An interesting failure analysis

[Jens]

This morning I started Thumper as usual. Everything was just fine until, about an hour later, I decided to go and fill up my diesel tank. As soon as I stepped out on the deck I could hear that something was terribly amiss as I could hear the slapping of a belt. Damn !!!!
I rush underneath the deck to check and sure enough, Thumper had wrapped her power transmission belt around her crankshaft and was beating everything silly. I shut her off and examined the situation .....

The belt was completely shredded (this is an 8 rib industrial belt, about $120 each, no longer available in town as the outfit closed down). The belt had jumped off (which it had done plenty times before) and somehow managed to wrap itself around the crankshaft (which it had never done before). Yesterday, I had switched my circulation pump from being powered by the generator to being powered by the house power to avoid the short term boiling of coolant that happens when the engine shuts down. This turned out to be a big mistake. In the past, when the generator stopped spinning, the cooling pump stopped which caused head temperature to rise which caused the over temperature sensor to trip which shut everything down. With the coolant powered by regular ac, nothing overheated and nothing shut down.
Chances are that the belt was just sitting there for a while as it always does and eventually, somehow, it caught and started whipping around. As it whipped, it caught my oil drain pipe (1/2" steel) and ripped that off and bent a couple of other bits of pipe. Luckily, I had a second shutoff that happened to be closed. Had it not been for that secondary shutoff (this was an afterthought, purely luck that it was there), all engine oil would have drained followed by lubrication failure and another engine rebuild !!!!
Had I installed an oil level sensor on my sight glass, it may or may not have caused an engine shutdown as it was also affected by the whipping belt.

The industrial belt being much heavier than a standard automotive belt was doing a fair bit of bouncing on the slack side which is why I think Thumper was prone to throwing her belt. I have a temporary automotive belt on Thumper now and there is absolutely zero slapping on the slack side. Unfortunately, with the pulley grooves not matching the belt ribs, starting Thumper is a bit of an issue as there is not enough friction on the generator pulley. Another odd side effect - zero chirping on the flywheel.

It looks like I will need to cut some new grooves on the pulley for the standard automotive belt profile.

A few interesting questions arise .....
My overheat sensor is the only temperature sensor on Thumper - what happens if it fails for whatever reason. I completely depend on it for shutdown each and every run. It might be a good idea to install a secondary temperature monitoring system of some kind.
The engine RPM is measured for overspeed ... but is measured at the generator and becomes inoperative when the generator doesn't spin. There is no sensor yet for underspeed.
Even if I had an oil level sensor, I can now see a scenario where failure can happen under the right circumstances.
There are entirely too many possibilities of failure to this setup ...... I thought I had things pretty well covered but this incident clearly shows that this is not the case.

A side question that is nagging in my mind ..... suppose you had a pressure lubrication system such as on a Changfa. Let's say you have a pressure sensor on it that shuts down the engine if you loose oil pressure. Will the shutdown procedure, with an estimated time to complete stop from between 30 seconds and 60 seconds, be fast enough so that no damage results? I have heard it said that in an automotive engine, by the time the oil light comes on you already have engine damage.

[LowGear]

"My kingdom for a nail" comes to mind.

Casey

[veggie]

A few thoughts.....

1] Damn !!!!!   Cummon Murphy....give this Jens guy a break !

2] Just as the secondary (redundant) ball valve saved your lube system, a secondary temp switch may be a good idea for the shutdown.
Especially since you rely on that switch to kill the system every day.
As a further precaution, the two shutdowns would not be interlocked so that a failure in either circuit could not kill both shutdowns.
BTW...The shuttle uses 1 main computer and TWO 100% redundant backups.

3] How can an oil pressure switch effectively save an engine?
The switch would be set at a low (but not a low-low) setting.
EG: if the normal running pressure is 45 psi, the switch could be set at 30 psi rather than 10 psi.
A drop in oil level usually manifests itself as an erratic pressure reading as the final gulps are captured by the oil pump.
Perhaps a switch set in such a way would kill things before they got worse. ( just a thought      )
Fine for a Changfa with a rotary oil pump (no pulsations)....not so useful for a roid pump which pulses from zero to 20psi.
So.....a roid would need an auxiliary rotary oil pump with pressure switch in the discharge line.

veggie

[mobile_bob]

the way i have my 195 setup, if the oil pressure dips enough for the indicator to drop even a bit, the fuel solenoid drop immediately
i don't want the engine to fire even one more time with the oil pressure dropping, much less run for 30-60 seconds with little to no pressure.

i can dial it in to where the cutoff happens at anywhere from just under full pressure down to about 10psi, although i would never allow it to continue running under about 20psi under load at 1800rpm.

not that the engine must have over 20 or might be damaged at or near 20psi, i just figure that is a good cutoff point to target for
that would allow some margin for drift over time.

i am also considering installing a valve to cutoff oil pressure to the indicator/switch assembly so that i can can periodically test the system while running and see exactly at what oil pressure the shutdown system works at.

bob g

[Lloyd]

The industrial belt being much heavier than a standard automotive belt was doing a fair bit of bouncing on the slack side which is why I think Thumper was prone to throwing her belt. I have a temporary automotive belt on Thumper now and there is absolutely zero slapping on the slack side. Unfortunately, with the pulley grooves not matching the belt ribs, starting Thumper is a bit of an issue as there is not enough friction on the generator pulley. Another odd side effect - zero chirping on the flywheel.

