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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: riots100 on November 25, 2015, 01:24:53 PM
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I just got a 1991 K75 with very low miles (kilometers actually) and it has an oil leak around the area where the exhaust pipe mates with the number three cylinder. Cylinders one and two are clean and pretty. Number three is oily and grimy, with small oil deposits being left on the floor.
The leak is definitely coming from this junction. Seems a bit unusual.
The bike was left on the side stand for a number of years (3-4) It's up on the center stand now.
What could be causing this leak? (And what might the remedy be?)
Thanks!
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Guessing that being on side stand caused oil to drain from crankcase into head. I would replace exhaust gasket, leave on center stand and see if it leaks anymore.
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Yeah, the rings take 30,000 miles to seat themselves to the cylinder walls. I have three bricks now, with 110,000, 71,000, and 35,000. The one with 35k is the only one that smokes noticeably when I leave it on the side stand.
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The oil leak saga continues...
I've been riding the bike for a couple of months now. I've put on an addition 5000 to 7000 miles on the machine and I always park it on the center stand.
The oil leak continues on the number three cylinder exhaust header junction. It will leave oil droppings on my garage floor after each ride. (epoxy floor, wipes right up) The corresponding number three spark plug is also fouled with oil as well.
There is also a telltale oily patch in the number three spark plug well, right over the outside of the exhaust valve. And peering inside the cylinder through the spark plug hole, the top of the piston appears oily as well.
Pictures attached. Best guesses welcome.
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Old and dried up camshaft cover gasket maybe? check carefully around the gasket for the source of the leak.
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Try adding an oil additive like Risolene or a similar high detergent additive, with a new spark plug in run it for at least 1000 K's. Then change the oil and filter use a fully synthetic oil. It might just be gummed up rings from sitting. It might take a few thousand kilometers to clear. It could also be a valve stem seal, have some one follow you and note if and when it is smoking. If it is smoking on take off it is probably the valve stem seal. BMW's don't like sitting for long periods and that can be the cause of a lot of problems.
Regards Martin.
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Bruce since getting the bike have you changed the oil and filter, and if so what oil are you using. You might want to do a wet and dry compression test although this does not nessarcerily show bad oil rings. And it looks like a gasket leak as well as per RBM.
Regards Martin.
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Take a day and clean things really well, as in totally spotless. Then spray the entire cylinder head with aerosol talcum powder. Run the engine for a while. The oil leak will be readily visible as yellow or black stains in the white powder.
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Bruce since getting the bike have you changed the oil and filter, and if so what oil are you using. You might want to do a wet and dry compression test although this does not necessarily show bad oil rings.
I changed the oil/filter as soon as I got the bike. It didn't run when I first got it. The fuel system was basically hosed after sitting for so long. New fuel pump/filter, injectors, plugs and many new rubber hoses got the bike running fairly well. The compression test showed normal in cylinders one and two. Number three was down slightly from one and two. (don't remember the numbers off hand) The bike does smoke a little on acceleration. The bike has very few kms on the clock and all the other systems are in very good shape. I have been suspecting the exhaust valve in number three as well. Just yesterday the bike started backfiring (after-firing?) on deceleration and seemed to be running a little rougher than normal.
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And peering inside the cylinder through the spark plug hole, the top of the piston appears oily as well.
Perform a vacuum test on each cylinder and see what you get. It's a simple test. Gauge and hose are widely available at department and auto parts stores. Do a compression test, too—more tools to buy. :musicboohoo:
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If you are burning oil it can only get in two ways, past the oil control ring on the piston, or past the valve stem seal. What was the condition of the old oil and how many K's have you done since resurrecting the bike? What type of oil are you running, it is possible it may settle down after more K,s under it's belt. You could just keep riding it, or put some Risolene in it to see if it frees up.Doing a vacuum test is a good idea it will give a better idea of what's going on. If you buy a gauge it should come with instructions on how to use it and what the various readings mean. If not there are sites that show you. I have a mate with a collection of bricks, a couple which had sat for quite a few years two were prodigious smokers one has settled down and only smokes after being left on the side stand. The other smoker is not registered, but it to could settle with more miles. if you suspect an oil leak Gryphs idea with the spray talc is a great idea. At this stage I would keep investigating and not do anything drastic, as I stated Bricks don't like sitting around.
Regards Martin.
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If none of the previous things work, and while we don't even have these products, you might as a last ditch effort look at Seafoam or Marvel Mystery Oil. A lot of people in the US seem to like them. I have never seen any success with compression booster cleaners, but we don't have the two I mentioned. Further comments from people who have used these products or any others would be helpful.
Regards Martin
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What is it about doing simple engine tests that sends people running to ring-job-in-a-can solutions instead? The possibility having to deal with bad news? That I can understand, but that leads to the futility of trying to drown your sorrows in Seafoam. Why not just do them?
