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#1
10-01-2004, 12:16 PM
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I just picked up my block from the machine shop.
This is the second time the block has been in the machine shop. Initially my main bearing clearance was a bit excessive (around .004). See my post '400 assembly: main and rod oil clearance not within spec, what can I do?'. . I brought the block back into the shop. The main bores were on the high side of spec while the crank main journals were on the low side of spec. The machinist decided to align bore the main saddles. The machinist cut "..a few thou.." of the main bearing caps. No material was removed from the block. He then did the align bore. He measured the rear main bearing clearances and they were .003. . I got the block back and I am just test fitting my BOP viton seal right now and posted yesterday to see if guys thought my seal fit looked ok (see post 'BOP viton seal; Does this seal fit look ok?'). . A few guys have mentioned that I may have a rear main bearing alignment problem. I would like to get some more advice before I ask the machinist about this bearing alignment. I will post a few pics of the bearings. Questions =========== 1. So, this alignment is definitely not acceptable and I can not run with the bearings being misaligned? 2. Could the cause of the bearing alignment be an improper align bore/align hone? 3. The alignment of the BOP seal looks ok, should not the seal also be out of alignment if there is a problem with the align bore? 4. How would I fix the bearing misalignment? 5. Any other advice before I go back to the machine shop? |
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#2
10-01-2004, 12:16 PM
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I just picked up my block from the machine shop.
This is the second time the block has been in the machine shop. Initially my main bearing clearance was a bit excessive (around .004). See my post '400 assembly: main and rod oil clearance not within spec, what can I do?'. . I brought the block back into the shop. The main bores were on the high side of spec while the crank main journals were on the low side of spec. The machinist decided to align bore the main saddles. The machinist cut "..a few thou.." of the main bearing caps. No material was removed from the block. He then did the align bore. He measured the rear main bearing clearances and they were .003. . I got the block back and I am just test fitting my BOP viton seal right now and posted yesterday to see if guys thought my seal fit looked ok (see post 'BOP viton seal; Does this seal fit look ok?'). . A few guys have mentioned that I may have a rear main bearing alignment problem. I would like to get some more advice before I ask the machinist about this bearing alignment. I will post a few pics of the bearings. Questions =========== 1. So, this alignment is definitely not acceptable and I can not run with the bearings being misaligned? 2. Could the cause of the bearing alignment be an improper align bore/align hone? 3. The alignment of the BOP seal looks ok, should not the seal also be out of alignment if there is a problem with the align bore? 4. How would I fix the bearing misalignment? 5. Any other advice before I go back to the machine shop? |
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#3
10-01-2004, 12:17 PM
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rear main bearing left side
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#4
10-01-2004, 12:18 PM
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right side
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#5
10-01-2004, 12:19 PM
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front of rear main
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#6
10-01-2004, 12:19 PM
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bop seal fit
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#7
10-01-2004, 03:14 PM
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Observation
=========== I did notice that when I placed the main bearings in the caps, there is almost no protrusion...the bearing does not protrude above either side of the cap parting...whereas when I look at the main bearing shell in the block, I can see there is a small amount of bearing protrusion (the bearing does protrude a small amount). I know that bearings have a 'crush' so that when they are torqued they use this 'crush' to get the correct diameter. So, I guess most of the crush (ie. bearing protrusion) is in the block half of the bearing shell. . Test fitted crank ================== I took out BOP seal and put the crank in the block. I tightened down each cap , one at a time to spec and then made sure the crank still spun easily. The crank did spin easily with all caps on and tightened to spec. It was taking less than 25ft/lbs to turn the crank (my torque wrench only goes to 25ft/lbs) with all caps torqued down. All the other main bearings look to be aligned ok. |
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#8
10-02-2004, 12:19 AM
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Uh, if youre torque wrench only goes to 25ft/lbs how did you torque the mains to spec?Nevermind...only goes as LOW as 25....Im slow sometimes.
I wouldnt trust that alignment....probably wear out in short order. Sounds like this machinist may not know what hes doing. Was the cap like that before? Is it the cap that came with that block originally?
