Belt Tension Guidance

[mswyka]

I am noticing on one of our 1980 Invaders that the drive belt looks loose.  And running it feels like there is quite a bit of slack before the primary bites into the belt.  Checking the center to center distance on the drives the manual says 12" and they measure  12"  center to  center.  When we put the sled together we pushed the cross-shaft back quite a bit.  There might  be a little more room to push it back, but not much.

With what I am seeing and with how the sled is running, I am half thinking that I should get a shorter belt.

I am interested if anyone else has experienced anything similar.

[Interceptor398]

My vote would be if the set up is good find a belt to fit it.

[rminier]

 MANY years ago after purchasing my 1st Invader in 1982, I battled with the sled being very unresponsive from a standing start.
I tore into the carbs several times. I had the center to center distance set at precisely 12"
 I was subscribed to 2 of the snowmobile magazines from back in the day. A new issue had an article on clutch tuning. One thing it discussed was belt deflection. At the time, something totally new to me.
 Over the years, I have found that several of the manufacturers use the belt deflection spec rather than the center to center spec.
I probably had a fairly new Dayco 1078 on the sled back then, but when I pressed down at the midway point of the belt, it was so soft I could push it down and make contact with the bottom of the belt.
 "As a general rule" it seems that pressing down at the midway point between the clutches with about 20 lbs. of force, you should see about 1 1/4" deflection from a straight edge  spanning the clutches.
 I know once I moved the jackshaft back to get the deflection near that measurement, the Invader was transformed.....I had it set so loose before that the belt was probably engaging way too high on the drive clutch, rather than at the inner circumference of the clutch.
 Once the drive belt has worn some, it is no longer 1 1/4" wide and it tends to sit down in the secondary clutch.....which makes it behave like a belt that is too long, and the belt deflection becomes more than 1 1/4".
 Here is a belt that I believe is an absolute bargain:
https://www.mfgsupply.com/hp3012-w2.html
 I tried one of these belts on my "new" trailer queen Invader that I got last year. We have received just enough snow around here a couple times that I just barely tried it out, but it looks to be equal in quality to the Dayco 1078's that I have used in the past.
 And, adjusting the jackshaft to get 1 1/4" belt deflection with that belt left a lot of room to move the jackshaft forward or backward more, if needed.

[mswyka]

I will need to measure deflection.  I am thinking that there is quite a bit right now.

[DougKauer]

I had something similar on my 79 Invader, but it was a clutch spring that I had to replace. Maybe this is it?

[mswyka]

This is the best photo I could take one handed.  This is a bit over 1.25".   I also measured the center to center distance on our other Invader and found that it was closer to 12.375"

I also measured the belt and that is a skootch less than 1.25"

So between the center to center distance and the belt width I think I have some adjusting to do and might even want to break down and buy a new belt.

[gixxer6]

Belts can vary in length quite a bit, I suspect this is why manufactures are going to a belt deflection spec. 

[kawhead]

if you move the jackshaft back you should move the chaincase top back also

[mswyka]

if you move the jackshaft back you should move the chaincase top back also

Understood.  Thank you.

[mswyka]

Today's meeting was cancelled so I took the afternoon off.  In the process I got another 1/4" of adjustment on the belt.  Of course then I had to spend some time riding across the farm.  She ran much better.  Still room for improvement, but I can't complain.