Chris Fix has a whole series of engine cleaning compound tests. Here (https://www.youtube.com/watch?v=u6UeJXkzDW8) he demonstrates Seafoam but in the description section he has links to a whole lot of other product tests.
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Laitch finally got around to watching some of those videos, and they just support what I already believed. But in saying that I do use Techron but as an injector cleaner. I cleaned my injectors by soaking the injectors in it, in a ultrasonic jewellery cleaner. ( in NO WAY do I recommend doing this as injector cleaner is highly flammable) I cycled the injectors using Techron, then put them back in the ultrasonic bath. The spray pattern before I did this, was noticeable in it's improvement after treatment. But who's to say what actually did the cleaning. I do also believe that a higher detergent oil and more miles may free up Riots bike.
Regards Martin.
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Pull the valve cover and checked all the cam/valve clearances. Everything fell into spec except the exhaust valve for the number one cylinder. Exhaust spec. calls for min->.25mm, max->.30mm. Exhaust on number one was tight and measured at .15mm.
I think I should fix this clearance issue and then try the Seafoam/detergent idea. See what gives.
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Things get curiouser and curiouser.
I thought that I would document the rest of the journey so that others via the search engine might find answers.
I pulled the cylinder head and found the exhaust valve in number three to be much darker than one and two:
(http://bdjohnson.net/photos/cylinder-valves-combustion-chamber.jpg)
Looking down through the throttle body ports to the intake valves, I found that the Intake Valve on number three to much more clean and less sooty than one and two.
(http://bdjohnson.net/photos/intake-valves-down-throttle-body.jpg)
Looking up through the exhaust ports to the exhaust valves I found that the Exhaust Valve on number three was much darker and more sooty than one and two.
(http://bdjohnson.net/photos/exhaust-valve-ports.jpg)
Looking at the pistons, each at top-dead-center, numbers one and two both have carbon build up, number three has very little carbon build up compared to the other two. Also one thing that is hard to see in the photos, number three piston will not rise up to the same level as pistons one and two: (more on this later)
(http://bdjohnson.net/photos/piston-condition-tdc.jpg)
The interior of the cylinder walls have very little wear on all three cylinders. You can still see some type of cross-hatching in the cylinder wall metal. (not sure if this is normal or not)
(http://bdjohnson.net/photos/number-3-cylinder-detail.jpg)
Next up, we'll pull the crankcase cover and have a look at the connecting rods.
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When I first acquired the bike, I had a grumpy, cranky, old, Zen Master, Jedi BMW bike mechanic look at it. Based on the amount of oil that he drained from the crankcase (a lot) and the fact that the bike was sitting on the side stand for such a long time, he suspected Hydrolock, https://en.wikipedia.org/wiki/Hydrolock (https://en.wikipedia.org/wiki/Hydrolock) in the number three cylinder. He didn't think it was very probable, but it seems that he was right:
(http://bdjohnson.net/photos/bent-number-3-connecting-rod.jpg)
This would account for the number three piston not rising up to the same extent as one and two. And would account for the lower compression reading in number three (it was rising as high) Less compression equals less combustion and less burning of any oil that might be in the combustion chamber. That unburnt oil is forced out the exhaust valve and then leaking around any opening that it can find. The damaged connecting rod and piston is probably letting more oil past the rings into the combustion chamber.
Now the question is what should I do. Obviously the engine needs work. But can I get a way with doing a bottom end overhaul, replace the offending connecting rod and piston? The crankshaft and bearing look good, and the cylinder walls all look almost pristine.
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Quick ebay search has piston with rod st arting at 40 usd. Short block at 150 .... Not a big cost to find out
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Curious if you can swap rings (would you want to? But could you?) when you get a new piston... Since technically dont you need to run the engine at lower rpm with new rings?
My Clymer manual states so.
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Replace the bent rod. Put it back together. . . . . an ride :2thumbup:
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With the suggestion of others, I will re-open this thread and wrap up my bike's engine overhaul experience and thus helping to contribute to the overall knowledge base of the motobrick.
I bought some used connecting rods/pistons on ebay from a parted out 1994 motor with 30k miles. It is important to note that the rods in the "newer" 1990's bikes are lighter that the ones from 1980's bikes. And you should not mix and match but rather find connecting rods from a similar year bike.
I pulled the cylinder head (and everything else that it took to actually pull the head) and crankcase cover. I only extracted the one offending rod from the engine. (number 3) I left the other two connecting rods/pistons in place. I removed the the connecting rod bolts and slid the piston/rod out the top end of the motor. The crankshaft was left in place, (and the two other pistons as well) I know that work is done to get the pistons/rods to be within a similar weight envelope. I weighed the old connecting rod on a postal scale and then the donor rod. They were almost exactly the same weight. I considered myself lucky in that respect.
I elected to re-use the old piston from the bent rod. I couldn't find any defects and was concerned with the weight balance issues and wear pattern in the cylinder itself. I attached the old piston on the new (donor) rod using the donor piston pin and clips, and started the process of re-assembly.
