Journal Measurments

[merc-blue]

G'day guys
I was wondering what level of accuracy you think is appropriate for measuring journals to get new bearings? this will be my first time buying bearings (instead of getting the machinst to do it) I have access to good quality mitutoyo micrometers (inside and out).
I just want to know how picky i should be with my measurements?
whats the minimum step from one bearing size to the next?
Cheers

[jonra23]

If crank has not been reground since motor has been disasembled you will need to check each journal at both ends (to check taper) and at different orientation around the journal (to check ovality) . From there you can decide if crank needs regrinding or is within tolerances.

You want to be as accurate as possible with measurements, with micrometers you will be able to get pretty good measurements.

Step sizes depend on motor, some motors have very small steps at original crank diameter to allow for small changes when originaly manufactured and then regrind sizes, genraly 25 and 50 thou undersize, some motors only have the regrind sizes.

regards
jon

[merc-blue]

Crank has been ballanced and reground,
The block is untouched

[kingmick]

They didnt tell you what size they took the crank to?

[merc-blue]

lol nup, cause it was done by a mate after hours, ill find out
I need to know the iner diameter of the block journals when torqued,should i lightly oil the bolts to make sure the torque numbers are good etc,

[jonra23]

If you have mics it should be fairly easy to work out what undersize, measure and deuct from original specs.

http://www.king-bearings.com/cat/ has standard and regrind measurements for a fair few motors.

Block tunnels should not be any different to standard.

regards
jon

[merc-blue]

cheers for the link,
I will just walk into bursons or meridian (need to visit them anyway) and find a ACL bearing set that matches what i need

[jeffro ra28]

First off. crank grinders fuck up to! Always no matter who ground your crank, check it FFS!

Second thing, a engine builder with 30 years experience uses there mic differently to a apprentice, (duh). You can see a differential of up to .002" just between one guy and the next. Over time you learn what is correct. Just remember not to use your mic like a G clamp! Iv been doing a shit load of cranks and im still learning!

[merc-blue]

yeah i will keep doign it untill i get consistent readings,
Cheers

[jonra23]

Good quality mics (Mitutoyo included) have a small slip clutch on the end of the thimble , if you use that it is fairly easy to good readings.

To double check use plastigauge on assembly.

regards
jon

[jeffro ra28]

I forgot to add.

With ANY engines we do, whether it be a shitter 253 or a 2000hp small block we measure each and every journal, tunnel and with cap and bearing installed and torqed.

If you can get ahold of some plastigauge it might help you with this. Not the most accurate tool but it might be more accurate then a first timer with a mic!. No offense

[jeffro ra28]

Good quality mics (Mitutoyo included) have a small slip clutch on the end of the thimble , if you use that it is fairly easy to good readings.

To double check use plastigauge on assembly.

regards
jon

True, some people tend to over rachet the clutch and go over board tho. It is accurate but alot of experienced fitters etc do not use it because they prefer there own feel.

Should be no worries for merc tho!

[merc-blue]

i guess we will find out when i spin a bearing after 100 hours of use LOL

[nb86]

you should be fine. like the others said, measure carefully when cheacking the crank, do each individual journal. double check with the plastiguage. with plenty of lube and careful torquing i can't imagine you'll have any issues.
unless of course you go 40,000 k's before the first oil change...

[ae86dave]

god bless micrometers