alright, hope this turns into a good one


been thinking about this for sometime , and as im not a fan of bolting things on and going
usually here is where i set things at

for a typical hot street use (basic street motor with track use etc)

i like to shoot for 0.0017-18" on the main bearing oil clearances
and about 0.0020-22" on the rod bearing clearances

there are times that during mock up it is pretty close to this
there are times i need to send the crank micropolished just to get a few hairs

now i know this is not the golden rule or the bomb , others may have better preferences
as to the climate they run on and the oil they use (im not preaching my numbers)

here's where im kind of lost and i hope some of our seasoned builders could shed me some good light

on to rod side clearances

usually we're ok having it around 0.0012-14" right? which is decent

i know going too tight in this or a tad loose impacts oil pressure by a small %
im not sure if its enough to be even worth worrying ,

i wonder though if someone can spark some light on the following

wat happens if we run a looser rod sideplay/endplay clearance
lets say "double" those numbers
example : 0.0024-30" do we kill oil pressure on the rods instantly?
is it ok.. having to adjust the other clearances maybe a hair tighter on the mains and rods itself too.. to compensate?


hope to hear from you guys soon '

 

The clearance after the bearing clearances are always bigger, so it will not affect oil pressure to the rods or mains. If the rod side clearance was smaller than the bearing clearance, this would be the new restriction and cause the oil pressure to rise...
Rod side clearances should be more like .012" not .0012"
Ive heard of some guys running up to .020" rod side clearance w/o problems. I'm going to shoot for around .010"...Again from how I understand it, this doesnt affect your actual oil pressures...
I imagine if you have full floating wristpins, you may want to stay on the smaller side. If you have pressed wristpins and the pistons guiding the rod, I would think you could go a little looser....

 

pointing out that , the clearances after the bearing clearances are bigger
= not impeding oil flow..

is pretty cool.. i have never thought of it that way, thank you!

and yeah.. brainfart on my side i meant 0.012" hehehe not 0.0012"


another - piston guided rod, is this when it is press fit? or does it have to
do with the side clearance under the skirt for the small end's width /sideplay?

is it the same if when on a "floating" set up? or no?

trying to see if i understood your message correctly hehehe


thanks alot though , much apriciated

 

con rod side clearance should be 4x your bearing clearance from what ive been told. This is also very close to oem specs... Im going to try .009" on current project.i

 

and so if i try 0.025-0.030 would people be interested on how much damage it did? hahaha

 

heres a related thread where I posed the same question...
https://honda-tech.com/forums/engine-machining-assembly-164/connecting-rod-side-clearance-2886470/

 

I was just reading along and this ^ didn't make sense to me. could someone elaborate what that means?

also had the question, when you plasti-gauge to find clearances, do you p-gauge the upper and lower journals separately on all journals? or plasti one side and use the same bearing color on both sides?

secondly, once my clearances are found I was gonna run one size smaller(looser clearance)bearings on all upper and lower journals (ex. say if one rod takes a brown and green, id use a black and brown, i think) would that affect oil pressure much?

thirdly, some of these engines don't flow oil through the filter, and should i run tighter bearing clearances to remedy that problem so I can make enough oil pressure to allow the oil to flow through the filter to make sure i get clean oil back in the pan?

fourthly, I'll be adding arp rod bolts to my stock rods, and i know the rod has to be resized, so how can i get the clearances after resizing, because i don't think if i use the old bearing i will get an accurate measurement.

hopefully this isn't confusing, lol.

 

Picture your connecting rod installed on your crank. Notice the slight side to side wiggle of the connecting rod?
That guy was asking if the side to side clearance would affect your oil pressure. It will not because the side to side play is much larger than the rods bearing clearance. So after your bearing clearances, the oil exits on either side of the rod through the space called your connecting rod side clearance. Hence the clearance after your bearing clearances.

 

When using plastiguage as the primary source of determining your bearing clearance, Just doing one side of the journal should work. Plastiguage isn't completely accurate, but it gets you pretty close.
Perfect example. Today, I was in the middle of checking clearances on my project motor and threw some plastiguage on the mains of my crankshaft. After smooshing the plastiguage and checking the thickness with the little paper guage, I saw it was about .0020". Which is OK for mains.
I then checked with a micrometer and a bore guage and found it was actually .0024" which has me a little concerned. I never woulda knew my clearances were that loose if woulda just used plastiguage.
As far as how much this will affect pressure, I do not know. I read on an MG forum, one builder stated .0005" extra clearance caused a 20 psi drop in oil pressure. That statement worried me.