Turbo Pro Partial throttle drumming sound

[sledhead9825]

I have a 2012 Silber Turbo on a 2011 Pro With a Boost-it Box (thanks Neil)
Running 7lbs boost
50/50 race fuel and 94
WOT sled runs awesome afr 11.8 to 12 doesnt miss a beat rips (8150 to 8200 RPM and 50 MPH track speed in the deep stuff)
Partial throttle sled runs great
Light throttle runs great but I here like a drumming noise. Hit the throttle no noise. No throttle down hill, no noise.
The sled runs great from top to bottom
Just this random drumming noise. It gives me a uneasy feeling but the performance is not affected at all.
Ideas anyone?????

 

[NM]

I have a 2012 Silber Turbo on a 2011 Pro With a Boost-it Box (thanks Neil)
Running 7lbs boost
50/50 race fuel and 94
WOT sled runs awesome afr 11.8 to 12 doesnt miss a beat rips (8150 to 8200 RPM and 50 MPH track speed in the deep stuff)
Partial throttle sled runs great
Light throttle runs great but I here like a drumming noise. Hit the throttle no noise. No throttle down hill, no noise.
The sled runs great from top to bottom
Just this random drumming noise. It gives me a uneasy feeling but the performance is not affected at all.
Ideas anyone?????

Bolts are broken on mag side motor strap. Starting to see a few now. It can be fixed without pulling the engine.
Making too much power now. Haha

 

[Gunnerthesnowman]

I have a 2012 Silber Turbo on a 2011 Pro With a Boost-it Box (thanks Neil)
Running 7lbs boost
50/50 race fuel and 94
WOT sled runs awesome afr 11.8 to 12 doesnt miss a beat rips (8150 to 8200 RPM and 50 MPH track speed in the deep stuff)
Partial throttle sled runs great
Light throttle runs great but I here like a drumming noise. Hit the throttle no noise. No throttle down hill, no noise.
The sled runs great from top to bottom
Just this random drumming noise. It gives me a uneasy feeling but the performance is not affected at all.
Ideas anyone?????

This noise , is it coming from the engine , under the hood or from the exhaust???

Bolts are broken on mag side motor strap. Starting to see a few now. It can be fixed without pulling the engine.
Making too much power now. Haha

Are you talking about the mag side motor MOUNT ( motor strap) where are these bolts and how do you tell if there are broken

 

[sledhead9825]

Its under the hood.
I have it running rich at WOT
Think it is unspent fuel, pooling in the crankcase then burning and small backfires at light throttle?
Nothing obvious broken, and I go over everything under the hood before every ride.

 

[WesG]

I would bet it is exactly what Neil said. The two bolts on the mag side that go into the bottom of the crankcase, through the motor strap, are possibly broken off in the case. These are the vertical ones that go through the strap and into the crankcase, not the horizontal ones that go through the rubber mounts. Only time you can hear it is at light throttle loads and it sort of thuds along. I just did this on mine also a 2011. You can reach the one by running your hand down along the recoil and reaching under the case along the strap. Has the sled gotten harder on belts? Those 115's are tough so they don't just break they hold in there with bad alignment for awhile. Is the tab that holds the airbox to the steering post still together or has it broke? Also fix it asap as it can damage the bottom of the case if you continue to ride it with those bolts broken.

 

[sledhead9825]

I will check it out. You should be able to tell by prying up, on that side of the engine. correct?
Might belt looks like new, and my RPM is the same. Thanks guys I will have a look.

 

[sledhead9825]

Whats worse than finding a bolt in the pan??
Finding half a bolt!!!!
Thats gotta be it.
Ripping it apart Friday
Thanks for your help guys

 

[NM]

Whats worse than finding a bolt in the pan??
Finding half a bolt!!!!
Thats gotta be it.
Ripping it apart Friday
Thanks for your help guys

Got a call from the dlr today and mag side motor straps are back ordered until end of March. Must be lot's of turbo pro's on the snow.

 

[WesG]

Good thing I have a new one in the package! How did the mag side support turn out NM? I am thinking pretty hard about the ftx plate.

 

[NM]

Good thing I have a new one in the package! How did the mag side support turn out NM? I am thinking pretty hard about the ftx plate.

I talked to the machinist today and he is working on one for us to try. I can send you a prototype if you want to test one for us.
The FTX plate is looking better all the time but I would sure like to make this torque stop work first.

 

[WesG]

Yup I am interested for sure. Have to stop that side from twisting when I put the flipper to the bar. I wonder if the issue is only the 11's? Did they make a change in 12? If I can keep the motor inline most of the thumpers better look out!

 

[moto5151]

Does anyone have any pictures of this? I realize it's a hard spot to get to for a picture. But if anyone had an engine out and had time for a few pics. My pro is a belt eating monster. I've had my clutching aligned, and endplay checked. I've installed slp torque stop arm, and solid engine mounts. Still pulling belts apart with 100 miles on them.

 

[NM]

Does anyone have any pictures of this? I realize it's a hard spot to get to for a picture. But if anyone had an engine out and had time for a few pics. My pro is a belt eating monster. I've had my clutching aligned, and endplay checked. I've installed slp torque stop arm, and solid engine mounts. Still pulling belts apart with 100 miles on them.

Usually means your clutching is not good. All the alignment in the world won't fix bad clutching.

 

[sledhead9825]

Fixed my sled today. Both bolts on mag side,rear one was broken,front one loose. Front one, new bolt and loctite.Rear one was a bit more work. Drill ez-out, drill tap. Anyway all fixed, try it Sunday. Looks like we got a bunch of snow this week. To Moto5151. Even down 2 bolts my clutching was dead on 8150 same belt with 700 miles boosted in heavy west coast snow and it looks like new. I think some credit must be due to Boost-it's motor mounts, cause they literally had to be working double time. Thanks Neil and Wes