Crankshaft problems

2trux · Jun 9, 2015

Hey all, I rebuilt the 2.9 in my 89 Ranger in January this year. The crank thrust surface was worn and needed to be welded and machined back to spec. On friday while troubleshooting a vibration at 3000RPM I noticed the vibration damper moving in and out. I pulled the engine and found that the thrust surface was trashed again. The guy at the machine shop said that the only way this would happen is if there was constant pressure on the crank that would not allow the oil into the thrust area. Since I don't hold the clutch pedal down while waiting for a light I figured it was not that.
The only thing I have noticed is the throw out bearing has a pretty stiff spring on it that pushes against the pressure plate. Rough measurements show that the pressure plate pushes the spring loaded part back about 1 1/2".

Is this how this is supposed to work, or do I perhaps have the wrong throw out installed? It looks like the clutch was replaced before I bought the truck so I have no history on that work.

I need to get another crank but don't want to take a chance on this happening again. Any ideas on what to check?

Thanks.

RonD · Jun 9, 2015

I believe the thrust bearing surfaces are tapered now, to allow for more transmission pressure against crank.
The "Must start with clutch pedal in" safety feature got that started.

Stiff throwout bearing shouldn't add any more pressure, wrong length slave could.

enjr44 · Jun 10, 2015

My first question would be, "Why did it fail the first time?"

I guess my second question is did the shop that did the crank rebuilt do it incorrectly. And that is the reason it failed again. Of course the answer is, "Who knows!!"

So, is the same problem that caused the first fail still there, ie. mismatched parts in the clutch department or did you put a bad crank back in it. Since it is apart and it is a PITA to get in there, I would put a different (good) crank in it, have the flywheel surfaced and replace everything between that and the front of the transmission.

Sorry, no crystal ball........

2trux · Jun 10, 2015

I got a replacement crank today so I will get the engine back together. From looking at pictures my slave looks different than the ones pictured for sale. Once the engine is back together I can make some better measurements to see if the slave is the wrong length.

2trux · Jun 19, 2015

Well my new bearings and gaskets came in so I have the engine back together. I also bought a new clutch slave/bearing, it looks identical to what is on the truck currently.
After I get the engine off the stand and have the flywheel/clutch back on I will make some measurements to see how far the release bearing is pushed back. I will do some mods at that point to relieve the pressure against the crankshaft.

2trux · Jun 25, 2015

Here is a couple of pics of what happened to the crank. This is less than 6 months since the rebuild.

enjr44 · Jun 25, 2015

From the first picture (where did the holes come from) I would say you put a bad crank in it when you rebuilt it. Of course, I am looking at it from a couple of thousand miles away. So, what do I know!!!

2trux · Jun 26, 2015

The holes were voids that were behind the welds. This crank was welded in the thrust area to fix the worn thrust surface. When the crank was put in it was perfectly smooth. The machine shop owner said there must have been constant pressure on the back of the crank at all times that kept the oil from getting into the thrust surface. I don't know how true that is or if the clearances were wrong. If it was a clearance problem I would have expected to see some damage on the thrust surface on the other side.

I did some measuring and determined that when the engine was in, the throwout bearing was pushed in 1.25 in. This is spring loaded with a pretty stout spring. I bought a new slave/throwout and cut the spring so that it is only depressed .25 in. There is very little constant force on the back of the crank now. I have not noticed any difference in the pedal feel since doing this mod. I guess time will tell if this was a good or bad idea.

As a side note: This thrust wear seems to be common in these engines with manual transmissions. Mine was worn, my sons B2 was worn, and all the 2.9's we tested at the u-pull were worn. I replaced my crank and my sons crank from engines that had automatics. None of the engines with autos had the thrust issue.

I am not sure why these throwout bearings have this strong spring in them. My older trucks with mechanical linkage did not seem to need to be spring loaded.

Crankshaft problems

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