__________________
"It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived."- General George Patton "Perpetual peace is a futile dream."-General George Patton "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them."-Thomas Jefferson "Any society that would give up a little liberty to gain a little security deserves neither and will loose both."-Benjamin Franklin |
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#9
10-02-2004, 01:33 AM
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The rear main cap is original, it has never been changed. All caps are original. I am not sure what exactly the rear main bearing alignment looked like before I took the engine apart. I basically just pulled the caps...and did a quick look at the bearings. I did not look at the bearing alignment. I learned my lesson and next time , I will check these things closer...and keep ALL parts. The engine was running ok and had good oil pressure before I took it apart, though it had high mileage. I am wondering how could align boring/honing the block affect the rear main bearing shell alignment? The machinst only took off a few thou from the caps (I believe .002 or .003?, I will confirm the exact amount), so not sure how that could affect the bearing alignment a lot. It almost looks like the bearing tab/cutout in the rear main cap is off...the block or bottom rear main bearing shell looks to be aligned properly...the cap bearing shell appears to be sitting forward approx 1/16".
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#10
10-02-2004, 05:38 AM
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If you want to correct the alignment just file back the locator slot in the cap . Then push the bearing back into alignment before you torque down the cap.
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#11
10-02-2004, 09:02 AM
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The bearing alignment is not a big issue unless the edge of the bearing is riding on the crank.It's progablly been that way since new OR the rear cap was replaced sometime in it's life.No way the machine shop coud do this unless he removed the dowels.I would be EXTREMELY concerned if the crank turns anywhere near 25 lbs.with no piston/ring installed.It should spin easily by hand.
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GOOD IDEAS ARE OFTEN FOUND ABANDONED IN THE DUST OF PROCRASTINATION |
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#12
10-02-2004, 10:25 AM
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Ken, it's peculiar that the cap and block look dead nuts and the one bearing is just forward of where it should be. Could this be a defect with the bearing itself? Understand I'm not a machinist guru, just trying to understand what to look for.
Will a misalignment of bearing halves interfere with oiling?
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____________________________________ "I work in high speed aluminum tubing." |
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#13
10-02-2004, 03:52 PM
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Are the caps originally from this engine? It looks like it is a bit "off". Ive seen this problem when you mix and match main and rod caps from different engines. Im no Pontiac expert, but have done more than my share of Chebby's... And engine assembly is pretty much the same..
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#14
10-02-2004, 06:30 PM
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what pontiac steve said.
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 1963 Cat SD Clone (old school) streeter 1964 GTO post coupe, tripower, 4speed (build) 1965 GTO 389 tripower, 4 speed, driver 1966 GTO dragcar 1966 GTO Tri power, 4speed, barn find 1966 GTO Ragtop 1969 GTO Judge RA lll, auto 1970 GP SSJ 1970 GTO barn find..TLB…390 horse?….yeh, 390 1973 Grand Safari wagon, 700hp stoplight sleeper 525ci DCI & 609ci LM V head builds Factory stock oval track car |
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#15
10-02-2004, 06:56 PM
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The edge of the Lower (ie. cap rear main) bearing looks to be about 1/4" away from the back of the crank, so the bearing will never touch the crank. The machinist did not remove the dowels, therefore it looks like it has
probably been this way since new. The rear main cap has never been changed, it is original. . I examined the bearings a bit closer. (i) The rear main upper bearing shell has two grooves. The groove nearest the rear main seal varies in width about .003-.004 from side to side. It is slightly wider on the side I have marked as Right Side. (ii) The width of the bearing face (face between rear groove and back of bearing) varies in width approx. .020" from side to side. Again, the bearing face is narrower on the side I marked as Right. (iii) I think this slight variation in groove width and bearing face width makes the alignment a bit more noticeable. Note, the rear main bearing is a fully grooved Clevite 77. There is an Upper bearing and a lower bearing. The Upper bearing is in the block and the lower bearing is in the cap. Note, all other main bearings in the set have only Upper grooves. On closer inspection, I have noticed that a few of the other rear main lower bearings are not erfectly centered in the main caps. They protrude a tiny bit from the the caps...a very tiny amount. The bearings in the block all seem to be centered perfectly. I think what makes the rear main alignment more noticeable is the grooves. As Clevite 77's use a fully grooved rear main bearing. I did put on my torque wrench , which goes down to 25ft/lbs. The crank was taking less than 25ft/lbs to spin, but not sure exactly how much torque. The crank does spin easily by hand. I am going to leave this rear bearing as is and assemble the engine. From the feedback I have received, I am satisfied that this will not affect the durability/performance of the engine. Thanks for your feedback guys. |
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