While the cylinder head was off of the bike, I took it to a shop that does cylinder head refurbishments. I just wanted the standard treatment, dunk tank to clean out the old carbon deposits, make sure the head wasn't warped and make sure the valve seats where good. One note about the cylinder head removal/installation. To remove the cylinder head, you have to remove the camshafts. And to remove the camshafts, you have to remove the cam sprockets. Be sure to keep track of which sprocket came from which camshaft, I even kept track of which cam sprocket bolts came from which camshaft (intake or exhaust)
My most OCD task was making sure the connecting rod was attached to the crankshaft correctly. I was using the bearing inserts that came with the donor connecting rod. I torqued, the loosened and then re-torqued the connecting rod bolts to make sure it was correct. In mounting connecting rods, you want to make sure that a thin film of motor oil is on the crankshaft surface and on the bearing insert. Since the crankshaft was still in the motor, I was concerned that I would not catch any binding of the connecting rod. So I rotated the crankshaft many, many times with a torque wrench, making sure that I was using a consistent amount of torque through out.
Assembly was pretty the reverse order of disassembly with new gaskets and other rubber bits. I checked the valve clearances with the cylinder head on the bench (camshafts in place) and made a couple of minor adjustments.
While everything was apart and I was waiting for shipments to arrive, I had the injectors cleaned, (Mr. Injector) cleaned the engine block, air box, clamps, in short, everything.
With every back in place and new oil and coolant, the moment of truth came to see if it would start up. It took enough cranks to get the fuel rail pressurized then the motor fired right up. Oh sweet joy.
But over the next couple of days, the bike continued to backfire occasionally and the number 3 cylinder was still running rich. It was returning to it's former ways. (the spark plug was wet with fuel when pulled from the engine) So even though I fixed the bent rod, there was still some other issue that I had not yet resolved.
I discovered the problem (and resultant solution) when I decided to perform a throttle body sync. When I pulled the vacuum line from the number 3 throttle body to attach the Carbtune, fuel came dripping out of the vacuum hose. That vacuum line goes from the number 3 throttle body to the Fuel Pressure Regulator. This was the "ah-ha" moment. I had a bad fuel pressure regulator, a very rare condition. A condition that has not been discussed here on Motobrick.com. I'm guessing that the diaphragm in the FPR started to leak and was allowing fuel into the vacuum line.
If the engine stopped when the piston was drawing in fuel/air mixture, that would also drawing in a fair amount of fuel from the FPR vacuum line. Then when the engine was started, that excess fuel would be trapped on the compression stroke resulting the aforementioned hydro-lock and damage to the number 3 connecting rod. Remember that the 1990s vintage connecting rods are lighter than their heavier, beefier 1980s versions.
I replaced the Fuel Pressure Regulator, synced the throttle bodies and I haven't looked back. The engine has been working flawlessly since then. I consider the problem fixed.
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Thanks for the great report and good to see a positive outcome.
Regards Martin.
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Excellent account, concise, clear, and wellwritten. Besides that, you are a hell of a diagnostician & mechanic! :2thumbup:
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Excellent report. Appears a good prevention is to replace or check the fuel pressure regulator.
Sent from my iPad using Tapatalk
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Thanks for the update, riots100. It's certain to help others with diagnosis and treatment.
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Appears a good prevention is to replace or check the fuel pressure regulator.
Or at least check to see if fuel is returning to the cylinder from the FPR through that vacuum line.
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Amazing -- 99% of people on the planet would have ridden it till it died, put in a new engine and only then figured out it was the FPR.
What did you do with the rest of the engine you purchased to scavenge the rod from? And forgive me for asking but why didn't you just use that 30k engine rather than take it apart to fix the old one? The only answer I can come up with is that, as the guy in Dirty Harry said as Clint Eastwood was about to shoot him I in the face, "I gots to know!"...
No disrespect intended -- I have nothing but admiration for your mechanical prowess and tenacity.
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No disrespect intended --
Al Contrario, thank you, and thank you all for your kind words.
I probably should have made it clearer, I only bought the connecting rods and pistons on ebay. They came from a parted out motor. I did not buy the entire motor.
Although I did consider doing so. But as old as the bike was and aforementioned condition, it only had 12,000 miles on the clock. So I elected to keep as many original parts as I could and only replace those that needed it.
Here's a screen shot from the eBay listing. I bought three connecting rods/pistons. I only used one connecting rod, bearing insert and connecting pin. The rest are sitting in a box, on shelf in my garage.
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I have a very similar issue. Oil from piston 3 and compression loss. Time to check the FPR. Hopefully no damage to the rods!
Thanks for the awesome writeup.
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I have a very similar issue. Time to check the FPR.
Your model don't have a vacum connection on the FPR.
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Thanks for the heads up.