Comp Test:Does my engine need to come apart?

Nicad

Nicad

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I was kinda hesitant to do this. AT first I thought my numbers looked quite good....till I squirted some oil in the cylinders.

I got the following numbers on my warm engine.
I had a very good Battery providing the cranking amps:


Dry With Oil


1) 190, 200

2) 182, 193

3) 196, 210

4) 188, 210

5) 190, 212

6) 190, 212


Do these numbers mean that my car likely has higher compression than stock? I was pretty pleased to see 190's, but quite surprised when it jumped so much with the couple of squirts of oil (It was quite heavy Way oil for a milling machine). I guess I have a ring problem.

I have not noticed the car smoking. So far it is barely running though. Installed a Pertronix today, cap and wires are new, but I suspect the carbs have some internal problems at the moment. I also suspect this car has overheated a few times, as the fan clutch is toast. Anyway. if I have to rebuild the engine, so be it. It is not a deal breaker, but means that I might not be driving this car for a long while.

Opinions greatly appreciated.
 
No, you don't have a compression problem. For a used engine, even a gently used engine, those are good numbers for street.

It's not so much the highest but a big difference.

Oil- describe the issue more or running bad.

Could be as simple as the wrong weight oil, valve seals, etc. Or just never used much, far, didn't get hot, no t-stat...... many things.

Yes, it's very likely you have high compression ( domed ) pistons.
 
For what it is worth, my <9.0:1 CR engine with 40,000 miles since rebuild ranges 170 - 180 dry. Uses 1/2 - 3/4 litre of 40w in 3,000mi (metric country and US odometer). From what I've heared a range of 10% in compression numbers with that mileage is reasonable.

I agree on the higher compression engine with cylinder 2 a little weak but still within the 10%. Interesting that it is my cylinder 2 that is lowest as well.

I still think you have the buy of the century (albeit we are only in year 12) given what you paid and what you got for it. You probably sit in it up on the stands drinking single malt and goosing the triple webers.

Check these performance numbers http://www.weatheroffice.gc.ca/city/pages/ab-3_metric_e.html


Doug
 
Nicad said:
Do these numbers mean that my car likely has higher compression than stock? I was pretty pleased to see 190's, but quite surprised when it jumped so much with the couple of squirts of oil (It was quite heavy Way oil for a milling machine). I guess I have a ring problem.

I have not noticed the car smoking. So far it is barely running though. Installed a Pertronix today, cap and wires are new, but I suspect the carbs have some internal problems at the moment. I also suspect this car has overheated a few times, as the fan clutch is toast. Anyway. if I have to rebuild the engine, so be it. It is not a deal breaker, but means that I might not be driving this car for a long while.

Opinions greatly appreciated.
Click to expand...

Your results are relative as numbers can vary between gauges and ambient temperature and number of crank turns - and other factors. Indeed, the shop manual covers compression testing:

"Good above 156 lb./in2"
"Normal: 142-156 lb./in2"
"Poor: 142 or below lb./in2"

As noted, unless we are all using the same calibrated gauge - results will vary. Different cam profiles can dramatically alter gauge readings, same with valve timing, valve adjustments, throttle position, oil viscosity and even a stuck or sticking ring. (Bet your numbers increase dramatically if you were to fill each cylinder with kerosene, but please do not. Hydro lock may yield diesel-like numbers and this is not necessarily a good thing.)

Not to be the fly in your ointment, but the fact that the fan clutch is either frozen or will not engage, may or may not be an accurate indicator of past engine overheating. I dealt with a similar model with an oversized radiator making it extremely difficult for the engine to reach normal operating temps. The fan clutch would not engage until we blocked off part of the radiator with cardboard.

Fluid/oil levels that are steady and remain segregated (i.e., where they belong), coupled with decent compression - would lead me to continue working with the engine to get it running acceptably. Naturally, a lot depends upon other factors, such as the condition of the valve train (gummed up? camshaft scored?) and your fuel delivery system, but your readings suggest you have a glass that is more full than empty.

