Topic: Why am I burning oil????

[Blitzburgh207]

I just posted this in my build thread but I thought I would get more views on here.  I'm trying to diagnose where/why I'm burning oil and any input is greatly appreciated!!!  I rebuilt my K8 motor last winter and put about 5k on it last season.

Whenever riding with friends, they would tell me that there would be a puff of smoke out my exhaust when I really cranked on it.  Otherwise no sustained smoking, sometimes a puff at startup. I figured maybe I damaged a valve guide seal on assembly.  There is definitely some oil on the exhaust side around the valve stems, but I can't tell if it's from the seals, or if the machine shop effed up my head when they installed the new guides.  Check it out: (btw the white fibers are from paper towels I stuffed in there for transport)

#1


#2


#3


#4


Heres the chambers:

#1


#2


#3


#4


Sorry for the long shots down the cylinders....I'm having a lot of trouble separating the head from the jugs 

And here's the pistons (1-4 left to right):


#2 piston looks to be burning oil like a mofo...do I have a ring upside down? How can I tell?

Thanks in advance for your help!!!

[lucky]

It is not just rings that need to be considered.
The valve wobble in the valve guide can be excessive.

Did you have the valves and guides fitted?


The letters and or numbers on the rings should all face upwards.

Were the cylinders and piston fit measured?

One piston was burning oil. I would check out the carb on that cylinder too.

[Blitzburgh207]

New superflow valves and guides from cyclex.  The clyinders and pistons were within spec so I just honed and re-ringed.

I guess I'll just replace all the valve guide seals and check the rings on #2 and try 'er again.

I'm still up in the air on throwing that cheap 836 kit in...

[Vinhead1957]

It is valve seals and or guide to stem clearance

[Blitzburgh207]

Got my fingers crossed for the seals...if the machine shop damaged the head I'll be pissed. 

[TwoTired]

The clyinders and pistons were within spec so I just honed and re-ringed.

Were they still measure within spec after honing?  Honing removes metal.

To narrow down and eliminate ring piston cylinder fit, do a leak down test.  And listen to where the air escapes.  Into the crankcase = rings,  Into the exhaust or intake port condemns the associated valve.   Valve wobble can make the valve leak from abnormal wear on the valve seat.  And THAT is cause by worn or to large valve guides or stem wear.

I wonder if Cyclex makes the guides oversize for race purposes (high heat), or your machinist made the guide bores too large for the stems.

Still, you need to do a diagnostic trail to lead to the real issue beyond speculative.

Do check you crankcase ventilation system to ensure blow by gasses aren't building up inside the crankcase.

Cheers,

[Blitzburgh207]

The shop checked my pistons and cylinders as I did not have the tools at the time.  How much psi would it take to do the pressure test on the head (min/max ranges) somewhere around where cylinder compression should be?  isn't it like 120psi  or something? I'm pretty sure I can hook up my compression tester fitting to my air compressor.

I'm pretty sure the breather is fine but I will check.

[neilc]

how do you check the breather its just a hose coming out the top of the motor??

[Rigid]

It is called "breather speed" the measure of the air being compressed inside the engine and expelled through the vents from ring blow-by. This is often accompanied by excessive oil vapor.  Plug the vents, pressure builds up and then it will really smoke from oil being forced past the rings. 

[TwoTired]

A leak down tester supplies a calibrate pressure to the cylinder when the piston is at TDC.  Then you measure what pressure the cylinder holds (ideal would be 100%) or what the cylinder looses (ideal would be 0 %).   The absolute pressure supplied can be high or low pressure depending on how the tester is set up.

I'm most familiar with testers that supply 80 - 100 PSI.  Such pressures will allow you to hear where air is escaping the cylinder.  Cylinders are seldom perfect.  So, it is helpful to identify where the pressure loss occurs. 
This gives you a very good idea about the mechanical integrity of each cylinder, beyond just whether it can make enough pressure to operate.

You can also supply shop air to the cylinder with piston @ TDC to listen for air loss.  However, this does not tell you the severity of the loss, only where it is losing pressure.  Few cylinders are perfect.

Cheers,

[Kaspar]

Hi,

Any news or resolve on this problem???

Sorry for me jumping in, but I have a similar problem with my CB 500 Four from '76. It started smoking/burning a lot of oil. It's been honed/bored up to fit 0.25 oversize pistons, assembled but still smoked!