Bad Day at the Car Show

Military Trucks 2 1/2 ton and greater, Wanted, For Sale (NO AUCTION or EBAY), and Knowledge Base

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mudflap
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Bad Day at the Car Show

Post by mudflap » Sun Jun 10, 2018 6:56 pm

So.... There I was, driving to a local show this morning.. I was going around 30, when BANG.. Followed by a terrible knocking noise coming from the engine. No warning, no symptoms, just a lot of noise. In the words of one of my old service managers, it sounded like the rods were having a coming out party...

Got the truck shut down and off the road OK. Was able to get a tow home. Pulling the lower oil pan revealed the crankshaft had broken at the #5 rod, just aft of the #3 main journal. :(

crankshaft Lo.jpg
crankshaft Lo.jpg (121.93 KiB) Viewed 1199 times


This engine was a government rebuild and kinda tired (low compression all cylinders), but was always quiet and ran well. Had anticipated swapping it out at some future date, so I have been building up a new engine. Looks like these activities will ramp up now.

At some point, though, I will want to put this one back together (assuming the block was not damaged). Any one have a good source for 270 cranks in my (Detroit) area?


Best Regards...


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Jon S
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Re: Bad Day at the Car Show

Post by Jon S » Sun Jun 17, 2018 4:19 pm

Wow!!! A sickening feeling, I know!! Good luck with the build on the new engine!
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D.R.H.
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Re: Bad Day at the Car Show

Post by D.R.H. » Sun Jun 17, 2018 9:07 pm

I had the same thing happen to me in 2006. I had taken my Chevy, (270 with 5 speed trans.), to the local mud hole with my Weasel in tow. I was climbing a slight grade on the freeway in 5th. gear at 45 M.P.H. when I felt a terrible vibration. I exited the freeway and the knock shook my teeth to their roots. When I pushed the clutch pedal to the floor, it went away. Upon release, it came back.
My crank had broken at the last rod journal right behind connecting rod #6. I tried to get the truck towed but AAA kept sending wimpy and his tow truck who was too scared to tow it, so I drove it the last 14 miles home. I repaired the engine, with the help of a friend who has lotsa 270 and 302 engines. I know your pain well Mudflap. I know that my suggestion is on the west coast, but Steve at; http://www.inliners.org/buffalo/ is very knowledgeable and helpful. I know that the military engine has a 4 bolt flywheel flange, but perhaps He can either supply or help find a correct crank shaft for you.
The replacement one I bought from him was .020 under stock and is still going strong in Tucson Az., 12 years later. :)
In Loving Memoriam: George R. Hancock. 20 Mar. 1938 - 11 Jan. 2017. U.S.A.F. 1956 - 1962. R.I.P. Dad.
In Loving Memoriam: Ann Hancock, 08 Mar. 1934 - 25 Sept. 2021. R.N. 1960 - 2005. R.I.P. Mom.
Thank You BOTH for always being there.

My YouTube Channel. https://www.youtube.com/channel/UCaMKEv ... M3g/videos.

mudflap
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Re: Bad Day at the Car Show

Post by mudflap » Mon Jun 18, 2018 7:57 pm

Thanks Guys...

I was lucky in that the truck they sent, while not huge, was up to the task. The driver was extremely conscientious, and very helpful in getting it home and pushing into the garage without a scratch to be found anywhere. Gave him a very nice tip for his efforts...

Still fighting with AAA. After a two hour wait, when the driver pulled up he informed me that AAA had denied my claim and that I would have to pay. After multiple phone calls and emails their position has remained the same: "We just don't cover certain types of vehicles". Strange, how they were happy to take my money all these years to cover this vehicle (I pay extra for the plus membership with RV coverage) but now they blow me off when I actually need it. After 35 years as a member it looks like it is time for a parting of the ways.

D.R.H, did you ever determine the cause of your crankshaft failure? (I am amazed that you were able to drive it home!) I have not pulled anything apart on this engine yet, but I am willing to bet that when the crank was ground during some past rebuild (there is an arsenal rebuild tag on the engine) the journal was cut without leaving sufficient radius at the corner. This created a stress riser, which in turn led to a crack, resulting in an ultimate failure.

Many years ago, I worked with an engine development engineer who kept a radius gage on his key ring. He would always stress the importance of maintaining that radius during manufacturing, or subsequent service. Will be interesting to see what this area looks like when it comes apart. On the list of catastrophic engine failures, this has to be one of the most insidious, as there was virtually no warning until it occurred.

Many thanks also for the contact information - I greatly appreciate it. As I said, once I get the new motor put together, I will concentrate again on scrounging parts - assuming the current block is not damaged.

Best Regards....

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gerrykan
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Re: Bad Day at the Car Show

Post by gerrykan » Wed Jun 20, 2018 3:55 pm

I broke a crankshaft in a 225 cubic inch Dodge 6 cylinder once.

