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Old 08-12-2015, 12:46 PM   #1
oliverguy
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Default hand scraped main bearings

If one wanted a winter project, would it be possible to hand scrape the main bearings in a model A engine? The line bore set up is pretty expensive and I can't afford to have a shop do it. I'd like to try my hand at pouring bearings.
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Old 08-12-2015, 12:54 PM   #2
Kevin in NJ
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Default Re: hand scraped main bearings

In a word, No.

Scrapping the bearings is done after a line bore has been done. You scrape bearings to get a final fit. You can not scrap bearings and hope to have them inline.

Without a lot of specialized tools and knowledge you will not be successful in pouring reliable bearings.
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Old 08-12-2015, 12:56 PM   #3
glenn in camino
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Default Re: hand scraped main bearings

Scrape away, but keep checking clearances with plasti-gauge
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Old 08-12-2015, 03:18 PM   #4
BILL WILLIAMSON
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Default Re: hand scraped main bearings

Think of it like this: If you wanted 2 very beautiful, graceful, ornate, turned wood POSTS, for your porch, would you carve them with a HATCHET, DRAW KNIFE, & FINISH THEM WITH YOUR POCKET KNIFE, or would you commission a FINE woodworker, to TURN them on his LATHE?--BUT, if you're BROKE, I understand. I'm still waitin' for my SHIP to COME IN!
Bill W.
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Old 08-12-2015, 03:24 PM   #5
George Miller
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Default Re: hand scraped main bearings

All three mains have to be in line, the right dia. and the right distance from the cam gear. Parallel to the top of the block and pan rails. And parallel to the center of all 4 cylinders. Answer no for most people. If you were some one that used to scrap machine ways maybe. But would take a lot longer than boring them. Take it to some one that has done a lot of A engines.

Last edited by George Miller; 08-12-2015 at 04:16 PM.
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Old 08-12-2015, 08:35 PM   #6
Kevin in NJ
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Default Re: hand scraped main bearings

Let me throw some more details.

You would need to have a bar placed in the exact correct position so the crank gear will mesh with the cam gear. The bar's diameter would have to be just undersized enough to account for the peening process that must happen after you pour the babbitt. The babbitt shrinks and must be beat back into the saddles in the block.

You would also have to figure out how to pour the caps.

The you need to make a tool to set the rear flange to place the crank in the proper spot fore/aft and have the proper clearance.

You can then scrap to fit.

Sound like something you can do?

Keep in mind you have to buy a lot of the correct babbitt as you need to have way more in the pot ready to go then you need. As it sits in the pot the metals oxyidize change the ratios making the babbitt change its properties. You combat this by having much more babbitt then you need.

Clearly I have left out A LOT of details.
Sorry it is not easy or cheap to pour your own babbitt. It is way cheaper to pay someone to do it right. Unless you want to go into business.
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Old 08-12-2015, 08:49 PM   #7
oliverguy
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Default Re: hand scraped main bearings

Ok thanks for your input. I just wanted to see if I could do it. The mold is like $100, the pot is $40 and the scraper is cheap. I was wondering why I couldn't use the crankshaft as the shaft with bluing on it to know here the high spots are.

I'm looking for an engine for a smith air compressor project. A professionally done engine is like $3k and the compressor set up is only worth $1500 on a good day. I can't find a running engine at all they all need bearing or machine work or are cracked. I'm a young guy on a budget. People wonder why there are no young people in this hobby.

I may just sell the compressor parts and forget the whole thing.
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Old 08-12-2015, 08:58 PM   #8
oliverguy
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Default Re: hand scraped main bearings

i probably should just spend $1500 on a loser air compressor to do my sandblasting.
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Old 08-13-2015, 02:45 AM   #9
Tom Wesenberg
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Default Re: hand scraped main bearings

You could have someone do just the mains, and do the rest of the engine yourself.
I've found running engines as cheap as $125 when they are removed for a hotrod project.
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Old 08-13-2015, 06:12 AM   #10
Kevin in NJ
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Default Re: hand scraped main bearings

Quite frankly, having been around the hobby since 1970, it has never been cheap to do a car right. I would guess it has just kept pace with inflation.

You do not need perfect bearings for a smiths conversion. It generates 40psi just above idle with enough flow to run a fairly large end coming out of a pressure pot. We have one based on a worn out B block with 'select' parts. Babbitt with cracks is likely ok as it does not come apart quick, that is one of the nice things about babbitt, it fails over a long time.

You will need a large coil of hose in water and a good way to separate a high flow of air from the water. You can go into a large tank and just keep the valve at the bottom cracked open to constantly drain the water.
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