Increasing Oil Level/Slightly Oily Spark Plugs

[fw66]

Hey Motobrickers,

I'm running into a peculiar problem with my 1990 BMW k75 and I suspect it's worn piston rings but I'm hoping someone can help confirm.

Essentially, my brick runs, idles, and accelerates fine if I am riding it regularly (one or two short rides a week). If left unridden for about a week, the bike has a hard time starting up or fails to start up entirely. It misfires/pops and eventually doesn't produce any ignition even when the engine cranks.

The brick starts up again like normal after:
1. I pull all plugs and clean them and leave pulled plugs out over night to dry out the combustion chambers
2. Or replace all plugs with new spark plugs

My notes/thoughts:
1. Spark plugs are slightly oily and wet when pulled from the brick after trouble starting
2. Oil level rises over time. I have a new oil level window and I definitely notice the oil level rising gradually over the course of a few weeks/months after a fresh oil change. I have done multiple oil changes throughout the years and can confirm that the oil level rising isn't a result of me adding too much oil or misreading the oil level due to pre-ride oil status or the bike being on it's side stand vs. leveled. Fuel is the only thing that could be contributing to the increase to my oil level correct?

I previously thought this may have been an over fueling issue, causing the spark plugs to get drenched in fuel and prevent ignition but I've since replaced the injectors and even the temperature sensor. Not sure how fuel would be able to mix with oil even with over fueling so I'm leaning towards piston rings?

Thanks in advance for the replies!

[The Mighty Gryphon]

Can you smell fuel in the oil?  When fuel gets in the oil it will make the oil smell different. 

Fuel in the oil will make the viscosity of the oil lower and more likely to get past the rings into the combustion chamber fouling the plugs.  You can get an idea of the oil viscosity by putting a small hole in a paper cup and measuring how long it takes a measured amount to flow through the hole.  Run a sample of new oil and then a sample of oil from your engine.

What is puzzling is how the fuel is getting into the oil.  On old auto engines it was from holes in the fuel pump's diaphragm.  Bricks have electric fuel pumps and there is no real contact point where it can get into the oil.

Does the engine smoke a lot after it's warmed up?
 
Do you smell fuel around the engine or in the exhaust?
 
Have you done a compression check? 

How many miles on the bike?
 
What does the air filter look like?
 
Have you checked the water temperature sensor resistance between pins 10 and 13 on the Jetronic box plug?

[Chaos]

Hard to imagine fuel leaking through the rings, another scenario might be misrouted fuel tank overflow.  I believe there is a fitting on top of the crankcase that I was for pcv or something but tended to mess up the fuel air mixture so it is usually plugged.  Somebody might have seen this and run the overflow there?  Just a wild guess, I may be hallucinating about the fitting.  Any mischievous spouse-siblings-neighbors have access to you oil fill plug?

[fw66]

@The Mighty Gryphon

Does the engine smoke a lot after it's warmed up?

Engine smokes only on initial startup and then it's clear. I'm aware that in stock models the side stand leaned the bike over quite drastically which allowed oil to be consumed on startup so I added a side stand pad with a hockey puck to reduce the smoking on startup.
 
Do you smell fuel around the engine or in the exhaust?

I haven't noticed a specific gas smell but it could just be me, smelled pretty much just like oil but I could be off with my senses.
 
Have you done a compression check?

I have, compression on all cylinders although I do not remember the exact values. I can easily do another test if we can confirm if there are piston ring failures based on compression values.

How many miles on the bike?

Shouldn't have more than 40K miles if that.
 
What does the air filter look like?

Air filter is custom...I took the original airbox and 3D printed a housing for 2 pod filters. I know the original bike operates on a snorkel but essentially the snorkel is gone and there are two pod filters on the intake before the actual OEM filter. I understand there are probably some performance limitations with this setup but I'm not sure it has direct impact of the issue I'm experiencing.
 
Have you checked the water temperature sensor resistance between pins 10 and 13 on the Jetronic box plug?

I have not done this specific exercise but I have cleaned all pins with electronic cleaner. I can conduct this exercise if needed + instructions.

Thanks again for the response.

[fw66]

@Chaos

I confirmed all my routings on the fuel tank lines with this forum so it's unlikely that I misrouted. Open to any ideas though... only thing I havent replaced is the vacuum actuated pressure pump. Could there be an explanation for what I am experiencing with a fault of that piece?

[Martin]

Check the vacuum line to the fuel pump regulator, a hole in the diaphragm can allow it to suck fuel into the engine.
Regards Martin.

