N62B48 - mid-rebuild - honing vs reboring / reusing bearings
Discussion
So I bought a car with an apparent head gasket fault, but having dismantled it entirely there are many more issues. The car has been standing for a long time and there is evidence of water in the bores, I'm figuring out if that's done any damage or if the HG leak means the car has slowly been weeping water into the bores. I'm waiting for penetrating oil to free up the pistons so I can get them out - I hope there's no bore damage.
How would I determine whether the cylinders need honing vs reboring? Also, how can I measure if the cylinders are round?
How would I determine if the bottom end and conrod bearings are suitable for re-use? A couple of them have extremely minor scoring.
Pictures to come later.
How would I determine whether the cylinders need honing vs reboring? Also, how can I measure if the cylinders are round?
How would I determine if the bottom end and conrod bearings are suitable for re-use? A couple of them have extremely minor scoring.
Pictures to come later.
There are likely tolerances for the bearings in the workshop manual. My view on it however is: you've stripped the engine right down, which is a major task. If you re-use the beaings and it turns out to be an issue, do you really want to strip it all down again? While you're in there, replace the bearings.
For the bors, a light honing would be a good idea, if only to !polish" them up, so to speak. You dont want a tiny little bit of oxide knicking a piston ring.
In for a penny, in for a pound.
For the bors, a light honing would be a good idea, if only to !polish" them up, so to speak. You dont want a tiny little bit of oxide knicking a piston ring.
In for a penny, in for a pound.
thatdude said:
There are likely tolerances for the bearings in the workshop manual. My view on it however is: you've stripped the engine right down, which is a major task. If you re-use the beaings and it turns out to be an issue, do you really want to strip it all down again? While you're in there, replace the bearings.
For the bors, a light honing would be a good idea, if only to !polish" them up, so to speak. You dont want a tiny little bit of oxide knicking a piston ring.
In for a penny, in for a pound.
Thanks for the reply - bearings are around £200 so I will likely get them - I'm trying to determine if the bores need more work / new block vs. building the engine with just honing. For the bors, a light honing would be a good idea, if only to !polish" them up, so to speak. You dont want a tiny little bit of oxide knicking a piston ring.
In for a penny, in for a pound.
Rough and ready bore checker.
First, Mark One eyeball 😊
Second, when you do get the pistons to move, take off one ring.
Replace it in the bore and move it up and down to check for smooth.
Gap the ring at various place in the bore. Obviously the gap should be the same until the very top and bottom.
Do this with the same ring in each bore.
You can get dial gauges that will measure Bore, and you will see if the bore is round. Never had the need for one myself.
I concur with replacing shells etc. Relatively minor cost. Likewise clutch replacement too.
First, Mark One eyeball 😊
Second, when you do get the pistons to move, take off one ring.
Replace it in the bore and move it up and down to check for smooth.
Gap the ring at various place in the bore. Obviously the gap should be the same until the very top and bottom.
Do this with the same ring in each bore.
You can get dial gauges that will measure Bore, and you will see if the bore is round. Never had the need for one myself.
I concur with replacing shells etc. Relatively minor cost. Likewise clutch replacement too.
If the pistons have seized in a N62B48 block, then the engine is most likely junk. The block is alusil, and there isn’t much space to bore. Also you are dependent on BMW selling you oversize pistons, which aren’t cheap. I am yet to hear of aftermarket pistons that work well with alusil.
Last but not least and please don’t take it the wrong way - if you are asking on line how to measure if a bore is out of round or how to figure out if an engine bearing is gone, perhaps you would be better off leaving this to a reputable workshop? It is not rocket science, but the N62B48 is a magnificent power plant build to pretty tight tolerances with some nifty tricky bits here and there, and perhaps is not what I would call a “starter” engine...
Last but not least and please don’t take it the wrong way - if you are asking on line how to measure if a bore is out of round or how to figure out if an engine bearing is gone, perhaps you would be better off leaving this to a reputable workshop? It is not rocket science, but the N62B48 is a magnificent power plant build to pretty tight tolerances with some nifty tricky bits here and there, and perhaps is not what I would call a “starter” engine...
Cheburator mk2 said:
If the pistons have seized in a N62B48 block, then the engine is most likely junk. The block is alusil, and there isn’t much space to bore. Also you are dependent on BMW selling you oversize pistons, which aren’t cheap. I am yet to hear of aftermarket pistons that work well with alusil.
Last but not least and please don’t take it the wrong way - if you are asking on line how to measure if a bore is out of round or how to figure out if an engine bearing is gone, perhaps you would be better off leaving this to a reputable workshop? It is not rocket science, but the N62B48 is a magnificent power plant build to pretty tight tolerances with some nifty tricky bits here and there, and perhaps is not what I would call a “starter” engine...
+1Last but not least and please don’t take it the wrong way - if you are asking on line how to measure if a bore is out of round or how to figure out if an engine bearing is gone, perhaps you would be better off leaving this to a reputable workshop? It is not rocket science, but the N62B48 is a magnificent power plant build to pretty tight tolerances with some nifty tricky bits here and there, and perhaps is not what I would call a “starter” engine...
If you need to unseize the pistons, the block is scrap.
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