Anyone had success reinforcing the mono front w-arm?
- Thread starter mdkuni
- Start date
sobfrogg
TY 4 Stroke Guru
Hey Bruce,
How's it going
You know how fat I am so weight is not the issue, But Strength is
How's it going
You know how fat I am so weight is not the issue, But Strength is
ROCKRTX
TY 4 Stroke Junkie
Bruce,do you have some pics of those suspension you are building?
If not post picture as soon as possible,i have interest in changing my crapy w-arm for a stronger one that don't rust and lose a couple pound.thank!
ROCKRTX
If not post picture as soon as possible,i have interest in changing my crapy w-arm for a stronger one that don't rust and lose a couple pound.thank!
ROCKRTX
I just fixed my W arm this weekend. I added a solid 3/4 in bar through the length of that pipe, and put reinforceing on all sides. Should be super strong now. I'll get some pics when it gets back from powder coater.
680
680
ReX
TY 4 Stroke God
We've reinforced our pivot arms several times and in several different ways. Unfortunately even with the top reinforced similar to posted here (strength wise), the vertical tubes converted into a box on both sides, gussets added on the inside at the top and an extra 3/16" plate added to the outside where the pivot arm attaches to the rails my buddies are still breaking the pivot arms (in the middle, 1/2 way up the vertical tubes now).
Without any reinforcements some of the guys were breaking these arms in around 1500-4000 miles. With all of the reinforcements, they are typically lasting at least 5000 miles.
The rear arms also break where the shock attaches (the shock mount tears away from the arm). We've reinforced them by adding an extra plate beside the mount and adding extra weld to the original bracket. The rear arms are holding together after this.
Last season I didn't have a single problem (strength wise) with the suspension in my 07 RTX, yet my buddies had lots of failures with their 06 Apex ERs riding on the same trails and conditions (some were back to stock parts again though).
This year I think everyone is back to running stock pivot arms again (warranty replacements). I expect if they end up riding the same sleds, they'll be breaking them again. Two of them have given up and are getting REV-XPs and one is considering a new skid (or a REV-XP). There will still be at least one on an 06 Apex ER.
In our experience, you can beef up the monoshock and it will be stronger, but if you really want to ride them the same way a REV or Polaris can be ridden, I'd recommend installing either a Skidoo skid, a Polaris skid, or a ProActive CK skid out of an 07/08 RTX.
We've never broken a Skidoo or Polaris skid yet and it looks like the 07/08 RTX is able to run with them without issues too (although the stock springs and shock valving is way to soft for aggressive riding - at least on the 07).
For aggressive riding, the problem with the monoshock is the loads that the pivot arms have to handle are absolutely enormous compared to the loads a typical torsion spring based skid have to handle.
With the Doo, Poo, and RTX skids, the rear torsion springs basically push down almost directly on the rails, the center spring pushes down fairly directly on the rails, the shocks push down on the rails fairly directly and the pivot arms essentially just have to handle locating the rails relative to the tunnel. The locating loads, shock damping loads, and spring loads are all applied through different paths relatively directly between the chassis and the rails.
With the monoshock, the front pivot arm has to handle pushing down on the rails by twisting about the upper pivot, has to handle an incredible amount of force applied by the monoshock spring and shock itself, and has to handle locating the rails (side loads, hits, etc.). It would be interesting to calculate the stresses within that front pivot arm on the monoshock. I suspect it is somewhere around 10x higher than the stresses in a standard torsion skid.
On the other hand, the monoshock does a great job for less aggressive riders. The ride quality, handling, etc. can be excellent and if it isn't pushed too hard, a stock monoshock can be reasonably durable.
2000srx, I don't know what your custom front pivot arms look like, but they are going to have to be very strong to not fail for aggressive trail use. I spoke to some guys at a custom shop in Ontario that started to make strong monoshock front pivot arms. They stuck pretty much with the updated Yamaha pivot arm design, but made them out of chromoly (no weight savings, but much stronger) and added a few gussets to make them even stronger. Unfortunately they closed up shop so these aren't available (and never really were to the public).
Without any reinforcements some of the guys were breaking these arms in around 1500-4000 miles. With all of the reinforcements, they are typically lasting at least 5000 miles.
The rear arms also break where the shock attaches (the shock mount tears away from the arm). We've reinforced them by adding an extra plate beside the mount and adding extra weld to the original bracket. The rear arms are holding together after this.
