Bearing Clearance

caladash · Mar 26, 2013

I have 2 engines Im rebuilding and Im stuck on one thing before getting things started. I bought the International Service Manual DVD and it has all tolerances needed for a rebuild but im not sure which description to use for main and rod bearing clearance. Granted, the tolerances are the same! I would like to know what each one is describing.

Main Bearing to Crankshaft Running Clearance
(0.0018 - 0.0046 in)

Connecting Rod Bearing to Crankshaft Running Clearance
(0.0015 - 0.0045 in)

Connecting Rod Bearing Running Clearance
(0.0015 - 0.0045 in)

Also is there a solid number that is preferably liked by most? My machinist said 20 thousandths is a good number which is within range. Lastly, is this the tolerance check that uses plastigauge? Or is there a better way? Thanks!

caladash · Mar 27, 2013

Bump!

golfer · Mar 28, 2013

TWENTY thousandths for bearing clearance??

negatron.

run within the Ford specs if this is a sub 500hp build.

PDT1081 · Mar 28, 2013

caladash said:
I have 2 engines Im rebuilding and Im stuck on one thing before getting things started. I bought the International Service Manual DVD and it has all tolerances needed for a rebuild but im not sure which description to use for main and rod bearing clearance. Granted, the tolerances are the same! I would like to know what each one is describing.

Main Bearing to Crankshaft Running Clearance
(0.0018 - 0.0046 in)

Connecting Rod Bearing to Crankshaft Running Clearance
(0.0015 - 0.0045 in)

Connecting Rod Bearing Running Clearance
(0.0015 - 0.0045 in)

Also is there a solid number that is preferably liked by most? My machinist said 20 thousandths is a good number which is within range. Lastly, is this the tolerance check that uses plastigauge? Or is there a better way? Thanks!

20 thousandths in decimal form is 0.020.

caladash · Mar 28, 2013

Should be sub 500hp! The above specs are from the international service manual. What is recommended for above 500 horse? Are the above specs the same as what ford wants?

caladash · Mar 28, 2013

PDT1081 said:
20 thousandths in decimal form is 0.020.

Yes!! With that being said, are the specs posted in my first post appropriate for a sub 500 horse rebuild?

caladash · Mar 30, 2013

suprhlr · Mar 31, 2013

If you are in the range of the specs you should be fine, I would not use plastigage to check clearances, use a micrometer and telescoping or bore gages

kyle43335 · Mar 31, 2013

caladash said:
I have 2 engines Im rebuilding and Im stuck on one thing before getting things started. I bought the International Service Manual DVD and it has all tolerances needed for a rebuild but im not sure which description to use for main and rod bearing clearance. Granted, the tolerances are the same! I would like to know what each one is describing.

Main Bearing to Crankshaft Running Clearance
(0.0018 - 0.0046 in)

Connecting Rod Bearing to Crankshaft Running Clearance
(0.0015 - 0.0045 in)

Connecting Rod Bearing Running Clearance
(0.0015 - 0.0045 in)

Also is there a solid number that is preferably liked by most? My machinist said 20 thousandths is a good number which is within range. Lastly, is this the tolerance check that uses plastigauge? Or is there a better way? Thanks!

I like to see clearances. In the middle of min max range or a bit loose( favoring the upper end).

Oil weight is a major factor when setting bearing clearances.

caladash · Mar 31, 2013

kyle43335 said:
I like to see clearances. In the middle of min max range or a bit loose( favoring the upper end).

Oil weight is a major factor when setting bearing clearances.

Regular 15/40 would be used. Mobil delvac to be exact. Where on the range spectrum would a higher horsepower motor be?

Thank you for those that have answered!

kyle43335 · Mar 31, 2013

Typically the higher horse power built engine, have loose clearances for heat purposes.

Old OutLaw · Mar 31, 2013

unless you are willing to pay to have the main saddles in the block Align-bored, have the block parallel-decked, the bores precision bored, and the crank checked for size and straightened, there's not much reason to fool with the clearances....if it was a running engine when it came apart, (unless it threw a rod or something Savage), chances are that the clearances are fine. put it together with Plastigauge, and you'll be fine.

now, having said all that, I personally would NOT build ANY internal combustion engine without doing the block, checking the crank, and balancing the whole works....it's cheap insurance.....

the block, crank, rods and pistons are the foundation the whole engine is built on..... me likey good foundation....