ezrollin

My book gives a horrible description of how to plastigage the rod bearings.
How do you do it?
thanks

nofearracing28

iTrader: (7)

clean under, around, and top of bearings. put the plastigage on the journals. put crank in and torque mains. do not turn the crank. remove mains and measure.

ezrollin

i did not remove the crank, its been in the whole time

1fastWS6

iTrader: (3)

I think there are better instructions on Clevite's site. Basically just like nofearracing28 said, except substitute rod instead of main.

CamTom12

iTrader: (1)

This month's GMHTP actually has a pretty good description in their 383 build, too

ezrollin

assuming I got the right bearings for my engine, i shouldnt need to check clearance

joecar

Bad assumption.

hammertime

iTrader: (1)

Plastigauge is the easy way (not to mention inexpensive) to check clearances. Setting up bore gauges and measuring the diameter of all the bores and respective shafts takes much more time.

Either way, assuming a clearance is correct and finding out later it wasn't takes the longest and costs the most!

jrgicehc

very bad assumtion
the measurements that are used are the ones coming from the factory, on a used engine there is wear and when there is wear those numbers are not correct. my engines teacher made us plastiguage even if you had a brand new crank and bearing. he said has seen a few bearings be in the wrong box or just cut wrong. its cheap enough / easy enough and verry accurate. Even if you do it and find everything is perfect, its better to know then guess

volumebikertom

yea, you definetly should check everythings clearance, to much or to little clearance on start-up could be very damaging. Also, remember to clean the plastigage very good from the area you checked before reassembly.

CAT3

iTrader: (9)

ezrollin... a nice thing about gauging the clearance is that if you find one rod too close and another too loose, you can swap bearings, whole or half and get all the clearances exactly where you want them. This will ensure longevity. GL

Charlie

2002_Z28_Six_Speed

iTrader: (19)

How do OEM's get thier tolerance numbers? Experimentation?

BrokeRacing98ta

I am going to plastigage my mains and rods as well and I was wondering if you are suppose to torque all the new bolts completely and reuse them upon final assembly or should I use the old bolts for measuring purposes. I am using all ARP fasteners with clevite 77 bearings and an eagle crank. Also when you set the plastigage on the bearing surface is it more accurate to lay it parallel or perpendicular to the bearing. Thanks in advance.

hammertime

iTrader: (1)

If I were you, I would install the bolts per ARP's instructions. Pay particular attention to the burnishing process. Usually they have you fully torque and then loosen the bolts a few times to reduce the friction in the fastener. Also, use whatever lubricant they recommend when installing.

When I've used plastigage, I laid a strip perpendicular to the bearing so that one end points to the front of the engine, and the other towards the rear.

fast377

iTrader: (52)

When you split an engine in half under boost at high rpm because a main bearing was cut wrong ensures you check all clearances from then on.

Chevy406

iTrader: (12)

I recently took some pictures while checking the bearings on my 406 SBC. With the rod cap off, set a short piece of the plastigage on the crank.


Install the rod cap and torque to spec. Remove the cap and compare the flattened thickness to the gauge on the plastigauge wrapper. You are looking for .0015" to .003" clearance.

blackz93

iTrader: (2)

That's a big variance!

DanO

Calculation, testing, manufacturability, cost, etc....

m6ls1maro

just like the other ppl said how to use it, it is very straight forward and easy (as i just used it today) but you can only figure plastigage is a true measurement if the crank or rod bearing journels are not out of round or tapperd... i would check for out of round and tappers before i plastigaged it....