Great compression but lots of blow by? - PeachParts Mercedes-Benz Forum

billhard · #1 06-30-2011, 10:02 PM

I bought a 616.916 off ebay to replace the blown one in my w115 240D. I have it in and running now and it really seem smooth compared to my 617. Today swapped out the injectors from the blown motor since they were recently rebuilt and pop tested with new Monarch nozzles. I took the opertunity to check the compression and got the following:

400#
380#
390#
390#

These numbers renewed my faith in man as the guy I bought it from claimed the motor was rebuilt at an MB dealership 8K ago. He couldn't back this up with paper work so I took that with a grain of salt. None the less I got a good vibe from the man and bought the motor, looks like maybe he spoke the truth.

On the flip side this thing has a lot of blow by which seems odd to me. No smoke out of the valve cover just a lot of pressure. When I pull the oil filler cap droplets of oil quickly begin to appear on the exterior surface of the valve cover, the cap dances actively but doesn't fly off. Anyone have thoughts on this?

I haven't yet adjusted the valves and that is next on my list.

Zulfiqar · #2 06-30-2011, 10:19 PM

check with hot engine at fast idle speed - the cap should not act like a kettle - if it does the compression timing also affects it - learnt that in VW diesel days

Diesel911 · #3 06-30-2011, 10:36 PM

If you think there might be sticking rings:
Marvel Mystery oil results sticky rings
Original thread also has + response
http://www.peachparts.com/shopforum/showthread.php?t=258757&highlight=Marvel

This stuff is from experience with rebuilt Gas Engines.

If the Piston Rings do not seat well you will have Blow-by.

I have noticed that when oversized Pistons are used there is more Blow-by than if the Block had been sleeved back to standard and standard Pistons and Rings were used.

junqueyardjim · #4 07-01-2011, 08:46 AM

Don't forget that the vacuum pump dumps it air into the engine crankcase also. So if you have a really bad vacuum system, you are working the pump to death and then they fail and ruin the engine, but in the meantime they make a lot of blowby.

layback40 · #5 07-01-2011, 09:25 AM

Quote:

Originally Posted by billhard

I bought a 616.916 off ebay to replace the blown one in my w115 240D. I have it in and running now and it really seem smooth compared to my 617. Today swapped out the injectors from the blown motor since they were recently rebuilt and pop tested with new Monarch nozzles. I took the opertunity to check the compression and got the following:

400#
380#
390#
390#

These numbers renewed my faith in man as the guy I bought it from claimed the motor was rebuilt at an MB dealership 8K ago. He couldn't back this up with paper work so I took that with a grain of salt. None the less I got a good vibe from the man and bought the motor, looks like maybe he spoke the truth.

On the flip side this thing has a lot of blow by which seems odd to me. No smoke out of the valve cover just a lot of pressure. When I pull the oil filler cap droplets of oil quickly begin to appear on the exterior surface of the valve cover, the cap dances actively but doesn't fly off. Anyone have thoughts on this?

I haven't yet adjusted the valves and that is next on my list.

You dont have bad blow by !!!!!!!

billhard · #6 07-01-2011, 10:17 AM

Quote:

Originally Posted by layback40

You dont have bad blow by !!!!!!!

I don't? Can you explain

Quote:

Originally Posted by junqueyardjim

Don't forget that the vacuum pump dumps it air into the engine crankcase also. So if you have a really bad vacuum system, you are working the pump to death and then they fail and ruin the engine, but in the meantime they make a lot of blowby.

This seems plausible, I will read up on pump failure as well.

layback40 · #7 07-01-2011, 10:21 AM

[QUOTE=billhard;2744744]I don't? Can you explain

The oil cap is not being blown off, just dancing.

leathermang · #8 07-01-2011, 10:51 AM

This kind of thing is way too subjective for you to have an opinion..

IF you are really really really worried about it..

the FSM says that MB has a machine which will measure the blowby..

Go to the dealer and ask them to measure it for you..

but I suggest with those great compression figures you go enjoy what looks like a great find on your part....

layback40 · #9 07-01-2011, 10:59 AM

Quote:

Originally Posted by leathermang

This kind of thing is way too subjective for you to have an opinion..

IF you are really really really worried about it..

the FSM says that MB has a machine which will measure the blowby..

Go to the dealer and ask them to measure it for you..

but I suggest with those great compression figures you go enjoy what looks like a great find on your part....

X2
Change the oil, set the valves & run it for a 1000 miles.
Report back if it uses oil or has any other problems.

kerry · #10 07-01-2011, 11:03 AM

Quote:

Originally Posted by leathermang

the FSM says that MB has a machine which will measure the blowby..

.

Or. . . this forum has invented it's own machine--known as the garbage bag blowby test. Search and read up on it and conduct the test if you are curious enough to go that route.

leathermang · #11 07-01-2011, 11:03 AM

Quote:

Originally Posted by layback40

X2
Change the oil, set the valves & run it for a 1000 miles.
Report back if it uses oil or has any other problems.

If it uses more oil than you think it should.... put new valve stem seals in it.... then drive, check, and report back...

leathermang · #12 07-01-2011, 11:04 AM

Quote:

Originally Posted by kerry

Or. . . this forum has invented it's own machine--known as the garbage bag blowby test. Search and read up on it and conduct the test if you are curious enough to go that route.

OH PLEASE let that thread lie in Peace.... lol

http://www.peachparts.com/shopforum/showthread.php?t=273409&highlight=garbage

billhard · #13 07-01-2011, 11:33 AM

Ok I will officially not worry about it unless I see excess oil consumption.

Besides I am just impressed by the fact that I bought something off eBay that appears to be as represented, the blow by was just a curious side note.

leathermang · #14 07-01-2011, 11:42 AM

YES !!! Count your blessings and enjoy what you found...