Last season I didn't have a single problem (strength wise) with the suspension in my 07 RTX, yet my buddies had lots of failures with their 06 Apex ERs riding on the same trails and conditions (some were back to stock parts again though).
This year I think everyone is back to running stock pivot arms again (warranty replacements). I expect if they end up riding the same sleds, they'll be breaking them again. Two of them have given up and are getting REV-XPs and one is considering a new skid (or a REV-XP). There will still be at least one on an 06 Apex ER.
In our experience, you can beef up the monoshock and it will be stronger, but if you really want to ride them the same way a REV or Polaris can be ridden, I'd recommend installing either a Skidoo skid, a Polaris skid, or a ProActive CK skid out of an 07/08 RTX.
We've never broken a Skidoo or Polaris skid yet and it looks like the 07/08 RTX is able to run with them without issues too (although the stock springs and shock valving is way to soft for aggressive riding - at least on the 07).
For aggressive riding, the problem with the monoshock is the loads that the pivot arms have to handle are absolutely enormous compared to the loads a typical torsion spring based skid have to handle.
With the Doo, Poo, and RTX skids, the rear torsion springs basically push down almost directly on the rails, the center spring pushes down fairly directly on the rails, the shocks push down on the rails fairly directly and the pivot arms essentially just have to handle locating the rails relative to the tunnel. The locating loads, shock damping loads, and spring loads are all applied through different paths relatively directly between the chassis and the rails.
With the monoshock, the front pivot arm has to handle pushing down on the rails by twisting about the upper pivot, has to handle an incredible amount of force applied by the monoshock spring and shock itself, and has to handle locating the rails (side loads, hits, etc.). It would be interesting to calculate the stresses within that front pivot arm on the monoshock. I suspect it is somewhere around 10x higher than the stresses in a standard torsion skid.
On the other hand, the monoshock does a great job for less aggressive riders. The ride quality, handling, etc. can be excellent and if it isn't pushed too hard, a stock monoshock can be reasonably durable.
2000srx, I don't know what your custom front pivot arms look like, but they are going to have to be very strong to not fail for aggressive trail use. I spoke to some guys at a custom shop in Ontario that started to make strong monoshock front pivot arms. They stuck pretty much with the updated Yamaha pivot arm design, but made them out of chromoly (no weight savings, but much stronger) and added a few gussets to make them even stronger. Unfortunately they closed up shop so these aren't available (and never really were to the public).
mdkuni
TY 4 Stroke Guru
ReX
TY 4 Stroke God
You'll probably have to do a little grinding on the upper reinforcement plate in order to fit the bushings and washers on.
Hopefully it will last for you. Unfortunately I suspect it will still break where the inner vertical tube attaches to the upper cross tube if you ride it aggressively. In this area we found it best to box in the area between each pair of vertical tubes (when I say vertical I mean the ones that go up and down on an angle - quite far from vertical really...).
If you weld plates on both sides of these vertical tubes, creating a box all the way from top to bottom these pivot arms last quite well. Note that boxing this area in is the modification that Yamaha's snow cross teams was doing when using the monoshock suspension.
We also found we had to reinforce the outer tab that attaches to the rails.
I don't have a picture of our most beefed up pivot arms, but here is the lower end of one of the earlier attempts (that did stop our most common breaks - search for older posts from me and you can see pictures of these breaks).
Hopefully it will last for you. Unfortunately I suspect it will still break where the inner vertical tube attaches to the upper cross tube if you ride it aggressively. In this area we found it best to box in the area between each pair of vertical tubes (when I say vertical I mean the ones that go up and down on an angle - quite far from vertical really...).
If you weld plates on both sides of these vertical tubes, creating a box all the way from top to bottom these pivot arms last quite well. Note that boxing this area in is the modification that Yamaha's snow cross teams was doing when using the monoshock suspension.
We also found we had to reinforce the outer tab that attaches to the rails.
I don't have a picture of our most beefed up pivot arms, but here is the lower end of one of the earlier attempts (that did stop our most common breaks - search for older posts from me and you can see pictures of these breaks).
