rod bearing clearances, need help!
Oct 10, 2017, 08:23 PM
#16
Evolved Member
i need advice on rod bearing oil clearance, i have a stock 4g63 crank which spun a bearing.
now after polishing it and with new standard size ACL bearings the clearence is .003
is this fine or should it be tighter? can i run the car like this or do i need to cut the crank and get oversize bearings.
i really hope i can get away with this clearence, what do you guys think?
now after polishing it and with new standard size ACL bearings the clearence is .003
is this fine or should it be tighter? can i run the car like this or do i need to cut the crank and get oversize bearings.
i really hope i can get away with this clearence, what do you guys think?
If it's 9000 rpm and 800hp then that's proper clearance rods and mains with heavy oil.
I have seen this is a bad question to ask on these forums because every Jambroni and his brother chime in telling you it's wrong without asking or knowing what your actually building.
Stock crank actually needs more clearance than a billet, this is because of flexing under high loads. Heck some guys are running .004" on the mains with a stock crank just to get it to live.
Fact is if the car is going to be over 600hp and your using 20w-50 that's better at .003" than .002" rods and mains.
Oct 10, 2017, 08:35 PM
#17
Evolved Member
Please don't get mad, just come to the realization that you don't know what your talking about. Do you have any idea what a BR shortblock runs for clearance?
Rule of thumb....on high horsepower builds go loose not tight my friends.
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bullet206 (Apr 28, 2020)
Oct 11, 2017, 03:28 AM
#18
Account Disabled
Once you spin a bearing, you always damage the crank.
If you take the crank to a machine shop they'll measure it with a micrometer and tell you it's out of spec.
You'd get it reground to 0.25mm UNDERSIZE and fit new bearings.
You'll end up with about 0.0025 inch clearance.
While you're at it they'll also measure the conrod and tell you that it's now out of round as well and it's easier to replace it than re size it.
If you take the crank to a machine shop they'll measure it with a micrometer and tell you it's out of spec.
You'd get it reground to 0.25mm UNDERSIZE and fit new bearings.
You'll end up with about 0.0025 inch clearance.
While you're at it they'll also measure the conrod and tell you that it's now out of round as well and it's easier to replace it than re size it.
Oct 11, 2017, 05:45 AM
#19
Evolved Member
Once you spin a bearing, you always damage the crank.
If you take the crank to a machine shop they'll measure it with a micrometer and tell you it's out of spec.
You'd get it reground to 0.25mm UNDERSIZE and fit new bearings.
You'll end up with about 0.0025 inch clearance.
While you're at it they'll also measure the conrod and tell you that it's now out of round as well and it's easier to replace it than re size it.
If you take the crank to a machine shop they'll measure it with a micrometer and tell you it's out of spec.
You'd get it reground to 0.25mm UNDERSIZE and fit new bearings.
You'll end up with about 0.0025 inch clearance.
While you're at it they'll also measure the conrod and tell you that it's now out of round as well and it's easier to replace it than re size it.
Last edited by 2winscroll; Oct 11, 2017 at 05:58 AM.
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ronaldo9 (Oct 11, 2017)
Oct 11, 2017, 09:22 AM
#20
EvoM Guru
iTrader: (1)
Bearing clearance, like 2winscroll said, depends largely on intended HP and RPM. And if you're concerned, you can run them a few ten-thou loose. If your bearings are too tight, everyone is gonna know, if they're a smidge too loose only you will know..
Unfortunately, asking this stuff on the internet is pretty much asking people with some know how what their secret sauce is, and it's a little hard to pry that info out of people.
Unfortunately, asking this stuff on the internet is pretty much asking people with some know how what their secret sauce is, and it's a little hard to pry that info out of people.
Oct 11, 2017, 01:39 PM
#21
Account Disabled
Neither of you have ever done any machining.
A 4G63 crank has a "standard size"
It's in the service manual......as are all the other specs if you bother to read it.
It's 45mm for the big ends.
There's a spec for max size, min size. out of round and for taper.
45.00 mm is top size. 44.98 mm is bottom size....that's the simplified version.
Whatever the clearance is it's determined by the bearing.
Jap engines metric.
Different brands and types of bearings have different clearances.
If you want a specific clearance then you buy undersize bearings of whatever brand and machine the crank to give the correct clearance.
The machine shop and only the machine shop can do this.
That's how it's done in this part of the world.
