Primary Housing vacume check????

[DougC]

I've got a tech question that I'm not sure about. I've got an 81 shovel and today while riding noticed a hairline crack in top/front of the inner primary case with oil leaking out. Went to reading the manual on replacing it and it refers to a vacume check, saying a vacume hose should be attached and read 9 inches of water at idle. Why does the case need to be vacume tight? It's a chain drive so oil is slinging around. I would think a vacume tight case with oil slinging around would lead to blown gaskets and such. Plus I was going to put some JB weld on the fracture keep riding it until I could save up the cash to buy a new inner case, so if it is that critical that it be vacume tight what damage would be done by continued use with the crack?

[coolvan]

I've got a tech question that I'm not sure about. I've got an 81 shovel and today while riding noticed a hairline crack in top/front of the inner primary case with oil leaking out. Went to reading the manual on replacing it and it refers to a vacume check, saying a vacume hose should be attached and read 9 inches of water at idle. Why does the case need to be vacume tight? It's a chain drive so oil is slinging around. I would think a vacume tight case with oil slinging around would lead to blown gaskets and such. Plus I was going to put some JB weld on the fracture keep riding it until I could save up the cash to buy a new inner case, so if it is that critical that it be vacume tight what damage would be done by continued use with the crack?

the problem is because of the clutch.the primary chain is lubricated by oil mist from the engine and a few oil drops.the engine then sucks the oil out from the primary case.if the housing isn't tight, the engine can't suck the oil out of the primary case but it will suck air and the case will be filled with oil.but since the clutch is a dry unit it will slip when soaked in oil!

[M.O.Ther]

What many shovelhead owners do, and what Harley did after a while, is to eliminate the vacuum deal and isolate the primary.
With the vacuum system, the oil from the primary, with minute chain wear particles and clutch wear particles and nylon from the shoe get sucked back into the motor. If you get an air leak, like your crack, it'll stop sucking but keep dripping 'til the primary gets full enough for the clutch to slip.
The solution. Re-plumb the oil system to isolate the primary, get a wet/dry set of clutch plates, and run the oil of your choice (ATF, Harley Primary Oil, etc) up to where the chain runs in it but the clutch doesn't, when it's level. I'm sure somewhere on this board is a plumbing diagram for the oil lines. And don't forget to vent it, otherwise when the primary gets hot, the heated air/oil mist will push out through the threaded holes and past the gaskets.

[DougC]

What many shovelhead owners do, and what Harley did after a while, is to eliminate the vacuum deal and isolate the primary.
With the vacuum system, the oil from the primary, with minute chain wear particles and clutch wear particles and nylon from the shoe get sucked back into the motor. If you get an air leak, like your crack, it'll stop sucking but keep dripping 'til the primary gets full enough for the clutch to slip.
The solution. Re-plumb the oil system to isolate the primary, get a wet/dry set of clutch plates, and run the oil of your choice (ATF, Harley Primary Oil, etc) up to where the chain runs in it but the clutch doesn't, when it's level. I'm sure somewhere on this board is a plumbing diagram for the oil lines. And don't forget to vent it, otherwise when the primary gets hot, the heated air/oil mist will push out through the threaded holes and past the gaskets.



Thanks M.O.Ther/coolvan
That makes sence now that I think about it with the oil feeds. At some point a previous owner sealed the primary so I have no oil lines running to it to mess with . I didn't make the connection (Doooooh). Now I have one big vent.
Thanks again