compression test & pressure test

[merrill]

so, I was reading the BBB procedure on how to do the compression test on my 66 230 sl,  the procedure is straight forward.

the next section talked about performing a pressure test.  basically setting the cylinder in tdc then applying air pressure then watching for the pressure to drop and listen for air escaping in the exhaust or watch for bubbles in the coolant.  


This test is supposed to give one an idea of the health of the valves AND the possiblilty of a failed head gasket  if you see bubbles in the coolant.

my question is what pressure should one use for this test?

Matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[JimVillers]

Matt .... I just use my air compressor pressure, about 100 psi.  Be sure to set the piston to TDC, in gear with the tires chocked and the hand brake on.  If you have an automatic, I don't know how to hold the crankshaft and keep it from turning.  

There is a special tool to perform this "leak down test" which will give you a percentage leak.  Just pressurizing the cylinders and listening to the intake manifold, exhaust pipe and crankcase via the oil cap can provide a lot of information.


Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor, MGB 5-Speed

[al_lieffring]

Matt, Jim

If the crank is exactly at TDC the piston will not move. In fact that is where the "dead" in Top Dead Center comes from, the dead spot where pressure inside the cylinder has no effect on the rotation of the crank. The term came from early steam engines, if the piston stopped exactly at the top the motor would not restart unless the crank was manualy turned off the dead spot.

Al

113-042-10-014715
built 11 Jan 66
904/396 blue, Ivory Tex
condition- rust bucket

[merrill]

Jim, Al,
thanks for the replies,   harbor freight has a leak down tester on sale till 12/4 for about $50.  

I may pick one up just for fun.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[rwmastel]

Matt,

Found it:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94190

I assume this tester requires an air compressor?
http://da.harborfreight.com/cpisearch/web/search.do?keyword=compressor

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[merrill]

Rodd,
I have not seen this leak down tester in person, however I sure would hate to have to repeat hand pumping each cylinder to 100 psi !!!



matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[merrill]

Joe,
picked up the tester today, it was just under $40 on sale.
nice set up, came with a case etc.

I am anxious to do the compression and pressure test now.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

Sounds like you're becoming quite a wrench! After you get all the plugs out crank the engine a few revolutions to clear any carbon out of the cylinders so it does not end up in your new gage.

Joe Alexander
Blacklick, Ohio

[merrill]

Joe,
so, have some good and some bad news.

the leak down tester is pretty cool, did each cylinder twice and all were basically ok.  no leakage in the coolant, exhaust between cylinders and (took the rocker cover off) no bubbles around the valve stems.

now for the bad news, my compression is really low.
(I followed the instructions in the bbb exactly,  got the car up to temp, opened intake venturi wide open, (after disconnecting inj pump)pulled fuel pump fuse)

             1      2       3       4      5       6  
11/07 dry    45     40      60      66     60      60
11/07 w oil  75     70      70      66     60      60
2/87         105    105     120     120    115     120
5/86         140    145     150     150    135     150

after the test today I noticed that the car started great with the oil from the compression test.
Also, I was curious that my compression guage was accurate, so I hooked it up to my compressor and adjusted the regulator to various pressures and the guage was just about dead on.

so, guess the rings are shot.  
At what compression would the motor stop working?
time to start saving to send the motor to metric motors.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[merrill]

Joe,
never mind, after re analyzing the numbers and the tests,  the leak down test was a bust.  there was so much air escaping thru the rings there was no reason that the air would leak anywhere else.

on each cylinder I could hear air escaping into the case (I had the rocker cover off)  The air never stopped going into the cylinders

just tried to drive the car and it did not want to start and when driving it had a stumble at 3000 rpm.

matt



Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

What is the history on the car. I cannot imagine the engine even running with compression like this.  I suspect you may have conducted the test incorrectly?

And if your rings are that bad you would be using a lot of oil!

Don't throw in the towel yet.  How about some history?

