Rebuilt Mercruiser 140 smoking on first startup..

[tcooke]

It is a 1978 Mercruiser 140hp, just rebuilt, just got it going tonight but it has a lot of smoke coming out of the exhaust. So much that it smoked me out. The compression tests were 140 on all four cylinders (spec says its fine).

So is this a normal thing for a rebuild?

 

[rbh]

Re: Rebuilt Mercruiser 140 smoking on first startup..

run at a high RPM for a minute or two, because you want to burn of the excess oil from the rebuild as well as seat the rings.
thats what ive been told.
rob

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

How much smoke should I expect? 2, 3 minutes? More?

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

OK, I was at the boat launch last night performing my break-in initial run, ran it at 2200-2600 RPM for 25 Minutes. It still smokes a lot, I would assume that the rings haven't seated yet. If they haven't can I expect them to? Is it too late for me? Should I take it on the water and put some load oin it?

Please help, thanks

 

[SS MAYFLOAT]

Re: Rebuilt Mercruiser 140 smoking on first startup..

If it was mine, I would pull the plugs to see what they tell. Then do a compression test and go from there. You say rebuilt, top and lower? was the head checked for cracks? If there is lots of smoke like a smoke bomb, I would pursue the matter..........SS

 

[joemamma]

Re: Rebuilt Mercruiser 140 smoking on first startup..

most engines will smoke on break in. What color is the smoke? Blue is oil black is rich gas mixture. If you used chrome rings you need to run it like you stole it!
if not pull the plugs and see if the plugs are starting to foul.
Was the head done? Sometimes a valve seal pops if there's not enough lub on the valves stems before lightoff.
good luck
Joe

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

The rebuilt was a complete one. The head was machined and built by the machine shop. The block was built by me (machine shop had taken it tested it with the crank and it was bored 020 over (pistons to match)

After the build was complete the initial compression tests were 140 across the board, however I had some trouble working out the kninks at it was cranked a number of times before the first start up. Also noticed last night the operating temperature was way above normal (tach said it was around 180, manual says 143) which I am going to check the thermostat today for proper settings. I am also going to go for a new compression test today.

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

Doing a little more research it seems that my rings have not seated yet. I am thinking that due to the higher temp the oil was thinner and unable to perform properly effectively keeping the rings from seating properly.

So here is the most important question I have, is it too late for the rings to find thier groove? Am I going to have to tear down and restart? Or is it at all possible things are going to work out if I can manage to figure everything else out.

 

[searay3]

Re: Rebuilt Mercruiser 140 smoking on first startup..

From past experience. Did you put the pistons/rings in or did the machine shop. The reason I ask is had very similar symptoms. No seat on the rings and running hot on a new rebuild. The guy who put the pistons in did not check the rings for proper endgap. Motor would spin fine by hand until you started it. It immediatley got hot, started smoking and shut off very abrubtly when the ign was cut. Didn't find it until another disassembly and pulled a piston. He thought since they were new and ordered oversize, they would fit out of the box...they didn't....

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

From past experience. Did you put the pistons/rings in or did the machine shop. The reason I ask is had very similar symptoms. No seat on the rings and running hot on a new rebuild. The guy who put the pistons in did not check the rings for proper endgap. Motor would spin fine by hand until you started it. It immediatley got hot, started smoking and shut off very abrubtly when the ign was cut. Didn't find it until another disassembly and pulled a piston. He thought since they were new and ordered oversize, they would fit out of the box...they didn't....

I was the one installing the piston/rings, just ran a compression test...the results not good (120/120/130/130).

What do I have to do? Pull the engine, tear down the block and try again? Hone the cylinders?

 

[cwoodffr]

Re: Rebuilt Mercruiser 140 smoking on first startup..

You might also check the cam. I had a 351 wipe a camshaft on first start (car)....don't know if marine has same sensitivity to break in. Ran rough and very hot until I determined that the lobes and lifters were toasted.

 

[FreeBeeTony]

Re: Rebuilt Mercruiser 140 smoking on first startup..

What about the rings............were they installed correctly? They are suppoesed to be staggered.................did you go by the manual?

 

[SS MAYFLOAT]

Re: Rebuilt Mercruiser 140 smoking on first startup..

As tcooke mentioned,,,,,End Gap is important. Rings are the very first thing that produces heat. Once they expand and have nowhere to go except outward, they overheat and loose their tinsel strength becoming weak. Then comes loss of compression because they cannot seat.

If you haven't pushed it, you maybe able to get by just replacing the rings and deglaze the cylinders.

I would ask your folks at the machine shop for their opinion also......SS

 

[tcooke]

Re: Rebuilt Mercruiser 140 smoking on first startup..

Ok well it looks like I have to pull the engine back out, tear it down then I am just going to hand over the block to the machine shop, get them to check it out and hone the cylinders, install the rings and pistons and get it back from them.

Awesome, just goes to show you not to rush anything