[The Mighty Gryphon]

First thing that comes to mind is that you may have a bad engine temperature sensor causing the engine to run excessively rich.  The reading on this sensor should be about 2500 ohms at 20C.  Take this reading on pins 10 and 13 on the Jetronic connector.

I don't know what you meant when you said you used the bike for short trips, but it may be that you aren't running the bike far enough to get adequate time at full temperature to burn the carbon off the plugs.  This could be exacerbated by a faulty engine temperature sensor.

When starting, the main control of the mixture is the air temperature going into the engine.  At room temperature the resistance across pins 8 and 9 on the Jetronic connector should be about 200 to 210 ohms. 

I you might want to check these sensors before going much further into your troubleshooting.

[Laitch]

What you've been describing doesn't seem to depart significantly from the condition you described in June of 2021. You installed a new temperature sensor then. Have you verified its performance and that it's the correct version?
You have latched onto this idea of a piston ring failure. You indicate you have done a compression test but state you cannot remember the results. You indicate you will do another compression test "if we can confirm if there are piston ring failures based on compression values." A compression test is a method to help determine failure of piston rings. Following a compression test with a leak-down test helps to narrow the fault. 

It is more likely to me that your habit of short trips—as Gryph indicates—is contributing to this condition by creating condensation of water in the crankcase because the engine doesn't run long enough to burn off water that has accumulated during idleness, which in turn raises the level in the sight glass. If a garage is being used for storage, it doesn't need to be heated to promote condensation. Tell us the brand of spark plugs you're using, their model number, and whether the coil wire connection to the plug is tight and takes some effort to remove the wire from the plug.
Another contributor could be excessive fuel pressure. That can be determined by a simple pressure test and the equipment for this test—and other tests or tasks—often can be obtained from a major auto parts store at no cost by your leaving a deposit until the equipment is returned. The fuel pressure regulator is not "vacuum activated." It controls fuel pressure by using spring pressure aganst fuel pressure that is modified by intake vacuum at the throttle bodies.
It's time to start testing. Beyond tests already discussed, there is coil resistance testing—for K75 primary ≈0.8Ω, for K75 secondary ≈10kΩ—and injection timing to be done later.

[Scott_]

Something that others have not mentioned yet could be worn/leaking injectors. Static fuel pressure in the line when the bike is turned off, could be 'relieving' thru a weak injector, that would allow the fuel to get the plug wet and get into the oil(so long as the intake valve is open).
Just a theory....
YMMV

[daveson]

You're right, it could be the fuel pressure regulator diaphragm leaking. As mentioned, if the diaphragm has a hole in it, the vacuum from the inlet manifold could be pulling fuel through the vacuum hose into the manifold and eventually ending up in the sump (even with the engine off, if cylinder three stopped on the intake stroke)

Although the regulator is hard to get to, the vacuum hose from it to the throttle bodies is easy to get to. Disconnect the hose from throttle body three, if there is any moisture there the regulator is leaking and needs to be replaced. It's a quick easy check. Remove the hose, if dry, lower it to check for fuel. Or connect it, crank it, and check again.

On first thoughts you would expect this to only make spark plug three damp, but it could also effect the others.

I don't like going theoretical but here we go, if your brick was on idle before you stopped it and the plugs are wet. The vacuum being on the same side as the spring, acts against the spring to reduce the spring pressure, therefore reducing fuel pressure. If the diaphragm has a hole, it's not working, so the fuel pressure is too high at idle (with high vacuum)

Usually the vacuum hose has a spring around it, and it should be bone dry.

The rich mixture part of this possibility I thinks would just burn up or go out the exhaust without raising the oil level, but fuel entering with the engine off condition mentioned, would go to the sump. If the oil level rises over a month while your brick is only parked, that would also be a pointer.

[fw66]

@The Mighty Gryphon
As laitch referenced in my thread from 2021, I purchased a new OEM temperature sensor from euro motoelectrics so I'm fairly certain the temp sensor isn't the issue.

My definition of "short trip" is a 0.5 mile ride to and back from a destination (total 1 mile), three times a week. It's possible that I'm not getting enough time to get the engine to full temperature on a regular basis but the plugs I pulled don't look to have a heavy carbon buildup/deposits.

I will check the resistance of pins 8 and 9 on the Jetronic, although I'm wondering how I can do this with a room temperature reference point if it's 52F out right now?


@Laitch
Right, appreciate you connecting to the dots to my thread in 2021. The temperature sensor I bought was directly from euro motoelectronics and it should be the correct OEM part. Came in a BMW box with the exact item number: https://www.euromotoelectrics.com/TEMPSENS-K197-p/tempsens-k197.htm

The compression test I performed last year was a result of the 2021 thread and I was trying to diagnose my starting issue. I don't remember the exact values for each cylinder but I remember crossing "not having compression" off my list. Within spec compression for K75 is around 150 PSI correct? Could lower values indicate potential failure of rings?

