Looking to split the case on '74 850 Commando. I figure since I have it down this far, and it had a troubled past, with a long period in storage, makes sense to replace them. Connecting rods appear OK, but it appears the main bearing aren't as smooth as I think they should be. Others have said don't worry about it and don't split the case. Any encouragement either way, and suggestions on bearings ? Thanks!
Replacing main bearing on a 74 commando
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lcrken
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Like Danno said, they normally last a long time.
My approach, which may not be all that technical, is to clean the bearing thoroughly, and examine the rollers and race with a magnifying lens for pits or defects. If that looks good, I lightly oil them with a thin oil like 3-in-1, and just rotate them with my fingers. If they turn smoothly, I keep them. If they feel gritty, I clean and oil them and try again. If they are still gritty feeling, I junk them.
On the other hand, there is something to the theory that as long as the engine is completely apart, you might as well replace all the bearings and seals with new ones. It's only money, right?
Ken
My approach, which may not be all that technical, is to clean the bearing thoroughly, and examine the rollers and race with a magnifying lens for pits or defects. If that looks good, I lightly oil them with a thin oil like 3-in-1, and just rotate them with my fingers. If they turn smoothly, I keep them. If they feel gritty, I clean and oil them and try again. If they are still gritty feeling, I junk them.
On the other hand, there is something to the theory that as long as the engine is completely apart, you might as well replace all the bearings and seals with new ones. It's only money, right?
Ken
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concours said:
Precisely, and if the crank cases aren't leaking, why take them apart? you do need to describe the lack of smoothness.
Dereck
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Sorry, AZ, but I apparently didn't read your post thoroughly, and thought you already had the cases apart. Since it's still together, I don't know a really good way to check the mains except the feel of the crank as it rotates. I don't see how you can do that unless you've already pulled the timing side gear train and oil pump. Even then it's kind of iffy. You can check the feel of the crank as it rotates, and you can see how much the rods move as you wiggle them, but the only way you're going to be sure of the condition of the main and rod bearings is to disassemble and inspect. If it was running well when put in storage, and was stored properly, the odds are pretty good that it is still ok. If not, I'd recommend going the rest of the way with it, just to be sure. Or you could just take a chance. Depends on how much you enjoy taking them apart and putting them together. In any case, good luck with it.
Ken
Ken
Thanks for all the comments, I really appreciate it. Let me explain my situation with the 74 Commando.
The case is still together, all timing gears are off, so the crank turns freely. It has been stored many years in Arizona (low moisture) and the engine appears to be in solid shape and no leaks. However I have no information from the previous owner. My original thought that I could sense roughness in the main bearings when spinning it, this was purely subjective, and looking at it again, not sure this is an issue. I am reading from most of the comments, bearings are very robust and not normally needing replacement.
So,.. leaning toward the camp that says, if it ain't broke, don't fix it,... heaven knows there is enough other stuff on this restoration to spend money on.
The case is still together, all timing gears are off, so the crank turns freely. It has been stored many years in Arizona (low moisture) and the engine appears to be in solid shape and no leaks. However I have no information from the previous owner. My original thought that I could sense roughness in the main bearings when spinning it, this was purely subjective, and looking at it again, not sure this is an issue. I am reading from most of the comments, bearings are very robust and not normally needing replacement.
So,.. leaning toward the camp that says, if it ain't broke, don't fix it,... heaven knows there is enough other stuff on this restoration to spend money on.
AZScott said:
It sure is nice to know that it's right, though.
Honest. spitting the cases is straight forward and hard to screw up. If they seal up good now, they will seal up good again.
Validating all those oil ways are clear is another bonus. I do not mean to offer horror stories but I swapped out a set of cases once and pulled a half a teaspoon of old ring matter and piston bits from the tunnels. I little detail now will offer a good nights sleep later. Knowing your hands have been in the heart of the Norton is very satisfying.
That being said, I did leave my clamshells and journals alone. The crank journals are surely one of those "if it ain't broke don't fix it" kind of things.
ashman
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I would go the next step and pull it apart, you are nearlly there and its not a big job splitting the cases, your main bearing will proberly be OK but it will be the rod bearings that will have a bit of wear on them, it better to replace the rod bearings before they wear the crank surface and if the motor has had a rough time it proberly be best to clean the sluge trap out in your crank to be sure, if you are keeping the bike I would go the full hog with it, take your time and do it properly then you will have trouble free riding for a very long time.
