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08-07-2020, 07:19 AM | #1 |
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Lightened Flywheel
I mostly see lightened flywheels used with counterweighted cranks. Are they only useful only together, or will they work well with a stock crank? If you had to choose from a 33# or 42# flywheel, what would be the best choice and what would be the advantages of either? I would think the 33# would get the nod.
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08-07-2020, 07:28 AM | #2 | |
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Re: Lightened Flywheel
Quote:
To answer your question specifically, they work well with stock crankshafts too. I would go with the 42# flywheel, ...and my reasoning is discussed in the link I posted. . |
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08-07-2020, 07:28 AM | #3 |
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Re: Lightened Flywheel
We had a flywheel lightened at a machine shop once and cannot tell the difference. from a stock flywheel. Stock crankshaft. No better and no worse.
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08-07-2020, 08:23 AM | #4 | |
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Re: Lightened Flywheel
Quote:
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08-07-2020, 08:32 AM | #5 |
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Re: Lightened Flywheel
I did not search for it, and was only working off of memory that you had asked something about it. The link I posted is the one I started several years ago.
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08-07-2020, 10:02 AM | #6 |
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Re: Lightened Flywheel
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08-07-2020, 10:57 AM | #7 |
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Re: Lightened Flywheel
Engines are beyond dumb, and well into stupid, the crank doesn't know or care what is behind it. I'd go with the 33 lbs. The lighter weight will accelerate and de-celertate quicker, and make quicker shifts possible. Do the math! It will not add horsepower.
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08-07-2020, 11:09 AM | #8 |
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Re: Lightened Flywheel
Must be another myth or old wives tale, but, I've always heard that at least 12# needs to be removed when using a counter weighted crank.
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08-07-2020, 01:24 PM | #9 |
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Re: Lightened Flywheel
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08-07-2020, 01:35 PM | #10 |
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Re: Lightened Flywheel
My '29 roadster has a stock engine with a lightened (weight?) flywheel. It helps with engaging/disengaging a Borg-Warner overdrive.
Bob-A |
08-07-2020, 02:12 PM | #11 |
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Re: Lightened Flywheel
Brent,
We may have discussed this before so sorry if it is a repeat. For the rest, it may be of interest. When using a lightened flywheel, I have had the experience of the "naturally occurring harmonic vibration" change rpm range. A few years back, while doing some component testing for my touring car, I discovered the following: On an engine with a counter-weighted and balanced crankshaft, using an extremely lightened flywheel caused the vibration to present itself between 50 and 54 mph with a standard ratio rear end. Normally I see this vibration between 42 and 46 mph. Having the vibration show at 50 - 54 mph could not be worse for driving average roads with a touring engine. The solution was to install a heavier flywheel, about 10#, and the harmonic vibration dropped back to between 46 - 49 mph which is much more drive-able. I believe if a standard weight flywheel were to be installed, the range would have dropped into the normal range of 42 - 46 mph. All the flywheels and matched pressure plates were balanced. We even tried Ron Kelly's method of modifying a SB Chevy front harmonic balancer and mount it to the inside of a lightened flywheel. It actually worked the best in narrowing the vibration range. Voodoo or fuzzy logic I know but it was hard to argue with good results. Good Day! Last edited by Dave in MN; 08-07-2020 at 05:21 PM. |
08-07-2020, 03:41 PM | #12 | |
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Re: Lightened Flywheel
Quote:
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08-07-2020, 06:12 PM | #13 | |
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Re: Lightened Flywheel
Quote:
Thanks for that observation Brent, It was my understanding that a harmonic dampener is most effective at the front end of the crankshaft? Having seen a a flywheel mounted dampener, not only did it look complicated, but one also has to remove the motor to fit it. Whereas the Harmonic dampener pulley is so much easier to fit, and in my experience, very effective. Last edited by wensum; 08-13-2020 at 06:24 PM. |
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08-07-2020, 07:11 PM | #14 |
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Re: Lightened Flywheel
While I'm no expert in this area, it seems to me that a heavy flywheel will cause greater torsional stresses in the crankshaft due to its inertia. For that reason, I have gone with a lightened one at the back and one of those Murray Horne (From NZ) harmonic balancers on the front. I have no reason to regret that.
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08-07-2020, 07:16 PM | #15 |
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Re: Lightened Flywheel
I had to look for it awhile but this is a VERY good explanation of what torsional vibration is and how it is dealt with. The pics don’t show because it is a very old post but maybe MikeK can be persuaded to re-post it.
It is from 2-24-13. Post #32 |
08-07-2020, 09:32 PM | #16 |
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Re: Lightened Flywheel
50lb B flywheel, stock A crank,Murray's balancer..no more 'harmonic' rpm..smooth all the way..
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08-07-2020, 09:45 PM | #17 |
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Re: Lightened Flywheel
During A engine development all the engineers involved with the work identified the torsional vibration,Harold Hicks had the temerity to bring it up to Mr Ford,who was a proponent of the heavy flywheel compensating for the issue..the engineers finally 'won' in '32,a mechanical advance distributor,larger crankshaft journals and later a counterbalancing addressed the issue..