It looks like I will need to cut some new grooves on the pulley for the standard automotive belt profile.

Jens....I don't know why anyone would use an industrial belt on a thumper...they are not designed to take the pulse of the combustion engine...they are designed for hook up to an electric prime mover which doesn't pulse with each combustion stroke. The automotive belt while in appearance may look like the weak sister to an industrial belt it is far superior when driven by a combustion prime mover.

Lloyd

[billswan]

Jens

I just don't know what to say other than $hit happens................

I have thought about all the little things that could stop my 10/1 and there are lots of different scenario that could happen I will have to admit.

Just yesterday I experienced my belt acting oddly and trying to hop back and forth changing grooves. It was the first time I have had an issue with it, luckily it was just slightly loose and I caught it before I left the area.

Now I have to add belt wrapping around crankshaft to my list.

I was starting to think about getting out the monitor you sent me and seeing about installing it I suppose I should move that up on the priority list. Very cold weather coming soon and I was thinking of running the 10/1   24/7 when that happens. Right now 14 to 15 hours a day is keeping the large shop nice and toasty.

Good luck and I hope the bad luck is over for you now.

Billswan

[bschwartz]

I was under the impression that lack of combustion pressure from low load allows the rings to not seat fully and allow crankcase oil to enter the combustion chamber and cause the slobbering.

[billswan]

Well at 50 hours I would say it has not seated the rings yet.

What type of oil are you using? A premium oil may be to slick and not allow ring seating these roids run low oil temps and an extended run type oil may cause problems in a fresh engine.

Some engine manufacturers used to use break in oil that would speed up ring seating. It was formulated to break down somewhat at piston ring temps a hasten ring sealing. I believe john deere  still does. I fact some years ago deere had problems with oil control and it was traced to fresh engines getting the break in oil changed out much to soon and extended drain type of oils being installed.

Not so sure about others.

A keystone ring needs cylinder pressure to help force it down and out against the cylinders and so needs a load to seal best. But a listeroid has no such design.

How long did the motor high idle. Some diesel engines do not like to run unloaded, maybe thumper is turning into one of those. I have a john deere tractor with 4500 hrs on it that will slobber if it is not kept in the harness. Of course it does have keystone rings and a questionable past history.

Your blue exhaust is most probably oil getting past the rings and being burned.

Billswan

[mbryner]

Jens, so sorry to hear about your latest bad luck. 

[Randybee1]

i can dial it in to where the cutoff happens at anywhere from just under full pressure down to about 10psi, although i would never allow it to continue running under about 20psi under load at 1800rpm.

bob g

Where can I get an adjustable oil pressure switch? The one's I've seen are pricey at about $40.00... or am I just being cheap?

Randy B

[bschwartz]

Let's see.... $40 to save an engine.......... You're being CHEAP!! 

[mobile_bob]

for my changfa i built my oil pressure switch, or rather assembled it with off the shelf stuff
and a microswitch.

it allows me to adjust the pressure points, one set of contacts for control of the fuel solenoid relay coil ground/starter circuit lockout,
and the other set of contacts for logic feedback telling my controller the state of the oil pressure.

i got maybe 5 bucks in the thing?

bob g

[Randybee1]

Let's see.... $40 to save an engine.......... You're being CHEAP!! 

Good Point!

[Randybee1]

Everything is working fine again except for the belt. It has insufficient grip on the generator pulley to turn the engine over without compression release when the engine is cold. .

Jens.. what is "cold" in your neck of the woods?
Randy B

[AdeV]

Everything is working fine again except for the belt. It has insufficient grip on the generator pulley to turn the engine over without compression release when the engine is cold. This could be an error in the pulley grooves, it could be the fact the belt is old and full of tiny cracks or it could be it is not wide enough. It is about as tight as it can be. To start I need to proceed as with manual start - put on decompression, spin up, flip the decompression lever and repeat until she starts. I will leave it for now but eventually something needs to be done.

TBH, I really think you should look at using a pair of V-belts; I think this will save you a world of pain. Although my engine is only a 6/1 single, that 12v starter that I mounted on the gen head will easily pull the motor through compression, even if it's "resting" against it (i.e. there's no "run up"). No belt noises, nothing untoward (you can hear the starter hunker down into the job, but that's about it).

I'm guessing you've got standard smooth flywheels? If so, either a) get one flywheel machined with a pair of B-section Vee grooves, or b) start watching eBay.co.uk for any SOM engine - doesn't matter how fragged it is, you're only buying for the flywheels; and get it shipped out on this UK->US container shipment.  Option b) might not be a sensible option if Thumper is internally balanced (crankshaft counterweights); you'd have to have the Lister flywheels balanced first. A thoroughly broken SOM engine would typically sell for £150 here, maybe £250 with the electric flywheels.