Bottom End Rebuild?

I'm picking back up where I left off on my 1971 Commando rebuild. The bike only has 13,000 original miles on it and so far everything I've pulled apart looks to be in great shape. I'm torn about whether I need to split the cases and rebuild the bottom end given the low mileage. Am I asking for more trouble than it is worth or should I just leave it alone, clean it up, and put it back together?

Also, what if I were to go in and just replace the main bearings leaving everything else as is...is that foolish? I'm kind of feeling like if it ain't broke don't fix it.

Rex

Rebuilt my 70 with 13K on it years ago and all I can say is everything was well within tolerances, but there was a lot of sludge in the trap. No oil filter then. I was still glad I put new bearings and pistons/rings in despite the cost and then I pretty much knew what I had (no slotted pistons). Of course I wanted to upgrade the main bearings no matter what. The shells are cheap. Up to you though.

I just went through the same process and asked myself the same questions with my '70 Roadster Rex.

I decided that, since it had been over 46 + years since it had been apart and since the patient was on the table, it was worth it to do the bottom end as well. Cleaning out the sludge trap and new main bearings provided a nice feeling of peace of mind. I had slotted pistons and my bores were in rough shape so I ended up needing an overbore and new pistons, rings, etc. as well. If you do it now it's done and you don't have to worry about it again. Save the paperwork and, down the road, neither does the next owner. Up to you though obviously.

Due to it's age... yes I would do it.

Thanks guys, it sounds like a pretty unanimous opinion.

Does anybody have thoughts or experience with this Bottom End kit from RGM, it seems like a pretty good deal:

https://www.rgmnorton.co.uk/buy/bottom-end-overhaul-kit-suitable-for-all-pre-mk3-commando_459.htm

This is mostly a philosophical dilemma as Nortons bottoms are pretty darn robust compared to everything else. Late Westly '71 got like 90K miles after a couple rebores/piston rings wore out, till last few 1000 miles could hear the looseness that siezed on hwy w/o much damage so just replaced bearings and rod big ends to carry on dicing it up with moderns. So how often do ya expect to have cases so convenient to open for preventive state of mind riding around feeling pensive-guilty-lazy? Full Nortneer status-respect requires Aztec like heart removal.
http://www.mexicolore.co.uk/images-3/358_00_2.jpg

@hobot I agree that there is something to be said for holding the guts of the machine directly in my own two hands. This is as much a learning experience for me as it is a repair/restoration job for the machine. As such, I should probably go all the way.

Wrecks, is the machine in question the same one that’s pictured in your avatar?

My reason for asking is, if the bike has sat unused and partially dissmantled for decades, in unknown storage conditions, then dust, rust, mice, dirty acidic oil, lack of motion etc will all have had chance to upset things. In this case, and especially if it’s a bike on which you have dismantled and rebuilt everything else, I would definitely do the bottom end as well. It would be asking for trouble not to IMHO.

Conversely, if it’s a bike that’s been in fairly frequent use, albiet on low mileage runs, and is in generally good original condition, I would definitely leave the bottom end alone, and have a very clear conscience about it.

Fast Eddie said:

Wrecks, is the machine in question the same one that’s pictured in your avatar?

My reason for asking is, if the bike has sat unused and partially dissmantled for decades, in unknown storage conditions, then dust, rust, mice, dirty acidic oil, lack of motion etc will all have had chance to upset things. In this case, and especially if it’s a bike on which you have dismantled and rebuilt everything else, I would definitely do the bottom end as well. It would be asking for trouble not to IMHO.

Conversely, if it’s a bike that’s been in fairly frequent use, albiet on low mileage runs, and is in generally good original condition, I would definitely leave the bottom end alone, and have a very clear conscience about it.

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Yes, it is the same bike and it has been partially dismantled and stored since at least 1980. All of those 13,000 miles were put on it in the mid 1970's and it has been stored in either a basement or garage since it was moved into storage. It may have spent a brief period outside under a cover. I did find some evidence of a mouse nest.

