4106 Engine Trouble? Weird Crunching Noises...

OneLapper · October 20, 2014, 06:40:18 PM

Hi everyone,

My 8V71 has a problem. The bus has been sitting for about a month. I drove it 400 miles round trip while towing my car trailer, it ran perfectly the entire trip. When I parked the bus it was running fine.... oil pressure good, antifreeze normal level, no noises, nothing notable.

Today I went to move the bus. The engine cranked over a bit slower than normal but I expected that since it's been sitting for a month. After about 10 seconds of cranking, the engine stopped hard. The starter would only clunk after that. From the rear controls I hit the starter switch a few times and by watching the clutch I determined the engine was coming up hard against something and stopping.

I used a pry bar to turn the engine back a few degrees and try to start it again. The engine stopped in the same spot. I turned the engine back about 20 degrees and tried the starter again. This time the engine cranked for a few seconds and started, but it made a horrible crunching noise, irregular, enough to cause the engine to shutter and shake. I shut the engine off within 10 seconds.

I pulled the Vickers pump and the coupler. Both were fine, the coupler was perfect and the pump turned smoothly. I started the engine again, this time without the Vickers pump. I had a friend depress the clutch in an effort to rule out transmission noise. The engine started right up, oil pressure was 65 psi, but the engine made the same irregular crunching, chunking noises, shaking and bogging when it crunched. I shut it down after about 15 seconds.

It seemed that the noises were louder at the back cover. There was no smoke at all from the exhaust.

I'm looking for suggestions as to what is wrong. It seems something is bind up in the accessory drive gears, but if it was metal wouldn't the engine just stop? Or just break gears and stop running? What should I remove next?

This timing of this sucks, of course. I'm in the middle of an expensive generator engine and alternator rebuild.

Thanks,

Mark

mung · October 20, 2014, 06:42:11 PM

Did you get a rodent in your blower?

OneLapper · October 20, 2014, 06:53:15 PM

Quote from: mung on October 20, 2014, 06:42:11 PM
Did you get a rodent in your blower?

I will check but I know the metal screen above the blower is in place.

luvrbus · October 20, 2014, 07:06:08 PM

If the alternator is still gear driven that is where I would start 1st then on to the air compressor

good luck on this one Mark

OneLapper · October 20, 2014, 07:25:35 PM

Thanks for replying, Clifford. Yes, the alternator is still gear driven. I put my hand on it when the engine was running and it didn't *feel* as if the crunching was coming from it. I didn't put my hand on the compressor. I'll remove both and hope for the best.

fortyniner · October 21, 2014, 06:54:47 AM

Darn good thing you were not on the road somewhere far from home. It's hard to imagine an accessory creating the hard stop as you described it but something stuck in the blower lobes seems like it might.

I'm following this thread with interest because if it can happen to Mark, who takes good care of his coach, it could happen to others as well.

-Tom P.

luvrbus · October 21, 2014, 07:07:30 AM

Bearings going bad in a accessory drive will lock one down, any blower problems they break the blower drive for safety, the compressor is keyed to shear if it seizes, a rod that come loose in a compressor they don't always shear the key

bevans6 · October 21, 2014, 07:55:33 AM

When you are building the engine you put a rag in the cam gears to lock it up, and then put around 400 ft lbs of torque on the crank pulley bolt. It doesn't take much to lock an engine. If it runs you know the gear train is still there, the cams and the blower are still spinning. Be interesting to see what it turns out to be.

Brian

OneLapper · October 21, 2014, 08:12:06 AM

Update: No solution yet but I've ruled out a couple of things and saw one very disturbing thing.....

It's not the blower. I took the intake horn off and it looks fine.
It's not the Vickers pump. I determined that yesterday
It's not the transmission fluid pump. The fiber disc is in perfect condition. There are no pieces of metal in the bottom portion of the trans pump gear housing. I used my finger to feel around and felt nothing.

I cranked the engine over with the fuel shut off. The engine spun over like it always does, no binding at all. I started the engine and it made the same crunching noise for about 15 to 20 seconds then it went away. Here's the disturbing part, SPARKS shot out of the tranny pump hole! I sh*t you not. Sparks.

After the sparks shot out, the engine ran perfectly smooth. I did not rev it up since the Vickers and tranny pump are out. I used a good light to look into the blower housing and both pump housings. I saw nothing out of the ordinary.

So..... something metal has fallen off and managed to get into the gears. I'll pull the generator off and look at the bearings, as well as the compressor. Right now the engine starts fine and sounds smooth.

One thing I noticed when I got this engine from the NYC Transit Authority. The engine was a rebuild with a new factory block, but when I took the engine apart I noticed a cracked lock washer on the left cam gear. It was cracked in half and the nut wasn't tight. I removed the washer and torqued the nut down since the manual didn't show a lock washer on the cams. I found the other half when I swapped rear engine covers. After that I was super careful to inspect everything, as well as retorque every nut and bolt I could find.

Ugh! I really don't want to pull the tranny and rear engine cover to find this problem!

mung · October 21, 2014, 08:15:16 AM

Really strange that it would happen from sitting though.

luvrbus · October 21, 2014, 08:41:38 AM

Stranger things have happen

bevans6 · October 21, 2014, 08:43:37 AM

Things usually don't happen from sitting, they happen when the engine stops, and then they just wait to jump out and bite you. Cam gear nuts are supposed to have a locking plate that bolts on to the gear and fits over the nut, you can see them in this picture. These pulleys don't have accessory drives bolted on to them.

That this point I would drop the oil and stick a magnet on a stick thingy in to fish around and see if I could find a few bits of whatever the gears ate. Then I would probably drop the pan and fish out the parts to see if any of them were gear teeth looking bits. Then I would probably take the back cover off to see how many gear teeth I lost.

Note to self - never try to spin a locked up engine, it's usually locked up for a good reason...

Brian

luvrbus · October 21, 2014, 08:49:51 AM

Yep the backlash when you shut a DD down works on the gears it does on a all large diesel engines the bull gear is a weak point on the series 60 also.
Could be he just lost a pilot bearing or the throw out bearing I hope it's not a gear train problem for him

OneLapper · October 21, 2014, 09:14:27 AM

Mine looks like this....

and ......

OneLapper · October 21, 2014, 09:28:19 AM

um, errrr... and to Brian's point, I found this photo of the original engine...... You can clearly see the star shaped lock washer on the left cam gear nut....... uh oh.

Time to pull the compressor.