Topic: Deleting the starter clutch and gear from behind the rotor on a cb750

[T1m32sh1n3]

Im getting rid of the starter clutch and gear behind the rotor. Is there a sleeve I need to press onto the crank to block the oil hole on the crank?

[scottly]

No, you don't need to block the oil hole. There is a 1mm jet in the hole that limits the oil flow, and the starter gear is such a loose fit that it doesn't restrict the oil flow at all. The only downside might be more oil sprayed around inside the alternator cover, but I've run both with the jet open and blocked and never noticed any difference.

[T1m32sh1n3]

Do you know of a good way to block it?

[scottly]

I tried threading it for a grub screw, but snapped the end of the tap off, which blocked the hole. When I wanted to re-install the starter, I had to grind the tap out with a diamond coated burr in a dremel, which was a pita. Some guys have used the inner race of a ball bearing that's the same diameter as the crank, (30mm??) but like I said before it's not necessary. I ran the bike for years without the hole blocked.

[T1m32sh1n3]

Thanks for the info!

[T1m32sh1n3]

Are you 100% sure that there won't be a loss in oil pressure if I don't block that oil feed hole?

[scottly]

Yes. Like I said, the bore of the starter gear is a loose fit on the crankshaft and doesn't restrict the oil flow. The seal on the gear is to direct the oil towards the engine case, rather than on the inside of the starter clutch.

[Don R]

 If I remember correctly dragracer mentioned he had raced for years without a starter gear or blocking the oil passage.

[PeWe]

I think it was a thread on this forum  about the oil hole in crank under the starter gear.

In that case starter gear was removed and oil hole was blocked.
Crud built up in that oil channel so the crank bearings on #1 were finally damaged due to oil starvation.

[scottly]

I think it was a thread on this forum  about the oil hole in crank under the starter gear.

In that case starter gear was removed and oil hole was blocked.
Crud built up in that oil channel so the crank bearings on #1 were finally damaged due to oil starvation.

The oil hole is at the end of the crank, and the "channel" that feeds it is the size of the bolt that holds the alternator rotor. Besides, oil goes to the bearings first, then into the crank, so there is no way any blockage at the end would starve the mains. On the other hand, if one of the steel balls that block the ends of the drilled passages in the crank comes loose, then it can bleed off oil pressure, damaging the bearings. This may be what you were thinking of?

[PeWe]

I think it was a thread on this forum  about the oil hole in crank under the starter gear.

In that case starter gear was removed and oil hole was blocked.
Crud built up in that oil channel so the crank bearings on #1 were finally damaged due to oil starvation.

The oil hole is at the end of the crank, and the "channel" that feeds it is the size of the bolt that holds the alternator rotor. Besides, oil goes to the bearings first, then into the crank, so there is no way any blockage at the end would starve the mains. On the other hand, if one of the steel balls that block the ends of the drilled passages in the crank comes loose, then it can bleed off oil pressure, damaging the bearings. This may be what you were thinking of?

I could not find that thread. It must have been the "High Performance and Racing Forum"

As I recall only as I wrote. It might have been more to it later on.

Time flies by very quickly. Before or after Covid? Just before is now over 5  years ago.
I might have found an earlier thread when searching. Can have been from late 2016 and to a few years ago.

I got the Billet block with 71.25 mm pistons and APE Ultra crank back in 2016 and had my eyes on the racing forum.

[Don R]

 Behind the steel ball pressed into the crank is a dead-end oil passage that can catch particles and sludge. That's the reason that the balls are removed and the oil pathway cleaned out. Since it isn't practical to replace the balls, the holes are then welded closed.
 If a motor had enough gunk in it (which I have seen) the passages could pack up.

[scottly]

Since it isn't practical to replace the balls, the holes are then welded closed.
 

Usually the holes are tapped and grub screws are threaded in.

[dragracer]

If I remember correctly dragracer mentioned he had raced for years without a starter gear or blocking the oil passage.

Correct Don. The crank end actually broke off. I cleaned up the end of the crank and kept moving. I didn't plug anything or try to restrict oil flow. Same crank is being raced today after 25 years in that condition. No bearing failure or indication of low oil pressure.

[dragracer]

It still lives.