Half shelling a whole shell?

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crazy_caseys_customs
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Half shelling a whole shell?

Post by crazy_caseys_customs » Mon May 21, 2018 1:09 pm

Hello,

I hope I’m posting this in the right spot. I’m a bit of a novice engine builder, completely self-taught, but tryin to hold my work to increasingly high standards. I’m putting together my third complete engine build, a mild Ford 289, with a goal of the much-lauded 1hp/cubic inch.

I had the block line-honed but I suspect the number 5 main bearing bore got a little bit large somehow (about 0.0005” larger than 1-4). I’m measuring with snap gauges, and I’m pretty good with them, but I have a Starrett dial bore gage on the way to confirm my suspicions.

Anyway, I’m assembling the motor with Clevite H series bearings. My preliminary math leads me to believe I’m going to “half-shell” with a mix of STD and X (+0.001”) bearings to hit my desired clearance of 0.0025”. I’ve never half-shelled a motor before, but have read a few articles that all agree it’s important to keep your standards and your +/- bearings in the same orientation (makes sense). My question is, if my #5 bore is truly a half thou bigger than the rest, can I half shell 1-4 and run 2 standard size bearings in number 5 to keep the clearance consistent across the board?

Thanks!

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Re: Half shelling a whole shell?

Post by Walter R. Malik » Mon May 21, 2018 1:54 pm

The actual block main bore sizes don't really matter much; as long as they're close.

Whatever it takes to get your final wanted bearing oil clearances is the important thing.
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Re: Half shelling a whole shell?

Post by PackardV8 » Mon May 21, 2018 9:11 pm

You'll never notice that extra half-thou. If your crank is that accurate, all is good.

Ford gives you a fair generous tolerance and the crank grinder and block machinist usually aim for the middle, unless asked to provide otherwise. Worrying about a half-thou on rear main is early days. What does your crank measure against the tolerances?
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Re: Half shelling a whole shell?

Post by modok » Tue May 22, 2018 4:53 am

One main bearing being .00025 off center (out of line)........is not major concern.
They probably are not that straight anyway.
Having an additional .0005 clearance on the #5 may also be favorable. Having all the same is good, but many engines do benefit from having slightly more clearance by the flywheel and/or on the thrust bearing.


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Re: Half shelling a whole shell?

Post by crazy_caseys_customs » Tue May 22, 2018 5:30 pm

PackardV8 wrote:
Mon May 21, 2018 9:11 pm
You'll never notice that extra half-thou. If your crank is that accurate, all is good.

Ford gives you a fair generous tolerance and the crank grinder and block machinist usually aim for the middle, unless asked to provide otherwise. Worrying about a half-thou on rear main is early days. What does your crank measure against the tolerances?
The crank is right in the middle at 2.2485”-2.2488”. It’s still standard and just got a light polish.
modok wrote:
Tue May 22, 2018 4:53 am
One main bearing being .00025 off center (out of line)........is not major concern.
They probably are not that straight anyway.
Having an additional .0005 clearance on the #5 may also be favorable. Having all the same is good, but many engines do benefit from having slightly more clearance by the flywheel and/or on the thrust bearing.


You really can't lose, either way you go.
I’m glad you brought this up, because I’ve always been curious about it. I’ve seen people recommend as much as an additional thousandth on the #5 (or #4 depending on the engine) main. But I wondered if that was only true for engines where the the rear main was also the thrust bearing. On the Ford, the thrust is on #3...

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Re: Half shelling a whole shell?

Post by modok » Tue May 22, 2018 11:27 pm

There are surely exceptions, but it is generally true. Keeping some, or all of the clearances tight can discourage harmonic resonance, but this is usually not a problem by the flywheel, because...well, it has a flywheel on it? LOL.....can't think of the best words......the sheer mass there, and forces of transmitting torsion to and from the flywheel are more dominant (keep it loaded). Sounds close to right. Being loser on the thrust bearing is just a matter of heat. If one main will overheat first, all else equal, it will probably be the thrust bearing.
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Re: Half shelling a whole shell?

Post by Carnut1 » Wed May 23, 2018 12:24 pm

289.jpg
Off topic, just wondering if you will be running stock heads?
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Re: Half shelling a whole shell?

Post by jac mac » Fri May 25, 2018 11:43 pm

I would not be concerned about # 5 main as it only feeds # 8 rod bearing. I would suggest that you run a filtered second pressure line to rear of main oil gallery along with the original from the filter pad or whatever adapter might be there.

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Re: Half shelling a whole shell?

Post by cjperformance » Sat May 26, 2018 2:36 am

jac mac wrote:
Fri May 25, 2018 11:43 pm
I would not be concerned about # 5 main as it only feeds # 8 rod bearing. I would suggest that you run a filtered second pressure line to rear of main oil gallery along with the original from the filter pad or whatever adapter might be there.
On a build like stated id not be concerned about #5 either.
Running a seperate oil feed on a stock sbf block is not as simple as a Cleveland or 385BBF that both have an easily accessible gallery plug at the rear.
The windsor has a gallery just for main feed and does not have any oiling issues to contend with at that hp level. A good oil pan, and some light deburring of accessible gallery junctions and filter pad are more than enough to serve anything you will throw at a factory block. Id use a HV pump on it only if extra oil was being tapped off for a turbo oil feed, even then a small single turbo does not even need that!
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