The condensation issue is an interesting one, the bike is parked in a shed outside that isn't heated. But i'm not sure what the best way is to address the condensation issue? Would it be to use sea foam or let the motor idle longer before and after riding? All my Spark plugs are "X5DC / BOSCH", coil connection to plug wires and plug wires to spark plugs are tight, I'm using "EnDuraLast" wires.

As for fuel pressure, I remember performing a test to ensure that the new injectors I installed had correct spray pattern and were not leaking. I started the engine and put all injectors adjacent to a piece of cardboard to check spray pattern and for leaks. Would excessive fuel pressure keep the injectors open even if they arent faulty/are also new?

@scott
Injectors are new and replaced last year.

@daveson
I'll check the vacuum hose but I remember doing this last year and identified that it was dry. I'll do this again and report my findings. The diagnosis seems inline with what I observe, oil level rises over the course of a month when parked...but what is strange is that I never saw any wetness in the vacuum line.

Maybe a silly thought but what if I installed a fuel valve between the tank line and the line into the injectors. When parked, I position this valve in the off position to ensure there is absolutely no additional fuel being pulled into the engine. I know this a little lazy but I'm just trying to brainstorm some solutions.

[The Mighty Gryphon]

The air temperature sensor should read about 200 ohms at 70F and around 215 ohms at 50F.  I wouldn't worry unless the resistance is way out of that range. 

If the resistance is much higher, possibly due to a dirty connector it will make the Jetronic it's colder than it actually is, and as a result will make the mixture too rich for proper running.

[daveson]

The oil level rises if left parked for a month, this might be due to a leaking regulator.

Spose you go for a ride then turn the key off. If it just so happens that cylinder 3 was on the compression stroke, the regulator might not leak. On another ride if it just so happens that cylinder 3 was on the intake stroke, the vacuum inside the cylinder could suck fuel in (with the help of fuel pressure) after an unknown number of minutes the vacuum in the cylinder, and the fuel pressure in the rail would drop, and there would be an excessive amount of fuel in the cylinder. This might take days or weeks to drain into the sump, but the fuel in the vacuum hose would have already evaporated, so would seem dry.

I thinks I'm getting too theoretical here, but this might be worth a try. Run it for a minute, then stop it, in the hope cylinder three is on the intake stroke, then check the vacuum hose. Or a few times.  Or maybe remove it while the engine is running. Or a not so easy check, run it,  wait five minutes while disconnecting the coils low tension wires and remove the spark plugs. While cranking, check for fuel coming out of one of the cylinders.

[Laitch]

@fw66
Lower compression values could indicate ring problems but there are other problems that cause that. Testing is more effective than discussion.

To combat the condensation problem created by taking 0.5 mile trips, ride a smaller moto or scooter with a smaller engine that will warm more quickly; otherwise use an electric moto, an electric bicycle or a bicycle. For the electric bicycle, I recommend a Gazelle Medeo. Idling a Brick’s engine brings its own set of problems, among them unnecessary pollution and poor fuel economy.

Excessive fuel pressure delivers excessive fuel per injector pulse.

The reference for correct compression values is the BMW K100/K75 2V service manual downloadable from this site, not some random loiterer on a forum.

[frankenduck]

It's the short trips that are fouling your plugs. The engine doesn't get warmed to normal operating temperature in that short of a ride and the fuel system pumps more fuel than normal when the engine is cold. Just letting a K75 idle for a long period will start to foul the spark plugs.

I agree with Laitch that you should use a different vehicle for frequent half mile trips.

At 40K the rings and compression should be fine unless somebody didn't change the oil for a long, long time.

[fw66]

@laitch/@frakenduck

Just completed a compression test on all cylinders with a cold engine. Throttle was kept all the way open for each cylinder, weather is about 56F today.

Cylinder 1: 120 PSI
Cylinder 2: 120 PSI
Cylinder 3: 90 PSI

According to the manual:
Good= Above 10 Bar = 145 PSI
Normal= 8.5 - 10 Bar = 120-145 PSI
Poor= below 8.5 = 120 PSI

It looks like my third cylinder is not within spec for compression which could suggest the issue of worn rings on the third piston?

[Laitch]

It looks like my third cylinder is not within spec for compression which could suggest the issue of worn rings on the third piston?