One last thought, SteveH posted something about E10 fuels. I drove a car recently that had been sitting for some two months. It idled poorly and once warmed up had substantial pinging. The tank was 3/4 empty. Filling the tank resulted in a dramatic improvement. I cannot confirm the fuel was saturated with H20, but I have my suspicions.
 
decoupe said:
For what it is worth, my <9.0:1 CR engine with 40,000 miles since rebuild ranges 170 - 180 dry. Uses 1/2 - 3/4 litre of 40w in 3,000mi (metric country and US odometer). From what I've heared a range of 10% in compression numbers with that mileage is reasonable.

I agree on the higher compression engine with cylinder 2 a little weak but still within the 10%. Interesting that it is my cylinder 2 that is lowest as well.

I still think you have the buy of the century (albeit we are only in year 12) given what you paid and what you got for it. You probably sit in it up on the stands drinking single malt and goosing the triple webers.

Check these performance numbers http://www.weatheroffice.gc.ca/city/pages/ab-3_metric_e.html


Doug
Click to expand...

Egads, those are very Mont Tremblant like temp numbers. Doug, you are not far off in your assessment of how I sit in the Coupe.
 
MMercury said:
Your results are relative as numbers can vary between gauges and ambient temperature and number of crank turns - and other factors. Indeed, the shop manual covers compression testing:

"Good above 156 lb./in2"
"Normal: 142-156 lb./in2"
"Poor: 142 or below lb./in2"

As noted, unless we are all using the same calibrated gauge - results will vary. Different cam profiles can dramatically alter gauge readings, same with valve timing, valve adjustments, throttle position, oil viscosity and even a stuck or sticking ring. (Bet your numbers increase dramatically if you were to fill each cylinder with kerosene, but please do not. Hydro lock may yield diesel-like numbers and this is not necessarily a good thing.)

Not to be the fly in your ointment, but the fact that the fan clutch is either frozen or will not engage, may or may not be an accurate indicator of past engine overheating. I dealt with a similar model with an oversized radiator making it extremely difficult for the engine to reach normal operating temps. The fan clutch would not engage until we blocked off part of the radiator with cardboard.

Fluid/oil levels that are steady and remain segregated (i.e., where they belong), coupled with decent compression - would lead me to continue working with the engine to get it running acceptably. Naturally, a lot depends upon other factors, such as the condition of the valve train (gummed up? camshaft scored?) and your fuel delivery system, but your readings suggest you have a glass that is more full than empty.

One last thought, SteveH posted something about E10 fuels. I drove a car recently that had been sitting for some two months. It idled poorly and once warmed up had substantial pinging. The tank was 3/4 empty. Filling the tank resulted in a dramatic improvement. I cannot confirm the fuel was saturated with H20, but I have my suspicions.
Click to expand...
Well, all your answers are reassuring. Thanks. I haven't checked the valve clearances, but that is next on my list. I am pretty sure it overheated, because in my limited street driving before parking it, it was overheating if I sat at a traffic light. The Rad looks pretty suspect, so I will be changing all the associated parts. This car basically sat from 1987 till now from what I was told, so maybe that is the problem with the fuel system and why it is barely running. (The plugs looked quite black after about 20 miles of use. (Also, I installed a new fuel pump and it is putting out more pressure than a Weber is supposed to get ...about 5 pounds). So I will get a regulator to bring it down to about 3 and rebuild the carbs. Hopefully it responds to this. One other thing, it seems to be a bit louder in terms of valve clatter than previous BMW's. Perhaps headers accentuate this?
I put some Castrol GTX in when I changed the oil. It is 20W50
 
Steve,

I've found that number two and number four cylinders tend to run richer. It's probable that on carb'd engines, the manifold shape has something to do with it. it's basically a straight shot to the referenced port(s), use of choke, pooling in the bottom of the manifold when cold, etc.

By tuning to the middle cylinder of each carb/ manifold as far as otimimum a/f ratio, you can fine tune the cylinder balance. It's subtle, but noticeable.

Once you've got the carbs balanced reasonably well, there are small adjustments ( much smaller than usual) to balance out the firing. Takes a little practice, record which adjustment was made if you need to, but worthwile in terms of power and smoothness.

I notice it more when doing a drop test... taking a spark plug wire off one at a time and notice how the rpm drops and how evenly it does from cylinder to cylinder.

Think of it as a clogged injector but with a carb. You're just trying to even things out or in this case the cylinder two and four. Chances are they are the ones that foul first, less compression, etc.
 
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