428 bearing clearances

[happystang]

I'm a little confused as to what bearing clearances are appropriate for an FE. I hear some people going as wide as .003, but after looking in the Ford shop manual, I'm reading numbers between .0008-.0026 to be allowable, and .0010-.0020 ideal for the rods and mains. I *believe* the machine shop had everything between .0015-.0020 which would be considered ideal per the shop manual.

However, many people are telling me that this is waaaay too tight? I'm running a precision oil pumps high volume pump with 10w30 oil, hot idle oil pressure @ 800 RPM is around 20 psi, cruising @ 2700 RPM gets me around 64 psi. I've got around 80-90 miles on the motor so far and it seems to be running great.

http://www.mustangtek.com/Library6/PDF/Vol-68-S1-L2_p1.pdf

[blykins]

Just like almost everything else, there's more than one way to skin a cat.  Lots of guys do things differently and arrive at the same destination, so you'll get a lot of different answers. 

With that being said, I think that Ford shop manual says "allowable" because it's showing what would happen if you hit the opposite ends of tolerances all at once......for instance, the high side of a journal spec versus the low side of a housing bore spec.  I don't think "allowable" is anywhere near what you should be shooting for and I don't think an engine would live at .0006" of oil clearance, nor would I call .0010" *ideal*...

Now, there are always different ways of doing things based on the parts used:  full groove bearings versus 3/4 groove bearings, BBC rod journals versus FE journals, coated bearings versus non-coated, street versus drag race, etc, etc.  However, what has always worked for me is to do what most bearing manufacturers recommend:  .001" of clearance per inch of journal and some extra for racy type stuff.  An FE main journal is 2.750", so I try to hit .0025-.003".  An FE rod journal is 2.438", so I'm usually .0025-.003" there too.  BBC rod journals are 2.200", so I'm generally at the low end of the 2's to a .0025".  If it's extra horsepower or extra rpm or both, I'll usually be inclined to add a little more clearance. 

Following that rule of thumb has always served me well and I can show you pictures of bearings on tear down that reflect it.  To me, if the oil pressure gauge is happy and the bearings look new on teardown, you can't do much better. 

[blykins]

Haven't done a freshen-up on an FE recently, just all new builds.  However, here's the bearings on a 620 hp 354ci Cleveland that turned 8500.  You can still see my mic tracks on both pictures.  A Cleveland has the same main size as an FE.  This Cleveland used a SBC rod journal, which is a 2.100" journal. 

[Ranch]

Was your block aligned honed and crank checked for straightness, are the rods checked for roundness and straight?  Any thing running off the center line takes up that clearance.  And it all depends what your intended use is.  Everyday cruise and an occasional foot to the floor and .0015-.002 I see no problem providing everything is straight. Now if you're running 500 miles flat out you might want bigger clearances to help cool those bearings.    10w 30 high zinc like a Brad Penn you should be fine.  Your Oil Pressure sounds about normal  about the same as mine and I'm running .002 clearances....JMO

[Barry_R]

Lykins is correct for both clearances and for noting that the "preliminary manual" is not showing good data.  When at F-M I asked about similar documents they produced, and was told that the numbers published were arithmetical possibilities with parts that meet individual specification tolerances, and not recommended clearances for assembly.  Even back in the proverbial "day" the various components were mostly in the center of a specified range, and clearances in the potential extremes for multiple parts combined were very unlikely.

Build an FE with bearing clearances at .0008 and you will have problems....

[happystang]

Thank you all for the responses. I know the rods were checked, but the block wasn't align honed.

I guess my next question is whether I'm safe running the motor with these clearances? Mains are .20 under and the rods .040 under.

[Barry_R]

If you have .002 and the crank spins smoothly I would run it in a mild street deal.
This is assuming (dangerous) that the shop was using accurate measurement tools and not plastiguage...

[jayb]

Ha!  I have to laugh at the plastigage comment Barry, I found out first hand a couple weeks ago that plastigage is not reliable.  I just did a 428 for a friend of mine who said his plastigage measurements were .002 to .0025 on the rods.  I found the rod clearances  from .0008" to .0014" using good instruments.  The mains were almost as bad.  Basically the shop that ground the crank went 9/9 under instead of 10/10. 