Joe Alexander
Blacklick, Ohio

[merrill]

Joe,
so I followed the compression test procedure in the bbb page 00-5/1.
section 6 said to have the throttle valve wide open so I disconnected the inj pump linkage and used a cord to hold the intake venturi open. water temp read 80 on the guage

previous compression results are in the post below
rebuild inj pump installed in 86
the car does not smoke at all, on start up or running
rocker cover vent tube is disconnected and vented to under the car
is has a high mileage award for 250K so 150,000 miles  probably in 1992

this car was bought back in 78 by my father in germany.  he was the third owner.
from all the receipts I have no, major engine work was done.  all minor tune up's, front crank seal etc

the car ran pretty good after adjusting the valves, i drove it to work on friday and it ran ok.  I noticed it took more cranks to start. when doing the valve adjustment all valves were so tight I could not get the feeler guage in to check the gap.

my recent troubles started when I tried the richness test posted by glennard.  Since adjusting the inj pump ccw 2 different times(a total of 7 clicks) the co% was down to 5.6 but the car did not idle well. it would tick and want to stall.

then the engine ran worse, with the car off turned the inj pump 4 clicks cw and it ran better,  turned it off probably turned the inj pump 3 more clicks cw.

Once I replaced the distro cap today and got it running it idled ok.
when I took it for a test drive it was rough at 3000 rpm, turned around and got the car into the garage it died.
tried to re start the car and of course it would not.

when I pulled the plugs to do the compression test the plugs were not wet,  just had carbon or black soot on them.

one note, while the car was a work in progress due to the low compression tests I tried to use diesel fuel to hopefully unstick stuck rings,  when I would put the diesel in I could hear it drip drip out.
also, when performing the leak down test today, on each cylinder I could hear air leaking into the crank case.  essentially the air leaked out not building up.

So, any suggestions would be greatly appreciated.  

matt


Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

It still does not make sense. The car ran good a few days ago and it does not smoke or use a lot of oil.

With around 150,000 miles the engine may be a little tired, however it would not be completely shot after just a few days of driving. I would suspect some kind of fuel related problem keeping it from starting.

I suspect your valves were open when you did the leak-down test?

It is not prossible that your engine is shot and run good one moment and bad the next!

It may be a good time to put a pressure guage on the fuel line and check fuel pressure.




Joe Alexander
Blacklick, Ohio

[merrill]

joe,

I suspect your valves were open when you did the leak-down test- I don't think so, started with the motor at tdc, distro pointing at number one spark, cam sprocket notch aligned.  both cam lobes for no 1 cyl pointing to the side of the car.  exhaust at about 3 and intake about 9 o clock.  i could hear the air clearly thru the timing chain opening on all cyl. (suspect rings)
the tester has 2 guages, one for the pressure built up and one to measure the loss.  I may do the test again because i did not measure the built up pressure, I just paid attention to the percent loss.

It is not prossible that your engine is shot and run good one moment and bad the next - i guess  that depends on how good or bad my skills are.  

It may be a good time to put a pressure guage on the fuel line and check fuel pressure. - ok, back to harbor freight,  just to note I replaced all the fuel lines period, from the tank all the way to the filter, including a new filter, tank is clean, I even put a clear filter in line bet the tank outlet and pump.
I drove about 40 miles the other weekend and the car ran great. so unless the fuel pump just failed?

I have read in the past about a micro switch, could this be the culprit?  would a 66 230 have one and where is it?  maybe that is what is causing my ignition problems.

also, I followed the bbb to the letter when doing the compression test and then double checked the accuracy of the guage,   I will do it again but I am fairly sure the guage is ok.

thanks
matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

I am just saying that bad piston rings and or valves will not work good one moment and be all bad the next. Your engine may be tired and worn but if ran good the other day, then your immediate problem is most likely somewhere else.

You are about to make some very expensive decisions. Parts and machine work will run you thousands of dollars for a complete rebuild. Your car will be down months. I just hate to see you jump into the project without knowing exactly the problem.  

Invest in another set of spark plugs, in case yours are fouled from all the diesel fuel and starting problems. Cheap fix and you can always clean up the other new fix and re-use them later.

Make sure the injection pump oil level is correct!

Joe Alexander
Blacklick, Ohio

[glennard]

Matt, I agree with Joe. The engine would not go from running with enough power to move the car to failure.  You said the crank was at TDC(No 1 piston at top), and No. 1 cam lobes pointing to side of the engine.   I don't think so.  Been awhile, but the cam shaft notch should be pointing up(aligned) making a V of the inlet and outlet lobes of No.1.  Both valves are shut with their nominal clearances. I think the lobe nearest you is No. 1 exhaust - about 15 degrees to the right(side of the V).  The second lobe on the shaft is the No. 1 inlet lobe - about 15 degrees(345  i. e. 360 minus 15) to the left of vertical.  As you rotate the crank by hand, 15 degrees or so, the inlet lobe will be straight up.  The clearance between the rocker arm and the back side of the lobes should be .003 inch.
     Without being overly pedantic---   As you continue to rotate the crank, you adjust 153624 on the inlets. Then 153624 on the outlets at .007.  Or do each as the come around in order.

