Scag 48" hydro rattling / knocking

[Skidplate]

Hi newly registered to the forum (but have visited it a lot via Google searches). I have a Scag 48" hydro SWZ48A-17KA, with the Kawasaki 17hp twin made in 2003-2004 (according to Scag) that is making some strange noises.

I'm hearing what I'm pretty certain is an engine knock at idle, and was ready to start hunting for a replacement. I pulled on the chain that releases the drive belt for the pumps and low and behold the noise is gone 100%, idle through hard rev, blades on and blades off.

I took everything apart from underneath related to the hydro drive. The idler pulley wasn't loose or wobbling - but making faint ticking noises and had the "feel" of being unbalanced (could just be me though) when spun, but the pivot arm bearing(s) were pretty stuck. After un-sticking them with wd-40, I put everything back together. The second I released the chain the noise started again. The pivot arm moves about 1/4 of an inch back and forth while at idle (normal?).

I've read threads (not for my exact model but I'm trying everything) that said to check the small drive pulley that may have worn out the keyway or that my pistons may be carboned up.

I would "think" that engagement of the blades would certainly be more of a load than the pumps (but maybe not because they don't engage at idle?) It purrs like a kitten with and without the blades on but the second I let that chain loose for the pumps it starts again.

Has anyone ever heard of the idle pulley causing these horrendous noises? What kind of compression numbers would tell me if this (carbon buildup) was the case?

[Weekend cut easymoney]

Doing you a favor and moving this post to top for more hits...Fridays are slow, try more during week.

[Skidplate]

I tried editing my post but couldn't. I also need to add that the shop where I've been buying parts gave me plugs with a heat range of 6 instead of 9. He said they always recommend these plugs in these engines. I know running cooler plugs in turbo cars helps with pinging (we usually go 1-2 steps cooler) so I'm not really sure if a 3 step cooler is having any kind of negative effect (this issue) or not. I'm also not a huge fan of Champion plugs. I guess I can throw the old 9's in there and see what happens.

[piston slapper]

Sounds like there is a chunk missing in your hydro belt..

[Skidplate]

Originally Posted by piston slapper

Sounds like there is a chunk missing in your hydro belt..

Belt has no gouges or anything at all missing. If it was the crank pulley keyway problem mentioned elsewhere wouldn't I be able to shake / move it on the output shaft?

This is perplexing me to no end. Literally the least bit of tension I put on the release chain the noise stops. I just don't see how the sound can travel that far through the chassis and sound like an engine noise, but I certainly hope it's a $40 idler pulley.

On a good note, if it is the engine I can find relatively low hour John Deere riding mowers in The Villages (piston slapper will know where I'm talking about) that have the same engine pretty cheap.

[piston slapper]

If the belt is ok...check all the pulleys to see if one is bent or if something is jammed in the groove..
If all is good...replace the idler pulley..
Also...with the belt off..turn the hydropulleys by hand....see if one is tighter than the other..

[dutch1]

Any chance that the engine mounting bolts are loose?

[Skidplate]

Originally Posted by piston slapper

If the belt is ok...check all the pulleys to see if one is bent or if something is jammed in the groove..
If all is good...replace the idler pulley..
Also...with the belt off..turn the hydropulleys by hand....see if one is tighter than the other..

Pump pulleys take same force to turn, nothing jammed in anything.

HOWEVER something I didn't previously notice.. there are two different pulleys on the pumps. The one on the right (standing at the operators position) has a heavy cast 3 spoke pulley, the left has a thin DEEP groove sheet metal kind of feels like moms clothesline pulley on it (this could also explain the difficulty setting the tracking). I'm guessing the right side is the correct one since it has the allen grub set screw like the one in the parts book? Things are certainly getting interesting now.