0.002 to to 0.0025 inch is what you normally run.
Factory clearances are a bit tighter.
Yet again, it's a waste of time asking a bunch of kids who have no machining experience.....keyboard warriors.
A 4G63 crank has a "standard size"
It's in the service manual......as are all the other specs if you bother to read it.
It's 45mm for the big ends.
There's a spec for max size, min size. out of round and for taper.
45.00 mm is top size. 44.98 mm is bottom size....that's the simplified version.
Whatever the clearance is it's determined by the bearing.
Jap engines metric.
Different brands and types of bearings have different clearances.
If you want a specific clearance then you buy undersize bearings of whatever brand and machine the crank to give the correct clearance.
The machine shop and only the machine shop can do this.
That's how it's done in this part of the world.
0.002 to to 0.0025 inch is what you normally run.
Factory clearances are a bit tighter.
Yet again, it's a waste of time asking a bunch of kids who have no machining experience.....keyboard warriors.
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NociEvo (Jul 2, 2020)
Oct 11, 2017, 01:42 PM
#22
EvoM Guru
iTrader: (1)
You can align hone the block, then mix/match standard and +.001" bearing shells to get to your desired clearances (mixing a +.001" shell with a standard shell results in +.0005" clearance). It takes time, and its the reason performance engine building is expensive.
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ArZem's garage (Mar 19, 2024)
Oct 11, 2017, 01:56 PM
#23
Account Disabled
You can align hone the block, then mix/match standard and +.001" bearing shells to get to your desired clearances (mixing a +.001" shell with a standard shell results in +.0005" clearance). It takes time, and its the reason performance engine building is expensive.
You should think about that more carefully.
That's only for the mains.
When you align hone (bore) the mains on a block, first of all you remove material from the mating surfaces.
That makes the tunnels out of round.
Then you put the hone through and it restores them to "round"and also back to the original size.
The sole purpose of that is to get the tunnels in a straight line.
With common V8 engines it's possible to buy "oversize" main bearings which are bigger in the tunnels (the outside diameter) but they're only used for repairing damaged tunnels.
Same goes for the conrods.
Once you remove them from a broken engine they're "out of round".
Machine a bit off the mating surfaces and hone them , they become round again.
It's lots of work and far less time consuming to machine the crank to the proper size, use a "standard" size rod.
Sure you can mix and match bearings and you'll need to buy several sets but what's the point when all you need to do is get the crank machined to the correct size in the first place to get the perfect clearance.
The reality is that everyone is some sort of engine builder or rather "parts fitter".
Not many "parts fitters" have access to a crank grinding machine although all good machine shops should have one.
So to summarise........take a standard but damaged 4G63 crank and machine the journals to 0.25mm undersize in both the mains and the big ends....fit ACL 0.25 mm undersize bearings...it'll work perfectly.
Another thing that most people don't know.....because they're keyboard warriors.
When you spin a big end bearing, it pulls the adjacent mains out of alignment so that the crank has a slight bend in it.
Machining the mains fixes it....makes it straight again.
Nobody in this part of the world EVER uses brand new cranks........they're too expensive when you can pick up a used one for about nothing.
Last edited by RightSaid fred; Oct 11, 2017 at 02:07 PM.
Oct 11, 2017, 02:05 PM
#24
Evolved Member
and you can also buy bearings with extra oil clearence, and ones with smaller oil clearence, all on stock sized crank....
Oct 11, 2017, 02:19 PM
#25
EvoM Guru
iTrader: (1)
[QUOTE=RightSaid fred;11777658]You should think about that more carefully.
That's only for the mains.
When you align hone (bore) the mains on a block, first of all you remove material from the mating surfaces.
That makes the tunnels out of round.
Then you put the hone through and it restores them to "round"and also back to the original size.
The sole purpose of that is to get the tunnels in a straight line.
It is not the sole purpose, just like the journal size of the crank, the tunnel has a size range. Also, align honing gets them all much closer to the same size. I've had undamaged 4g63's with main bearing bores that varied up to .0005".
With common V8 engines it's possible to buy "oversize" main bearings which are bigger in the tunnels (the outside diameter) but they're only used for repairing damaged tunnels.
This wasn't what I was talking about.
Same goes for the conrods.
Once you remove them from a broken engine they're "out of round".
Machine a bit off the mating surfaces and hone them , they become round again.
