Whats up H-tech,

This is my first engine build and I'm determined to get this done the right way, so before I go finalizing, I'd like to run it by a few who have more experience.

Ok so I'm using the Laskey bearing chart to calculate my bearing thickness so I can order these bearings. Now I used the formula to determine the rod bearing thickness and it came out fine:

IDBT - ODC - (2 x BT) = BC
( Bearing Thickness = 1.501mm )

(1.89" - 1.77" = .12" = 3.048mm


(2 x 1.501mm ) = 3.002mm

(3.048 - 3.002 = .046mm )

Convert .046mm to inch. and its .00181" which is ok bearing clearance for a boosted engine.


Now when I do the main journals with the same formula it doesn't seem right, let me explain to see if you find my mistake?


IDBT - ODC - (2 x BT) = BC
( Bearing Thickness = 2.000mm )

(2.3236" - 2.1545") = 0.1692" = 4.2976mm


(2 x 2.000mm) = 4mm

(4.2976 - 4.000 = .2976mm)

Convert .2976mm to inch and you get .0117"



Service limit itself is .002 and I should be aiming around .0009 - .0018 (closer to .0018). Am I missing something or did my crank get machined too much? Also is there a solution to this besides, i'd hate to say, a new crank?

Need some help here as everything was going smoothly until now.. When I plastigauged the main journals, the plastigauge barely got squished.. literally smaller then the .003 (maybe .0035). If I can even get some bearings that size would it be safe? I'm shooting for 550-600whp.

Thanks in advance for any help y'all

 

I haven't built my first motor yeat, I'll be doing that later this month. So this thread hopefully will help me out to.
But, i'm kinda lost as to how you came up with your bearing thickness.
If your aiming for a .0009 BC on the mains than why can't you just use your crank/cap bore measurements????
So .1691-.0009 BC=.1682 BT and get the bearing made to that thickness?

 

Noobs givin noobs advice lol

Don't hold me to this but if I'm not mistaken the bearing clearance is the space left for the oil to lubricate the journal. So your formula would have the bc and bt added.

If you look at evans tunings articles/video, he got somewhat similar numbers but when I did the formula with his measurements, it still came out funny.

I get the bearing thickness from measuring each actual bearing in various locations with my mic. I plastigauged the main journals with standard sized acl bearings (measured to 2 mm) and after torque and disassembly the plastigauge measured to smaller then .003. That's way off.

So I measured the main cap inner journal and it was on dot to spec but the crank measured to about 2.154 which is .010 smaller then the minimum measurement.

Am I crazy or please some one chime in?

 

Ya know whats funny is I watched that for like the 3or4th time right after I sent that message last night. I also watched these to better examples IMO

I just don't understand why you use a ("2" X BT) what the hell is the 2 for and why do you use it?

Sorry to thread jack ya. I thought I knew exactly what needed to be done until I seen this thread and that formula. I all ways thought you just
Measure;
Journal-Crank=Total gap ,, Total Gap-Desired Bearing Clearence=Bearing thickness.

This has just thrown a wrench in my thinking I guess

 

yea I've mastered the use of these tools already, but the "2" is because there are "2" bearing halves..

 

https://honda-tech.com/forums/tech-misc-15/gsr-crank-oversized-rod-bearing-polishing-question-2014294/

Looks like I need a new crank

 

I like to measure with the bearing halves installed in the block. It gives you a direct reading and you can see it change real-time with the dial bore gauge to find the tightest spot. If I scratch it really bad, I'll replace it after verifying the thickness.

My general steps are:
1.) Install bearing halves
2.) Install caps (rod or main)
3.) Measure OD of crank journal
4.) Lock micrometer to crank journal OD
5.) Set dial bore gage baseline
6.) Insert dial bore gage to directly measure oil clearance