Main bearing clearance

[BruceH]

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.

Like I said, I trust the Ford specs and I know that I don't have the education or experience to deviate from it. It would seem to me that machining a heated block would increase the room temp clearances but it's just an opinion.

You are just restating the obvious about needing clearance. That's the topic of this thread.

 

[Dubstep Shep]

My builder actually mentioned another builder or company that will run coolant through a block and get it to temp before
machining it. Not sure how the clearances work out, but basically you can get them closer to ideal with the block at temp, which makes sense.

You said these clearances tighten up as the system gets hotter. That seems wrong to me. I'm just wondering where you heard that.

 

[BruceH]

My builder actually mentioned another builder or company that will run coolant through a block and get it to temp before
machining it. Not sure how the clearances work out, but basically you can get them closer to ideal with the block at temp, which makes sense.

You said these clearances tighten up as the system gets hotter. That seems wrong to me. I'm just wondering where you heard that.

Metal expands with heat. It contracts with cold.

Are you going anywhere with this?

 

[Dubstep Shep]

Metal expands with heat. It contracts with cold.

Are you going anywhere with this?

Exactly.

So if have a metal circle, the ID, OD, and thickness will all get bigger with temp increase, and smaller with temp decrease.

Think of a clearance as a thickness. If the metals have the same coefficient of thermal expansion, then heating it up will make that clearance larger, not smaller.

 

[BruceH]

Exactly.

So if have a metal circle, the ID, OD, and thickness will all get bigger with temp increase, and smaller with temp decrease.

Think of a clearance as a thickness. If the metals have the same coefficient of thermal expansion, then heating it up will make that clearance larger, not smaller.

You don't have to believe me. This is America where you can believe whatever you want.

 

[Dubstep Shep]

You don't have to believe me. This is America where you can believe whatever you want.

I'm not trying to convince you.

I just don't want people to have bad information.

 

[hamish]

You don't have to believe me. This is America where you can believe whatever you want.

^That was awesome

 

[BruceH]

Like I said, I trust the Ford specs and I know that I don't have the education or experience to deviate from it. It would seem to me that machining a heated block would increase the room temp clearances but it's just an opinion.

You are just restating the obvious about needing clearance. That's the topic of this thread.

I'm not trying to convince you.

I just don't want people to have bad information.

Like I said in my post, it's an opinion. Based in part on conversations I've had with very knowledgeable people. It's possible I misinterpreted the conversations. They had to do with endurance motors and 0w-2 oil.

A quick internet search is showing that clearances increase at operating temp. So you probably have something there.

This is a very good example of why I use factory specs wherever possible. I don't have the knowledge to engineer a motor from scratch. Ford has already crunched the numbers and spent a lot of money and time getting it right.

I would like to know what the differences are between room temp and operating temp. I'd also like to know what is used for an operating temp clearance and how it's determined.

 

[Dubstep Shep]

Like I said in my post, it's an opinion. Based in part on conversations I've had with very knowledgeable people. It's possible I misinterpreted the conversations. They had to do with endurance motors and 0w-2 oil.

A quick internet search is showing that clearances increase at operating temp. So you probably have something there.

This is a very good example of why I use factory specs wherever possible. I don't have the knowledge to engineer a motor from scratch. Ford has already crunched the numbers and spent a lot of money and time getting it right.

I would like to know what the differences are between room temp and operating temp. I'd also like to know what is used for an operating temp clearance and how it's determined.

I can't say I know anything about endurance motors running 0w-2 oil, so I'm out there hahaha.

Using factory specs is almost never a bad idea. I'm not trying to rag on you for doing that, and I'm certainly not saying I'm some sort of expert.

I was also relaying what I was told by someone more experienced than I, but I also know a little something about engineering. Enough to be able to make a little bit of theoretical and mathematical sense of what I was told.

I've actually run into the "temperature vs. clearance" conundrum before as a ME student, which is why I was trying to see where you had heard it from. There are instances where clearances would get tighter with heat, so I wanted to make sure we weren't mixing stuff up.

I'm with you on the temp stuff as well. Anyone ever stuck a thermocouple in a motor before hahahaha?

 

[go302]

Would the main bores and rod bores not expand (smaller OD) along with the main and rod journals on the crank (larger ID) create a tighter clearance?

 

[Dubstep Shep]

Would the main bores and rod bores not expand (smaller OD) along with the main and rod journals on the crank (larger ID) create a tighter clearance?

The bore and journals would expand "outward" by a factor proportional to their size and their coefficient of thermal expansion.

If the materials are identical, the bore would expand more than the journal because it's larger.

 

[lito]

^ Think it is a circle.

(was replying to go302)

 

[Dubstep Shep]

^ Think it is a circle.

(was replying to go302)

Exactly. It all expands outward.

 

[go302]

Hm, gotcha. Well if anyone wants to know anything about biochemistry or the human body get at me lol

 

[BruceH]

Hm, gotcha. Well if anyone wants to know anything about biochemistry or the human body get at me lol

Edited my misguided attempt at humor.

 

[lito]

Now I won't be able to sleep at all. Involved thermal expansion of human holes?

Sent from my Nexus 7 using Tapatalk

 

[Dubstep Shep]

Now I won't be able to sleep at all. Involved thermal expansion of human holes?

Sent from my Nexus 7 using Tapatalk

Heh. Heheh.

 

[sportinawoody]

Now I won't be able to sleep at all. Involved thermal expansion of human holes?

Sent from my Nexus 7 using Tapatalk

now thats some funny shit right there.

thats what bush told me about checking clearances on these aluminum mod motors, he torqued mains with bearings, measured with a bore gauge at 70 degrees, then he installed in his washer and heated block to 200 degrees and immediately measured mains upon removal, on average he said the expansion was .005 from 70 to 200 degrees on aluminum blocks. this was his on test to satisfy his own curiosity back when building teksids became the newest fad how many years ago