How deep is too deep?

The drive side cheek of the crankshaft on my '73, 750 has a concentric score where the seal held an abrasive mixture of primary crapola against it. I sent it to Mile High Crankshafts to be turned down as the big end clearance was over the tolerance; I asked them to repair or polish the spindle. I got it back with a note saying that a good polish should eliminate any issues; guess they don't do that service ( I will say that the big-end work looks first rate---I'm a bit away from doing the actual pre-assembly measurements) . So I polished the circumferential score, but noticed, even before I started. a scratch at 90 degrees to the scoring that crosses the score; this 90 degree scratch can catch my fingernail.

So I polished and polished without encroaching on the main bearing journal. My fingernail, now, doesn't catch anywhere, but I can still see the score and 90 degree scratch, which I can make my fingernail catch.

My question is: How tolerant is the seal? I plan to run a belt drive and already have the reed valve breather.

I tried to photograph the area, but with the camera's resolution and the lighting it's just a no-go. Your experiences with similar problems (are they problems?) is greatly appreciated.

I would think if you can catch it with your fingernail, or even perceive it passing your nail over the scratch, it will not seal oil.

What Next? Possibilities:

Insert a sleeve over the surface and fit an undersized seal.

Take it to a plating shop and nickel plate the area, then turn down to size.

Good luck with it.

Slick

My Gold Star has no seal between the engine and the primary. In normal operation, the engine oil in the sump does not enter the primary at all. However, if I left the engine sit long enough, and it sumped, then eventually some engine oil will get into the primary.
Okay, different bike, different design. But it raises the point, what is the seal on the Norton doing?
Not a heck of a lot, in normal operating circumstances.
So what are you risking with a small scratch on the seal surface?
Worse case scenario, if the engine is thoroughly sumped, the primary level might rise, eventually, if ever. In which case, drain some oil from the primary.

Gentlemen, commence volley firing.

Stephen Hill

Stephen Hill said:

My Gold Star has no seal between the engine and the primary. In normal operation, the engine oil in the sump does not enter the primary at all. However, if I left the engine sit long enough, and it sumped, then eventually some engine oil will get into the primary.
Okay, different bike, different design. But it raises the point, what is the seal on the Norton doing?
Not a heck of a lot, in normal operating circumstances.
So what are you risking with a small scratch on the seal surface?
Worse case scenario, if the engine is thoroughly sumped, the primary level might rise, eventually, if ever. In which case, drain some oil from the primary.

Gentlemen, commence volley firing.

Stephen Hill

Click to expand...

Good logic, but I am committed to a belt drive primary; goes with the CNW starter kit. Otherwise I wouldn't have posted as the engine oil and the primary oil would be the same and your observation would perfectly acceptable. Crankshafts aren't inexpensive, but I'd rather cut back on the single malt than to do the engine over a second time...I'm looking to produce a motorcycle that I can first-start and run 20 miles without carrying a tool or a chase van before its first oil change/re-torqueing/ re-do of all the other settings.

Yes, a belt drive changes things. This sounds like a good candidate for a seal repair sleeve. Only .010 wall thickness, lots of sizes available.

Stephen Hill

Yes, I was wondering if a SKF Speedi-Sleeve, like what we're using on my camshaft, might work.

pantah_good said:

Yes, I was wondering if a SKF Speedi-Sleeve, like what we're using on my camshaft, might work.

Click to expand...

I'm going to look into this strategy, but there is just not a lot of real estate between the inner race of the DS main and the belt sprocket. Interestingly enough the effected area is a-concentric and ranges from about 2mm to 4mm.

RoadScholar said:

pantah_good said:

Yes, I was wondering if a SKF Speedi-Sleeve, like what we're using on my camshaft, might work.

Click to expand...

I'm going to look into this strategy, but there is just not a lot of real estate between the inner race of the DS main and the belt sprocket. Interestingly enough the effected area is a-concentric and ranges from about 2mm to 4mm.

Click to expand...

You most likely will have to shorten the length of the sleeve. You will need machine shop services if you do not have access to a lathe. I am not a machinist, but I suspect a mandrel will need be made to support the sleeve while trimming it.

Good luck with it.

Slick