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Thread: possible spun bearing

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Posts: 1-9 of 9
2011-12-13 11:43:33
possible spun bearing
How would I know if I have a spun bearing? Would I be able to move the piston rod up and down, side to side or foward and backwards?
2011-12-13 13:32:43
2011-12-13 13:43:06
Originally Posted by snapon


To the OP - generally if you had spun a bearing, you'd definitely hear it (rod knock). Piston play is not how you determine rod knock if the motor is out of the car. With the oil pans removed and the crank girdle removed, you should be able to move the rod where it is connected to the crank with ease. Aside from that, you'd generally know if you drained the oil and pans and found tons of metal shavings.

As for your piston moving freely in the block, i'd look into the piston rings.
2011-12-13 16:10:17
If you already have the pans off... at the very least, just replace the rod bearings regardless of your findings. It's not a hard job, it's inexpensive and its worth the trouble.
2011-12-13 18:34:03
I found no shavings and as far as I can see there's no damage to the walls I thought the problem was that one of the rods came lose at the crank witch made the rattling noise but it wasn't. I do plan on build the bottom end just don't have the funds right now. ill try replacing the rod bearings hopefully that would by me some time
2011-12-13 18:36:05
Sorry for the confusion with the origanal post its were the rod connects to the crank. I made this post when I woke up this morning
2011-12-14 10:11:11
Rod bearings are an easy fix if you have a slight knock only at certain rpms. Spun Main Bearings aren't as Bad as they may sound. I was told they create a constant loud knocking sound.
2011-12-15 03:11:26
Any tips on replacing them?
2011-12-15 03:45:36
There is a how to on replaceing the bearings in the How to section.

As far as if the motor is out of the car or apart already its pretty easy to tell just by pulling the rod caps. You will know if the bearing spun. If the motor is still running in the car you can normally tell by lifting up the spark plug wires one by one until the knocking goes away. Whichever one you lift and it goes away is the one thats spun.

Normally depending on how long it has been spun and how hard of use on the spun bearing will determine the damage. If its heavy knock more than likely you will have to replace the crank because it will be scored and possibly replace that rod because they will easily oval the big end to where it isnt perfectly round. When that happens you can put a new set of bearings in all you want and it will spin them again because the side clearances of the bearing where the rod cap meets the rod to the crank are too tight.
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