broken crankshaft?

[scrappy isb67]

My MF 50 has a definite noise in the engine. The noise is louder when the engine is revved. Engine starts very well and, except for the noise, runs well.

I have been told (by the dealer who is trying to sell me another tractor), that the noise is a broken crankshaft. He is also offering me a very low trade-in value due to the 'broken crank'. He says that this year of Continental engines had a crank problem.

My questions are, is it possible to have a broken crank and a running engine? Has anyone ever heard of a crankshaft problem with this engine?

I am wondering if it could be a rod bearing going bad? If so could this possibly be fixed by dropping the oil pan and if able to identify the offending bearing, replace it without engine removal.

Any other ideas appreciated.

Yes it COULD RUN with a broken crank! It all depends where it is broken.
I had a GM 2.8L v-6 that was making a clattering noise. I was trying to diagnose where the noise was coming from and ran it for about 2 hrs. At idle the noise was there, it would go away at just off idle. It finally locked up after I brought the rpm up to 3K and released the throttle. when I tore it apart I found the crank snapped in 2 pieces at a rod journal. IT had fractured diagonally in the middle of the journal, the rod was holding the 2 pieces together and letting it run.
it never lost oil pressure and didn't really hurt the rod bearing!

 

[Soundguy]

such ancedotal evidence is really the exception to the rule here. for all practical purposes.. if he's loaded it and nothing blew a windo thru the block.. it's likely not a broken crank...

possible? given.. though entirely improbible... I'd still find another dealer...

 

[bobmisi]

I can tell you all that it is possible for an engine to run with a broken crankshaft. My David Brown 990 was idling while I was putting on my snowplow and the crank let go.The engine made a loud banging noise, but continued to run until I shut it down. It went while I was in the house getting a drink, so it probably ran that way for a couple of minutes. I called my mechanic who came over a couple of days later. He had me try to start it and it fired up and ran, so I moved it about a hundred feet to get it out of the way. I had it moved to his shop where he dropped the pan and we found a broken crank. I sold her as is and moved on. But I will tell you it is possible for it to run..................

 

[wrenchturner]

I can tell you from experience, an engine can run with a crank broken into two pieces and I do not mean cracked. A 351 Ford truck engine pulled a boat from a lake for about 10 miles with the crankshaft knocking. I pulled the pan and the crank was broken at an angle. As the crank turned it pushed against the crack to turn the other part. I would not have believed it if I had not seen it my self.

 

[Nasty135]

Well not being able to hear in person, makes it pretty difficult to diagnose But here goes an attempt. First does it run smooth while it running? If so an old motor with lots of hours may just have some serious carbon deposits on the pistons or valves from years of blow by and build up creating an interference issue with the head and or valves, which can sound just like a knock. Before I did any dismantling I think I would warm it up good get and atomizer bottle with some water in it and set it to spray rev the engine enough to keep it running as you squirt the water spray right in the carb which will be basically steam cleaning the head & piston while running but it has to be done slowly or it will not continue running.
This method has worked in the past but its never a guarantee to make it clear right away or may never clear but without being there in person its a crap shoot. Remember we are not drowning the engine just atomizing some h2o into the chamber. It could be more serious as the others have described...
Good Luck

 

[frankroberts]

Thanks for all the replies and ideas. I am following all.

Last week I had a neighbor who is a mechanic come over for a look. He listened to my tractor run and did not think it was a broken crank but he wasn't sure just what it was.

We took off the sheetmetal hood and side panels. Then removed the gas tank. Then valve cover. I told him that I had recently adjusted the valves. He wiggled all the rocker arms to see (I guess) if any springs were broken or if anything was obviously wrong.

He took off the whole rocker arm assembly and felt the bottom of the rockers where the push rods push. There were burrs there from years of 'pushing'. He also took off some little 'caps'. We ordered new caps and he took the rocker assembly home to de-burr with a dremel tool.

He is thinking that the burrs would cause a false 'feel' on the feeler gauge and cause the valves to be adjusted too tight or too loose.

Caps come in tomorrow afternoon so it will be Wed. when we try it with new caps and de burred rockers. It seems unlikely to me that this could be making the noise but Earl says it could. At any rate it is a place to start.

I'll come back when I know more. Thanks again.

btw there are a couple of pictures of my tractor here....

http://www.tractorbynet.com/forums/kubota-buying-pricing/229873-kubota-v-massey-2.html

frank

 

[Soundguy]

can't wait to hear..

 

[Mike476]

Never too old to learn I guess, I've never heard of a motor that runs well through all rpm ranges with a broken crank, guess anything is possible.

 

[Soundguy]

you might get hit by space junk too.

I wouldn't hold yer breath on either one, as both -almost- never happen outside of discussion forums

 

[Johnp33]

If the crank is broken and it still runs, which is quite posible, it will produce metal flakes as the pieces wear together, the oil pump will pick them up and you can cut apart the oil filter to look for steel flakes, with a magnet. If it is a rod the metal powder will be in the center of the filter, an amazing amount.
Also if you take a bar, against the engine and on your skull, you can hear every little thing going on in the engine front to back anything abnormal you have found the area,
Putting water into the carb, it works great that is how I use to get the deposits out of engines for years. I use a pop bottle, 3/4 full, with the engine hot, and the rad covered, remove the air intake, and rev it up to about 1,500 RPM, start adding water and opening the throttle, regulating the water to keep the speed the same, you will be amazed at how fast it will take the water. When you have used the water, leave it running for a couple of minutes and rev it up, that will blow the carbon out of the exhaust.
It needs to be HOT, I cover the rad with a plastic bag, and monitor the coolant into the engine from the rad bottom hose. 170 degrees in temp works great. when you have done the water, remove the cover and it will cool off real quick.
Just a thought!