How much upper gearcase noise is normal?

[ken226]

The drive unit is an SX-C 1.85 ratio attached to a 4 bolt 6.3 liter. I built the engine myself to replace the 5.7 which developed a cracked block last winter :facepalm:
The engine runs great with tons of torque, its a helluva lot of fun for tubing and kneeboarding.

The noise is definitely coming from the upper gearcase, it sounds like loose gears meshing. Kinda a metallic rattling. Its consistently there when idling on the muffs and is the same in neutral, forward or reverse gears. It doesn't seem to change when I turn the drive left or right, or if I raise or lower the trim a little. If I put it in forward gear and add some rpms with the throttle to get it above idle, I don't notice it so much anymore. The oil in the drive looks brand new, ive never found so much as a spec of metal on the magnet plugs when changing the oil.

Also when at the lake and the drive is submerged, I can't hear it, quiet as a mouse. Its only noticeable on the muffs, but on the muffs I can hear it from 10 feet away.

Its possible this noise was there before and I just never noticed it, but im not so sure.

Other VP SX owners, how much noise does yours make on the muffs?

 

[skydiveD30571]

Re: How much upper gearcase noise is normal?

There have been some complaints about some of the sx-a drives being noisy, but generally it is only once the drive is nice and warmed up and only in neutral. In gear the sound disappears. Volvo says this is normal and nothing to worry about. But hearing it while engaged in fwd/rev and on muffs is a different animal I'm afraid.

 

[ken226]

Re: How much upper gearcase noise is normal?

There have been some complaints about some of the sx-a drives being noisy, but generally it is only once the drive is nice and warmed up and only in neutral. In gear the sound disappears. Volvo says this is normal and nothing to worry about. But hearing it while engaged in fwd/rev and on muffs is a different animal I'm afraid.

I just rechecked the plugs for metal particles and everything is sparkling clean, oil looks nice and new.

started it up to listen again. In gear I can hear a change in the frequency of the "rattle", but not any louder. It has a very similar sound to when you rotate an SBC oil pump by hand, not like a grinding, more like gears meshing with some slack. Like possibly the slightly lopy idle is magnifying the effect of any backlash in the upper gears.

standing at about 6 feet away I can just barely start to hear the rattle, further away and I can't hear it. It gets a little louder when warmed up, but not much.

Edited to add:
I retract what I said earlier about it being consistent wheather in gear or neutral. After playing with it some more, its a good bit quieter when in gear, though its still there. When increase the rpm from idle up to 1500 in gear, I can barely hear it anymore. Given the way the frequency changes when I increase rpm, im leaning toward there being a little slack in the gears that's letting the driven gear move freely between the teeth of the driving gear. I'm wondering how much of this "slack" may be normal and when I should consider replacing the upper gears.

 

[bunker108]

Re: How much upper gearcase noise is normal?

I too have some gear case noise from my SX drive. It is hardly noticeable when cool, but after some extended running it is a bit more pronounced in neutral. It goes away as soon as I engage the drive.

 

[Don S]

Re: How much upper gearcase noise is normal?

It's from the backlash in the gears. The rattling is really common, and normal, with diesel engines. It's the rough idling that does it. Gas engine don't normally have the problem because the idle smoother. Your "Built" engine may have a lope at idle that may be accentuating the sound of the backlash sound.

Poor running gas engines with a miss really cause a gear rattle.