Author Topic: compression question (Read 21927 times)

merrill · « **on:** March 26, 2006, 18:37:50 »

went thru some receipts for my 66 230 sl today. found the following info from previous compression tests.

5/86 1. 140 2. 145 3. 150 4. 150 5. 135 6. 150
2/87 1. 105 2. 105 3. 120 4. 120 5. 115 6. 120

the compression was checked at the dealer, seems strange that it would drop in such as short time. the car starts like a champ and runs ok. no spring chicken. I do know the cam is just about out of spec and the motor, head is original.

I am trying to figure out if I should just pull the motor and send it to metric motos.

any ideas
matt

68_white · « **Reply #1 on:** March 26, 2006, 19:40:35 »

Consider having the compression test done at two or three independent shops.

You will be surprised with the variation in the results.

I had my engine tested at two places. I got very significantly different readings. So, I went to a third shop that confirmed the the first shop's reading.

Good luck.

HARRY

68_WHITE

ja17 · « **Reply #2 on:** March 26, 2006, 20:28:12 »

Hello Merrill.

The compression should be taken when the engine is warm, or it will be lower. I agree it is not likely that the compression dropped in all cylinders in such a short period of time.

Joe Alexander
Blacklick, Ohio

Raymond · « **Reply #3 on:** March 26, 2006, 20:40:19 »

Compression tests can vary with the temperature of the engine, the style of the gauge, and the technique of the mechanic. So a second opinion, or third can be helpful. The most important thing is the variation between the cylinders. More than 20% difference between any two cylinders is an indication of problems. Then, other test can more specifically pinpoint the issue.

If the engine isn't burning oil, or exhibiting other problems, it could run for a long time before you have to have a rebuild. If you just want a rebuild, that is a measure of vacuum in your wallet.

Ray
'68 280SL 4-spd Coupe

merrill · « **Reply #4 on:** March 28, 2006, 06:44:21 »

Heard from Gernold at SL tech. he thinks the compression issue is stuck rings due to the car sitting.

and after dad died mom started it once in a while but it did not get drived until I went home to visit every 6 months.

so, here is the real question, gernold suggested sending the motor to metric motors for a rebuild, will stuck rings unstick with driving or is the damage done?

Ben · « **Reply #5 on:** March 28, 2006, 07:29:06 »

I know a guy who had the same situation with a '64 230SL, he filled the cylinders with penetrating fluid and left it for a month, turning it over every once in a while . Then flushed it out, changed the oil and the problem was gone !

Regards,
Ben in Ireland.
'64 230SL 4sp.

merrill · « **Reply #6 on:** March 28, 2006, 11:50:22 »

Ben,
that is interesting, any input from anyone on if this is a good idea?
if so, any particular penetrating oil and how would one flush the system? (change the oil a few times)?

matt

Ben · « **Reply #7 on:** March 29, 2006, 02:40:50 »

I'm not sure what Pentrating Fluid he used but as far as flushing goes yeah the oil was changed a few times and the motor spun over without any plugs fitted !

I reckon the fluid would seep down the cylinder walls into the sump over a few days/week, so this would need topping up too, before a very full sump was emptied !

Regards,
Ben in Ireland.
'64 230SL 4sp.

merrill · « **Reply #8 on:** March 29, 2006, 07:06:24 »

ben,
talked to a guy at work yesterday about this, he had the same problem and used diesel fuel!

I guess I can call around and see if any hot rod shops have any ideas

matt

Ben · « **Reply #9 on:** March 29, 2006, 07:31:00 »

Matt,
I just confirmed my guy used deisel too !

Regards,
Ben in Ireland.
'64 230SL 4sp.

merrill · « **Reply #10 on:** March 30, 2006, 19:19:17 »

follow on info from th mb club. my concern is I really do not know the mileage of this car.

If that's the case, can you give the mileage readings for the two compression tests? - well this is hard be hard, since this car was bought in germany in 8/77.
the first receipt I have with a mileage reading is Jan-79 96619 KM. I have no idea how many times the odo has rolled. is 60,000 miles in 10 years reasonable for a european car? could it really be 120,000 miles?
Either way, here is my guess

compression 1 75,299.4 miles or 135,299.4 miles
compression 2 81,066 miles or 141,066 miles

Also, is there any chance that different compression meters were used for the two tests? - dunno, the work was done at the mb dealership in hawaii

If one makes the assumption that you drove the car very little between the two reported tests, there is a possibility that you do have frozen piston rings, but there is also some possiblity that you have some valve or stem problems.
- my dad retired in 85. so the car was driven less and less. more short trips etc.
oahu is a small island.

Did the dealer repeat the second test after putting some oil in the cylinders so as to make up for any leakage past the rings? That's a pretty standard thing to do in connection with that test.
- yeah, I know, unfortunately there are no real notes on the receipt

The oil works, just temporarily, as a seal so that the readings eliminate the rings as a problem.

