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Hi guys just got my block back from the machine shop. So I started measuring bearing clearance and I am a little worried about the variance from front to rear. Here is what I get #1 main .0022 #2 main .0024 #3 main .0025 #4 main .0023 #5 rear main .0027 average .0025 I am ok with .0025 average but I am concerned with the .0005 variance front to rear and #1 being so tight is this normal to see this type of variance? I have rechecked it with two sets of standard bearings and got the same results. I could get a set of xk bearings this would allow me to mix lowers to increase clearance on the tighter caps by .0002 per bearing half. But the front #1 would need both halves of the xk to make .0026 #2 lower xk .0026 #3 leave alone #4 lower xk .0025 and leave alone. I have heard its ok to mix some but would this be ok? Or am I just being to anal about this? This is a bbc bracket engine 468 with 7000 rpm redline around 600 hp. I just dont want to put it together and spin a bearing first time out or even 1 year in I want it to last a few seasons. Sorry for the long post.
 

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Hi guys just got my block back from the machine shop. So I started measuring bearing clearance and I am a little worried about the variance from front to rear. Here is what I get #1 main .0022 #2 main .0024 #3 main .0025 #4 main .0023 #5 rear main .0027 average .0025 I am ok with .0025 average but I am concerned with the .0005 variance front to rear and #1 being so tight is this normal to see this type of variance? I have rechecked it with two sets of standard bearings and got the same results. I could get a set of xk bearings this would allow me to mix lowers to increase clearance on the tighter caps by .0002 per bearing half. But the front #1 would need both halves of the xk to make .0026 #2 lower xk .0026 #3 leave alone #4 lower xk .0025 and leave alone. I have heard its ok to mix some but would this be ok? Or am I just being to anal about this? This is a bbc bracket engine 468 with 7000 rpm redline around 600 hp. I just dont want to put it together and spin a bearing first time out or even 1 year in I want it to last a few seasons. Sorry for the long post.

What are you checking clearances with?
 

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Dial bore gauge , mic crank then lock mic, 0 bore gauge check clearances then reck bore gauge against mic. These results are repeatable over and over again. I thought I was measuring wrong but I checked like 6 times exact same result on each main every time
 

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bearing itself can vary .0001 to .00012"lots of times if you want it that close, you can switch them around and change the end result.... as carl asks.. the mannor of doing the measuring can influence results
 

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Dial bore gauge , mic crank then lock mic, 0 bore gauge check clearances then reck bore gauge against mic. These results are repeatable over and over again. I thought I was measuring wrong but I checked like 6 times exact same result on each main every time
Which dial bore gauge hopefully a Sunnen and not a ridged finger cheap gauge.
 

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YUP as carl speaks of.. the rigid plunger type will actually result in a larger diameter as read beccause the point will push down with more force and displace bearing material ( scratch it too) ..a sunnen unit at just a measly 1000 dollars is a pretty good investment...
 

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.0028-.0032 should be good on clearance.

Not sure what BRG you are using.( Sounds like king?) Just buy a set of extra clearance.
If you have to split them, do it. As long as it is same manufacture.

Your oil pan and pump will dictate a lot of your pressure at higher rpms.
 

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As far as taper goes. It is common too see from align hone. Taper of hone itself. Check it without brgs see if it has taper?
 

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Discussion Starter #11
They are clevite 77 h bearings ms829h. Callies compstar crankshaft. I am thinking taper from line honing is most like the cause, but I will have to measure without bearings. I am thinking the machinist did not torque the mains to spec when he line honed it cause he couldn't tell me what he torqued it to.I am using arp main studs just a 2 bolt block. Arp spec is 110 ft lbs. I think he torqued to stock spec.
 

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"This is a bbc bracket engine 468 with 7000 rpm redline around 600 hp."

If this was my personal engine with those conditions, I would not be afraid to put Red Line Racing Synthetic 30w in it and go have some fun. Sometimes we tend to over think stuff.

Blessings.......Ron
 

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I have a Mitutoyo 2"-6" dial bore gauge, and it has a fairly stiff, pointy stylus that digs into the bearings when attempting to check a bearing clearance. You can see the scratch it leaves. This makes you think the bore is larger than it truly is, fooling you into believing there is more clearance. I used some different methods to determine those readings were flawed....

One was Plastigauge. I double checked everything with it, and this method showed less clearance.

Next, I installed just the front and rear main bearings and crank DRY. I then fixed a 0.0001" dial gauge next to the bearing and lifted the crank up and down to directly get an idea of the clearance. It agreed with the Plastigauge.

I then measured the raw diameter of the mains without the bearing inserts, measured the thickness of the bearings with a round end mic, measured the crank, did the math... and got about what the Plastigauge said.

In conclusion... Do NOT use a dial bore gauge that has a sharp, stiff stylus on bearings!!!!!! If it leaves scratches in the bearings, do NOT use it! It can be off a full thousandth, and leave you scratching your head about why your engine blew up!!! :rolleyes:

Second moral of the story... Plastigauge works surprisingly well, as long as it is used correctly, and isn't OLD, shrunken and dried up! :) It's good to at least use as a quick, final check.

Good Luck!
 

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If the machine shop has a little taper on the stones on their mandrel they should flip the block while line honing.

But I would be more concerned with the tight ones than the loose ones. .0027 would be great.
 

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It's a BBC.......2.750 mains...........Put the HX's in it (extra clearance) and RUN it........

Too loose no one knows, to tight everybody will know.................LOL
 

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Hi guys just got my block back from the machine shop. So I started measuring bearing clearance and I am a little worried about the variance from front to rear. Here is what I get #1 main .0022 #2 main .0024 #3 main .0025 #4 main .0023 #5 rear main .0027 average .0025 I am ok with .0025 average but I am concerned with the .0005 variance front to rear and #1 being so tight is this normal to see this type of variance? I have rechecked it with two sets of standard bearings and got the same results. I could get a set of xk bearings this would allow me to mix lowers to increase clearance on the tighter caps by .0002 per bearing half. But the front #1 would need both halves of the xk to make .0026 #2 lower xk .0026 #3 leave alone #4 lower xk .0025 and leave alone. I have heard its ok to mix some but would this be ok? Or am I just being to anal about this? This is a bbc bracket engine 468 with 7000 rpm redline around 600 hp. I just dont want to put it together and spin a bearing first time out or even 1 year in I want it to last a few seasons. Sorry for the long post.
I would get a set of x bearings, and recheck everything. You may be able to mix and match your tight with loose ones and come up with something in the middle.
 

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I have a Mitutoyo 2"-6" dial bore gauge, and it has a fairly stiff, pointy stylus that digs into the bearings when attempting to check a bearing clearance. You can see the scratch it leaves. This makes you think the bore is larger than it truly is, fooling you into believing there is more clearance. I used some different methods to determine those readings were flawed....

One was Plastigauge. I double checked everything with it, and this method showed less clearance.

Good Luck!
Your Met bore gauges are not made to measure a hole with bearing eccentricity. I have had many bore gauge wars at my shop and my sunnen gauges always show less clearance against a gauge with ridged fingers. Your gauge is good for measuring round holes.

A good thread to look over.
http://www.performanceboats.com/dyno/192129-inside-michrometer-measuring-bearing-clearances.html
 
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