[daveward]

With great anticipation the newly rebuilt 380SL engine ('82) found it's own moment to start, adding a hint of drama (leading to the: 'is it going to start?' question)...and then vroom-vroom, it began purring like a kitten from the very start.

Fast forward to the test drive: "shucks"...and other more colorful expletives...as bluish-grey smoke began to pour from the exhaust when the gas pedal was pressed...and the pedal seemed unable or unwilling to coax any power out of the newbie. Embarrassed by the lack of power and the billowing smoke on it's maiden voyage, the wundercar turned tail and went home. I have a long uphill driveway and the pedal was floored all the way up as we barely made it.

The analysis: (in retrospect)

1. No high idle to start...idled smoothly and smoke free at 500-600. Would not have taken it on the test drive had I noticed any smoking during the warm-up.
2. Gas pedal seemed like it had difficulty moving past idle speed...finally, during the warm-up phase the revs were increased successfully to 2500...but it seemed like it needed babying to do it. Not linkage...engine responsiveness seemed in question.
3. Compression check today..all 8 cylinders 150-160.
4. Heads professionally rebuilt...I won't exclude valve seals , but I suspect they are not the immediate issue.

Searching the forum has lead me to the warm up compensator as possibly supplying too much fuel (pressure) after warm-up which would lead to the "richness".

I disassembled the compensator( regulator) and found it unrevealing. All seemed perfectly well. Except there is an adjustable 'piston' of sorts that moves up and down as the diaphram moves in relation to engine vacuum. I noticed the adjustability of this item seems infinite and would appear to have a major impact on the workings of the compensator. But I do not find any literature or commentary about "tuning" the warm-up compensator. For example, I would expect that somewhere there are instructions to make the initial setting thus and so.

Any expertise on this? Thanks

 

[deathrattle]

Blue/grey smoke signifies oil burning-black for rich fuel mixture.

Has it been re-bored? If yes,then maybe the oil control rings have not sufficiently bedded yet and you are getting some fouling.Having said that,it should still run ok even if producing some smoke.

 

[buckwyatt]

when you build a "smoker"

for sure, the hone job was bad, or pistons were wrong size, or maybe rings were wrong size.

You can take it apart, mic everything, and see what went wrong, in a worst case, you will need more pistons, rings, and another bore job.

If your mechanic did not have the pistons when he bored it, or did not measure each one, that is what went wrong.

 

[daveward]

It's hard to imagine the honing was "bad", but I'll take your word for it consideriing the situation I find myself in. Before I start taking things apart...is it logical and possible to have what seems like good and consistent compression AND a "bad" hone job? Thanks

 

[buckwyatt]

honing

it is way more important than some think, if you don't get it cross-hatched, (can mess up by going in and out too slow, the rings will never seat, and it will always smoke.

but, believe what you want, I aint sellin' anything

ring gaps on same side, pistons too small, bore too big, lots can go wrong. I have a good a machinist, the best, in Alameda, Ca if anyone is interested.

if you get pistons more than .001 difference from each other, that will also do it.

 

[strife2]

Honing is more complicated on a high-silicon content aluminum engine like this one. I think the goal, on a microscopic scale, is to have silicon crystals embedded in the aluminum actually contacting the piston, not the aluminum itself of the block. This may be key to why the bottom ends of these engines seem to last forever if kept in clean oil. Putting a honing attachment on a drill and zipping up and down with it isn't going to cut it, so to speak, unless luck is involved.