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View Poll Results: What sustained car MPH will babbitt bearings in a stock Model "A" reliably withstand?
50 MPH 54 49.09%
55 MPH 29 26.36%
60 MPH 14 12.73%
65 MPH 6 5.45%
70 MPH 7 6.36%
Voters: 110. You may not vote on this poll

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Old 05-10-2018, 11:04 AM   #1
Bob Bidonde
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Default How Fast Will It Go?

Please vote your actual highway driving habit.
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Old 05-10-2018, 11:40 AM   #2
wmws
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Default Re: How Fast Will It Go?

The question should be what RPM will the babbitt withstand. I would say not over 2000 RPM for any sustained driving. I never cruse over 1750 but then I have a Mitchell OD.
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Old 05-10-2018, 12:19 PM   #3
Kurt in NJ
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Default Re: How Fast Will It Go?

I have been trying to damage my Babbitt for the last 30 years, I did have the Babbitt come out of a rod at near 70, it hadn't been tinned properly, have driven the entire PA turnpike at 65-67mph

I have talked to Mercedes owners that drove "A" to college, these were mostly just average cars, they drove them flat out(over the speed limit),never had engine failures, but they did say that it took a lot of stops to refill with used oil
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Old 05-10-2018, 02:03 PM   #4
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Default Re: How Fast Will It Go?

My car likes 47mph.
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Old 05-10-2018, 03:49 PM   #5
BRENT in 10-uh-C
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Default Re: How Fast Will It Go?

Bob, when you mentioned stock, the only thing I can relate this to is a standard bore, standard crankshaft, correctly balanced reciprocating assembly in a low-mileage car that I have driven, and they can do very well at 60 mph with stock gearing.


Where things start going 'haywire' is when the balance of the reciprocating assembly is bad, then abnormal stresses are created causing failures. Remember, old 20's & 30s diesel engines had over 3X the compression ratio as an 'A' engine did, and they were very reliable for long periods of laborious operation. Therefore it was not the compression that caused babbitt failures.
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Old 05-10-2018, 07:43 PM   #6
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Default Re: How Fast Will It Go?

Quote:
Originally Posted by wmws View Post
The question should be what RPM will the babbitt withstand. I would say not over 2000 RPM for any sustained driving. I never cruse over 1750 but then I have a Mitchell OD.
Agreed itís all about RPM thru gearing and tire size. Then again there are other considerations such as higher compression heads and driving habits. Very complicated question I think.
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Old 05-10-2018, 07:58 PM   #7
wmws
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Default Re: How Fast Will It Go?

I don't believe the stock A crank was dynamically balanced. With a 3.78 rear and 21 inch tires 70 MPH is turning at 3100 RPM. That's a lot for a stock A engine.
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Old 05-10-2018, 08:28 PM   #8
Kurt in NJ
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Default Re: How Fast Will It Go?

from the crankshaft print--
shaft must be in balance dynamically within 3 ounce inch at any one point of reference, shaft must be in balance statically within 3 ounce inch

on the rod print there is a weight tolerance of +/- 1 gram at each end ----modern engines mostly have larger tolerances

what percentage of rebuilt engines do you think have been restored to original tolerances
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Old 05-11-2018, 03:41 AM   #9
BRENT in 10-uh-C
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Default Re: How Fast Will It Go?

Quote:
Originally Posted by wmws View Post
I don't believe the stock A crank was dynamically balanced. With a 3.78 rear and 21 inch tires 70 MPH is turning at 3100 RPM. That's a lot for a stock A engine.
That is one of the biggest issues I encounter in this hobby today as I field phone calls for tech support is that hobbyists unfortunately have erroneous preconceived opinions that affect performance. As Kurt mentioned, the cranks were very well balanced as was the entire reciprocating assembly. When balanced that well, and because 60 mph is between first & second stage harmonics, help me understand exactly what is happening where the engine is supposedly destructing at 60mph? For example, don't just say the Babbitt is, ...specifically tell what is happening to cause the failure.
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Old 05-11-2018, 04:14 AM   #10
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Default Re: How Fast Will It Go?

Chiefs' Friend drove his Model A to work & shopping for YEARS, then during a head gasket job, discovered it had 3 Standard Pistons & 1 that was .080" OVERSIZE----"SURPRISE"!!!!
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Old 05-11-2018, 10:17 AM   #11
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Default Re: How Fast Will It Go?

RPM is relative to speed. 30 MPH is approximately 1500 RPM with a 3.78:1 differential.
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Old 05-11-2018, 02:34 PM   #12
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Default Re: How Fast Will It Go?

I keep it around 45mph,occasionally hit 50
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Old 05-11-2018, 03:32 PM   #13
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Smile Re: How Fast Will It Go?

I cruise "Virginia" around 50-55. However, I have found myself in traffic doing 60, in order to not be run over. Virginia is a '31 deluxe roadster
that was refurbished in the early '50s, so I was told by the former owner.
"B" block with a counter-weighted crank, "A" head and sidemount bowl
Zenith. Cam is most likely a stock B. I've never opened the motor, but I'm
pretty sure, knowing the history it is a babbit bearing one. Also, I believe the read-end is a 3.54. My biggest fear is not blowing the motor, but out-running the car's brakes!

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Old 05-13-2018, 12:24 AM   #14
Mike V. Florida
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Default Re: How Fast Will It Go?

I don't like the wording of the question. Based on the chooses are you asking maximum speed?

Are you asking what do we think the max speed of a babbit engine is? We have read here of babbit A engines racing at Bonneville. But you say stock engine? Are you asking about non-pressurized oiling engines when you say stock?

The max speed has little to do with babbit and more to do with engine design and gearing.
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Old 05-13-2018, 07:22 AM   #15
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Default Re: How Fast Will It Go?

Don't know what my max speed is. never been there, never will. My counter balanced engine likes speeds below 45 and so do my brakes. The engine in these cars will definitely out run the brakes.
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Old 05-13-2018, 07:52 AM   #16
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Default Re: How Fast Will It Go?

I routinely cruise on highways at 55 to 65 MPH, and driving my Model A's since 1962 I have not yet had any bearing fail due to speed.
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Old 05-13-2018, 08:59 AM   #17
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Default Re: How Fast Will It Go?

My engine was never past 2200 on the tach. Never cruised at more than 2000 to 2100 as per the builders recommendation. Lost the Babbit at 5500 miles.
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Old 05-13-2018, 09:39 AM   #18
barkleydave
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Default Re: How Fast Will It Go?

Basic stock engine and 3 speed 3.78 Synder HC 5.1 head which improved performance in hilly KY. and TN.


My Truck loves 42-45 MPH. Will run over 60 on a flat run.


Do not forget some of our cars will run well above 65 MPH... however can you stop and control it?


I would hate to have to do an emergency stop at 65 in my Truck. I am pretty sure my tailgate would pass me!
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Old 05-13-2018, 09:42 AM   #19
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Default Re: How Fast Will It Go?

We also have a Slant with a F150 4 speed. What a wonderful combination for touring!
It will roll at 55 at 2000 rpms all day without effort.
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Old 05-13-2018, 09:47 AM   #20
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Default Re: How Fast Will It Go?

babbitt is lost because of bad babbitt jobs, loose bearings, lack of oil to the bearing, lugging.
I use to race chev 6 cylinders with babbitt rods and babbitt line inserts in the mains. never lost the babbitt, did break a couple of pistons.
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