strange noise

[redwood logger]

my 93' 12 valve makes a noise best described as a really loud "ting" that sounds like its coming from the front of the motor once every couple minutes at idle and repeatedly under hard acceleration. anybody had this happen before?

[pulltilbroke]

Fan hittin the shroud?

[redwood logger]

that was my first thought but the shroud is plastic and has clearance. I should check that out more though.

[Oddfire]

Fan hitting rad., alt. pully, belt's, a loose wire, A/C clutch?

Hampster fell off the wheel?

[redwood logger]

I am starting to think it may be the fan hitting my aux. vacuum pump for the trailer brakes. It is only a half inch or less from the fan to the pulley. I cant tell because now it will only do it when im driving. I really doesnt look like anything has hit it though. Its not a torque thing though, it's a high rpm thing. everything seems tight on the fan and pulleys.

[Mark Nixon]

Are you running an early ('89-'91 nonI/C) vacuum pump assembly?

Reason I ask is the '90 Cummins I have with a broken cam lost it's bearings and the race was just hanging loose riding the shaft and it should have made a sound similar to that.
It does it just spinning the shaft as-is.

Not trying to "gloom and doom" you, but once bitten twice shy.
The early pumps are NOT pressure lubed like the later ones, not a great design, IMO.

Mark.

[redwood logger]

Are you running an early ('89-'91 nonI/C) vacuum pump assembly?

Reason I ask is the '90 Cummins I have with a broken cam lost it's bearings and the race was just hanging loose riding the shaft and it should have made a sound similar to that.
It does it just spinning the shaft as-is.

Not trying to "gloom and doom" you, but once bitten twice shy.
The early pumps are NOT pressure lubed like the later ones, not a great design, IMO.

Mark.

You kind of lost me there, Im new to the diesel world. As far as I know everything is stock on my 93" with the exception of this redline vacuum assist trailer braking system that has a pump mounted up high on the passenger side of the engine and its real close to the fan. Quarter inch from fan blade to pulley. Maybe the fan clutch is going out, causing it to hit at higher rpms.

[Mark Nixon]

Okay.
Put a large glob of axle grease where you suspect it's hitting and fire it up.
{edit}The glob method obviously won't work if the point being struck isn't a fixed point. {end edit}
Wait for the noise, then shut it down and look, if the glob is disturbed, or gone, you found the striking point.

When bearings go out of a fan clutch, the fan tends to oscillate around the center point moving closer, then further, then back closer in a cycle.
This may explain why it only happens now and then and at certain speeds.

Mark.

[redwood logger]

What is the best way to tell if your fan clutch bearings are going out?

[ahale2772]

should be able to hear them when the fan freewheels

[Mark Nixon]

Wobble test.
Grab the fan (engine not running ) on 2 blades as close to directly across from each other as possible and rock it back and forth. Anything more than 1/2" at the TIP is unacceptable.
As to zero as possible is nice, but even NEW ones seem to have a little.

If it's locked up and does this in the wobble test absolutely change it!
I've seen locked up ones fly apart and send fan and clutch into radiators.
Also, with the Cummins' torque, I've been victim of the "tossed blade" scenario, it's not pretty, destroys radiators, shrouds AND hoods.
A locked clutch puts direct torque, at RPM, on those thin little fan blades, they fracture, come apart and go where they want to.

Mark.

[redwood logger]

There is no wobble to the fan at all and I cant find any places where its hitting. It is getting worse and i havent a clue where its coming from. Its doing it all the time now and i have held my hand on different places trying to feel something hitting anything and so far nothing!

[dpuckett]

Do you have a stethoscope? You could use it to help pinpoint the source. Is it high or low pitched? Can you tell the general area?

I know all too well about the fan hub bearing- ask Bill. 1AM rad, fan hub, and related perpherials on the side of I70 east of Terre Haute. As soon as I get some cash, I'm giong to stock up on them from the ebay vendor who has them cheap.

[redwood logger]

I do have one i will have to try that. Its just one real loud "ting" every so often that happens more often when i turn higher rpms.

[Oddfire]

Wheel making contact w/ housing "scrubbing" on cold side of turbo?