   These engines are pretty rugged.  Once bought a 230E(grey market 190E 4 cyl.) with a nice body in the dark for $200.  Crank would turn about 10 degrees with a loud metallic sound.   Next day in the light you could see a hole in the block large enough for a hand.  Reached in and pulled out a connecting rod.  Put some gas in it. hooked up the battery--and it ran!   At 1200 rpm you hardly missed the 4th cylinder and no oil poured out of the hole.

    Back to your problem.   Seems all is not lost.

[merrill]

Joe, Glen,

so, I will double check the inj pump oil level, I checked the level the other day, initially the level was about 1/16 of an inch from the end of the dipstick,  I addeda little oil bringing the level up to closer to the max level mark.

Glen,
with the crank at zero, cam sprocket lined up and distro rotor pointing to no 1 plug wire the cam lobes did not point exactly to the side, both were angled up, maybe degrees would be more accuarate however I used 3 and 9 o clock rather than maybe 17 deg and 50?  

would a weak battery cause problems?  I have a meter in the car, when running the generator puts out close to 14v, If I just turn the ignition on the meter reads about 11.5 v.

I will get some new plugs, maybe the ngk's suggested in the other post.  
I think my current problem is more ignition related to no spark rather than the low compression issue.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[merrill]

guys,
quick question, I was double checking my ignition system and noticed that the voltage dropped after the ballast resister,

12 v in
6 v out

is this right?  the resister is new. bought from k and k

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

Yes, remove all the plugs for a compression test and have a good strong battery. It is good idea to pull the fuel pump fuse so it is not running. Unburnt fuel going into the cylinders, washes down the walls and breaks the oil seal lowering compression. Give each cylinder a little squirt of engine oil since the car has been flooded with fuel already.  Sorry to be repetitious but I am not sure what you have done so far.

Joe Alexander
Blacklick, Ohio

[merrill]

Joe,
remove all the plugs for a compression test - did that
have a good strong battery - no
pull the fuel pump fuse - did that

I think I found out why the car would die,  this morning went out and started re ohm'ing and voltage testing the ignition components.
car still did not start

checked the coil and found low voltage at the positive terminal =5.6v
jumped online did a search on ballast resisters and checked my manuals

I had 11.2 volts going into the plus side of the ballast resister and 5.6 coming out.
jumpered the ballast resister and the car started almost right away

got the car running and with the generator on there was 13.5 volts going into the ballast and 9.27 coming out going to the + of the coil.

once running the car ran fine.   off to get a new battery, the one in the car never would charge enough to hold 12v.

I will call my favorite indie to have him do a compression test as well.

thanks
matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[merrill]

Joe,
remove all the plugs for a compression test - did that
have a good strong battery - no
pull the fuel pump fuse - did that

I think I found out why the car would die,  this morning went out and started re ohm'ing and voltage testing the ignition components.
car still did not start

checked the coil and found low voltage at the positive terminal =5.6v
jumped online did a search on ballast resisters and checked my manuals

I had 11.2 volts going into the plus side of the ballast resister and 5.6 coming out.
jumpered the ballast resister and the car started almost right away

got the car running and with the generator on there was 13.5 volts going into the ballast and 9.27 coming out going to the + of the coil.

once running the car ran fine.   off to get a new battery, the one in the car never would charge enough to hold 12v.

I will call my favorite indie to have him do a compression test as well.

thanks
matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[Naj ✝︎]

Matt,
 

quote:got the car running and with the generator on there was 13.5 volts going into the ballast

This voltage should be nearer 14.4 V.
Maybe thats where the R Sake is coming from  :?:  :evil:  (not the battery's fault)

naj

68 280SL

[merrill]

Naj,
the 13.5 volts is at idle,  at speed I have seen the voltage jump to at least 13.9 but I will check for 14 or more.

So, I asked my mom to try and find the high mileage certificate for the 250 KM to try and date the mileage on the motor,  she found it but no date.

She also found a 500 KM high mileage certificate for the sl!!!!  I need to call mercedes  to see if I can get confirmation on the mileage and dates awarded. If the 500 km certificate is verified I guess this old car really is worn and the low compression should not be a suprise.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230