Replace main bearings routinely?

Re -doing an approx 50,000 mile 850 with two roller main bearings. They look and feel good. I am tempted to re-use. Maybe the current replacements are not as good for proper running clearance and case fit? Or would everybody replace, and go through the end-float shim fitting?
Thanks
Doug

If the main bearings are good, why replace them ? I don't recall a lot of main bearing related engine failures when using 'superblend' bearings.

Greg

tough call

I would leave them in there but only because I ride maybe 1000 miles a year and I am 63

as such I would likely be close to death before those bearings failed and so would not care

IF I thought I was going to put more than 20K more miles on then I would want new ones in now since you have it all apart anyway

One way to objectively feel though a decision is to completely de-lube the bearing so dry metal and slowly roll and roll and roll and roll, feeling for any sense of an instant of hesitation or tick like vibration. Its so short and subtle it may take a bunch of round and rounds to decide if was your imagination or is reproducible every few dozen rotations cycles it take to line all the round things up so they all encounter a slight fault impressed into them when so aligned on the fly. That itty bitty tick will happen a bunch of times on a ride under a lot more speed/loads. If ya can really tell stick em back in and check again in a few more dozen 1000's miles more.

You have to decide if it's worth the possibility of bearings coming apart in the near future and having to take the engine back out/apart, or go ahead and pay the up-front cost on new bearings. Hobot makes a good observation of getting the bearings completely clean and dry, but be very subjective in your analysis.

Douglass Harroun said:

Re -doing an approx 50,000 mile 850 with two roller main bearings. They look and feel good. I am tempted to re-use. Maybe the current replacements are not as good for proper running clearance and case fit? Or would everybody replace, and go through the end-float shim fitting?
Thanks
Doug

Click to expand...

The later bearings should do considerable mileage even if they are a little out from the original spec wear wise.
My 74 Mk2a when I stripped it was on a stock bore and its original pistons with a bit of blow by only so have elected to do no more than a hone and replacement pistons and rings.
The crankshaft journals were also stock and needed no more than polishing and new shells.
The main bearings (FAG) by all accounts were still good but elected to replace them and did as HoboT says,removed them by heating them in the oven (after cleaning the case halves spotless) and giving them a rap on a wooden surface.
After cleaning and drying them,looking at both the rollers and inner sleeve surface with a magnifier they looked re usable,spinning by hand dry showed the timing side bearing to be a tad noisier than the drive side so went for new ones.
I think it removes any drama down the track,even if the top end (bore) did go off in the future,doing that job is easy compared to pulling the engine to split the cases.
It has a shade over 21000 miles on the clock and although the valve seats need cutting along with a new set of valves I think it has had a easy life.
The bearings could most likely be reused so are up for grabs,I was tempted to put them in the 71 750,its original DS roller bearing had detectable up and down movement at the crank,the TS ball was not to bad.

If you have your botton end pulled apart then I would replace them even if they don't need to be replaced, they do last a very long time, but if you don't go down to the bottom end I would not worry about it.

Ashley

The real issue agains the 'change them because it is apart' brigade is.....

Will you source better bearings and will you do as good a job of fitting and shimming them?

And will you ask this question of yourself and give an honest answer?

We probably underestimate how many mechanical maladies stem from, well I had it apart so I changed them anyway.......

I chose to have Norman White fit an shim my new bearings in my new cases because he does it every week and has tools I don't.

Doesn't mean I can't (I have done it before with no issues) or won't do the job at some time, but I have a significant investment in the bike and I am going to abuse it (see comment on Chris' threat about his Rickman that I rode last year!)

Only you know the answer and what you will really do with it, and if you will be happy to strip it again in a few years if the mains begin to rumble.

Why have you split the cases?
My engine had alot of metallic grit in it an signs of an old poorly done repair after some major failure. I found a stelite pad stuck on sump magnet an it was not one off the followers that running on cam!! The bearings were not super blends even though engine was a 74. They felt good an looked good but due to grit an obvious sloppy work it was a case of change them for peace of mind.

Mine was an easy choice but is your engine that bad??

Why have you split the cases?
My engine had alot of metallic grit in it an signs of an old poorly done repair after some major failure. I found a stelite pad stuck on sump magnet an it was not one off the followers that running on cam!! The bearings were not super blends even though engine was a 74. They felt good an looked good but due to grit an obvious sloppy work it was a case of change them for peace of mind.

Mine was an easy choice but is your engine that bad??

There's an old & very wise saying "If it isn't broken, don't try & fix it."

Leave well alone. If they fail, & that's a big 'if', they will rumble & very unlikely to fail catastrophically so you'll have plenty of warning.

Ian

same make & model bearing SHOULD be shimmed as was , as theyre PRECISION thingos .

Oil Filter in the works ? or itd require de sludgeing , prsumeably .

Likely crank flex at mega revs would be biggest load factor . If your not the stop light grand prix type - a good inspection should tell you their condition .
Strog light & magnifyer / eye glass or etc .

