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Old 09-21-2015, 02:04 AM   #1
jfreddie
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Default Light flywheel on regular crank

Does a lightened flywheel, 43#, have any harmful effect running on a standard, original crank? I've run this setup for about 6,000 miles with a 5.0 head and acceleration is great. Recently I found a small metal piece in the oil. Took the pan off and the center main had "cammed" out. Rear main showed fracturing and had started leaking oil. Was it just it's time to go? Had checked clearances about two years ago. Does running the heavier original flywheel provide some dampening for the center main? Thanks for your input.
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Old 09-21-2015, 02:25 AM   #2
Mike V. Florida
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Default Re: Light flywheel on regular crank

Once you start the car with the spark lever all the way up, how do you adjust it to drive?
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Old 09-21-2015, 03:41 AM   #3
jfreddie
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Default Re: Light flywheel on regular crank

Thanks for your interest!
I use a centrifugal advance in the valve chamber and set max advance at 26 deg.
I meant the babbitt had beaten itself into thin pieces about 1/2" across that I could bend with my fingers. Those pieces stayed in the upper part and came out as a mosaic when I pulled the crank. The cap had an oiler in the center(from a port in the oil pump cavity). The babbitt was fairly thick in the rotation direction from the oil port. Babbitt in the rest was mostly gone. The crank was riding on that thicker part and wasn't damaged(miraculously).
It appears the upper part may have starved for oil since the damage was heaviest there, and the metal in #3 dipper tray was mostly small flakes(about a rounded teaspoon).
With an oil tube on the bottom and open oil tube on top, not sure how it could lack for oil unless the grooves got hammered and interrupted the delivery and then one thing would lead to another.
Guess thats my question. Could that flywheel/ crank setup cause increased flexing that might hammer the oil grooves?
Sorry to be long wind. Having a rebabbitt done with Mr. Barlow. Hope that helps.
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Old 09-21-2015, 03:47 AM   #4
colin1928
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Default Re: Light flywheel on regular crank

A light weight flywheel will not hurt bearings in fact it tends to prolong bearing life IMO
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Old 09-21-2015, 04:00 AM   #5
Synchro909
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Default Re: Light flywheel on regular crank

At what speed do you drive this car and at what speed do you change gears? Sounds to me like you may have been a little too exuberant. The middle main bearing is the weak link in these engines and should be looked after.
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Old 09-21-2015, 07:29 AM   #6
Bob Bidonde
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Default Re: Light flywheel on regular crank

A lighter flywheel is beneficial because it reduces the stresses in the main bearings and crankshaft.
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Old 09-21-2015, 07:44 AM   #7
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Default Re: Light flywheel on regular crank

To your original question:
"Does running the heavier original flywheel provide some dampening for the center main?"

Crank dampening is a term that defines controlling torsional twist and resonance along the main bearing centerline from intermittent but regularly indexed and timed loads (cylinders firing). This is generally not what will cause a bearing to cam out. Yes, the rotational mass at each end of a crankshaft (flywheel at rear end , pulley and other mass, like an added "damper" at the front) have some function in controlling the resonant shock wave that concentrates rotational or torque force at the stress rises in the crank main bearing fillets. It is a balancing act, never perfectly controlled in any design of crankshaft engine.

A cammed babbitt bearing is caused by one of two forces: 1) Excessive shock and pressure on the power stroke. This would be detonation or spark advance and/or compression that exceeds the deformation limit of the bearing material. 2) Centripetal force bending the crank main off it's centerline when there is anything less than 100% counterweighting evenly distributed on each side of each main bearing. Most counterweighted cranks are in the 40 -60% range and are much stiffer (5 vs 3 mains) to resist bending. This is a function of RPM & % counterweighting vs material strength/stiffness. A stock A crank has zero counterweighting, low stiffness, and only three mains.

