Unintentional crank case ventilation

When overhauling my -69 Commando I discovered a missing piece of the right side crank case. My guess is that a prevoius owner has been trying to remove the crank shaft sprocket without using the Norton service tool pulley, and failed.....





The support of the crank shaft bearing in the crank case does not appear to be affected.

What worries me is what effect might this have on the crank case ventilation.

The bike has allready been modified with an extra breather hose fitted to the back end on the timing side.

Does anybody have an idea of what will happen once I fire up the engine? Will the crank case pressure for example blow the timing cover seal?

Since later models have their breathing pipe located on the left timing side there must be an 'enginered' route for the over pressure to escape through the timing cover side.

Another area is the effect this might have on wet sumping.

Is it possible to repair a crank case with this kind of damage?

I would not be so worried about the crankcase ventilation but I would be concerned with flooding the bearing with oil from the timing chest. Ball or roller bearings don't like that much oil as it makes the rollers skid instead of rolling.
What I have done to repair it was cut a shim from stainless stock with a hole in the center large enough to just clear the sealing plate that sets against the bearing. I installed it in the case before I installed the bearing to shield the bearing from the excess oil. Jim

Looks like from Photo 1 that the bottom end is in in one piece so what I would do as a minimum is drain out all residual oil and get in there with a light or 2 and search the bottom for that missing chunk of aluminum casting or any pieces seeing as you do not know the history of the boo - boo. Can't see the proper puller doing that kind of damage ,P.O. probably did not have the puller and tried some brutal prising method to get the gear off. Which would mean the piece could have flown inwards ,no ?

Its a total non issue on ventalation except that it will improve-suppress some of the pressure spikes as adds easy access to TS volume to compress above outside.
I made that much extra hole in my hot rod Peel for just this purpose.

Likely not even a over oiling bearing issue as so low down its lowers the oil
level in the TS case. It may not even be a strength issue either as crank
end is also held some what by the oil feed/seal in cover.

By my own experience I've guess this damage resulted from an over rev event
and that the area the crank ends get jerked on jerking pistons from TDC,
slightly forward of BDC. Check cover oil feed boss and crank end bends
and the oil pump drive snout. Also inside alternator stator for collision evidence.
I don't suspect a prying damage as don't think ya can get a lever in there.

If this was me and it has been twice now, once d/t stuck throttle and once by rod bolt let go going 3000 easy rpm, I'd just JBWeld it up trim back and run it
in normal use but not over 6000 or so for long. If welded be prepared to have crank bores re-line bored true as distortion is guaranteed that much and close
to tight fitting items. Even Comstock recommends JBW to fill in lose bearing clearance. Wet finger/glove, tapping and smearing allows smoothing JBW w/o dragging it all over the place, but sag factor on set up would be hard to over come. I'd forget about it myself if ran ok prior.

If you carry on running the motor with broken case, then it might be fine for a long while. Alternatively it may well blow to pieces as the damage is in a highly stressed area, and a spun bearing, or cracks originating from the damaged area are both possible. Currently the case is easily repairable, but obviously the motor would need to be stripped to do this.

Depending on your peace of mind away from home the easy way out is source another case set, my first call would be to Baxter's Cycle but plenty to pick from to see how much to sway your judgment. Dilemma with that is the case serial numbers to match the stem and STATE registration record. I've race cases that will be stamped for matching numbers but it don't have any to remove first.

There is an amount of oil to be maintained in the timing chest as seen here by the hole for flow back to the sump and the fact the there is a cupped crank bearing washer to keep free flowing oil from the bearings. You at least need to patch that back up and if structure integrity is in question, replace the cases. They are out there. Just keep looking.


I have a set of early 72 cases but the spindle hole will have to be drilled and bushed. Not nearly as tricky as what you need to have done.

Those damaged cases can be easily repaired in about 40 minutes, so no real need to replace them unless a spare set is less costly than a repair.

