What Is Your Main Bearing Clearance???

[AutoXRacer]

So I posted this question in my build thread, but didn't get many replies probably due to the subject title.

This is the situation:

My local engine builder is assembling the short block. He ordered the same Speed Pro 149M main bearings as was installed originally. When he checked the clearances, he says they were too tight. Not sure what that clearance was.

So he is putting in +0.001" extra clearance bearings to achieve 0.0025"-0.0028".

Ford Specs for the 4.6L main bearing clearances are:
0.0019"-0.0009" (GT500 5.4L: 0.001891"-0.0009")

My JDM build sheet speced them to:
0.0022"-0.0021"

My local builder is aiming for:
0.0025"-0.0028"

What is this going to do to the motor overall?
Why is he trying to go with so much clearance?

My local builder is not using the Ford specs. He is using some formula to calculate clearances.

What advantages/disadvantages are there running a larger clearance?

He keeps saying its the formula that dictates clearances plus adding in performance application factors.

He had me order two sets of bearings...
Clevite MS2259H (std) and MS2259HX (+0.001" extra clearance)

This is so frustrating. I know my builder knows his stuff, but I just hate it when things stray so much from OEM... Plus you have all these opinions.

I would have felt every comfortable with a final clearance of 0.0021"-0.0022". I'm just uneasy with the 0.0025"-0.0028" range.

So what is your motor clearanced to?
How many miles?
Do you race your motor/car?
Hows it running?
What oil do you run?

 

[hamish]

Mine is .0025
Mine was built in your neck of the woods.
Who is your builder?

 

[19COBRA93]

On my 5.4L, I set it up at .0020, and I thought that was pretty loose. The only thing I can think of is they have primarily built pushrod motors, like 460's and a lot of Chevy motors. They run loose tolerances like that. So that's what they're comfortable with.

The first machine shop I used years ago had never touched a modular, and wanted to go outside of Ford spec, because they felt it was too tight. I personally like staying within Ford spec on most things, so I didn't use them.

While that's pretty loose, I don't think it will cause any harm. I just think it may change your oil pressure a bit, and they may recommend a thicker oil (which with VCT isn't a good idea).

Maybe get a second opinion? JDM, MMR (Yeah I said it), or any other well known shop who builds modulars.

 

[BruceH]

My current motor is either .0014" or .0016". Can't remember which is the rod and which is the main measurement. I asked the machine shop to target .0015" and supplied them with oversize/undersize .001" bearings because the crank was going to need a heavy polish.

Like we discussed earlier imo you should also have them make the rod clearance bigger and go with the larger end of the scale for side rod clearance so that when you use a higher viscosity oil it won't affect the other parts of your motor.

Something most don't think about is the cam journals. Clearance on them is speced to be from .001-.003" iirc. You could see where you are right now since you have the heads and cams. I have some plasitgauge if you need it.

You could also tell the shop to keep the clearances in spec. I had to do that with my first mod motor build. They didn't want to put the pistons at .002" and they didn't like the stock bearing clearances but respected my wishes when I reaffirmed what I wanted. You are the customer and have final say. There are plenty of examples with stock clearances that are doing just fine after many years of abuse.

 

[Dubstep Shep]

My builder did the same thing and advised me to run 5W-30. In his words, that allows the bearings to have a thicker oil sheet to ride on, which is necessary for hotter engines like those with superchargers.

 

[BruceH]

I thought you put a stock longblock into your car? No? Who is your builder?

My builder did the same thing and advised me to run 5W-30. In his words, that allows the bearings to have a thicker oil sheet to ride on, which is necessary for hotter engines like those with superchargers.

 

[Dubstep Shep]

I thought you put a stock longblock into your car? No? Who is your builder?

Lol no.

Mike Henson of Henson racing engines. He's done a lot of the engines in the cars on Street Outlaws.

 

[AutoXRacer]

Mine is .0025
Mine was built in your neck of the woods.
Who is your builder?

My short block is being built by C&D Engines in Kirkland. They were highly recommended by various shops, including Brads Custom Auto. According to Brad's C&D builds all their engines. At least thats what they told me.

While that's pretty loose, I don't think it will cause any harm. I just think it may change your oil pressure a bit, and they may recommend a thicker oil (which with VCT isn't a good idea).

Maybe get a second opinion? JDM, MMR (Yeah I said it), or any other well known shop who builds modulars.

VCT will totally be disabled and removed; phasers locked and solenoids removed.
I did speak with JDM, they recommend no more than 0.0022". But said that 0.0025" should not be exceeded; that it should be OK.

Something most don't think about is the cam journals. Clearance on them is speced to be from .001-.003" iirc. You could see where you are right now since you have the heads and cams. I have some plasitgauge if you need it.