Ashley
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AZScott said:
My 71 was parked in a barn for about 20 years. Got it running and it didnt sound so good. Had it pulled down, (I didnt do it) but the main rollers had come apart and some of the ball bearings were loose in the case.
Not good.
Inspect them closely.
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if you don't check them it will always be in the back or your mind, so split them and replace them (and clean the crank sludge trap) - peace of mind means a lot on an old bike - that is of course if you actually plan on driving it any distance :shock:
OK, you just flipped me back to the camp where I can sleep well at night, (I plan to split the case).
The latest comments all make sense. Have a question however, where is the sludge trap ? I have done many Triumphs,
and I am familiar with wrestling with and removing their crank sludge traps. I thought Nortons were more sophisticated and had a bottom screen to catch the grunge, that is removable through the bottom of the case (Sump Filter Body # NM 16945), as well as an oil filter.
This is the first Norton that I have torn down, so where is the sludge trap ?
The latest comments all make sense. Have a question however, where is the sludge trap ? I have done many Triumphs,
and I am familiar with wrestling with and removing their crank sludge traps. I thought Nortons were more sophisticated and had a bottom screen to catch the grunge, that is removable through the bottom of the case (Sump Filter Body # NM 16945), as well as an oil filter.
This is the first Norton that I have torn down, so where is the sludge trap ?
Hortons Norton
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inside the crank
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If you already have removed the timing side gears from the crank, then strip the crank case and have a look. Removing those parts is the hardest part of the job. Just do it. At least when you put it together with the best sealant available, you'll know it wont leak.
Dereck
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OK, I'll play the devil's advocate.
So how many miles on this beauty? And what sort of mechanical issues did it have? Pictures would be helpful.
I agree that it's nice to pull it completely apart for peace of mind, and it can be satisfying work assuming you have a good
work space and you have the correct tools (pinion puller). But if you're not comfortable with this level of work you run the risk of something going wrong during the rebuild. This is how a lot of basket cases start.
Is there any physical evidence that the cases have been split before? Are the pistons oversized? Is there any play in the big end bearings? If the big ends are tight I'd leave it alone. Spinning the crank in the crank case doesn't tell you much. There's too much mass on the crankshaft and the cases resonate weird noises from the rotating bearings. The `74 has an oil filter as a first line of defense too. It's a slippery slope. You might as well replace the big end bearings too, maybe a regrind, maybe dynamically balance the crank, maybe a new cam shaft, and you'd want to clean out the sludge trap, and new nuts+bolts, perhaps a slick new breather modification. And there's nothing wrong with any of this, it's just time and money. Just be prepared.
Like others have posted, Superblends are extremely robust and extended storage shouldn't be an issue, especially if the thing wet-sumped.
I just haven't heard of many SB failures. Unless it's got over 50K miles, or someone ran it out of oil, or someone did a shoddy rebuild, they should be fine.
So how many miles on this beauty? And what sort of mechanical issues did it have? Pictures would be helpful.
I agree that it's nice to pull it completely apart for peace of mind, and it can be satisfying work assuming you have a good
work space and you have the correct tools (pinion puller). But if you're not comfortable with this level of work you run the risk of something going wrong during the rebuild. This is how a lot of basket cases start.
Is there any physical evidence that the cases have been split before? Are the pistons oversized? Is there any play in the big end bearings? If the big ends are tight I'd leave it alone. Spinning the crank in the crank case doesn't tell you much. There's too much mass on the crankshaft and the cases resonate weird noises from the rotating bearings. The `74 has an oil filter as a first line of defense too. It's a slippery slope. You might as well replace the big end bearings too, maybe a regrind, maybe dynamically balance the crank, maybe a new cam shaft, and you'd want to clean out the sludge trap, and new nuts+bolts, perhaps a slick new breather modification. And there's nothing wrong with any of this, it's just time and money. Just be prepared.
Like others have posted, Superblends are extremely robust and extended storage shouldn't be an issue, especially if the thing wet-sumped.
I just haven't heard of many SB failures. Unless it's got over 50K miles, or someone ran it out of oil, or someone did a shoddy rebuild, they should be fine.
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