I hope this puts some light on your question about dampening the center main.
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Old 09-21-2015, 07:59 AM   #8
Kurt in NJ
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Default Re: Light flywheel on regular crank

If you can bend the "babbitt" with your fingers it is most likely soft lead based babbitt---there is not much you can do to "save" a bad babbitt job no matter how you drive
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Old 09-21-2015, 10:48 AM   #9
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Default Re: Light flywheel on regular crank

I'm not familiar with the advance unit in the valve chamber. Is that set for 26 cam/distributor degrees or total crank degrees ?
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Old 09-21-2015, 11:18 AM   #10
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Default Re: Light flywheel on regular crank

Quote:
Originally Posted by jfreddie View Post
Does a lightened flywheel, 43#, have any harmful effect running on a standard, original crank? I've run this setup for about 6,000 miles with a 5.0 head and acceleration is great. Recently I found a small metal piece in the oil. Took the pan off and the center main had "cammed" out. Rear main showed fracturing and had started leaking oil. Was it just it's time to go? Had checked clearances about two years ago. Does running the heavier original flywheel provide some dampening for the center main? Thanks for your input.
What, if anything, do you know about the Babbitt job that is being destroyed ? Did you have it done or did you get block with it done. And, how old and how many miles is on that Babbitt job ?
All I've read/heard form the most informed (re:babbitt) here, is that the Babbitt material must be best quality to last/endure.
As to lightened flywheel, I second Colin's answer. I would add though, that 'other things' must be considered and/or done when changing things in an engine....think balancing first.

Last edited by hardtimes; 09-21-2015 at 11:20 AM. Reason: .......
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Old 09-21-2015, 11:21 AM   #11
jfreddie
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Default Re: Light flywheel on regular crank

The 26 deg is crank advance on the crank pulley scale.
The advancer fits in place of disturb lower shaft so you can use original dist. The advancer is installed in the valve chamber and gives 30 deg total advance. I set mine on 26 degs based on having higher compression than standard.
The rods looked fine. Thats what has me puzzled.
I could bend the babbitt with my fingers because it was pounded so thin, like 1/32".
Thanks again for all the input. I get a sense that the flywheel itself was probably not the issue.
Anyone running a lightened flywheel on an uncntrwtd eng? Happy with it?
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Old 09-21-2015, 11:34 AM   #12
Patrick L.
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Default Re: Light flywheel on regular crank

Quote:
Originally Posted by jfreddie View Post
The 26 deg is crank advance on the crank pulley scale.
The advancer fits in place of disturb lower shaft so you can use original dist. The advancer is installed in the valve chamber and gives 30 deg total advance. I set mine on 26 degs based on having higher compression than standard.
The rods looked fine. Thats what has me puzzled.
I could bend the babbitt with my fingers because it was pounded so thin, like 1/32".
Thanks again for all the input. I get a sense that the flywheel itself was probably not the issue.
Anyone running a lightened flywheel on an uncntrwtd eng? Happy with it?





OK, just wondering about detonation. Apparently thats not the problem, 26 shouldn't be a problem.

I wouldn't think the lighter flywheel would be problem either, I think the lighter wheel should take some stress off the center and rear main.

Just wondering how old the babbitt is and if it was proper babbitt to begin with.
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Old 09-21-2015, 01:28 PM   #13
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Default Re: Light flywheel on regular crank

I wonder if the Babbitt is the Original? It may be fatigued from some previous owner lugging or over advancing the timing long before you owned it.
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Old 09-21-2015, 04:39 PM   #14
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Default Re: Light flywheel on regular crank

I have used a lightened flywheel with a standard crankshaft for many years and many miles. No problems.
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Old 09-21-2015, 06:09 PM   #15
jfreddie
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Default Re: Light flywheel on regular crank

Thanks, that's what I wanted to hear.
I think the babbitt may not have been first rate. When I got the car it supposedly had fresh babbitt but it was leaking oil. The rear main cap babbitt was cracked like a mosaic and fell out when I turned it over.
Also the oil grooves and side bevels were cut with a dremel tool rather unevenly. Maybe I was lucky to get 10 years out of it?
Thanks.
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Old 09-21-2015, 11:34 PM   #16
Mike V. Florida
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Default Re: Light flywheel on regular crank

Quote:
Originally Posted by Patrick L. View Post
OK, just wondering about detonation. Apparently thats not the problem, 26 shouldn't be a problem.

I wouldn't think the lighter flywheel would be problem either, I think the lighter wheel should take some stress off the center and rear main.

Just wondering how old the babbitt is and if it was proper babbitt to begin with.
Exactly why I asked about the lever settings when driving. As he has auto advance that is a moot point.
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