Clunk or "Hitting Rock Sound/Feel" at 100 mph+

[snowcaine]

'20 SW. 1.25" lugs. 192 1.575" Gold Diggers. Track tight tight per the Precision EFI video that Turboflash helpfully posts whenever track deflection issues come up. When the Dream Meter ticks past 100 mph (usually ~106 or so), it feels like the track/studs hit a rock or "slip/jerk" that makes a jarring clunk sound and feel.

When riding in the lower UP, I thought I was just digging down too deep and hitting rocks. But I get the same sound/feel on Trail 3 in western UP Keweenaw with miles of base. Thoughts??

For comparison, same trail, same day, same conditions, my '21 Cat with 1.25" lugs and 144 1.325" Gold Diggers cranks 115 mph on the dream meter with no "hitting rock" sounds. I appreciate any advice. Thanks.

Edit: I already have heat exchanger fin damage from last year when I ran the track too loose (until TF posted the Precision EFI vid!).

 

[Crossfire12]

Put bigger studs in, just saying!!!!iilook in tunnel, any hits from studs.

 

[KnappAttack]

Either the track is indeed ratcheting, or the belt is slipping in the secondary.

I have to run a VERY tight track, tighter than even the video shows. If the suspension is moving it is more likely to ratchet the track.

What are you running in the secondary for helix and spring? Reason I ask is another area of concern.

Not enough spring pressure and/or too much helix in the secondary the belt will slip the belt, making you swear the track is ratcheting. Typically it also will not MPH upstairs well. I must run heavy spring pressure in the secondary to prevent this as well. On my drill press scale I must have around 330-335 plus lbs at full shift to keep belt slippage at bay. Which is more than you can imagine.

192 studs cut a lot of cords and is a lot of weight slinging around at high speeds vs a lighter 144 studs with less cords cut in the track. I'd start by tightening the track more. Still want to hear your secondary setup though to rule that out too.

 

[74Nitro]

I've had this also. It is the studs hitting the fins on the front heat exchanger. Tighten track more.

 

[DooZ]

Just spitballin' but...is chain adjusted properly in chaincase? Stretched?

 

[snowcaine]

Either the track is indeed ratcheting, or the belt is slipping in the secondary.

I have to run a VERY tight track, tighter than even the video shows. If the suspension is moving it is more likely to ratchet the track.

What are you running in the secondary for helix and spring? Reason I ask is another area of concern.

Not enough spring pressure and/or too much helix in the secondary the belt will slip the belt, making you swear the track is ratcheting. Typically it also will not MPH upstairs well. I must run heavy spring pressure in the secondary to prevent this as well. On my drill press scale I must have around 330-335 plus lbs at full shift to keep belt slippage at bay. Which is more than you can imagine.

192 studs cut a lot of cords and is a lot of weight slinging around at high speeds vs a lighter 144 studs with less cords cut in the track. I'd start by tightening the track more. Still want to hear your secondary setup though to rule that out too.

I'm running a touch (0.25") looser than the Precision EFI video, but I've also noticed it at exactly 0.5" like the video says to do. Feels like a "slip" in looser base snow that "catches" when it bites on something harder below. Sorry for the descriptors. Trying to describe.. it's like hitting something or washing out loose snow and then biting on better base, so it jerks.

Secondary is Pro 4 with 43/34 Dalton helix and the green Cat spring. Pro 4 wrap is set dead center in the middle (ie, equal distance from least wrap and most wrap). It's not numbered like a traditional Yam secondary. Belt temps on long UP RR beds are ~180-185 F at 8200-8500 RPM for long stretches (via Razorback infrared gauge). Thanks!

 

[snowcaine]

I've had this also. It is the studs hitting the fins on the front heat exchanger. Tighten track more.

This is what it sounds/feels like, but I don't know what a ratcheting track sounds/feels like or if secondary slip is similar like Knapp is discussing. Thanks!

 

[snowcaine]

Just spitballin' but...is chain adjusted properly in chaincase? Stretched?

Adjusted chain before last trip! Finger tight, then one turn out. Thanks.

 

[KnappAttack]

I'm running a touch (0.25") looser than the Precision EFI video, but I've also noticed it at exactly 0.5" like the video says to do. Feels like a "slip" in looser base snow that "catches" when it bites on something harder below. Sorry for the descriptors. Trying to describe.. it's like hitting something or washing out loose snow and then biting on better base, so it jerks.

Secondary is Pro 4 with 43/34 Dalton helix and the green Cat spring. Pro 4 wrap is set dead center in the middle (ie, equal distance from least wrap and most wrap). It's not numbered like a traditional Yam secondary. Belt temps on long UP RR beds are ~180-185 F at 8200-8500 RPM for long stretches (via Razorback infrared gauge). Thanks!

I'm running tighter than video because mine will ratchet if not, so will my buddies and we both have 192 studs. Only sleds with less studs can get by running a bit looser.

What you describe above sounds like a track spinning and hooking, if it feels like you are running over a 2x4 on the trail its typically track ratcheting and will clunk, typically on these sleds its right up there about 100-105 MPH. I've also had it ratchet on hard braking and slip over the sprockets and have the studs have hit the front exchanger before if getting a bit too loose. Brake ratcheting was violent as the track bunches up and ratchets. These things need tight studded tracks with 270 plus HP. If non-studded it is no where near as critical to be that tight.

 

[Sledroll]

Adjusted chain before last trip! Finger tight, then one turn out. Thanks.

Finger tightening is so ambiguous , depending on if you have strong or weak fingers !!!!!
Whereas lbs. of torque are a real measurement !
As someone previously mentioned , you really need to set the chain tension with the chaincase open and then some kind of chain deflection measurement would be really helpful . Unfortunately this is not a real world acceptable solution , of having to open the chain case .

 

[snowcaine]

I'm running tighter than video because mine will ratchet if not, so will my buddies and we both have 192 studs. Only sleds with less studs can get by running a bit looser.

What you describe above sounds like a track spinning and hooking, if it feels like you are running over a 2x4 on the trail its typically track ratcheting and will clunk, typically on these sleds its right up there about 100-105 MPH. I've also had it ratchet on hard braking and slip over the sprockets and have the studs have hit the front exchanger before if getting a bit too loose. Brake ratcheting was violent as the track bunches up and ratchets. These things need tight studded tracks with 270 plus HP. If non-studded it is no where near as critical to be that tight.

Thanks Mr. Knapp and 74Nitro I'm going to tighten up the track then and try to eliminate potential causes starting there.

Sledroll, I agree "finger tight" is a ridiculous standard. After reading numerous threads on here, I settled on tightening the tensioner bolt as much as possible with my bare fingers and then backing off one full turn. If you know a torque spec, please advise!

 

[Sledroll]

Thanks Mr. Knapp and 74Nitro I'm going to tighten up the track then and try to eliminate potential causes starting there.

Sledroll, I agree "finger tight" is a ridiculous standard. After reading numerous threads on here, I settled on tightening the tensioner bolt as much as possible with my bare fingers and then backing off one full turn. If you know a torque spec, please advise!

There is apparently no torque spec .
My only chain tightening experience was tighter is better , on my SX 700 , and on a Rev , and blew up both chaincases !!!
In the scope of my world ,that may have been one of my least expensive lessons in life !!!
As far as the track goes , there seams to be a fine line between too loose , and just right .
I have had that clunking at higher revs , that this site helped me to realize , that tightening in the track's case is usually a good thing , and particularly on this chassis .
I am better at asking questions , than providing answers , and so on TY , I am never afraid to ask for help , no matter how stupid it may seem .
And if you don't want to look stupid , than you can always go the PM route .