Do any of you have step by step instructions on checking main bearing clearence. I got my main bearings for Christmas and want to check everything out this weekend. I still have to send the rotating assembly out for balancing so I guess now is the time to make sure everything is correct. Do I torque the mains to spec? Do I use assembly lube even though its all coming back apart again? Do I need to have the rear seal in place?

Going to NAPA tomorrow for some plasti guage could use some advice.




[Modified by BlackRat, 6:35 PM 12/25/2003]

 

No to the rear seal and no to the assembly lube. I assume you are using Plastigage . You must torque each main to full torque specs. I also like to lay the crank in the block on only the top halves of the bearings installed at the front and rear, lightly lub them with light oil, lay the crank in and with a dial guage on the center main check it for runout or if it is bent.
If you are not sure what and why you are doing things you should get someone who knows to help you. The forum can answer most questions but it is the little thing that you will miss or forget to ask that will screw you up. Like which way to install the rear main, lip in or out????

 

plastigage is pretty good, but to do it right, get a bore guage. not sure what your building, for most motors plastiguage will work fine. you have to torque your mains in steps. get the cap set and snug first, then torque her up in three to four stages. this makes sure that the cap does not flex and give an incorrect reading, also nice to do on final assembly! i like my mains from .0022" to .0025", other guys run different clearences for different oil flow/pressures. it is also a good idea to assemble and check two or three times, it's **** but i like to safe with the lower end. Brian

 

Plastiguage is OK for main bearings but will give false readings on connecting rods. You will get "ballpark" plus/minus 0.0005") readings with Plastiguage and connecting rod side clearences will cause the rods to rock giving false compressions on rod journals. I would ask the machine shop to check clearances or buy a set of snap guages and micrometeters on Ebay and learn to correctly measure clearances (you can then have journals properly sized while balacing is being done.) Take the mic and measure each journal with it going to 3 clicks of the thimble and then taking reading (if crank is new you can take one reading from center of journal but, if it is used, you need to check for journal "taper" by going from outer edge to middle and far edge on each and every journal (rods most important here.) I also run around 0.0022-0.0027 on mains and 0.0025-0.003 on rods of small blocks but rough rule of thumb is 0.001 for every 1.0" diameter of journal diameter. You can help Plastiguage reading on rods by inserting feeler guages to take up side clearances while measuring rod journals. One other old "Okie speed rig" method is the newspaper trick (in lieu of Plastiguage) that inserts newspaper between the bearing and jornal, if you can rotate-it's OK, if not too tight (probably as good as Plastiguage.) Bearing clearances can be set by properly sizing journals, mixing bearing sets (made in 0.001 under/over sizes and mixing 1/2 shells for 1/2 thousands adjustments of clearances.) Measure for real, set clearances 0.0025 mains, 0.0028 rods and get a Melling 10555 oil pump 10% higer volume with "real" steel gears in it (a very nice economical part!) Don't forget to check rod side clearances (0.014-0.020) and crankshaft endplay (0.005 or so.) Good luck, Eric B.


[Modified by Solid LT1, 5:35 AM 12/26/2003]

 

Wade, what they said above.

Looking back, I would have had the shop assemble the short block for me. I think they charged about $400, checked the clearances, install crank, pistons rings, set ring gap, bearings, rear seal, degreed the cam & timing chain. That would've saved me a lot of time. BUT, I didn't have the $$ at the time. :sad:

 

lt1 is on the $$$$....get a set of micrometers from ebay or harbor freight. It's so easy to use them. One thing about micrometers vs plastigague...micros give you the exact specs, plastigagues give you ball park estimates.

Don't be a Bubba, get a set of Micros and do the job right.

when u use the micros, no assembly is required.....check each crank journal, with the crank and the rods out of the block, put the bearings in the rods and mains, torque to specs....dry, no lube...mike the inside of each main and rod. The difference between the corresponding main and rod on the crank is your clearance...it's so simple and right on the money


[Modified by GDaina, 9:48 AM 12/26/2003]

 

i have mic's from "harbor" they're ok for some things but i use a better set on
auto engine's i use the cheap one's when i tare-down but not after machine
shop work or during assembly

 

next time i will try a dial indicator :cool:

 

What's the best way to measure the bearing bores "mike the inside of each main and rod" without a bore gauge ?

 

In all due respect, and by the nature of your question, you need to have all the specs checked out by a professional.

All of these responses to your post are very correct, but with your inexperience, and considering the cost to obtain the necessary mics/guages, I think you would be better off to have it "double checked" by a professional that you trust.

If you intend to do many of these rebuilds, well, then, maybe invest in the measuring tools, and learn the process, but if this is the only one you will be doing, there's no way you can come out ahead, considering the cost of the tools, and the risk that you measure it wrong, or don't quite understand the dynamics.

Best of luck to you!!!!

 

Bill Oxley I agree with you 100%
Give an ammature a mic and I bet he will read it wrong. Snap guages are also not that easy to use/read. I have the best measuring equipment and 40 years of experience and I still have to take my time and concentrate on feel. It takes years to develope the proper technics.
I teach engineering and my 4th year students still have problems measuring and they have had 3 years with hands on experience.
Get help or someone else to assemble it.

 

mics are not needed, they are are hard to read and costly.
Plastigauge on the mains.
feeler gauge on the rods.(1 at a time)
No way i would trust the local "pofessionaiels".