I'm from the camp that says if your in there replace them. 50K on bearings is the reason here. If it were lower mileage maybe, but the problem is if they fail in the near future you will kick yourself for not replacing them. Are there new bad main bearings out there? I haven't heard much about that. So replace them.

dennisgb said:

I'm from the camp that says if your in there replace them. 50K on bearings is the reason here. If it were lower mileage maybe, but the problem is if they fail in the near future you will kick yourself for not replacing them. Are there new bad main bearings out there? I haven't heard much about that. So replace them.

Click to expand...

Dennis, I for one wasn't suggesting that new earings might be bad.....but there probably are some if you don't buy from the right places....

But it is certainly possible to fit bearings badly!

Although I think SteveA rasies a very valid point, at 50k, I'd put new ones in.

Whichever way you look at it, provided you buy good bearings, and fit them properly, new ones will last 50k longer than your current ones!

Having siad all of that, if you're 86, then, no offence, but your old ones will be fine!

I'd replace them, as stated above, be careful to do a proper job. The shimming will likely remain the same, as it compensates for cases/crank machining variations. The bearings typically are reapeatedly the same within microns (unless the vendors have changed the dimensions, which can happen).

For best peace of mind and least flak from who ever - now is the time to put them out of your mind and wallet hung on the wall. Over the dozen years+ I've been paying attention there are many reports of non-superdupers being about pristine in Nortons and other brands but mis-undertanding of what actually occurred in Combats tends to get reflex trashing of proven lasting non-superduper bearings. Might be braver than most and have the used proven bearings cryo tempered then dry friction coated for saving peace of mind and spend savings on tires and chains. I've read lots of reports that non-supers were found fine inside, like I did twice on 2 hi mileage Combats and had first flat rollers out of regional famous pre-Peel show room test bike checked by nit picking penny pinching builder that said still plenty good to go. I built Peel like old school racers told me so Peel had superduper on DS and 11 ball on TS and ran routinely into red zone crank whip sports bike spanking and beyond fun plus the tach needle bouncing invisible over rev event that broke oil pump snout, flattend a cam lobe and melted alternator stator resin and steel laminates from rotor off centering from crank jump rope, but crank bearing found fine so now a couple years use in Wes's '71 that went most of 100K miles on non superdupers originals but finally seized on hwy after making some noises a few 1000 miles before the rod shells let go. I tried to find online references on how to check crank bearing but only found info on plain shell-bushing type not anything on roller type but did find statements that roller element bearings never wear out unless something else happened no fault of the roller elements. Unless an obvious fault found it boils down to philosophical and money decision.

I'd replace them and here's some reasons why.
The next owner of that bike will be happy you did. The bike will be more desirable to buy and easier to sell.
If I was buying a Commando, I'd steer away from a bike with 50K miles on original main bearings. It's good for your Norton parts seller. He needs the business. There HAS to be some wear on those bearings with that kind of mileage, despite what you think the condition might appear appear to be. It all depends on how carefully the previous owners checked/changed the oil, and how it was stored.
We are just temporary stewards of these bikes. It's nice to make them better while they're in your garage.

If you've already removed the engine and split the cases you've done most of the hard work. Seems a shame to quit so close to the finish line. Besides, it's satisfying (fun) work, and It's a good opportunity to check other components inside the crankcase like the big ends, cam bushings, etc. You never know what you'll find inside unless you open her up.

Whenever I buy some old crock, I like to get inside the engine and lay my hands on the innards and make improvements where I can.
This process really makes the bike "mine" in my tiny brain.

I've got the original roller+ball main bearings from my 63 Atlas sitting on my work bench (24K miles) and I can't bear to discard them.
I installed Superblends of course.

Boy oh boy what a spot of wisdom thinking about those that inherit our Commandos will think about us. As there seems no way we can judge life left in seeming good to go bearings but subjective sense - if not lab equipped - best stick with almost universal No brainer safe bet way * always spend extra * to replace all bearings every time possible as what ever caused opening cases [but in my current Trixie case] implies some un intended load on bearings that could shorten the rest of their life. Someday maybe i'll have a sonic sampler to pass around to judge engine components going sour before it costs more. Oh yeah as fun and tempting to do, don't air spin dry a bearing unless you are already done with it. Here read this and get back to us with how to judge bearing wear we can use.

http://www.timken.com/EN-US/Knowledge/F ... -Guide.pdf

SteveA said:

dennisgb said:

I'm from the camp that says if your in there replace them. 50K on bearings is the reason here. If it were lower mileage maybe, but the problem is if they fail in the near future you will kick yourself for not replacing them. Are there new bad main bearings out there? I haven't heard much about that. So replace them.

Click to expand...

Dennis, I for one wasn't suggesting that new earings might be bad.....but there probably are some if you don't buy from the right places....

But it is certainly possible to fit bearings badly!

Click to expand...

Steve,

No problem. Was wondering if someone had gotten bad bearings. Hadn't heard this about mains before.