Main bearing clearance

[sportinawoody]

I've looked the shop manual over and over and don't see the main bearing clearance. Maybe looking to hard but I see inside journal, taper, inside bore journal, etc,,, but no allowable clearance. Makes it hard to set my clearances with no reference. Please be gentle, I did search and came up with 1000 of useless threads not pertaining.

 

[niner555]

OEM spec on the mains is .025-.050mm (.0010-.0020 in.), rod journals are .027-.069mm (.0011-.0027 in.)

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.

 

[Dubstep Shep]

My clearances are at the loose end of the spec. My builder recommended that for a supercharged engine along with a heavier oil.

Pretty much what he told me is that more space in between the bearing and so forth means more oil film in there. Combined with a heavier oil, it keeps the bearings and races much cooler and better lubed.

 

[niner555]

^^^
This!

 

[RED09GT]

My clearances are at the loose end of the spec. My builder recommended that for a supercharged engine along with a heavier oil.

Pretty much what he told me is that more space in between the bearing and so forth means more oil film in there. Combined with a heavier oil, it keeps the bearings and races much cooler and better lubed.

I got this from the SHM book so take it for what it's worth but it would explain why ford sets the bearing clearances so tight for the aluminum mod motors:

"The aluminum-block main bearing bore grows 0.002 in vertically at 200 degrees, so we have to set the cold bearing clearance tight in order to achieve the correct hot-running clearance"

I've ran across this bit of information somewhere before and this is likely why the consensus is to only go with builders that have real mod motor experience or to do your own research and give the intended specs to the machine shop before starting.
It's bits and pieces like this that make a normally competent engine builder fail with mod motors.

 

[Dubstep Shep]

So that quote is saying the main bore grows vertically when it heats up? Makes sense. Aluminum has a pretty high coefficient of thermal expansion. The mains would prevent the block from expanding horizontally a whole lot, as they wouldn't expand as quickly as the aluminum. Same with the crankshaft and bearings.

Steel has about half the thermal expansion rate as aluminum, so if the block moves up 0.002" vertically, then the crank and bearings are expanding about that much because they expand half as faster, but the bearing bore is only half the length. The mains would likely expand vertically about 0.001" as well. So really the clearance you set would increase about 0.001" overall.

Those figures are just approximations though. Who knows what it all actually is. I would certainly like to know how SHM measured the vertical expansion of the main bores.

The guy that did my motor has done more than his fair share of mod motors though. He's quite experienced with the aluminum blocks and the 3V in particular. Doesn't hurt he's been working on them basically since they came out. I trust his determinations.

 

[sportinawoody]

I would certainly like to know how SHM measured the vertical expansion of the main bores.

I've been told by my machinist he actually torqued the bearings in the mains and run it thru a parts washer until the block gets 200 and run a bore gauge thru before and immediately upon removal. Not my block but a " test unit " he has. I learned this today as I couldn't call him last night when I was setting up my bearings to find clearances. but his conclusion on tolerances were spot on with what you guys have presented for the aluminum mod's mains. he obviously has a great deal of knowledge with these also as he has shared some secrets of the mod motors just as free advice

 

[Dubstep Shep]

I've been told by my machinist he actually torqued the bearings in the mains and run it thru a parts washer until the block gets 200 and run a bore gauge thru before and immediately upon removal. Not my block but a " test unit " he has. I learned this today as I couldn't call him last night when I was setting up my bearings to find clearances. but his conclusion on tolerances were spot on with what you guys have presented for the aluminum mod's mains.

Interesting.

Where's the 200 degrees figure coming from?

 

[sportinawoody]

average operating temp i guess. what does oil temps average ?

 

[s8v4o]

Interesting.

Where's the 200 degrees figure coming from?

Because that's close to operating temperature.

 

[Dubstep Shep]

Because that's close to operating temperature.

By operating temperature, I'm guessing you mean the operating temperature of the coolant, right?

 

[go302]

My main and rod clearances are at 0.0025 and I will be running 10w40 if that helps.

This is with coated clevite race bearings btw.

 

[s8v4o]

By operating temperature, I'm guessing you mean the operating temperature of the coolant, right?

Yeah coolant. I'm assuming it's to get the most accurate measuring of clearances.

average operating temp i guess. what does oil temps average ?

Typically between 230 and 260 degrees is ideal.

http://www.hotrod.com/feature_stories/1310_engine_oil_temperature/

 

[Dubstep Shep]

Yeah coolant. I'm assuming it's to get the most accurate measuring of clearances.

I'm not sure the block at that location is the same temp as the coolant. Seems like that might be a ballpark approximation, but I seriously doubt it's exact.

http://www.hotrod.com/feature_stories/1310_engine_oil_temperature/[/URL]

If the oil temp is 230 to 260, then I doubt the block is any cooler than that seeing is it's the primary heater of the oil.

 

[BruceH]

http://iihs.net/fsm/?dir=158&viewfile=SPECIFICATIONS.pdf

Factory specs^^^^^.

