smoke on acceleration after coasting

[mastercraft10]

280SL 1971    Fresh engine rebuild, top and bottom, and it runs beautiful.  correct idle, great acceleration and torque and very smooth.  However, after coming down a hill and then accelerating I get a serious blue smoke out the tail pipes.  I know the common cause is bad valve stem seals but mine are new as are the valve stems.  Normal driving on flat roads I see no smoke.  is there a way that the extreme vacuum could be pulling oil from the crankcase other than threw the valve stems?  I only have about 150 miles total since rebuild.  Temp is 180 F.  Do I just drive it and put miles on it to see if it gets better???

[ja17]

It could be that your engine is not broken-in. What was done on the total rebuild? What oil are you using to break in the engine? My advice is to put more miles on it and monitor the engine oil level and transmission fluid level if it is an automatic.

[wjsvb ✝︎]

Unlikely, but possible, is that a valve stem might be scored or a stem seal is faulty.  Have you pulled the spark plugs?

[wayne R]

I agree with Joe here,so i will give a few tips on breakin here now, hope its not to late for you  Wjsvb,
but break in is most critical, in the the very start  and first 100 to 300 miles.
Fill oil filter about at least half full,
Only use mineral 5/30 or 10/30 engine  break in oil that has a  additive ZDDP or Zinc,premium brand filter and oil.and camshaft additive.
Prime the oil pump to avoid dry start up.
On startup for for first and after runs, drive with short 1 to 2 mile drives of varying speeds up to about 2000revs than continue
the same  up to  about 3000 revs  varying speed  and revs total of about 5 to 8  miles then  return home and switch off.
Let cool down that day , than do the same next  few days until you have completed about 100 miles.
Never on start up drive away and cruise for  say 3000revs for 100 miles at same speed and revs.---
Im not a expert ,i leant this from a General motors and toyota dealership service manager back in 1976 to1989,
that rebuilt hundreds of engines all his life ,i was sales manager of the same dealership in New Zealand.

[Mike Hughes]

Use only regular petroleum based oil when breaking in an engine.  Synthetic oils are too "slick" and prevent rings from breaking in properly, which will result in excess oil consumption.

[Benz Dr.]

Smoking after a rebuild isn't normal. Assuming you used new parts I'm going to ask a few questions.

Did you use new pistons or just new rings?

Did you use shims under your cam bearings?

How much thread do you have showing on your ball studs?

[mastercraft10]

Thats what I thought about the faulty seal.  I have pulled the plugs and they look good, no real carbon deposits but the ceramic near the tip is black.  all look the same.

[mastercraft10]

Thanks Joe, that's what I hoping, is that it's just not broke in.  I used the oil that was recommended on this site plus the zink additive.  This was a good running engine so I thought I would "freshen" up with new rings, valve stems and seals, all new bearings etc.  The work was all done by a trusted engine builder here in Denver.  I'm not in a big hurry so I think I will put some miles on it  and see what happens.

[mastercraft10]

Thanks Wayne, I printed out your instructions and will follow threw as instructed.  It's pretty close to what I've done but I have run the engine up to about 3000rpm a few times.

[LJHAMILTON]

Having a similar problem after a complete rebuild. Have about 500 miles on it since than. My mechanic suggested it was a leaky valve seal on the exhaust side. Did your problem clear up after driving more miles. Thanks