You could also tell the shop to keep the clearances in spec. I had to do that with my first mod motor build. They didn't want to put the pistons at .002" and they didn't like the stock bearing clearances but respected my wishes when I reaffirmed what I wanted. You are the customer and have final say. There are plenty of examples with stock clearances that are doing just fine after many years of abuse.

I don't have the heads and cams. I dropped them off at the builders so they can mill the heads and verify clearances.

I will talk to C&D when I drop off the bearings on Monday afternoon. Thanks for the advice Bruce.

My builder did the same thing and advised me to run 5W-30. In his words, that allows the bearings to have a thicker oil sheet to ride on, which is necessary for hotter engines like those with superchargers.

So your builder set your main clearances to 0.0025"-0.0028"?
How many miles on your motor? Power? Use?

 

[Dubstep Shep]

So your builder set your main clearances to 0.0025"-0.0028"?
How many miles on your motor? Power? Use?

Close to that, yes.

Currently about 2000 miles. Making I would guess about 500 at the wheels. He said I could run as much boost as I wanted before lifting the heads and the engine would take it. Over a grand if desired. Use is daily driving and mild track use.

 

[Paps]

Sub'ed
...so you all have a builder there. Guess i'll be my own, i don't trust people here in tahiti. I'm even sure that there is no one that can do that. Going with plastigauge and fingers crossed.

+0.001 extra clearance refers to grade 2?

 

[niner555]

I built my engine with .0017-.0020 in. on the mains and .0023-.0025 in. on the rods and have right at 30psi of idle oil pressure (750rpm) with 5W-30 oil. I would be a little concerned with running .025"-.028" on the mains, unless you plan on running some thicker oil. Even high HP mod motors seem to be happy with Ford OEM bearing clearances, I wonder why your builder sees the need to deviate from them?

 

[Dubstep Shep]

I built my engine with .0017-.0020 in. on the mains and .0023-.0025 in. on the rods and have right at 30psi of idle oil pressure (750rpm) with 5W-30 oil. I would be a little concerned with running .025"-.028" on the mains, unless you plan on running some thicker oil. Even high HP mod motors seem to be happy with Ford OEM bearing clearances, I wonder why your builder sees the need to deviate from them?

For him it had a lot to do with the street/track aspect of the motor. Tighter clearances are better for racing motors as they're rebuilt more often and aren't used for as long as a street:track motor would. He wanted to make sure I had a nice thick curtain of oil to ride on so the engine would last longer.

Honestly I think a lot of it comes down to preference. That's what's worked best for my builder in the 20 years he's been doing this, I'm sure other things have worked for other people.

 

[BruceH]

No. The guide to Ford bearing size is in the assembly manual. It's a very minor amount between grades. The factory uses them to get repeatable clearances no matter what the slight variations are in the crank and motor.

Here's the assembly manual. The bearing guide is in the first part of assembly.

http://iihs.net/fsm/?dir=158

Sub'ed
...so you all have a builder there. Guess i'll be my own, i don't trust people here in tahiti. I'm even sure that there is no one that can do that. Going with plastigauge and fingers crossed.

+0.001 extra clearance refers to grade 2?

 

[sportinawoody]

allows the bearings to have a thicker oil sheet to ride on, which is necessary for hotter engines like those with superchargers.

not necessary if you run the joe gibbs oil or any good oil with the correct amount of zinc and phosphorus.

 

[Dubstep Shep]

not necessary if you run the joe gibbs oil or any good oil with the correct amount of zinc and phosphorus.

The larger clearances went hand in hand with a heavier, full synthetic oil with zinc and phosphorous like Joe Gibbs. In fact my builder runs Joe Gibbs in his drag car.

 

[o2sys]

JDM built:

.0021~ .0024

 

[sportinawoody]

The larger clearances went hand in hand with a heavier, full synthetic oil with zinc and phosphorous like Joe Gibbs. In fact my builder runs Joe Gibbs in his drag car.

I guess it's a matter of preference as long as vct is being locked out. Very good info in this thread.

 

[hamish]

^Nope

 

[sportinawoody]

^Nope

I was referring to clearances vs. oil weight because OP's ? was about clearances on the mains, initially

 

[Redrocket06]

My builder builds more old pushrod and lsx motors than anything else, my motor was his 3rd 3v shortblock to build. He set mine right at .002, I told him I wanted to run ~18psi at some point during the motors life, and he recomended 10w30 and no thicker than 10w40 pending on operating temps. The motor itself has been solid and I have no complaints over it after 20,000 miles. It has seen 14psi noncooled and now 11psi with a2a.