289 oil burning

[tom slick]

a friend of mine has a rebuilt 289 with 6000 miles on it. it has always burned a little oil but we blamed it on "still breaking in". he drove his car around about 250 miles last weekend and it burned 2.5 quarts. there is slightly noticeable smoke at higher rpms (when followed on the road) but he also has a rich carb. the car otherwise runs excellent. there is not excessive pressure out the breather system and the pcv is in good shape. i am going to run a cyl leakdown test on it but i don't think that will really give me much info unless the compression rings are shot.
what do you guys think? is there a way to trouble shoot bad oil rings or valve seals/guides?

 

[sbc350gearhead]

valve seals and guides will usually smoke on startup fairly bad, and lessen while driving. Try a compression test. If you have low compression in one or more cylinders, then squirt a few ounces of oil into the cylinder and repeat test. If you gain compression, then your rings are shot.

 

[Propflux01]

If it has always been running rich, during break in, it has probably glazed cylinder walls from that rich mix and therefore won't seal well. This is the most common cause of rebuilds short of improper machining/assembly, due to the fact that most people richen there mixtures or have to have it because of an over aggressive camshaft installed.

 

[tom slick]

quote:

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Try a compression test

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is there a benefit to doing a compression test over a cyl leakdown test?

TimH- the rich carb/glazing could be the case. the guy is a good "car" mechanic, but not a good "tune-up" mechanic so it wasn't really tuned right until he let me get my hands on it about 1000 miles ago. he doesn't drive the car much so we figured if the carb is a little rich we didn't care.

 

[tom slick]

if anyone cares, we have tracked the problem down to the repro cobra valve covers having a crappy baffle design and the extra tall roller rockers squirting oil directly at the pcv valve.

 

[tom slick]

we figured it out by chance

we disconnected the pcv tube from the carb spacer and noticed at idle it was sucking quite a bit of oil. then we pulled the v/c and figured out what was up. we are going ot try messing with the baffle, i may design a whole new baffle. the car is a near concours 66 fastback mustang so the engine has to stay looking stock, otherwise we'd just swap in better aftermarket units.

 

[Propflux01]

How did you figure that out? chance change of them? let us know!!

 

[tom slick]

UPDATE!!!
i built a much larger baffle that fits the interior profile of the valve cover very closely and sheilds the pcv valve from oil spray. in 250 miles the engine hasn't used a drop of oil.