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| Polishing the Crankshaft | |
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| Tweet Topic Started: Apr 18 2012, 06:45 PM (2,451 Views) | |
| catfishWhisperer | Apr 18 2012, 06:45 PM Post #1 |
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Is polishing the crankshaft journals really necessary? I have the crankshaft out and the journals look smooth. I don't see any scratches or pitting. The engine won't be used for racing. I want to do a good job but not spend money on things that are not a necessity. Is there a chance that polishing could loosen up the bearing clearances? This is on a 1991 1.0L 3 cylinder. |
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| dayle1960 | Apr 18 2012, 07:02 PM Post #2 |
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Fastest Hampster EVER
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I say if they look dull why not hit them with 2000 grit paper. Shine them up a bit and it will not hurt the tolerances. Just don't use anything less than 2000. Welcome aboard. Hope you will find many answers to your questions. Don't be afraid to ask, we are here to help. Terry |
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| Deleted User | Apr 18 2012, 07:09 PM Post #3 |
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If they look good, and measure out right, and your clearances plasti-gauge within limits. Put it together and run it. Put all the bearing shells back where they came from. |
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| catfishWhisperer | Apr 19 2012, 04:29 PM Post #4 |
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I mic'd the clearances, instead of using plasti-gauge. These are the clearances that I got: Piston 1 rod bearing clearance = .0025" Piston 2 and 3 rod bearing clearances = .002" Main bearing clearances all measured at .001" This is on a metro with 93,000 miles on the odometer. I don't know if the odometer has rolled over, but I suspect it has judging on the overall condition of the car. -------------------------------------------------- I found the following info from a search: Clearances for rod bearings are 0.0008" - 0.0019" with a limit of 0.0031" Standard main bearing clearance is 0.0008" to 0.0015". If the clearance exceeds 0.0023", relpace the bearing. -------------------------------------------------- Do you think these bearings will be good for another 100,000 miles with good oil? |
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| Deleted User | Apr 19 2012, 04:48 PM Post #5 |
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Those are all within acceptable limits. The main bearing clearances are within new limits. The #1 rod bearing clearance is a little on the high side, but it will work. I'd still give it the plasti-gauge test. Like t3ragtop says, "Measure it with a micrometer, mark it with chalk, and cut it with an axe." Plasti-gauge results are very repeatable. They're just not down to the knat's ass. You get a comparason chart that has 0.001", 0.0015", 0.002", and 0.003". Green is the color you want. P/N SPRG-1 at most auto parts stores. Do you have a ball tipped micrometer to measure your bearing thickness? What are the diameters of your rod journals on the crankshaft? |
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| metrout | Apr 19 2012, 04:51 PM Post #6 |
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Ours had 230k on it and the crankshaft was still just fine as far clearances go. I was told by the machine shop that polishing wasn't necessary, but he could do it if we wanted to. We opted not to, since said that for ours it was a pretty useless thing to have done for $35. |
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| catfishWhisperer | Apr 19 2012, 05:44 PM Post #7 |
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With the crankshaft removed, I torqued the caps down with the old bearings still in place and used a telescoping gauge to get the inside diameter of the installed bearings in conjunction with a regular micrometer to get the measurements. The diameter of the rod journals are 1.6535". |
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| clarkdw | Apr 19 2012, 08:39 PM Post #8 |
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Correct method with caps torqued in place.
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| Deleted User | Apr 19 2012, 09:37 PM Post #9 |
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1.6529" - 1.6535" is the Standard Crankshaft Pin diameter. Yours are at the upper limit of new. You would get better service life out of your engine by replacing the rod bearings. If you are able to measure the thickness of your current rod bearings, you would be able to determine the thickness of new rod bearings that would tighten the clearances. Don't just go buy a set of rod bearings expecting them to be thicker than the ones you have installed. I have many sets of rod new bearings. They range in thickness from 0.0580" - 0.0585". I rarely see rod bearings above the 0.0585" thickness. From what I understand, the maximum thickness of a rod bearing is 0.0587" GG |
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| Old Man | Apr 19 2012, 09:47 PM Post #10 |
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If it was mine I would do a quick 2000 grit polish using the old "shoe shine" method agbout 10seconds on each journal and toss it back together. might only get another 60,000 miles out of it. but......its just too damn easy to remove the engine and replace the rod and main inserts when they go bad to worry about the measurements you are getting. |
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| clarkdw | Apr 19 2012, 10:19 PM Post #11 |
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If I am not mistaken he is talking about the id of the bearings , not the od of the crank. Measuring the diameter of the bearings as installed, torqued down caps etc is the accepted method of getting the crank bearing clearance. This insures correct clearance of the bearings. Best method to check rod bearing clearances is the same. Torque the rod up to spec with the bearing installed and measure the id of the bearing. |
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| Deleted User | Apr 19 2012, 10:55 PM Post #12 |
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Installing crankshaft and rod bearings over the internet = virtual engine overhaul.
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| catfishWhisperer | Apr 19 2012, 10:57 PM Post #13 |
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Yep, I measured the rod bearing clearances the same way. To avoid any confusion, I'll just give all my measurements. The id of the rod bearings measured 1.656" (piston 1) and 1.6555" (pistons 2 and 3). The od of the crankshaft rod journals all measured at 1.6535". The id of the main bearings all measured at 1.7725". The od of the crankshaft main journals measured 1.7715". "Shoe shine" method for polishing sounds easy, I'll give that a try. |
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| Deleted User | Apr 19 2012, 11:06 PM Post #14 |
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Thanks for clarifying that. Do you have one of these?
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| catfishWhisperer | Apr 19 2012, 11:12 PM Post #15 |
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No, the only micrometers that I found at Harbor Freight all had the blunt tip. |
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