take apart crankshaft?

Hi all,

A Norton newbie question - Is there any reason to take the crankshaft apart for a basic engine rebuild?

The reason to take apart the crankshaft on any rebuild is to clean out the sludge trap in the middle of the flywheel. This is designed to collect any solids and keep them in the middle of the crank out of the oiling system, also if you are planning on regrinding the big ends there is insufficient space to get the machining tool in without dismantling. Before you dismantle anything mark the left and right crank cheeks and the flywheel so that they go back together the same way they came apart, otherwise your balance will be incorrect.

I seem to remember from info I read long ago, that if you dismantle the crankshaf, that you should NOT reuse the fasteners. Is this correct, or am I just remembering that you should not reuse the con rod bolts?

Just something a newbie may not be aware of.

Hi Guys,

Thanks for the info! Yes, I'd read about needing new con rod bolts and nuts (same thing with some car engine rebuilds I've done in the past), so I guess it makes sense that new crank fasteners are needed too after breaking apart the crank assembly.

BTW, great site! I'm finally diving into a ground-up rebuild of a 1972 Interstate that I bought 20 years ago and that has traveled around in boxes with me ever since. It was complete (matching frame and engine numbers, April 1972 build date) but not running (9400 miles), but the engine did turn over using the kick start lever, so it seemed OK. I have not yet split the crankcases, though. It does have the combat engine, so I hope I don't find any nasty surprises in there! It had been in storage for about 10 years before I bought it - I hope that the reason for that wasn't a ruined crank and bearings.

norflog76 said:

I seem to remember from info I read long ago, that if you dismantle the crankshaf, that you should NOT reuse the fasteners. Is this correct, or am I just remembering that you should not reuse the con rod bolts?

Click to expand...

Actually the factory manual says that it is not necessary to renew the con rod bolts, only the nuts.

John Hudson said (in the NOC engine rebuild video) that he didn't see any reason why the crankshaft bolts shouldn't be re-used, as he had never known them to fail and that the original bolts were probably better quality than the new ones anyway!
He also remarked that he didn't see any reason to change the con rod bolts as they would be unlikely to stretch if torqued to the correct figure.
But the underside of the eccentric con rod bolt heads can have a sharp edge that should be filed so that they didn't scrape a shaving of alloy from the rod hole which could lodge under the bolt head as it was tightened.

L.A.B. is correct the con-rod nuts are deformable one-time-use lock-nuts and should not be reused under any circumstances. The con-rod bolts can be checked for length and if within spec reused.
I have found with crank shaft studs and nuts that they are often peened over to lock them in position, consequently they damage the nuts upon removal, however if they do manage to come apart undamaged I see no reason not to reuse them.

Dave M, L.A.B.

Sounds reasonable to me. Just like the new folks to be aware of these things, so they can at least verify wether or not it is an issue.

BTW, Dave M. - bought my first Commando in Hong Kong in 1972, had it shipped home on an LGS (Large Gray Ship)

Norflog76, British bikes including Norton had a stong presence here up until the early 70s, My best chum came 2nd in the Macau Grand prix production race on a Commando in 1973 in his first ever race, which included quite a few Japanese profesionals.
There are still a decent number of them here (Nortons that is!).