along the way.

1. I don't believe the 108EXP responds the same as a 102 when its running the same cams and spring. I seem to recall finding a chart somewhere and I ended up changing the spring to get the RPMs in the same range that the 102 ran.

2. Be careful when you say purple spring. I believe there are two different purple springs. I think my 108 EXP is running "the other purple spring".

3. The 108EXP is a larger diameter clutch. Theoretically it could shift out to a higher ratio. However, there is a limiter shim in the secondary. This will limit how far the primary can close. Basically you would need to mess with the limiter shim to take advantage of the larger diameter primary sheave. I never messed with this. Just accepted it and tried to make it operate like the 102.

I was thinking the stock setup used one of the B profile cams and I believe you are correct that they are obsolete. Only source is used. I'm sure others have setups that they prefer using different combinations.

[Mark633CSi]

I'm by no means a clutching expert but I do have a 108 EXP on an 80 liquifire. In all honesty, I wouldn't do it again. For me the biggest issue is that I live in Ohio and the snow doesn't last enough to fiddle around with the setup.

I can share a few things that have tripped me up along the way.

1. I don't believe the 108EXP responds the same as a 102 when its running the same cams and spring. I seem to recall finding a chart somewhere and I ended up changing the spring to get the RPMs in the same range that the 102 ran.

2. Be careful when you say purple spring. I believe there are two different purple springs. I think my 108 EXP is running "the other purple spring".

3. The 108EXP is a larger diameter clutch. Theoretically it could shift out to a higher ratio. However, there is a limiter shim in the secondary. This will limit how far the primary can close. Basically you would need to mess with the limiter shim to take advantage of the larger diameter primary sheave. I never messed with this. Just accepted it and tried to make it operate like the 102.

I was thinking the stock setup used one of the B profile cams and I believe you are correct that they are obsolete. Only source is used. I'm sure others have setups that they prefer using different combinations.

Good advise. Thanks!

If we're lucky, we have about 4-5 months of snow were I am. That should be enough time to fiddle with one but the key is to find the B1 or C2 cam arms. Maybe I’ll do what I can with my 102C and tinker with a 108EXP later on.

[JoeRainville]

Hi Guys,

I have updated clutching on both my 80 and 84 Liquifires and am happy to share what I learned. My 80 has Cat ZR era drive and drive clutches running an updated M69170 belt that is stock for the 82-84 Liquifires. For the driven, an 80's Cat 1" jackshaft was needed to adapt the clutch into the Liquifire chassis. I run a 44 deg billet helix and yellow/white spring I think. I may have had a custom 1" diameter space made for end, or I may have use a Cat part, not 100% sure on that exact part.

For the drive, I am using a Cat 43.5 gram weight. When you increase the clutch diameter, you need to reduce the weight mass from 6-8% depending. I am using a spring that give me a 5k engagement, but I think it's and older D&D "Black and Blue" I had laying around. The bore depth on the back of the clutch needs to be shallow so it doesn't hit the frame, or alternatively, you can turn a little material off the back side of it. I later found that Firecat versions of the Cat drive are bored shallower and would use one of those instead of a ZR version that I had to have machined a bit.

For gearing, the going from a 7 1/2 drive clutch to an 8 1/4" of course affects the final gear ratio. The 80-81 Liquifire is geared pretty steep, 22:35 or 1:59 if I remember correctly. An overdrive clutch ratio would just be overkill and lug the motor. The 82-84 ratio of 21:39 or 1.85 is a good place to start with a 108 or similar clutch.

One of my 84's used a regular 108 with "B" weights are are not "B-1's". There are the lighter version and work pretty well, and I think they were 42 ish grams, but I have to measure one to be sure. That one uses a stock Deere secondary, M69170 replacement belt and stock 21-39 gearing.

As for the secondary on an 80 LF, I would either updated it to a newer roller unit, or find one from an 82-84 that is wider to fit the 1 /3/8" wider belt. I am not sure about adapting a 108 to a 1 1/4" belt as I have not attempted it.

Good luck and I hope this helps,
-Joe Rainville

[Mark633CSi]

Good luck and I hope this helps,
-Joe Rainville

That is fantastic info! Thanks Joe!

Mark