He had it all together and was ready to run it, but it was clicking or ticking inside when he turned it by hand.  He handed it over to me because he is not an experienced engine builder, and decided it had better be checked.  The ticking sound turned out to be the rod nuts hitting the windage tray, which was some Chinese piece that had the louvers punched backwards, so that they were sticking up towards the crank instead of away from it.  The rod nuts were dinging on the raised louvers.  Good thing though, because if not for that he would have run it and knocked the bearings out of that engine in no time...

[RustyCrankshaft]

Ha!  I have to laugh at the plastigage comment Barry, I found out first hand a couple weeks ago that plastigage is not reliable. 

A few years ago we had some issues with Cummins M11's that all had low oil pressure. It's a long story with a lot of politics and corporate coverups, but the short version is a bunch of Cummins reps and engineers showed up to inspect these things. After hours of arguing I threw a set of main bearings in an empty block and mic'd that and a new crank and came up with about .010-.011 of clearance on the mains. The Cummins guys said we don't tell people to measure that way in the manual, we use plastigauge. Which showed about .035 when they checked using the "approved" method. Basically they squished some playdough in there and said your mic is invalid....but........have a nice day!

And that's even without the Chinese part problems you ran into on the 428!

[My427stang]

I grew up with Plastigauge and never saw a problem, but also don't know if there were any close calls., because you don't know what you don't measure.  Later in life, weaning myself off it,  I had a run where I would measure then check with Plastigauge and saw that it is so inconsistent, that all it did was add worry.  Sometimes so hard it would push into the bearing, sometimes squished so wide it was in error the opposite way.  I just don't trust it for anything but a worst case scenario, maybe stuck far away from my tools and someone needs some help troubleshooting a crank that wont turn or something like that.

That being said, in a street FE, measured correctly, I have no issue at all with .002.  Assuming the crank is straight and no taper, I'd even run .0015 in that situation as a bottom end (although that would be a very unique situation and mild build).   The issue is, I don't see that scenario exist much anymore.  Cranks are usually good when ground, but blocks are all over the place, especially with main saddle taper.

In fact, the last 3 I did, we just bit the bullet in block prep: touch the mains, square the decks, and torque plate hone. Then things are straight, additionally, it allows you to be on the tighter side of bearing crush specs which makes me feel a little better too

With all that said, I sure wouldn't take a good running .0015-.002 engine apart without a reason, and with the oil weight you are running, oil pressure looks pretty good to me, if it behaves nice, they probably hit the numbers closer to .002

[Falcon67]

I used plastigage on my first engine build, but as a mechanical inspector I knew it was just a whiz and could not be especially accurate.  Eventually I acquired all the tools to do accurate measurements.  I do have some import precision tools but I also keep a tool room grade set of Jo blocks to check calibrations before work. 

I have a 351C crank that needs another .001 taken off - Most places shy away from trying to take that little off.  Too bad nobody makes 351C rod/main bearings that are .001 over in the standard turn down sizes.  Even the stock diameter .001 over items are discontinued.  Need hone-able rod bearings LOL.

[happystang]

I just called the machine shop to confirm the sizes, they said .0015 on the mains and .0020 on the rods. The motor has Clevite 77 bearings in it. If there was an issue, would I have experienced some kind of oil pressure issue by now? Should I switch from 10w30 to a thinner oil?

[cjshaker]

I wouldn't go any thinner on oil if it were my engine, and oil pressure doesn't always show up as an issue if there is bad bearing wear. I've seen more than one engine that had good pressure, even with a couple of wiped out bearings.

This is all just my opinion, so take it for what it's worth. That's definitely on the low side on the mains, but if you don't have a heavy foot, or it's just a mild street cruiser, and the journals are true and not tapered, you'll likely be ok. What you can do is cut your filter open and see if there are any signs of metal or bearing material in it. I'd do that before I tore it completely down for a re-do, IF it was a street cruiser. And I'd do that now instead of waiting for the first scheduled oil change. If there are any signs of foreign particles in the filter, then I wouldn't waste any time in doing the tear down, before real damage occurs. Once you have a few oil changes and filter checks under your belt, you'll get a real feel for how the engine is doing internally, and that could/will give you some piece of mind, provided they look ok.