I've always had my motors set up for stock clearance. Always run 5w-20 too. Never had an issue. I'm a believer in Ford's engineering. Mod motors last for a long time with the tight clearances even when boosted.

The GT500 specs are a little tighter than the 3v and it is known for not having issues unless the power is taken above what the rods will handle. The only spun bearings I can recall reading about in a mod motor occurred in rebuilt motors or in motors running thicker oil.

GT500 specs: http://iihs.net/fsm/?dir=168&viewfile=SPECIFICATIONS.pdf

 

[Dubstep Shep]

The GT500 had a cast iron block though, which has a similar thermal expansion rate to steel and this the crankshaft and bearings.

So I would think the GT500 block doesn't expand anywhere near as much as the 3V aluminum block. It actually should have almost identical clearances at room and operating temperature.

It also is a completely different motor, albeit similar to the 3V.

 

[BruceH]

The GT500 had a cast iron block though, which has a similar thermal expansion rate to steel and this the crankshaft and bearings.

So I would think the GT500 block doesn't expand anywhere near as much as the 3V aluminum block. It actually should have almost identical clearances at room and operating temperature.

It also is a completely different motor, albeit similar to the 3V.

FWIW the main bore housings are magnetic. Not sure if they are made of iron or steel but they are ferrous. This is with an aluminum block. The newer GT500 blocks are made of aluminum btw.

Cranks have been made from nodular iron and steel. The clearance specs are at room temperature. The clearances get tighter when at operating temp. This is accounted for in the factory specs. Believe it or not they think of things like this. Many people are of the opinion that the factory has no idea what they are doing. I am of the opinion that they do know what they are doing and that they have good reasons for it.

The point is that Ford uses tight clearances in the mod motors and is very successful with them. The newer GT500 blocks are made of aluminum btw.

 

[Dubstep Shep]

FWIW the main bore housings are magnetic. Not sure if they are made of iron or steel but they are ferrous. This is with an aluminum block. The newer GT500 blocks are made of aluminum btw.

Cranks have been made from nodular iron and steel. The clearance specs are at room temperature. The clearances get tighter when at operating temp. This is accounted for in the factory specs. Believe it or not they think of things like this. Many people are of the opinion that the factory has no idea what they are doing. I am of the opinion that they do know what they are doing and that they have good reasons for it.

The point is that Ford uses tight clearances in the mod motors and is very successful with them. The newer GT500 blocks are made of aluminum btw.

Are the newer GT500 blocks made of aluminum? I'm not quite sure I read that correctly... Twice.

Lol just kidding.

So let me double check this to make sure I'm reading this right.

All the motors have main bore housings, on both the top and bottom of the crankshaft, that are magnetic, regardless of whether the block is aluminum or cast iron?

The reason I brought up the cast iron is that the link you posted is to a GT500 with a cast iron block. I'm not sure when they switched to an aluminum block, or if when they did they changed anything else.

Don't get me wrong, I think the amount and quality of engineering that goes into these cars is phenomenal, but these are production line vehicles. Your design is limited by what you can actually make and what it will cost to do it. It's a whole different game than hand built racing engines. If Ford, or any mass manufacturer can make a part more cheaply at the expense of quality and they no it won't effect their warranty, they're going to do it almost every time. But I digress.

Also, I'm not following on the whole "clearances get tighter at operating temperature" deal. How's that work?

 

[BruceH]

The aluminum GT500 block uses the same main clearance as a 3v. .0009-.0019".

http://iihs.net/fsm/?dir=831&viewfile=SPECIFICATIONS.pdf

It is my opinion that Ford uses higher quality components than some other manufacturers. It is also my opinion that tighter clearances are a result of having very precise machining equipment that can hold the tolerances.

This thread is about peoples experiences with bearing clearance. I gave mine and my reasoning. Ford specs have worked very well for me with a variety of blocks. I've never built a race motor and wouldn't want one in a street car.

 

[Dubstep Shep]

The aluminum GT500 block uses the same main clearance as a 3v. .0009-.0019".

http://iihs.net/fsm/?dir=831&viewfile=SPECIFICATIONS.pdf

It is my opinion that Ford uses higher quality components than some other manufacturers. It is also my opinion that tighter clearances are a result of having very precise machining equipment that can hold the tolerances.

This thread is about peoples experiences with bearing clearance. I gave mine and my reasoning. Ford specs have worked very well for me with a variety of blocks. I've never built a race motor and wouldn't want one in a street car.

Lol wait, I'm still curious about the mains and temp v. Clearance deal.

So the aluminum GT500 block uses the same clearances as the aluminum 4.6L 3V? But the cast iron used a tighter clearance?

Being able to hold the tolerance is one thing, and that's definitely important, but even if you could machine those parts to a tolerance we can't possibly imagine, you would still need some level of clearance.

A similar situation that comes to mind is backlash in a ring and pinion. The gears have to have some "play" to them, otherwise they heat up way too quickly from all the friction and fail. Conversely, if they're too far apart, the momentum of the gear before it contacts the other gear can cause a tooth to snap.