Trouble splitting case

Sirwompus · Feb 16, 2021

For the last week I've been trying to get a 750 case to split that I recently bought. There is rust inside the bottom end and evidence of big-end rod bearing failure/case damage so I'm probably not loosing to much if I don't get it apart but I'm curious if anyone has any ideas.

All bolts/screws are out and I've removed everything in the timing case including woodruff keys. WD40/PB Blaster has been soaking in every potential trouble area. When I tap the ears of the case and both ends of the crank only the bottom portion of the case wants to separate. The top of the case close to where the barrel meets is stuck hard. If the cam journals were rusted could that hold the halves together? If not what else towards the top of the case could be holding me up?

If pictures would be helpful I'll get some uploaded

Sirwompus · Feb 16, 2021

Oh and I've tried a bit of heat to

gortnipper · Feb 16, 2021

Maybe a spreader, or using a small jack?

marshg246 · Feb 16, 2021

Gorilla method: Get three longer screws to replace those that hold the inner primary and screw them in evenly until they are against the crankshaft. Some heat around the seam can help and keep tightening the three screws a little at a time and evenly until the seam breaks. Just don't go crazy and strip the threads. You may only get two to contact at a time.

The last on I did had a sealer that was some sort of very strong glue, not sealer.

CanukNortonNut · Feb 16, 2021

Tap the timing side on the areas where it protrudes with a hide mallet or a rubber mallet.
It should let go and you can walk it off a tap at a time.
Cheers,
Tom

ILLF8ED · Feb 16, 2021

I just got a set of 750 cases to separate two weeks ago that were really stubborn. The front and rear crankcase dowels were rusty on mine. Continue what you’re doing with heat and penetrating oil...go slow and take a break before the cases break. If you can find a foot hold for a piece of wood close to where the dowels are go ahead a hit the wood drift with a hammer, just not too hard.

swooshdave · Feb 16, 2021

Patience and light tapping until you run out of patience and get a bigger hammer. I usually jump right to the bigger hammer.

grandpaul · Feb 16, 2021

Yep, those 2 dowels are always the culprits. Focus on them and don't damage the cases any worse than they already are.

Torontonian · Feb 16, 2021

Yes to tapping (rubber mallet ) lightly all around the timing side. The drive side will be your more solid base point.

marshg246 · Feb 16, 2021

Just looked more closely at your picture and original post.

You've almost got it apart but you have the bottom/back separated making the front location dowel crooked. Try putting a plastic putty knife (or similar) in the seam at the very bottom and then pull the back of the case back together - that should lever the stuck part of the case apart. If that doesn't work use a rubber mallet to bring the bottom/back of the case back together and then tap apart again, repeat.

The cams won't hold it together as long as the cases come apart evenly. It would take massive rust for the crank to hold it together. So the front location dowel is probably what is stopping you, but you have it slightly cracked loose so it won't keep stopping you if you get the cases evenly separated.

My longer screws method will work, but it's important the the case comes apart evenly so the cams and location dowels don't bind.

chaztuna · Feb 16, 2021

When all else fails, use the proper tool. Make one of these

Crankcase puller

grandpaul · Feb 17, 2021

The more you skew the case halves relative to each other, the more likely you will need to replace the cam bushes (which almost never NEED replacing), due to the improper pressure forcing against them.

Sirwompus · Feb 19, 2021

Still struggling with this. The dowels some of you are taking about are the two, one at the front and rear of the case (relative to the engine as it's mounted in the bike) correct? In my eyes there is slight case separation around these dowels, but right up top where the cases meet the jug seems to be where it's stuck. I've got one piston out but the second piston/pin is very stuck. My approach now is to get that second piston out so I can make a jack that will separate the top part of the cases.

As mentioned before I'm wondering what I'm even gaining from this. My top end/jug seems useable but I'm really wondering if this bottom end even has any useable parts. *sigh*

swooshdave · Feb 19, 2021

Sirwompus said:
Still struggling with this. The dowels some of you are taking about are the two, one at the front and rear of the case (relative to the engine as it's mounted in the bike) correct? In my eyes there is slight case separation around these dowels, but right up top where the cases meet the jug seems to be where it's stuck. I've got one piston out but the second piston/pin is very stuck. My approach now is to get that second piston out so I can make a jack that will separate the top part of the cases.

As mentioned before I'm wondering what I'm even gaining from this. My top end/jug seems useable but I'm really wondering if this bottom end even has any useable parts. *sigh*

You don't need the cases themselves?

If it seems to be sticking at the top then push the bottom together and work on the top. But keep in mind the more even you keep it the better.

marshg246 · Feb 19, 2021

If you can get the the inside of the drive side of the case, use a piece of wood 1/2" down from the top edge and hit the other end with a hammer. A 1" oak dowel works nicely. There is nothing to hold the cases together with all the bolts/nuts removed except the two dowels, corrosion, and/or whatever sealant was used. As before, I would close the bottom/rear gap first. The dowels are a tight fit and having the case cocked makes them really hard to get apart.

kommando · Feb 19, 2021

There are 2 studs up at the top screwed into the timing side case which run through holes in the driveside case.

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

Parts 32 and 29, see if you can send some de-rust fluid down the holes as the studs could be rusted up and expanded in the holes on the driveside case.

marshg246 · Feb 19, 2021

This sat in a junk heap outside from 1976 until 2017. The cases were difficult to get apart but came apart undamaged.

Sirwompus · Feb 20, 2021

^^^^ There's hope then!

chaztuna · Feb 20, 2021

marshg246 said:
This sat in a junk heap outside from 1976 until 2017. The cases were difficult to get apart but came apart undamaged.

View attachment 21917

Greg, was this Commando broken down for parts or restored?

marshg246 · Feb 20, 2021

chaztuna said:
Greg, was this Commando broken down for parts or restored?

The rods and crank are running fine in a Combat today. I restored the engine and gearbox cases to new looking. The gearbox case was sold and most of the other gearbox parts have been used to fix other boxes. The inner primary was too corroded to restore and the frame was too rusted to restore.

The bike was wrecked and the owner bought a parts bike to fix it. Instead of using those cases, he ground off the serial on the parts bike and re-stamped. When I sold the bike, the original cases went with it so there was no confusion over the serial number.

It is all documented here: https://www.gregmarsh.com/MC/Norton/Norton_1972.aspx including showing the cases just split.

Pretty amazing that one can sit in the rain for 41 years and till have a lot of good parts!

Trouble splitting case

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