So how does one repair such a damaged case? (I do not have the missing piece)

Dick

You could literally cut, grind, and shape a piece of aluminium comparable to the thickness of the surrounding material and, if no structural or stress related issues exist, JB it in place. If structural or stress related issues exist, then have it welded in. Either way, make a patch.

To be honest, when looking the bearing from the wrong side of the case, you need a new/use crankcase half at least. If you can find a half you can keep your numbers but may have to line bore the cam bearings. I have seen many halves for sale, usually the timing side.

Anyhow, matching numbers is over rated and cannot compare to a solid, dependable crankcase. My bike is registered off the frame number which, interestingly enough, matches swooshdave gearbox numbers. Small freaking world. My fresh crankcase number isn't nearly as close as it used to be either. :lol:

I've said it before, these bikes are an assembly of assemblies. If all the assemblies are good, the whole is good. That being said, and for touring and distance riding, a chain is only as strong as it's weakest link. Let's hope that your weakest link will be something less critical than the crankcase.

I tell you what else you need to repair is the sealing surface for the timing cover gasket along that area. I think that's reaching the limits of Hylomar Blues gap filling abilities. Alumalloy might work there. Fill it, file it flush. Although this is another reason to replace.

dick danielson said:

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dick danielson said:

So how does one repair such a damaged case? (I do not have the missing piece)

Dick

Click to expand...

You dont need the missing part...........leave the bearing in place and fill in the hole with 4043 flller rod. Damage on the joint face can be dealt with at the same time, and the material these old Brit casings are made from is very easy to weld. Is important not to put too much heat into a part like though, so you would need to find someone who does know what they are doing.

The crank cases and covers are about pure Al alloy not like the duller head alloy so mention to welder to pick correct rod. I used a pancake head propane tank top heater unattached from tank to get cases as hot as possible and keep it mostly that way while welder does his horror procedures to witness up close. If me I'd not weld on the seam area but fill with JBWeld or really risk distortion sealing trauma. I'd consider also leaving the crank installed and cases clamped together, the bearing and crank mass should keep its temper fine. I'd even consider leaving the barrel bolted on to boot.

Things like crankcases are generally LM6, which has 10% silicone. In most cases pre-heat is not required, other than for helping to remove oil from the pores of the casting to be repaired. The best way to make these sort of repairs is to try to put as least heat into the casting as possible, as more heat than is really required can lead to distortion, and in some cases cracking.

hobot said:

The crank cases and covers are about pure Al alloy not like the duller head alloy so mention to welder to pick correct rod.

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I'm not quite sure what you mean by "pure Al alloy". The cases are certainly not "pure Al", but they are an alloy. An alloy is a mixture of metals, so by definition not "pure". Typical aluminum casting alloys also contain copper, silicon, iron, magnesium, zinc, lead, titanium, tin, etc. If you tried TIG welding the cases with a pure aluminum filler rod (1100 rod), I can guarantee you'd get cracks in the weld. I use 4043 filler rod to weld aluminum castings, including Commando cases and heads. If you were casting new Norton crankcases in the US today, you would probably use A356 alloy, or something very similar. I think Steve Maney uses LM25 for his cases, the British Standard LM Series near-equivalent to A356. If I recall correctly, Norton used a lower strength alloy, maybe something like LM4 or LM6, but I don't recall the actual alloy designation.

Welding a large patch in this area of your crankcase is certain to cause some distortion in the main bearing bore. I don't doubt that it could be done, with the right choice of patch and filler rod materials, but you might have to machine the bearing bore just to get it round enough to insert the race, or it could be so loose you'd have to sleeve it. You might also find that the case has cracks in the damaged area that would also need to be welded. A replacement case, or case half, sounds like a lot better solution.

Ken

If an old bearing is left in the case, and the right welding techniques used, there will be little if any distortion on a simple job like that. Distortion generally occurs due to excess heat, which is easy to avoid if the jobs done right.