rebuilt engine blowing white smoke from breather tube

[akbear]

I just fired up a rebuilt Z600 and I have white smoke coming out of the valve cover breather tube. Is this normal during an initial start and perhaps will correct itself once the rings are seated? It's running well and exhaust is fine. Once it was up to operating temperature, I had it running under load for about half an hour at half-throttle. I held a paper towel over the breather hole and there wasn't any pressure, just a thin film of oil. I appreciate any insight. Thanks!

 

[Kubota Newbie]

Never had a fresh rebuild on any motor do that.

 

[Dave_eng]

I just fired up a rebuilt Z600 and I have white smoke coming out of the valve cover breather tube. Is this normal during an initial start and perhaps will correct itself once the rings are seated? It's running well and exhaust is fine. Once it was up to operating temperature, I had it running under load for about half an hour at half-throttle. I held a paper towel over the breather hole and there wasn't any pressure, just a thin film of oil. I appreciate any insight. Thanks!

In your world explain what rebuilt means.................
Dave

 

[akbear]

In your world explain what rebuilt means.................
Dave

Machine shop rebuilt the head with new valves/ guides, checked the block, polished and installed the crank, pressed in new sleeves and bored them out. New pistons, rings, bearings, injectors. New springs and seals in injector pump.

 

[ctfjr]

Is there a pcv valve on that motor?

 

[akbear]

Is there a pcv valve on that motor?

Negative on the pcv, just a vent hose.

 

[North Idaho Wolfman]

Did the injectors and injection pump get rebuilt?

 

[akbear]

Did the injectors and injection pump get rebuilt?

New injectors from Kubota and new springs and seals in the pump, Wolfman.

 

[North Idaho Wolfman]

New injectors from Kubota and new springs and seals in the pump, Wolfman.

Ok everyone says new injectors from Kubota, and they really mean new injectors from Amazon or eBay or someone that says that they are factory Kubota injectors.
The reason I say this, as there is a rash of junk injectors running around and they will all test bad too.
They have a poor atomization pattern and improper pop off pressures!

I'm not calling you a liar or anything of the sort, I have just seen too many of them.

 

[akbear]

Ok everyone says new injectors from Kubota, and they really mean new injectors from Amazon or ebay or someone that they are factory Kubota injectors.
The reason I say this is there is a rash of junk injectors running around and they will all test bad too.
They have a poor atomization pattern and improper pop off pressures!

I looked at the knock-off injectors online and they were so ridiculously cheap that I didn’t trust them. So I took the original injectors to the Kubota dealer and he matched them up. Do you think injectors could cause this problem?

 

[North Idaho Wolfman]

I looked at the knock-off injectors online and they were so ridiculously cheap that I didn’t trust them. So I took the original injectors to the Kubota dealer and he matched them up. Do you think injectors could cause this problem?

Yes it could, that's why I mentioned it.
Sounds like you have that covered.

How much run time do you have on it?
Have you gotten it up to temp running?

 

[akbear]

I only have an hour of running time under load at varying rpm’s but keeping it under 3/4 throttle. I really don’t have a way to put it under a heavy load, like bailing hay or plow a field, just running a mower. I was reading a discussion started by Anonymous-O back in 2012 with the exact same issue of blow-by in a new rebuild. The consensus of that discussion was to run the snot out of it and get those rings to seat, which is heartening. Some were saying 100 hours of hard work before there would be a difference.