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10-25-2022, 03:12 PM | #1 |
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New Babbitt Mains - How Tight
How tight should a Model B crankshaft be in a newly rebabbitted engine block? After shooting 10/30 oil into the oil ports for each bearing - without camshaft, rods, or pistons installed - the crankshaft will only turn with a minimum of 25 lbs of torque. This seems pretty tight to me as I've never worked with newly babbitted mains before. What should be the appropriate level of torque to turn the crankshaft in this situation?
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10-25-2022, 03:43 PM | #2 | |
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Re: New Babbitt Mains - How Tight
Quote:
If the bearing has been burnished, then it is too tight. If not, then the journal pin(s) is likely just touching the high-spots of the bearing and the assembler chose to set the clearances tight in order for it to "self-clearance" during the initial run-in. Not my preferred method however there are many successful rebuilders who choose this method due to budget/time constraints. |
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10-26-2022, 11:33 AM | #3 |
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Re: New Babbitt Mains - How Tight
I usually put an extra .001" shim under one side of each bearing, this gives another .0005" clearance. I also do this on the rods.
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10-26-2022, 12:53 PM | #4 |
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Re: New Babbitt Mains - How Tight
Brent has the right advice. The bearings will get hot on the initial run and the babbett will expand to tighten up the clearance. The tight bearings will wear down the high spots. On cooling the clearance will loosen up again. This will repeat until the correct clearance is obtained. This is one advantage of poured bearings. The first run should be short, about 15 minutes, followed by longer runs. And not high speed or high load. Ford recommended 25 mph for breakin. I think it was 500 miles. Ford did an initial breakin of his engines using an electric motor to turn the engines.
Use the normal detergent multi grade oil for the breakin. Change the oil after 500 miles. The next change can be longer.
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10-26-2022, 05:17 PM | #5 | |
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Re: New Babbitt Mains - How Tight
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On a Model B clearance should be .002" on rods and mains There will be a distinct pull to initially get the crank moving this is called "Stiction". Once you break the death grip the crank will spin freely it work was done properly. |
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10-26-2022, 07:25 PM | #6 |
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Re: New Babbitt Mains - How Tight
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Now there's one possible fly in the ointment! Suppose the 3 journals are not concentric! For whatever reason! I had model A engine that the crank and babbitt were ground and repoured. This engine was well done and was tight as heck, but never seized. When I brought it home, the crank could not be turned by hand,(no pistons) but it gave me no trouble. Terry |
10-27-2022, 08:18 AM | #7 |
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Re: New Babbitt Mains - How Tight
When you work on the bearings, make sure to use some assembly lube when you put it back together. That will help with the initial startup.
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10-27-2022, 11:19 AM | #8 |
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Re: New Babbitt Mains - How Tight
Ask the person/company that built it. They are who you are going to go to if a problem later.
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10-28-2022, 11:34 AM | #9 |
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Re: New Babbitt Mains - How Tight
Some good advice above.
As J and M said, it'll take just a bit to get it turning and then should spin freely. If its still not assembled, I'd recommend checking the clearance. I like .0015". |
10-29-2022, 10:24 AM | #10 |
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Re: New Babbitt Mains - How Tight
A lot depends on what type of align boring machine the builder has and what shape the crank is in. The mains are generally sized to the crankshaft journals to be used. The clearance should be close but it has to have some clearance to allow oil to get in there. It should be good with .001" to .0015" With less than .001", it' going to be tight. As long as the caps are shimmed properly at the outset, follow on adjustments can be made if necessary.
Ford turned the engines with the big electric motors and monitored the current draw on the motors. They had it down to a science for their initial bedding in process. If it took to much current to turn then it went back to a separate line for repair consideration. I'm not one for running newly overhauled engines with no way to pull a load on them. They won't break in well with no load. Some get lucky but I don't like to leave things to chance. |
10-29-2022, 07:44 PM | #11 |
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Re: New Babbitt Mains - How Tight
I think its best if you put it together on the loose side, then in a 1000 or so miles drop the pan and set the clearances to proper spec. I understand why builders don't want to do that as its more shop time and depends on the customer bringing the car back. If someone is capable of doing their own work then a little extra time spent could save you some serious headache later. Just my two cents. I've heard lots of horror stories about seizing from too tight of build, although a cold seize isn't nearly like a hot seize.
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10-31-2022, 04:59 PM | #12 | |
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Re: New Babbitt Mains - How Tight
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Work pretty much done he calls. "Your bearings are done but we noticed a problem Houston. Your crank is not straight. Block fits the crank fine but when everything is bolted together the crank is seized. We traced it down to the crank is about 0.020 out of alignment (non-concentric between the three journals.) The solution is to have the grinder "straighten" the crank. Large press, foot pedal, "bounce" the hydraulic piston on that crank about 2" out of concentric and hope it springs back straight. It took a few heart rending minutes. But as he left it it was within 0.0005. And then he checked it with magnaflux/dye check (forget.) "Now when this crank heats up will this stay the same?" "Dunno - bring it back if you find it is a problem." Easier said than done. Now many miles later I would say it did stay the same. I would say in the future would be best to have someone with experience in Model A engines do the grinding - the crank is considerably more flexible than most modern crank grinder experience. If you go there make sure the flywheel flange is "faced" and perpendicular to the rotational center. Joe K
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11-01-2022, 09:34 AM | #13 |
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Re: New Babbitt Mains - How Tight
Regarding not wanting to go back to the original rebuilder: if I rebuilt it, no matter how far out of warranty it is, I would prefer you to bring it back. Under the circumstances you have outlined, I would be glad to stand behind it.
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11-01-2022, 10:08 AM | #14 |
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Re: New Babbitt Mains - How Tight
Also, make sure that the flange is is centered to the rear main journal.
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11-01-2022, 02:39 PM | #15 |
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Re: New Babbitt Mains - How Tight
As the OP I appreciate all the great advice and commentary from the experts here.
I traced the tightness down to a bit of a kink in the center main where the journal had about 0.0013" run out and was able to correct that to a total of 0.0007" run out. It was still a bit snug at that point due to a high spot on the forward end of the bearing. This was reduced with a modest 10% mixture of extra fine Timersaver in 0-20 weight oil and things are now moving smoothly with the normal level of "sticktion" noted by J & M Machine. All seems well with that part of the assembly although further progress will be delayed because of an injury to my right hand. Here's hoping it doesn't put an end to my Model A hobby. Cheers, all! |
11-02-2022, 04:56 PM | #16 | |
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Re: New Babbitt Mains - How Tight
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Terry |
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