My machinist told me to get another crank and vibration dampener/harmonic balancer and throw the old balancer away.
He said that the only thing that breaks crankshafts is vibration.
He also said to get a new oil pump, as metal particles went through it.

I do not know if his statement is true, or if the GMC 270 uses a balancer with a rubber cushion between the inner and outer parts like the Dodge.
Just passing this along in case it may help.

I got lucky like DRH, and it broke at an angle, allowing the engine to keep running.
I beat his distance though, I was about 50 miles from home, then drove it an additional 30 miles the next day to the workshop for disassembly.
Roy

vj
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Re: Bad Day at the Car Show

Post by vj » Thu Jun 21, 2018 6:08 am

Well, that would be a bad day for anyone. I would have like to went to the Auburn Hills Chrysler show in MI. june 9 , But too far for me. I did live in westland mi. We did all the car show, air show back in the days. fun fun
I have got four running halftracks,plus 5 ton ww2 semi-truck,1943 willys jeep and other ww2 vehicles,plus a lot of parts to trade on. Wendell in Tn.

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Re: Bad Day at the Car Show

Post by D.R.H. » Mon Jun 25, 2018 4:25 pm

Hi MudFlap, sorry for the late reply. I forgot that I had commented on your thread. Burbank Speed and Machine of So. Calif. rebuilt the engine after I had rescued it from a vineyard. It had been sitting in the field for God only know how long. After the tear-down and inspection, Dave the owner told me that the steel just gets old after so many years and becomes more brittle and is prone to break when just the conditions occur.
In my case, slight incline, too high of a gear selection, too low R.P.M. range, pulling 5000 lbs. of Weasel and trailer and too much torque = KABLAMMO. The rod journal bearing wore out very fast which caused the piston to make contact with the head. This crushed the top of the aluminum piston and destroyed the rings. It didn't hurt the head or the cylinder, and Egge Performance made 1 new piston and the engine went back together and is still going strong in Tucson Az. :)
In Loving Memoriam: George R. Hancock. 20 Mar. 1938 - 11 Jan. 2017. U.S.A.F. 1956 - 1962. R.I.P. Dad.
In Loving Memoriam: Ann Hancock, 08 Mar. 1934 - 25 Sept. 2021. R.N. 1960 - 2005. R.I.P. Mom.
Thank You BOTH for always being there.

My YouTube Channel. https://www.youtube.com/channel/UCaMKEv ... M3g/videos.

mudflap
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Re: Bad Day at the Car Show

Post by mudflap » Tue Jun 26, 2018 7:00 pm

Thanks to all for the responses.

I do have an NOS damper that I plan on using on the replacement engine. I have not looked at it closely, but I would be surprised if there isn't rubber isolator in there.

Replacement engine block is headed to the machine shop later this week for a magna-fluxing, boring, and a light pass over the deck just to clean things up.

Will hopefully get it back in a week or two.

Best Regards...

mudflap
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Re: Bad Day at the Car Show

Post by mudflap » Mon Jul 16, 2018 9:20 am

Found a few spare minutes to look a little deeper into the crank failure on my CCKW.

Appears to be kind of a bad news/worse news scenario...

Bad news is I don't have to go searching around for a crankshaft.

Worse news, is I will need to find a new crank, block, cam, and at least one rod and piston... OK.. Maybe a complete short block, it I want to have a spare engine.

Seems that when the crank broke, it took out a section of the camshaft, which in turn ventilated the engine block.

In the first pic, (front of the engine is to the left) you can see where the cam broke off, along with the missing piece jammed in between block and a remaining piece of camshaft. I was actually able to slide one of the #5 cylinder lifters out of the bottom - however the pushrod remained stuck in the bore, presumably because it is bent. You can also see daylight coming through an oval shaped hole in the block.

20180715_192956 Lo.jpg
20180715_192956 Lo.jpg (187.12 KiB) Viewed 585 times
The next pic shows the break in little greater detail.
20180715_193024 Lo.jpg
20180715_193024 Lo.jpg (96.18 KiB) Viewed 585 times
The bearing shells have a 0.010 stamp on them, so I am assuming the crank was ground during some previous rebuild. While 0.010" is obviously not a lot, it does not appear that very much of a radius was left in the corner between the journal and throw. Some areas (especially on the rod) actually look quite square. This, I am told, is a big no-no, as it concentrates the stress in this area, leading to a crack and ultimate failure. So, it is quite probable that the seeds of this failure were sewn many years, or many decades, before it occurred.

I am speculating that perhaps the crack started at the interface between the rod journal and crank throw, then worked its way through until it made it to the main journal. Can't tell for sure until the crank comes out and I can look at it a little more closely.

Best Regards......


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