Broken crankcase under camshaft

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Colin_McKellar

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Aug 11, 2008
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I carefully rebuilt my Mark 3 Commando engine and used all new bolts and torqued them up to the factory specs. Got the bike running and it was sounding good. I noticed an oil leak and when I checked it it there was a burst through under the (camshaft?) bulge on the left hand crankcase. It is around 1cm long and is above the isolastic mounting.

I am gutted and cannot work out what could have gone wrong to cause this problem. I'm not sure whether to rebuild the engine again or sell the bike!!
 
Colin,

You are somewhat unlikely to get a good price for it if there is damage to the cases, from your description it doesn't sound too serious and could surely be welded by a competent chap. Is it possible that the camshaft got displaced during assembly, was it hard to put the cases together the last inch or so? I'd strip it fix it and then decide.
 
It is a mystery to the guys in the Norton Owners Club as well.

All the parts went in correctly with plenty of clean oil used during assembly. Everything was rotated many times to ensure that there were no tight spots. Before the engine was started I kicked it over until oil returned to the tank. When running the oil was returning to the tank.

I am going to see a set of open cases to try and work out exactly where the break out has occured.

One of the guys said to pack it with Araldite and use it for the summer and rebuild over the Winter. Not sure if that would work in practise.
 
Colin_McKellar said:
I noticed an oil leak and when I checked it it there was a burst through under the (camshaft?) bulge on the left hand crankcase. It is around 1cm long and is above the isolastic mounting.
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Maybe something came loose and got trapped between the cam lobe and the case?

Colin_McKellar said:
I am gutted and cannot work out what could have gone wrong to cause this problem.
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Rightly so, as I think anyone would be.


Colin_McKellar said:
I'm not sure whether to rebuild the engine again or sell the bike!!
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If I'd done all that work, then personally, I'd at least want to know what went wrong?
 
Are you positive the crack wasn't there before you dismantled the bike? You could try an epoxy steel like 'JB Weld, but I would be inclined to see why the case cracked for peace of mind. I have just popped down to my workshop and had a look at some empty 750 cases, the first lobe on the left side of the cam sits centrally in line with the left side top engine mounting boss where the isolastic assembly abuts it. This sounds like where you are describing the breakthrough in which case the cam has almost certainly hit something loose inside the case.
 
hi colin,could it be one of the small screws that hold the cam follower guide plates in position,come out and got behind the cam lobe
 
Man, you're scaring me to death. I'm about to fire up a rebuild also and I've never been so paranoid. My heart bleeds for you, I would be devastated.
 
For what it's worth when I got my bike with a "supposedly rebuilt engine", it had a good size crack in the same place. I got it welded up for a reasonable price, the repair is hardly noticeable unless you look for it, and it has never given me a problem.
 
Hi there, " LAB" is a real Sherlock Holmes, as effectivly when looking backward to this previous post ther could be a link to this damage.......as soon as you had dismantled your engine you will find out the reason , then after a good TIG weld and keep on riding , but try to find a buddy to help you checking and refitting that engine.
Don't give up !
 
I really feel for you sport, I was disappointed last night when I put a rig together and had a short (I found it in ten seconds in the morning), much less have a case crack.
Here's the good part. I used a welded case every day for ten years with no ill effects and she ran fine when i gave her away. My current Norton has a huge brace welded in the spot that Combats used to crack in, no problem at all.
If she were my baby I'd take her to a very good alloy welder, put the ground next to the crack and weld it. If that fails you have to take it apart. If it works you'll have to take it apart in ten years.
My guess is that since there have been so many different cams and such that your might just be a bit over tolerance, a bolt or something is also possible so looking at the oil should show some metal with a magnet if so.
If it spins freely odds on a weld would work forever.
 
i think it needs investigateing, to at least take the head and barrells off,crankcases dont just decide to crack on startup,maybe the crack was allready there and missed during rebuild
 
Well,

I did just successfully take the CJ 750 to the car wash, carefully avoiding all the wheel bearings and such. It will do at least a couple of shows this year and after about 200 riding days has needed spiffing up and service.
No doubt the absolute correct thing to do is go in and see what is going on, if it was an aircraft I would. Regardless I'd be having the oil analyzed for a while.
If she was turning free I'd probably weld her though.
 
chris plant said:
hi colin,could it be one of the small screws that hold the cam follower guide plates in position,come out and got behind the cam lobe
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This sounds like a possible culprit. On my 850, these screws were drilled for safety wires, which I installed when I assembled the engine. Perhaps these screws were not wired in place?

Sounds to me like a teardown is in order - you'll want to make sure whatever caused this is determined so it doesn't happen again.
 
You didn't fit a plain, unscrolled camshaft,into a plain bearing and hydraulic the end of the case as you bolted it up by chance did you???
 
Ya know Splatt, that was one thing I kinda wondered. It could work just like a little hydraulic jack.
 
The screws on the cam plates were wired into place. I took the magnetic plug out tonight and there is a fair amount of coarse swarf on it. next step is to tske out the big crankcase filter out and see what lurks in there. I also looked down the line of the bike and the burst out is in line with the cam followers so it definately looks like something has come loose and rattled around before ending up under one of the lobes.

I really cannot undrstand it at all. Everything was wired, loketite and/or punched along the threads before assembly.
 
Somebody correct me but I think years ago I may have just taken one side off a case to change a cam. I think you have to pull the studs to do that and there may not be enough time saved to justify the fudging. This was 40 years ago and I'm pretty sure that was my G15CSR I did that to when I found out a cam that was good for racing, and all the magazines loved, could suck on the street.
 
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