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Discussion Starter · #1 ·
If someone was rebuilding an engine , say a 360 AMC . You want to do as much as possible yourself , so you send out the block and crank for boring/turning etc... Have the shop install the cam bearings and stuff . Now when you install the crank and rods and check for crank end play and rod clearances , what if the end play and or rod clearances arent to spec ? How would you rectify that situation ? Or would that mean that the machining that was done was of poor quality ?

Jeff /wwwthreads_images/icons/cool.gif
 

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Is it possible they had to put in undersized bearings after machining and you have a standard crank?

It's all a state of mind, and if you don't mention the state of my mind, I'll be happy to overlook yours!
 

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Never seen "undersized bearings", either Standard or various oversize for cranks, etc. that were turned to clean them up.

Caver Dave
'72 Commando
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Hey Jeff,
What I like to do is to have the machine shop that did the machine work put the bottom end together; the crank , rods and pistons. That way, they are responsible for their machine work. They will probably want to supply the bearings and rings instead of you bringing them in. That's OK too, again they are responsible for the fitment. The bottom end is the most critical part of the engine, if you aren't comfortable with doing it, let them.
I've done it myself a lot, but not anymore, I think it's cheap insurance.

have fun,
Chris
'84 CJ7

 

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The bearings are either standard or undersize, the pistons are what are standard or oversize. Remember where the measurement is taken and what removing material does to that measurement.

 

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Discussion Starter · #6 ·
Ya I tend to agree with ya .

Jeff /wwwthreads_images/icons/cool.gif
 
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Here is what you do, talk to the machinist BEFORE he does the work. Find out what he is going to grind the crank to and what the rod and main bearing clearances are going to be when he is done. Find out what the spec is and then when YOU put the bottom end together measure the clearances with Plastigauge. If you put it together and make the measurements then you will know if it's been done right or not. If you've discussed it before hand with the machinist then there should be no surpries. Most machinist take a great deal of pride in their work, and if they have told you ahead of time what spec's they are shooting for they usually make that extra effort to make them come out to what they've said.

I've also been told there are some general "rules of thumb" for main bearing clearances and rod bearing clearances. I forget what they were, it was something like 0.75 thou for every inch of main diameter.
Perhaps some of the "Engine Experts" can chime in here and give us a lesson on different bearing types and any variations in clearences, if any, that might be required.

One other thing, and someone correct me if I'm mistaken but I believe that bearing clearances (main and rod) are a tighter spec and more important and will affect the life of the engine and the amount of oil pressure you end up with, then the crank end play and rod side clearances. So don't skip the Plastigauge.



 

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Gleened from one of the many online providers of rebuild kits:

Crankshaft and rod bearings are available in standard, +.010", +.020" & +.030" for reground cranks.

So what gives?

Caver Dave
'72 Commando
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/wwwthreads_images/icons/tongue.gif That's pretty basic stuff for engine builders, and there is A LOT more non-basic stuff that you need to know when putting the bottom end together if the engine is to go long term./wwwthreads_images/icons/crazy.gifCrankshaft journal end clearances will affect the oil pressure to a very great extend AS WELL AS the wear on the con rods as the crank goes endo more than it is supposed to, so crankshaft end play is CRITICAL, especially in a stick-shift rig./wwwthreads_images/icons/tongue.gifThose clearances are all set at the machine shop by the difference in finished size between the turned crankshaft journal and the true bore of the torqued-up undersized crankshaft journal inserts. You can only check it, you can't really change it except make it looser with shim stock/wwwthreads_images/icons/mad.gif inder the main caps, and that would be in a dire emergency only./wwwthreads_images/icons/crazy.gifI never put up an engine with more than .0015 clearance on the crankshaft journals. If it tightens up when the mains are torqued, then the crank is bad or the block must be align bored so you wouldn't want to continue anyway. Cranks can be metallized to reduce the end play on the thrust surface of the one main bearing that controls end play. HEAVY CLUTCH SPRINGS will cause excessive wear on the thrust surface of the main bearing insert which controls end play, so you NEVER sit at a stop sign with your foot on the clutch if it is going to be for very long. My ace Chev-Lay engine builder guy always asks his clinetel if they have an auto or a stick. If it is a stick, he tightens up on the crankshaft end play to the absolute minimum./wwwthreads_images/icons/tongue.gif

CJDave
A moonguy-operated Jeep Skunkworks in the "Heartland".
 

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Discussion Starter · #10 ·
This is all good info. guys . I am getting a 360 AMC engine for peanuts and want to rebuild it . I want to do as much of the work as possible , not only to save a few bucks but I enjoy doing that sort of thing . I was all set to buy a 5.0 L Mustang motor but this offer of a Howell Injection setup from my friend came up(dirt cheap) so I thought I would keep it all AMC /wwwthreads_images/icons/tongue.gif and build a fresh 360 to go with the Howell . I know your thinking , why would he choose an AMC over a newer 5.0 L Ford ? Truthfully I`ve been pretty happy with my 304 , after the oiling upgrades and TR Ignition it runs great and gets about 16-18 MPG and never lets me down . I just have this itch to build myself a 360 /wwwthreads_images/icons/smile.gif . Thanks for all the help !!

Jeff /wwwthreads_images/icons/cool.gif
 

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Carver Dave, as I understand it pistons are available in standard and oversized (.10 over, .20 over and such) and bearings are available standard and undersized (.10 under, .20 under and such). I double checked with my father, (a 60 year old mechanic who has been rebuilding engines since he was 15) as I wasn't sure I had my terminology correct (I've rebuilt several engines, but it runs a couple years in between!). I think what we are running into in this case is simply folks using different terms for the same thing. When a crank is reground it ends up being smaller diameter. You then need bearings that have a smaller inside diamter, but are thicker--that's why they are called undersized. I understand they used to be called oversized due to the extra thickness.

Now that I am thinking about it, I was backwards in my original post. It is possible the crank was reground (undersize crank) and that the bearings are standard creating a sloppy situation! *grin*

It's all a state of mind, and if you don't mention the state of my mind, I'll be happy to overlook yours!
 

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That's what I was thinking Bob. Thinking about it, the pistons are called oversized because their larger and bearings are undersized because their OD less than stock. Could be he has the situation you described, reground crank and either std. or not enough undersize on the bearings.

Caver Dave
'72 Commando
Oo=====oO
 
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