It's lots of work and far less time consuming to machine the crank to the proper size, use a "standard" size rod.
You can hone/resize conrod big ends the same as the block, by removing a few thou from the cap, and rehoning the bore. And just like the main bearing bores, the big end bore has a size range.
Sure you can mix and match bearings and you'll need to buy several sets but what's the point when all you need to do is get the crank machined to the correct size in the first place to get the perfect clearance.
For mix/match bearings in the 4g63, you only have standard, and +.001", so you only have to by two sets of bearings.
The reality is that everyone is some sort of engine builder or rather "parts fitter".
Not many "parts fitters" have access to a crank grinding machine although all good machine shops should have one.
Taking material off the crank is not a good method to obtain bearing clearance.
So to summarise........take a standard but damaged 4G63 crank and machine the journals to 0.25mm undersize in both the mains and the big ends....fit ACL 0.25 mm undersize bearings...it'll work perfectly.
You're willing to bet on that without measuring? LOL
Another thing that most people don't know.....because they're keyboard warriors.
When you spin a big end bearing, it pulls the adjacent mains out of alignment so that the crank has a slight bend in it.
Machining the mains fixes it....makes it straight again.
If a crank is bent, it needs to be bent back before being cut, and then balanced before being put back into service.
That's only for the mains.
When you align hone (bore) the mains on a block, first of all you remove material from the mating surfaces.
That makes the tunnels out of round.
Then you put the hone through and it restores them to "round"and also back to the original size.
The sole purpose of that is to get the tunnels in a straight line.
It is not the sole purpose, just like the journal size of the crank, the tunnel has a size range. Also, align honing gets them all much closer to the same size. I've had undamaged 4g63's with main bearing bores that varied up to .0005".
With common V8 engines it's possible to buy "oversize" main bearings which are bigger in the tunnels (the outside diameter) but they're only used for repairing damaged tunnels.
This wasn't what I was talking about.
Same goes for the conrods.
Once you remove them from a broken engine they're "out of round".
Machine a bit off the mating surfaces and hone them , they become round again.
It's lots of work and far less time consuming to machine the crank to the proper size, use a "standard" size rod.
You can hone/resize conrod big ends the same as the block, by removing a few thou from the cap, and rehoning the bore. And just like the main bearing bores, the big end bore has a size range.
Sure you can mix and match bearings and you'll need to buy several sets but what's the point when all you need to do is get the crank machined to the correct size in the first place to get the perfect clearance.
For mix/match bearings in the 4g63, you only have standard, and +.001", so you only have to by two sets of bearings.
The reality is that everyone is some sort of engine builder or rather "parts fitter".
Not many "parts fitters" have access to a crank grinding machine although all good machine shops should have one.
Taking material off the crank is not a good method to obtain bearing clearance.
So to summarise........take a standard but damaged 4G63 crank and machine the journals to 0.25mm undersize in both the mains and the big ends....fit ACL 0.25 mm undersize bearings...it'll work perfectly.
You're willing to bet on that without measuring? LOL
Another thing that most people don't know.....because they're keyboard warriors.
When you spin a big end bearing, it pulls the adjacent mains out of alignment so that the crank has a slight bend in it.
Machining the mains fixes it....makes it straight again.
If a crank is bent, it needs to be bent back before being cut, and then balanced before being put back into service.
Oct 11, 2017, 02:36 PM
#26
Account Disabled
What a joke?
I've reground hundreds of cranks.
You've got even less than no ****ing idea at all.
If you've got a bend of 1 thou inch.......how are you going to bend it back so it's perfectly straight without making it a 10 thou inch bend the other way?
You're only arguing for the sake of arguing and it's such a shame that you're so stupid that you don't even know it.
Here's one of my own custom strokers being ground.
No, it's not a 4G63 but it IS a Mitsubishi.
Turning a 6G74 into a 3.9 litre TT....Pajero Evo TT spec.
So it's STILL an EVO.
Last edited by RightSaid fred; Oct 11, 2017 at 03:15 PM.
Oct 11, 2017, 03:25 PM
#28
EvoM Guru
iTrader: (1)
Are you talking about the crank being bent, or the journal being smashed out of round?
Oct 11, 2017, 05:46 PM
#29
It's perfectly safe to unbend a bent crank. They have machines exactly for this purpose. Obviously there is a limit to how far something can be damaged before it isn't usable, same goes for damaged journals.