Benson Ford research center oral histories..right from the horses mouth.. |
08-08-2020, 06:19 AM | #18 | |
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Re: Lightened Flywheel
Quote:
I agree, it added weight and that was key in lowering the range of vibration. The same happend when a flywheel of approximate equal weight, that was solid...no balancer added, was tried. The difference between the two was the range of vibration was much tighter and less in intensity to almost not noticeable. The mounted balancer appears to take the edge off the torsional pulse, when a cylinder fires or the maximum pressure is reached on the compression stroke. I now run that version of flywheel in my Phaeton. I tested these varying flywheels with the engine on the dyno. By varying the load at the rpm the vibration was most evident, the vibration could be intensified and clearly observed. The battery of tests taught me how to better build and tune an engine. Again...some say fuzzy logic but the dyno and results don't lie. I have tried one of Murray Horne's combination front pulley/dampers. It also helps lessen the observed harmonic slightly. I need to complete more tests on his product when I have time. Available time seems in short supply of late. Hope you and family are doing well...Good Day! Last edited by Dave in MN; 08-08-2020 at 12:38 PM. |
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08-08-2020, 07:07 AM | #19 |
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Re: Lightened Flywheel
This is all interesting. I enjoy the conversation.
What I have learned is that I can put my flywheel money into a new cam and will get more usable benefit. |
08-08-2020, 07:30 AM | #20 |
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Re: Lightened Flywheel
When you try to accelerate the flywheel will suck the energy created by the cam and release it when you decelerate.
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08-08-2020, 07:38 AM | #21 |
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Re: Lightened Flywheel
The flywheel dampens the torsional impulses in the crankshaft from the power stroke, the compression stroke, acceleration and deceleration of the crankshaft's RPM (changes in momentum: Force x length of time applied = mass x velocity). Putting a small damper on the front of the crankshaft is money wasted because it has a minuscule mass and radius of gyration relative to the flywheel.
The flywheel is also a gyro, so it opposes changes in its rotational axis and dampens the engine's tendency to rock vertically about the rear engine mounts. Lightening the flywheel gives the engine a mechanical advantage to accelerate / decelerate quicker (change engine's momentum). So lightening the flywheel a significant amount (pounds, not ounces) improves acceleration, shifting, braking, reduces rear main bearing stress and should improve gas mileage. On the other hand, lightening the flywheel decreases its ability to dampen the engine's impulses and vibrations. Thus it is a trade-off to lighten a flywheel. The trade-off is worthwhile in my opinion, so I favor lightening the flywheel for improvement of the car's performance. By the way, the weight of a stock flywheel and clutch is 80 lbs.
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08-08-2020, 09:11 AM | #22 | |
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Re: Lightened Flywheel
[QUOTE=Bob Bidonde;1917902]The flywheel dampens the torsional impulses in the crankshaft from the power stroke, the compression stroke, acceleration and deceleration of the crankshaft's RPM (changes in momentum: Force x length of time applied = mass x velocity). Putting a small damper on the front of the crankshaft is money wasted because it has a minuscule mass and radius of gyration relative to the flywheel.
OK, so how about putting a damper on the front AFTER removing much of that excess mass from the flywheel?? Quote:
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08-08-2020, 11:23 AM | #23 |
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Re: Lightened Flywheel
Every modern engine uses a useless harmonic balancer.A flywheel stores kinetic energy and dampens impulse. On one end of the crankshaft....what about the other? Henry Fords heavy flywheel cure for torsional vibration was seen by his engineers as ineffective by years ago,it remains today..
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08-08-2020, 11:29 AM | #24 |
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Re: Lightened Flywheel
the next time you change a cracked or broken front pulley ask yourself " why did this happen?"..think about the effect that cracked the cast pulley has on main bearings..dont just run out and buy a two piece pulley to make the "next time" easier...fix the root cause
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08-08-2020, 02:31 PM | #25 |
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Re: Lightened Flywheel
12 lb.
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08-08-2020, 02:46 PM | #26 |
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Re: Lightened Flywheel
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08-08-2020, 03:09 PM | #27 | |
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Re: Lightened Flywheel
Quote:
The closer you can get the weights on each end of the crank, the less TORSIONAL vibration and the longer the crank lasts. |
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08-08-2020, 04:05 PM | #28 | |
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Re: Lightened Flywheel
Quote:
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08-08-2020, 04:17 PM | #29 |
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Re: Lightened Flywheel
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08-08-2020, 04:19 PM | #30 |
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Re: Lightened Flywheel
Every modern engine uses a useless harmonic balancer.A flywheel stores kinetic energy and dampens impulse. On one end of the crankshaft....what about the other? Henry Fords heavy flywheel cure for torsional vibration was seen by his engineers as ineffective by years ago,it remains today.
If they are ineffective, why to the penny-pinching manufactures put them there? Think about it! |
08-08-2020, 04:39 PM | #31 | |
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Re: Lightened Flywheel
Quote:
Your comment; "Put one of murrays on my car.. can feed a B width belt sideways to install. Bronze cam gear chatter minimized.Logic says reducing harmonic vibration should help extend main bearing life with a dynamically balanced crankshaft..time will tell." https://www.fordbarn.com/forum/showt...monic+balancer See this thread: https://www.fordbarn.com/forum/showt...monic+balancer Last edited by Y-Blockhead; 08-08-2020 at 04:51 PM. |
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