Now if you have a heavy foot, or like to play around a lot, I wouldn't be comfortable with .0015. If you do like to play and run it hard, and the clearances are true to what the machine shop says, a simple change to .001 under bearings would take care of the issue quickly, provided you can get them.

BUT, the real issue is, in my opinion, you're strictly going by what the machine shop is telling you. They said they are at .0015, but it's very tough to hit that measurement exactly, on every bearing. Even good shops can vary by 2-3 tenths of a thousandths. Mediocre shops can vary much more than that. So when they say .0015, I have to question if that is the "average" that they were shooting for, with a variance of up to .0005, which is NOT uncommon in mediocre shops. That's why a good shop should give you a sheet with the specific clearance measurements for each journal, main and rods. I've seen some shops, and personally experienced it, where the clearances varied by as much as .0015, and in my opinion, those people have no business doing engine work.

[blykins]

I wouldn't go any thinner on oil if it were my engine, and oil pressure doesn't always show up as an issue if there is bad bearing wear. I've seen more than one engine that had good pressure, even with a couple of wiped out bearings.

This is all just my opinion, so take it for what it's worth. That's definitely on the low side on the mains, but if you don't have a heavy foot, or it's just a mild street cruiser, and the journals are true and not tapered, you'll likely be ok. What you can do is cut your filter open and see if there are any signs of metal or bearing material in it. I'd do that before I tore it completely down for a re-do, IF it was a street cruiser. And I'd do that now instead of waiting for the first scheduled oil change. If there are any signs of foreign particles in the filter, then I wouldn't waste any time in doing the tear down, before real damage occurs. Once you have a few oil changes and filter checks under your belt, you'll get a real feel for how the engine is doing internally, and that could/will give you some piece of mind, provided they look ok.

Now if you have a heavy foot, or like to play around a lot, I wouldn't be comfortable with .0015. If you do like to play and run it hard, and the clearances are true to what the machine shop says, a simple change to .001 under bearings would take care of the issue quickly, provided you can get them.

BUT, the real issue is, in my opinion, you're strictly going by what the machine shop is telling you. They said they are at .0015, but it's very tough to hit that measurement exactly, on every bearing. Even good shops can vary by 2-3 tenths of a thousandths. Mediocre shops can vary much more than that. So when they say .0015, I have to question if that is the "average" that they were shooting for, with a variance of up to .0005, which is NOT uncommon in mediocre shops. That's why a good shop should give you a sheet with the specific clearance measurements for each journal, main and rods. I've seen some shops, and personally experienced it, where the clearances varied by as much as .0015, and in my opinion, those people have no business doing engine work.

That is all very true.

You have to think about how small a .0001" is, but it all can stack up against you if you're varying a tenth or two here, a tenth or two there, etc. 

I spend a long time getting bearing clearances right because I'm anal about it.  It's easy when it's all standard and common and there are standard bearings available, .001" under, .001" over, etc., but when you get to the .010", .020", and .030" undersizes, there's just not that much available. 

When I have access to a lot of different bearings, I'll mix and match sizes, dress the backs of the bearings, and have even been known to use a couple different brands in one engine, but things will still vary by a couple tenths.  I will also measure the crank in two different spots 90° to each other to see if there's any diameter swing and will grab a quick measurement across the journal's width to see if there's any taper.

If someone says they're at .0015" main bearing clearance, then the tolerance swing could potentially put you at .001".......or .002". 

Personally, I think Doug has a good idea.  It's easy to cut a filter apart and see what's going on.   If it's looking good, then you can carry on and drive it like you've been driving it. 

[CaptCobrajet]

Just a quick note to add.  ".001" bearings will tighten clearance.  It takes ".001X" to add clearance.  Sometimes this can be confused and could send you the wrong direction.....