When you grind a journal it is brought back into round (assuming proper machine setup). There's definitely a lot of misinformation in this thread. Align hones are to bring all main bores concentric to the same axis (hence the name align). The main bore size should never change from factory specs as this can cause too much or too little crush on the bearing which can lead to catastrophic failures. The same applies for big end rod bores, the cap (or rod) is ground to decrease the bore size and then it is honed back round and to the proper size.
As for bearing clearances, unless you're doing something really exotic like making a nitro race fuel engine that is going to make power levels high enough to cause the crank to deflect (usually thousands of horsepower) then you should not be setting bearing clearances above .003". Bearing clearances ARE NOT like ring end gaps. Ring end gaps vary largely based on fuel used, power goal, material of the ring, environment the engine will operate in, etc. so ring end gaps are VERY different on a built engine compared to a stock engine.
As for setting bearing clearance, in terms of an engine that is having the crank ground, you will always set your bearing clearances by grinding (polishing actually) the crank. The bearing is a set size, so the only way to get your desired clearance is to grind and polish the crank to where it needs to be to get desired clearance.
And as for offset grinding (since that's what's shown in the video above), it barely increases displacement since you're limited on how far you can grind the journal down. I never advise people to get their cranks offset ground as it removes service life from the crank. Once the crank is offset ground, if it gets damaged from a spun bearing, you won't be able to grind it usable again without welding the journal (but that brings its own issues to the table).
When you grind a journal it is brought back into round (assuming proper machine setup). There's definitely a lot of misinformation in this thread. Align hones are to bring all main bores concentric to the same axis (hence the name align). The main bore size should never change from factory specs as this can cause too much or too little crush on the bearing which can lead to catastrophic failures. The same applies for big end rod bores, the cap (or rod) is ground to decrease the bore size and then it is honed back round and to the proper size.
As for bearing clearances, unless you're doing something really exotic like making a nitro race fuel engine that is going to make power levels high enough to cause the crank to deflect (usually thousands of horsepower) then you should not be setting bearing clearances above .003". Bearing clearances ARE NOT like ring end gaps. Ring end gaps vary largely based on fuel used, power goal, material of the ring, environment the engine will operate in, etc. so ring end gaps are VERY different on a built engine compared to a stock engine.
As for setting bearing clearance, in terms of an engine that is having the crank ground, you will always set your bearing clearances by grinding (polishing actually) the crank. The bearing is a set size, so the only way to get your desired clearance is to grind and polish the crank to where it needs to be to get desired clearance.
And as for offset grinding (since that's what's shown in the video above), it barely increases displacement since you're limited on how far you can grind the journal down. I never advise people to get their cranks offset ground as it removes service life from the crank. Once the crank is offset ground, if it gets damaged from a spun bearing, you won't be able to grind it usable again without welding the journal (but that brings its own issues to the table).
Last edited by Ayoustin; Oct 11, 2017 at 06:07 PM.
Oct 11, 2017, 07:18 PM
#30
Evolved Member
Ayoustin,
Very nice post Thankyou for clearing the air. As for bearing clearances which is what this post is all about, your correct, the major reason for increased bearing clearance in a 4g63 is crankshaft flex. All these others can spout numbers all they want but the fact remains that the stock crank does indeed flex a lot @ levels above 750hp. That's equivalent to a 2500hp small block or 3500hp big block, so yes fairly exotic at that level and lots of people on here are running those numbers or more. So I'll say it one more time .....without knowing the goals of his build, it's impossible to give a recommendation for bearing clearance.
As for Wrongsaidfred he screws up every thread he posts on with off topic garbage. The guy wants to know what bearing clearance to run, not how many crankshafts you have ruined. Got it?
Very nice post Thankyou for clearing the air. As for bearing clearances which is what this post is all about, your correct, the major reason for increased bearing clearance in a 4g63 is crankshaft flex. All these others can spout numbers all they want but the fact remains that the stock crank does indeed flex a lot @ levels above 750hp. That's equivalent to a 2500hp small block or 3500hp big block, so yes fairly exotic at that level and lots of people on here are running those numbers or more. So I'll say it one more time .....without knowing the goals of his build, it's impossible to give a recommendation for bearing clearance.
As for Wrongsaidfred he screws up every thread he posts on with off topic garbage. The guy wants to know what bearing clearance to run, not how many crankshafts you have ruined. Got it?
