Hey guys,
I am trying to find out if I should increase my rod and main bearing clearances if I run a thicker oil...
Why you might ask? Well because I have almost unlimited Mobil 1 0w-40 oil through my work and Id like to use this exclusively for my engine...(free oil changes)
The engine will be a 92mm X 85mm thats going into a street car with 93 octane
Factory spec is 10w-30, but not much in this engine will be factory...

How much should I increase (if any) my clearances with this viscosity oil? Im not looking to rebuild every 10k miles either...
Any suggestions?

and since everyone likes pictures.....

 

what should work in theory doesnt always work in practice. just keep everything within spec.

 

Nik, what are your clearances?

 

I would stay within the honda specs if i were you... What were clearances you were using before???

 

This is a brand new crank. On my last 2 builds(89x84/84.5) I ran factory B18C5 specs. I dont have the exact #'s in front of me, but I know I went strictly by the service manual... After disassembling those engines, all bearings looked really really good, almost flawless.

This engine is spec-ing out to .0022" on the rod bearings and .0017"-.0018" on the main bearings. Im getting pretty consistent measurements with a max deviation of maybe
.0002" so im fairly sure the numbers are pretty accurate...Im currently going by the service manual (again B18C5).
Im just unsure if I should go a few ten thousandths looser to compensate for the 40w oil Id like to use...
Ive heard or read somewhere that you should set your clearances for longevity and run whatever viscosity to achieve the correct pressures...

Hey Scott! This is the same JDM ITR block you swapped in my hatch back in 2000! LOL

 

Alright...I think Ill just go ahead and run with the #'s I have...
Now I just need some time and motivation.
Thanks for the inputs guys.

 

I would go with what you have done in the past and has worked for you

 

Ok then...
I just wasnt sure if running a slightly thicker weight oil would justify a tenth or two looser on the clearances...
(Regarding possible increased pumping losses)
Gonna go with pretty much stock specs.

 

What would be the pros and cons if you were to run the clearance at .0022 does it mean that there will be less oil to flow in between the crank and bearings on the rod.

 

In my mind, a hair more clearance would yield a HAIR less oil pressure across the board,a HAIR more oil flow to the rod bearings(more volume) and less everywhere else, and a HAIR more "oil cushion" for the rod bearings...

Cons- Its almost at the service limit for factory specs, thicker oil may be necessary which would increase internal pumping losses...

Im thinking near stock is the best, so the oil has the correct pressures and correct volume to every part of the engine...

 

So the more clearance you have there will be more oil flowing in between the crank and bearings. But if the clearance is to small there it won't have enough oil to flow in between the crank and bearings for lubrication. So you will have to go with a thicker oil that may cause the oil pressure to drop but provide better petter protection cause of the thickness of the oil. I'm assuming the thicker the oil the more protection it provides but will cause loss in oil pressure. If you run a thinner weight oil you won't lose oil pressure but cause it is thinner it won't have the protection of the thicker weight oil because of the clearance.

Am I understanding this right?

 

With thinner clearances you run thinner oil. Why do you think newer engines require thinner oil viscosity versus older engines. Newer engines are made with tighter clearances than engines 20-30 years ago.

 

Bigger clearances = less oil pressure
smaller clearances = more oil pressure
thicker oil = more oil pressure
thinner oil = less oil pressure
Im gonna run near stock clearances with 0w-40 weight oil...Ill let you guys know what the pressures are once its all together someday...

 

So with all the new advancement in oil that the oil company's claim these days then it should be ok if you have a little tighter clearance. I am looking at the chilton book and it says .0013in -.0020in for a b18c5 so if he has .0022in then he should be good. Right? Will 0.0002in (is it two ten thousandth how you say this number) make that much difference in the performance and longevity of the motor?

As for when they say break in period usually what it does is that it wears out some of the metal that is rubbing against one another so that will take off some of the material so that it can flow with the another. Like when the piston rings seat to the walls or something like that. It takes off a little off the rings right so won't it do the same thing to the bearings.

Let's just say it has a clearance of .0022in on the rods so once it breaks in it should take some materials off the bearing like the rings so then it may end up to be .0020in of clearance after it is all broken in or driven for X amount of miles. Can this happen or am I totally off here?

 

The rings will break in to the cylinders, but the bearings dont really "break in" in the same sense.
The bearings and journals should never touch metal to metal. There should always be a film of oil preventing the 2 from touching (in a perfect world).
If they were to contact for any length of time, bearing material would start to be rubbed off(BAD) and eventually clearances would increase to the point of rod knock (BAD) and eventually you would ruin the rest of the engine.
And yes..
.0002" is said "two ten thousandths of an inch"
If you started at .0022" rod clearance and some bearing material rubbed away(BAD), your clearances would INCREASE and you might get .0024" not .0020"
Remember .0020" is tighter than .0022".

 

So then if you run the rod clearance at 0.0022in then there should be more oil lubricating your crank and rods which is a good thing right. Then you just run a thicker oil to compensate oil pressure.

Then 0.0002in looser should not be to bad but if the crank is spinning at high RPM would it then make a difference. Like for example a person playing with a hula hoop I'm just thinking that the rod is like the hula hoop and the crank is the person spinning inside the block. But .0002in is so small and should not make that big of a difference right?

 

That is my question...A respected engine builder told me .001" for every 1 inch of journal diameter. This is also recommended at Clevite or ACL's website. So a rod journal that is 1.8890" is diameter should have a .0019" bearing clearance.
Will 40 weight oil make up for the extra .0003" clearance I have? I think Im gonna get some new bearings from honda and try and "tighten" things up a bit...Id rather play it safe than sorry.