Inliners International Forums General Discussion Engines 292 crankshaft end play - ruined crank

I have a 78 GMC C15 with a well modified 292 driving a 700R4/1800 stall to a 3.73 posi rear. The engine has maybe 4000 miles on it and I bought it from Leo Santucci when he lived in CT. and his engine shop built it with all ARP studded lower end and 30cc pistons. The head came from Walt Pierce by way of Tom Lowe and is highly modified. Motor has a stage 1 Crower roller cam. On the wheel dyno it showed 199 HP at the rear wheels. It was fine for a long time and then started making a lot of noise, a chattering - squealing noise and we determined it was coming from the lower end. End play on the crank was found to be about 3/16". We could push the crank back and forth and watch the pulleys move. We pulled the motor and found that the crank was somehow being pushed forward and the rear main bearing cap ate into the crank itself. The bearing and cap is shot. I had put a magnet on the pan when the noise started and it has a plugged bypass so it doesn't look like anything else got trashed but the magnet was loaded with metal. Regardless, the motor needs major repairs. The problem is we cannot figure out why the crank would push forward. The stage-2 trans from Bowtie Overdrive seems OK, flexplate is ok, it all looks ok though we have not torn apart the trans yet. Has anyone ever seen this problem with extremely excessive crank end play and have any idea why it would happen?

Assuming the end play was fine before you installed the engine, this type of problem is often the result of incorrect converter installation, meaning it wasn't seated all the way into the front pump of the tranny when the converter was tightened up against the flexplate. That will wipe the thrust bearing out quickly. With that much excessive forward movement of the crankshaft, the counterweights can also rub the block and the small end of the rods can rub the inside of the piston bosses, chewing them up also. Visually inspect all components thoroughly, you may have to end up replacing some major components.

The motor was new rebuild when installed. Everything in it was new and built to spec. Thanks for the info. The converter installation is looking to be the main culprit but are there any other possible reasons for this? Is it possible for the trans pump or input shaft to somehow push forward?

Its not likely the tranny itself is the culprit, but you should check it as well. An automatic transmission is a fairly precision assembly, and its internals rotate at a much higher RPM than the engines does. So chances are you would have encountered transmission issues before engine issues if there were any hiccups in the transmission.

There are and can be several engine assembly and even machine shop errors that could have led to this problem, but since they were outside your purview, we can only leave those as unknowns until you can systematically eliminate the things you do have knowledge of and see if any of them can be a plausible reason for this.

1) As already mentioned about the torque converter being seated fully. Did you rotate the converter back and forth about a 1/4 to a 1/2 rotation as you pushed it toward the transmission? You should have heard or felt a series of "clunks" indicating the spline on the input shaft was engaging inside the different sections inside the converter.

2) Pulley alignment? This is also an often overlooked but serious mis-step that can lead to quick and premature crank thrust wear and failure. The crank is intended to "float" unimpeded forward and backward within its range of thrust clearance as the engine performs its acceleration/deceleration periods and having periods of heavy load such as hauling. A misaligned pulley setup will keep the crank pulled forward and constantly rubbing the thrust bearing surface, overheating it and causing it to wear quickly. Did you check this as the engine was installed in the vehicle?

3) Since you mentioned getting this engine from Leo and having his engine shop prep the engine, that was a long, long, long time ago that he lived up there. Long term engine storage is very hard on an engine, regardless of the environmental conditions. Assembly lubes and oils dry up and no longer can provide protection on start-up, even if you prime the engine. Since the thrust face surface does not have pressurized oiling, even using a priming tool is a 50-50 shot at ensuring oil reaches all the necessary areas before you hit the key for the first time. Did you prime the oil thoroughly before starting the engine? If so, good! But again, it could only be a 50-50 shot that the thrust bearing faces received any lube to prevent scuffing upon start-up. A short term storage of 4 to 6 months may be fine, but years of being idle on the engine stand or even in the vehicle could be a cause.

Hopefully, you can sort through these scenarios and eliminate or more directly see a better explanation as to what may have caused this problem. I could list a number of things that could have happened in the machine shop or even engine builder errors, but again, since you yourself didn't perform any of those things they will just have to remain unknowns.

It was tough getting absolutely perfect alignment between alt., PS and compressor but they were all less than 1/8 inch. I never threw a belt or had any belt problems. Would 1/8" misalignment be enough to cause this damage?

I would try to get it closer aligned. An 1/8" doesn't sound like a lot, but it could still be enough to keep the crank pulled forward contacting the thrust bearing, especially with the belt tight.

Any other issues I pointed out a likely possibility?

I am sending out the trans to be looked at by a performance trans shop. It was a new stage 2 trans built by Bowtie Overdrive so is heavy duty to start with but I am being told that overly high pressures in the trans can push the converter forward so that will be checked. When installed there were 3 distinct clunks as it seated and it spun freely when bolting to the flexplate. The pulley alignments will be carefully gone over and adjusted as close as possible. Everything in this drivetrain all the ways to the rear wheels was new and I sure don't want this to happen again, it is costing me a fortune. As to the motor sitting what happened was that after I bought it in 2011 from Leo (I picked it up at his house in CT) I got in a very bad motorcycle accident, I rolled over my sidecar rig and hit a tree, and it sat in a garage for years before work was again started on it, that was in 2018. It was taken apart and checked and lubed and carefully reassembled. Even now, other than the rear main thrust bearing which is totally gone, the other mains look like new. I had a magnet on the pan and that caught a load of metal and when assembleed the bypass was plugged so nothing got past the filter. A new oil pump will be installed now. Thanks for your help, it is really appreciated. If you think of anything else to check please let me know. You can contact me here or at sodell3@gmail.com.

Ok, you've mentioned an important piece of the puzzle not mentioned before, and that was the engine was disassembled after its initial assembly. There is a fairly precise method to establish the thrust bearing and seating upon assembly. It is often done incorrectly and is more than just a replacing of the cap and torquing it down. What was the thrust clearance when it was re-assembled? Was it checked?

I just saw this post. Try checking bellhousing alignment. Crank centerline to trans centerline. There are offset dowel pins that can be bought to correct mis alignment.
I have a feeling there may have been some problem with it before you dynoed it. The dyno session overly pressurized the tq convertor and aggravated the problem

I checked torque but did not remove any caps. The timing cover area was worked on and changed to a Lowe cover, new balancer added, different head installed, went to roller rockers, painted, mostly front and top area stuff. Made pan rails to help avoid pan gasket leakage. Pictures here if you are interested.
https://www.smugmug.com/app/organize/1978-GMC/292-rebuild-2018

I will definitely check that, thanks. I may need to get a crank from you to. What would that cost?

link does not work unless you sign up????