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09-06-2011, 09:08 PM | #1 |
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Location: Cincinnati, OH
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Why it's so important to NOT point fingers until the data is all in....
I posted a few days ago about how I found broken babbitt for the second time after a dismantle to find the cause of a rear main leak. Both times the motor only had a few thousand miles. See the first picture. I was really disheartened. Well, I visited the shop today, and the proprietor allowed as how something was certainly not right, and encouraged me to bring the whole motor in for inspection. He noticed a shiny arc on the rear of the main cap (see the second picture) which had escaped my eye. I spent time staring at the whole thing tonight after dinner. Guess what? A shiny flywheel bolt protruding a bit too far through the crank flange (see third picture) was just barely interfering with the main cap. I put the cap back on and rotated the crank; with my free hand on the cap I could feel that bolt just barely touching the main cap with every revolution. This is the perfect recipe for fatigue failure: every revolution pulled the crank back against the cap, not very hard, but enough to fatigue the babbitt.
The shop that poured the babbitt wasn't at fault. Both times they delivered me a short block; I installed the flwheel, etc. and neither time caught the fit problem from the bolts that protruded a few thousandths too far. Ouch. But I'm glad not to have named names when I was upset with what I thought was an inferior babbitt job. |
09-06-2011, 09:19 PM | #2 |
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Re: Why it's so important to NOT point fingers until the data is all in....
Thanks for posting your findings, I feel for you in your 3rd go at it, but it sounds as though you did find the issue. Another good thing to keep in the back of the mind, when assembling things.
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09-06-2011, 09:40 PM | #3 |
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Re: Why it's so important to NOT point fingers until the data is all in....
Also : Thank you for sharing " what happened " a lesson for all of us.
Gerard |
09-06-2011, 10:02 PM | #4 |
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Re: Why it's so important to NOT point fingers until the data is all in....
What a bummer!
Most likely you are missing the "Flywheel dowel pin retainer plate" that goes under the 4 flywheel mounting bolts. In addition to retaining the dowel pins in the crankshaft flange, the plate spaces the flywheel bolts out so that they do not hit the main cap. After a quick look ... I did not find the retainer plate in Mac's, Snyders or Bratton's catalogs. I know Bert's at 1-800-321-1931 has some originals for sale. They should be able to supply it from my description. In Les Andrews' manual Vol#1, page 1-147 under "NOTE" he mentions the plate and calls it "the Flywheel bolt spacer plate" and mentions to check the length of the bolts. Last edited by Benson; 09-06-2011 at 10:47 PM. |
09-06-2011, 10:08 PM | #5 |
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Re: Why it's so important to NOT point fingers until the data is all in....
There is a article in the Service Bulletins about the change in bolt length for mounting the flywheel.
You are not the first to have this problem; a fello drove his A to the MAFCA national in Reno, said he had a noise when the engine was running. In the repair tent we pulled the flywheel inspection plate; you could see the end of the bolt sticking thru the flwheel flange and it was polished from hitting the rear main cap. He was lucky, have seen an engine that locked up after just 1/4 turn, bolt so long it wouldn't pass the cap. Ron |
09-06-2011, 11:33 PM | #6 |
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Re: Why it's so important to NOT point fingers until the data is all in....
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09-07-2011, 12:07 AM | #7 | |
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Re: Why it's so important to NOT point fingers until the data is all in....
Quote:
Last edited by Kohnke Rebabbitting; 09-07-2011 at 12:12 AM. |
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09-07-2011, 06:37 AM | #8 |
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Re: Why it's so important to NOT point fingers until the data is all in....
Kurt:
Yes, there was a very slight knock that would come and go and was unrelated to load or spark advance. Hmmmmm. Herm: Great idea and I will post a picture tonight after work. |
09-07-2011, 06:38 PM | #9 |
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Re: Why it's so important to NOT point fingers until the data is all in....
Herm:
Here are the images I just took of the center main. The first is after bolt removal; gives an idea of clearance on each side. The second is looking at the side of the crank throw that would be loaded by the flywheel bolt contacting the rear main cap. I was unable to detect any crankshaft endplay but didn't spend a lot of time trying to move it. Your comments are very welcome! As an aside, the first time I was inside this particular motor, I was 15. I'm 54 now. |
09-07-2011, 11:49 PM | #10 |
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Re: Why it's so important to NOT point fingers until the data is all in....
To me it looks like the crank is a little too far forward, usually the front and rear thrust faces are closer to the same thickness, and the crankshaft is more centered at the center main. ---perhaps it was done that way to accomadate the stuff packed in the oil slinger drain channel.
Is it just the picture or does the radius at the front end of the journal have a sharp corner where it joins the bearing surface? |
09-08-2011, 01:32 PM | #11 | |
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Re: Why it's so important to NOT point fingers until the data is all in....
Quote:
Last edited by Kohnke Rebabbitting; 09-08-2011 at 01:42 PM. |
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