It could suggest any of several problems as has already been mentioned.  Squirt some engine oil in that cylinder then crank it up to its highest reading. If it's significantly higher, that might suggest worn rings, but worn rings are usually accompanied by blue smoke from the exhaust and oil consumption, not by mysterious oil production. Christmas is coming though; maybe Santa will bring you worn rings, if you haven't been naughty.

[The Mighty Gryphon]

If indeed your bike has been doing a lot of short trips of around a mile, I could see a fair amount of carbon building up in the cylinders and sticking the rings.  I know from experience that my bikes take at least a mile and a half, usually more to get to full operating temperature.  Your bike appears to be spending a lot of time running rich with a cold engine. 

I have had decent luck with Marvel Mystery Oil loosening up the rings on old engines.  It has some ingredients that are good a dissolving carbon and has a long history of use going back at least to WWII when the Army Air Force used it to prevent loss of power from carbon buildup in the radial engines used in heavy bombers.

You might want to add 3 ounces to a full tank and take the bike out for a good run of at least 20-30 miles several times until all the fuel is used up.  At the same time replace a half quart of crankcase oil with the Marvel Oil.  This should clean up the combustion chamber, valves, pistons and rings to improve compression and injector operation.  Then do another compression check to see if it has improved. 



 

[daveson]

The reference for correct compression values is the BMW K100/K75 2V service manual downloadable from this site, not some random loiterer on a forum.

Comon Laitch, you can do better than that, I know you can do better than that.

[Laitch]

 

[daveson]

Although your regular rides are short, maybe you have the odd longer rides. When I got back into bike riding a few years ago it was mostly weekends. After a while it dawned on me to ride to work, and other regular, usually car rides.

Hopefully the compression improves after Gryph's suggestion. Hopefully the compression isn't low in cylinder 3 due to say excessive fuel, which would wash the oil off the cylinder walls and promote early ring wear, or worse.

If the vacuum hose was disconnected before engine shutdown and parked, and the oil level didn't then rise, that would be a good clue.

[fw66]

Closing the loop on this: I added a fuel valve between the fuel tank and the fuel rail and this seems to have solved my issue.

The oil level is now stable even after weeks without riding and will start up fine although with a decent amount of smoke which I know is somewhat normal.

I suppose I have not identified the true root cause of my original issue but I can say with some degree of confidence that the oil level was rising due to fuel flow and that the bike would not start after a week or so as the plugs got too wet/soaked with fuel.

What's strange is that I never got any liquid in my vacuum hose which would've indicated an issue with the fuel pump regulator...not sure what else could be causing a fuel leak into my oil.

[Laitch]

I suppose I have not identified the true root cause of my original issue but I can say with some degree of confidence that the oil level was rising due to fuel flow.

This assertion, if accurate, returns us to Reply #8 made by Scott—sticking injectors. The three common Brick manuals caution us to depressurize the fuel system before disconnecting the supply hose, because the supply hose could be under pressure if detached shortly after the engine is shut down. It can take ≈40 minutes for the system to depressurize after operation. If one or more injectors are stuck open then fuel could have an opportunity bleed from the ailing injector(s) into the combustion chamber for that period of time. Installing a fuel valve limits the amount of fuel leaking into the chamber after shutdown.

You should check your injectors' operation. The reason fuel would leak from the fuel pressure regulator's vacuum hose is failure of the regulator's diaphragm, not failure of injector operation. You seem to indicate system fuel pressure is at spec. Leaking injectors might cause starting problems, fuel economy problems and other performance problems.

You should also do a leak-down test to determine what is causing low compression in cylinder #3.

[Past-my-Prime]

I previously thought this may have been an over fueling issue, causing the spark plugs to get drenched in fuel and prevent ignition but I've since replaced the injectors and even the temperature sensor. Not sure how fuel would be able to mix with oil even with over fueling so I'm leaning towards piston rings?

Thanks in advance for the replies!

Obviously NOT piston rings if fuel valve solves the problem And as far as I'm concerned, more power to you! But my irritation of *something not working the way it's supposed to* would get the better of me. Everyone else with normal and functioning fueling system isn't having this problem so the fuel is getting into your oil somehow! And a leaky fuel injector makes sense to me.

Maybe one of your replacement fuel injectors is the root of the problem, but is this the same problem as you had before?

Curious minds who can't do anything motorcycle-wise in these temperatures want to know (and I don't have a heated garage).

[daveson]

Turning your tap off won't stop fuel downstream of it from seeping into the oil, and it won't fix the problem while you're riding. The oil won't be able to do it's job's if it's contaminated with fuel. I it's better to find the problem and fix it, or this problem could cause engine damage.

The low compression in cylinder three might be due to a bent con rod. This is rarely the case, but if you remove the crank cover, you might find that as the cause.