No mice or their excretions can reach inside cases and if mostly covered inside stored the mild humidity swings prevent much moisture sucked in so with only 13K miles i'd flush with diesel and spend time money other stuff. Might help decide if ya knew reason it stopped being ridden but its almost never a bottom issue - unless a early Combat, whose reputation stains - skews opinion of just how enduring a heart Commandos got. I'd leave diesel/gas inside long enough to make sure nil leaks. Sense of self worth plays into this, scoring points following idealist rule book logic or happy go lucky reasoned risk taker.

You realize there is 37year old solidified oil in your sludge trap along with bits of metallic sludge. Agree with group. Superblends, better pistons, replace all seals, clean out crankshaft, service oil pump. Recommend adding an oil filter while you are at it.

LOL!!! ***ALWAYS CLEAN THE SLUDGE TRAP OR ELSE!!!
A British Iron Motto Dumped Into People Proper Heads That Does Not Apply to Nortons only Triumphs and maybe BSA. Triumphs infamous for clogging journal feeds, as requires mean destructive plug removal/replacement nuisance that so puts off even expert shops it became iconic for skipped over maintenance.

Fact of the mater - hobot observations believed on not - is only a real bypass filter can remove the dust level accumulations as regular filters only meant to catch larger passage clogging junk, so in a few 1000's miles you'all have similar accumulation layer slung by centrifuge force to form a layer exactly like D shape best flow contour of exhaust port with enough pressure and flow to always keep flow path to journals always full flow open forever.

I've analyzed a few old and fairly new crank trap sludge layer to find only about 1/3 the nano dust layer is magnetic the rest alu or nano non-magnetic rust from oxidation/reduction chemistry metal grain size flaking. Was shocked at 1st seeing Peels new crank after 1.5 yrs routine use, almost as much as when bent crank 1st opened - which was about exactly same layer as found in 30+K mile factory Trixie opened up for foolish inspection after oil hole comma piston crack siezure going 50.

Triumph crank passage seems too restrictive so dust collects til clogs while Norton passage is too large and fills in like a stream self streamlining.

Peel had oil filter, everything cyro tempered and tungsten oxide dry friction coat impregnated, 1000 mile synthetic Mobile One 15/40 oil changes always still translucent greenish, so pissed off then enlightened.

Not likely to get fastened as securely either after disturbing factory harsh nip ups and no locktite can exist for long at crank temps, dahik. Nip down & stake if can't be talked out of split crank w/o reason.

A new husband as why wife cutting the ends off the ham to be told that's how my mother did it, piqued, called mother in law to be told, couldn't afford a bigger pan.

hobot said:

A new husband as why wife cutting the ends off the ham to be told that's how my mother did it, piqued, called mother in law to be told, couldn't afford a bigger pan.

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Great opportunity to shot peen the rods and get the rotating/reciprocating parts dynamically balanced.

Very very rare, if Ever, Norton factory rods fail before pistons or lifters or cases or crank fail 1st then rod suffer and get blamed. Ask TC on seasons endurance of 150 hp on factory part engines. Leave rods as is or polish up by lengthwise action and place rod shells to block useless Norton mistake of oil holes. Balance if significantly off but usually pistons more significant that rod differences. Tricky part is getting rod big end shells razor scraped to perfection.

hobot said:

Very very rare, if Ever, Norton factory rods fail before pistons or lifters or cases or crank fail 1st then rod suffer and get blamed. Ask TC on seasons endurance of 150 hp on factory part engines. Leave rods as is or polish up by lengthwise action and place rod shells to block useless Norton mistake of oil holes. Balance if significantly off but usually pistons more significant that rod differences. Tricky part is getting rod big end shells razor scraped to perfection.

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Is this razor scraping of big end shells a thing regular people do or is it a @hobot thing?

wrecks said:

Is this razor scraping of big end shells a thing regular people do or is it a @hobot thing?

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Razor scraping is still done today; I saw a video of the process, it was being done on a 107,390 BHP Wartsila marine diesel engine's big end bearings...

The replaceable bearing shells used in modern mass produced engines are not meant to be hand scraped. At all. Ever.

concours said:

The replaceable bearing shells used in modern mass produced engines are not meant to be hand scraped. At all. Ever.

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S’what I thought!