You also have to be sure that there isn't a stuck throttle valve or some other constriction in your intake system, depending on what type of engine you have.
- could be, I will check, other stuff. I do know that the cam is about shot and I am willing to bet I need new valve stems etc

merrill · « **Reply #11 on:** June 10, 2006, 20:28:24 »

uh oh,
so while I have been waiting for some parts to show up I have pulled the spark plugs and manually turning the motor and keeping the clylinders re filled with diesel to hopefully un stick the piston rings.

well, today I turned the motor and topped off esch cylinder, well, since it was so quiet I could hear a drip, drip drop, went back under the hood and sure enough it was coming from one of the cylinders.

so, any suggestions, should I do a compression test, pull the head,
maybe one cylinder is at BDC and the diesel was able to run thru?

frustrated

ja17 · « **Reply #12 on:** June 10, 2006, 20:41:21 »

Hello Matt,

How does the car run? Are you getting a lot of smoke. Driving should not hurt as long as you keep oil in it. Driving it may give you some clues. I agree with Dan, compression tests may vary a lot depending on the condition of the gauge.

The heating up and cooling off cycle from running the engine may help free up rings if they are stuck. If you start oil fouling spark plugs, then the handwriting is on the wall, at least the head will need to be removed.

Keep us up to date.

Joe

Joe Alexander
Blacklick, Ohio

Benz Dr. · « **Reply #13 on:** June 11, 2006, 11:07:42 »

Notice how the second test is roughly 30 PSI lower than the first on all cyinders? I'd say it's a faulty gauge or testing method if the engine sarts and runs well.

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

JimVillers · « **Reply #14 on:** June 11, 2006, 19:14:27 »

Matt .... Did you have the throttle open when you took your compression test. It must be wide open to get a good reading.

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

Benz Dr. · « **Reply #15 on:** June 11, 2006, 20:45:57 »

No it doesn't. We've been through this before and I'm 100% sure on this. The engine will idle on the small amount of air that gets by the air acrew with the throttle closed, right?
In this case you will have all the spark plugs out and will only be trying to fill one cylinder with air. It won't make one bit of difference. The maximum will be the same open or closed throttle.

Some engines are VERY sensitive to throttle opening for compression testing ( I remember this Alfa once ) but not these cars. So that's not the problem.

Sorry Jim.

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

merrill · « **Reply #16 on:** September 06, 2006, 06:37:53 »

so, this is interesting,

last weekend I found that the thermostat for the injection pump was not working, AND the pin that connects the thermostat to the injection pump was missing.

so, the car was running rich all the time.

To make this more interesting the injection pump was replaced between the compression tests.

I bet I have fried rings due to excess fuel being pumped into the system. I doubt I had stuck rings.

Either way, when I used diesel to un-stick the rings, I could hear one cylinder a drip drip as the fuel ran out of the cylinder #5

I will get the pin, a rebuilt thermostat and see what happens.

sure wish I could pull the lower pan while the motor is in the car to pull the pistons inspect the cylinders etc...

matt

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

Vince Canepa · « **Reply #17 on:** September 06, 2006, 09:03:01 »

I'm with Joe and Dan on this one - I don't think those readings are reliable enough to make a decision. Also, I wouldn't get too excited by the "drip drip". Piston rings have small gaps at the ends. A light fluid like diesel oil will work its way past the gaps and drip into the crankcase. I wouldn' be surprised if all the cylinders were dripping. After you have amused yourself with the diesel, drain the oil and refill with fresh oil before starting the engine. Then run the car. I would drive it 1,000 miles or so and recheck the compression before making any decision.

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

merrill · « **Reply #18 on:** February 14, 2007, 19:25:39 »

so,
heard back from metric motors today, they gave me the following update

Your cylinder head has some corrosion but is fine (actually better than most).
The block is standard bore but has substantial wear from ring travel (the 4-ring piston version will do that, as well as an enriched fuel condition). So we will need to finish it at the 2nd repair stage of +1.00mm = 83.00mm (no worries = standard procedure).
Crankshaft and camshaft have normal wear. All in all just a tired assembly

I need to ask them about the status of the piston rings when they removed the pistons from the car.

matt

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

Nate · « **Reply #19 on:** February 14, 2007, 21:29:32 »

What does Metric Motors charge for a small block rebuild?

merrill · « **Reply #20 on:** February 15, 2007, 07:51:03 »

Nate,

short block rebuild - 3,700.00
long block rebuild - 6,200.00

http://www.mercedesengines.net/products.asp?cat=15

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

rwmastel · « **Reply #21 on:** February 16, 2007, 14:13:28 »

quote:
Originally posted by merrill

short block rebuild - 3,700.00
long block rebuild - 6,200.00

Is a 230SL engine a short or long block?

How many miles were on your engine, or do you know?

What's your engine number? I wonder if I have the same 4-ring pistons.

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

George Des · « **Reply #22 on:** February 16, 2007, 15:25:55 »

Rod--Long and short block refers to the type rebuild. A long block rebuild is everything including the head unit i.e. valves, camshaft, etc. in addition to the block components i.e. pistons, crank, etc. A short block rebuild includes just the block unit and none of the head components.

George Des

merrill · « **Reply #23 on:** February 16, 2007, 20:51:16 »

Rodd,

Is a 230SL engine a short or long block? - george answered this

How many miles were on your engine, or do you know? - actually I do not know, I have many recipts however the odo is in km

What's your engine number? I wonder if I have the same 4-ring pistons
I think the number is 12781-12-00419

matt

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

rwmastel · « **Reply #24 on:** February 17, 2007, 15:20:30 »

quote:
Originally posted by George Des

A long block rebuild is everything including the head unit i.e. valves, camshaft, etc. in addition to the block components i.e. pistons, crank, etc.

OK, so I have more money to save before making that call.

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

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Author Topic: compression question (Read 21927 times)

Ben

Ben

Ben

Vince Canepa

George Des