Howling at idle - uh oh

[steveg_nh]

So many of you may recall the extensive work I did to the 2007 Attak I bought in July. I went through this thing with a fine tooth comb. So I'm a bit concerned I missed something. Here's the story...

Yesterday, I finished up the work I was doing on my son's Polaris, so since his sled doesn't have reverse, I moved mine out of the trailer (we had about 6" of snow on ground, so went SLOW), and around the trails behind my house to turn around to reload from the front of trailer after loading the Polaris.

When I came to a stop I had a howling sound. Not a squeal or squeek, but almost like a consistent wind noise. Odd, I know. I wish I had my phone in my pocket to record the video. It goes away once the clutch starts to engage, and isn't present when riding, just at idle. Goes away in reverse too. This is the first time I've run the sled in cold temps too, so maybe the belt is just settling in? The belt isn't brand new, but darn close to it. It never made this noise when I was testing it out/running it after doing all the work I did. It has been sitting in the trailer about 3 weeks.

For history, I've done a ton, but the stuff that seems most relevant are that I replaced the driveshaft bearing, repacked the jackshaft bearing (looked really good when clean, no rust), changed chaincase oil and checked chain tension, replaced the secondary spring with a new one (stock Yamaha spring) and replaced the stock primary spring with the soft start spring from BOP. Both clutches were cleaned and secondary has new buttons. Engine oil and filter changed as well. Clutch alignment and offset (play) checked and confirmed. I didn't see anything about proper belt deflection in service manual, but did make sure belt was sitting in secondary at proper height.

I know diagnosing "noises" without hearing them is difficult, but given the symptoms, I thought I'd start here.

Thanks guys.

 

[musselman]

Was it the rad fan that came on? Usually it can only be heard at idle.

 

[Pete_man26]

did you run it with the belt taken off?

 

[steveg_nh]

Was it the rad fan that came on? Usually it can only be heard at idle.

Nope defintely not. Clutch side. I've heard the fan, and it's still fairly quiet, and it wasn't on long enough for the fan to kick on.

did you run it with the belt taken off?

I would say no. But let me clarify. When I was doing all the work to it (I did A LOT), here and there, I would test run it for a minute or two with belt on, but skid out, to test progress and results. In hindsight I shouldn't have, but I needed to. Anyway, that was in the summer, and it never made this noise until now, and it ran plenty with belt on since I did that without making any noise. And even when I did what I said, never gave it gas, just idling.

 

[kinger]

You still on stock airbox? Howling sounds intake related. Did you get all the hoses back on?

 

[steveg_nh]

Yup, stock airbox. All hoses connected. Remember, I've also never really heard this thing in the cold temps, and never ridden it until yesterday, so could be completely normal!

 

[musselman]

It shouldn't sound different in the cold vs warm weather, may have to get a video capturing the noise.

 

[kinger]

Check the IAC hoses, mine was loose one time at the IAC and it looked like it was on there, and i just started moving hose around and it fell off. So the howl was coming from a leaking hose on the IAC.

 

[steveg_nh]

I completely agree. The reason I mention the cold is maybe the belt is a little stiffer until it warmed up so it was just making the noise on the clutches? I’ll go start it up tonight and see if it does it. If so I’ll capture a video.

Is there a belt deflection check/measurement on these?

 

[steveg_nh]

Check the IAC hoses, mine was loose one time at the IAC and it looked like it was on there, and i just started moving hose around and it fell off. So the howl was coming from a leaking hose on the IAC.

This is the idle air controller, just in front and on top of the left most air intake? Where you adjust idle speed rigth? Man I hope I can check the two hoses without pulling the pod off. I hate pulling the pod off! I did have these hoses off to tighten up the clamp. But am 99% sure they are on solid, but I will check.

 

[JROCK]

Sounds like the belt is a little tight causing the noise since it goes away with engagement and does not occur while riding. I know that sounds more like a squeal noise but everyone hears things different.

 

[Redbeard]

They'll howl at idle if the drive belt is too tight. As mentioned above, remove the belt, restart engine and see if the howl goes away at idle. If it does, your belt deflection probably needs adjusted.

There are (3) small hex head screws on the backside of the driven pulley. The depth of these screws are what determines just how far the pulley will close when stopped. My guess is the pulley is closed too much and needs opened slightly, which will loosen the belt. Remove one small washer from each of the three screws, then reinstall. This will allow the screws to go deeper into the bore and force the pulley open xx thousandths of an inch and should loosen the belt. A little goes a long way with this adjustment. There may be different thicknesses of washers already in there, so be cautious to remove the same thickness washer from each screw.

I'm thinking the top edge of the belt should be flush with the outer edge of secondary sheaves. I will look in my shop manual for the spec and report back.

 

[steveg_nh]

Thanks guys. So I went into trailer earlier and no noise! My buddy was over and he thought the belt might be tight but agreed with how I had it sitting in the secondary. It’s about 1mm above. I have a few each of the two different size shim washers if I need to adjust.

I did that earlier in the fall as the old belt had it sitting way too low. I’m within spec now. Anyway here’s a video. Sounds sweet. What the heck.

 

[musselman]

The belt usually only squeels after the sled has moved, it won't when everything is cold for some reason.

 

[steveg_nh]

Thanks. I just fixed the broken link to the video above too. So that must be it then, the belt, as I didn't hear it until after I did the run aroud the yard.

So if the belt is a bit tight, but it's sitting correctly in the secondary, what should I do? Let the belt break in a bit before messing with anything, or adjust the clutch so the belt is flush, vs above 1mm?