Attachments
mdkuni
TY 4 Stroke Guru
ReX said:
I did need to cut down the top metal plate to get the bushings and bolts in. I am afraid my limiter strap will brake as well as the hole where the strap goes around the top tube is a tight fit. It is a very difficult place to grind though. All I could do was use a file and opened it up some. So time will tell. I hope it will last as I am out of options. I will still carry duck tape with me and check the suspension frequently as I love to ride very aggressive!
I am not sure as to what tubes you are talking about boxing in. Are they the ones that have the upper shock mount on them as shown in my first picture? Would you be boxing them against the outside tube on each side?
I am curious to know with the arms you are your riding buddies have gone through, how often are you guys bottoming out the suspension. I am curious to know if it is simply the stress the arm endures during normal travel that is casuing the problems or is the bottom outs?
Thank you for all the info Rex.
ReX
TY 4 Stroke God
mdkuni said:
I'm talking about the two pairs of tubes that run from the bottom of the pivot arm to the top. We created a box out of these tubes on each side (left and right) by welding plates on each side (front and back) of them. This is also what at least one of the Yamaha race sleds used (when they were using the monoshock in snowcross).
mdkuni said:
If anything, the sleds set up with the stiffest valving and stiffest springs are the ones that end up with broken pivot arms the fastest. The sleds that are left with stock valving that bottom out all the time seem to hold up better (although the bump stops eventually get broken and then the rails, where the front idler wheels mount, hammer against the front pivot arm).
Personally I refuse to ride a sled that bottoms out all the time (with the way I ride), so if I was riding a sled with a monoshock skid I'd be revalving the shock, installing a heavy duty spring, boxing the front arm, adding extra gussets, adding the reinforcement to the lower tabs that attach to the rails and reinforcing where the shock mounts to the rear pivot arm.
One thing for sure is the monoshock can be set up to work very well for aggressive riding with the right valving and spring. If only the stress in the pivot arms (front especially) could be lowered a bit it would probably be a great skid for everyone...
We spent a few hours going over sled options with the guys I ride with last night. It looks like we'll probably be down to only one monoshock left for this season and it turns out the guy with that Apex just finished totally reinforcing his pivot arms. It will be interesting to see if his 6th attempt (I think it is #6) at reinforcing the front pivot arm is enough.
mdkuni
TY 4 Stroke Guru
Well I am really tight with money right now so that is all the welding I can afford. If something breaks then I will have no choice, so here is to hoping! I will definitley use your info if I have any more damage so thank you. I just hope I do not end up blowing thorugh the track or anything if something brakes. This is only arm #3 for me with the second one lasting unding 2,000 miles. None of them were reinforced.
I just bumped the cam up to four in the garage the other night on top of the things I had already done as listed in my first post.
If you would, keep me updated in regards to your buddies reinforced arm. I would like to know what works. Hopefully these arms did not sway the other guys to other brands.
I just bumped the cam up to four in the garage the other night on top of the things I had already done as listed in my first post.
If you would, keep me updated in regards to your buddies reinforced arm. I would like to know what works. Hopefully these arms did not sway the other guys to other brands.
ReX
TY 4 Stroke God
mdkuni said:
I hate to say it, but they all went to Skidoo and the reason was the monoshock suspension failures...(no one I know has broken an MXZ skid yet).
They're still giving me a hard time, razing that the suspension will fall apart since I'm on a Yamaha (claiming that we need to stop litering the trails with broken parts - environmental reasons...).
The one last holdout on a monoshock sled (with beefed up pivot arms) has already stated he will be on a REV-XP 800R MX-Z next season (once the bugs are worked out). Next season everyone but me (most likely) will be on a Skidoo.
barnstormer
Extreme
Just a silly question. But has anyone on here tried to anneal the welds on the factory skid? Yes the factory skid may have a design issue, but in many factory shops they never stress relieve the welds. It would sure go a long way to heat it up and cool it down a few times and then see how long they last.
ReX
TY 4 Stroke God
I've thought about it, but I don't really think that would do it.
These parts are made out of a mild steel so they yield slightly in any pre-stressed areas when the stresses get high.
The failures are also all fatigue failures, not single overload type failures.
If the pivot arms were made out of heat treated chromoly on the other hand...
These parts are made out of a mild steel so they yield slightly in any pre-stressed areas when the stresses get high.
The failures are also all fatigue failures, not single overload type failures.
If the pivot arms were made out of heat treated chromoly on the other hand...
