Advice for 85 k100rs engine breakdown

[beamercon]

The last compression test I had on the K before I garaged her two years ago showed compression ranges in the 20's on all but one. But in the next few weeks, months, I am going to revive this old girl. New rings, gaskets, shims.
Any and all advice, experience, necessaries, etc would be greatly appreciated as I dive into this project. What to look for, what to expect, pictures, anything. Thanks

[deilenberger]

Umm... when you say "20" - 20 what?

Normally the rings/bore on a K bike engine are good for 200-300,000 miles. When they wear out - the engine is considered dead since it can't be bored, and it costs more to rebuild it than buy a good used one. Going price for good used K100 engine is $300-500, depending on mileage on it.

[beamercon]

Thanks for the response Don.
27, 24 some other "20" were the numbers told to me by a BMW center when I took her in to figure out what was going on. They said that those were the numbers of the compression in the first three cylinders and the fourth was under 10 which was ok.
Here's what prompted the bike to go in to the shop: 90miles per tank and the K was bucking like a bronco, no power obviously, and the smell (perhaps the sight of gas coming from the exhaust pipe).
It is my assumption the compression was causing the problems. And the cure, might be, new rings. But I am a novice wrencher. I have to assume the bike only has around 100k on it. I got it with 14k on the odometer, and put 40k on it. Then discovered several coats of paint. Now that doesn't mean the fellow who sold it to me changed the odometer, but I have to wonder.
So if the cylinders aren't the culprit, what do I look for.?
Here's what I did before I gave up and took her to a BMW store.
Swapped the motronic, new injectors, and other items that needed to be replaced on a 20 yr old.

[deilenberger]

It sounds like it's running grossly rich.

Usually - on elderly K bikes - when this happens it's the engine temperature sensor crapping out and telling the ECU the bike engine is cold all the time, when it isn't. There are some hints on diagnosing this on the IBMWR K-tech site (www.ibmwr.org - look under K tech.) You'll need an ohmmeter. The sensor value can be read at the FI computer connector, which is a bunch easier than where it's located on the bike. IF this sensor is defective (it's located in sorta a PITA spot to get to) - PM me off-line. I have a brand new one sitting around that is of no use to me..

It's also possible the fuel-pressure-regulator has stuck closed, and that is causing it to run awfully rich. To test that - you'll need a pressure gauge that reads to 50PSI or so (100PSI is fine too), some lengths of FI rated fuel-line, a T fitting and some hose clamps.

If neither of these are the issue - THEN it might be worth checking compression.

As far as the numbers the shop gave you - they are nonsensical to me. I'd suggest buying your own compression gauge (get a screw in one with a hose..with dual-sized screw-in adaptor) - and doing your own measurements. Follow the directions that come with the compression tester, but:

1 - Remove fuel pump fuse so you don't flood things (or disconnect under the tank, front left corner)
2 - Remove wires from the ignition coils
3 - Remember how the plug wires are routed (they are numbered on the wires, and #1 is the forward most plug)
4 - Hold throttle fully open when doing the compression test

Then get back to us with the readings.

HTH,

[bikerfish1100]

a few comments:
I agree with Don- compression numbers should be in the range of 130-160 psi, or thereabouts. 10s and 20s makes no sense at all.
it is very likely that a previous owner changed out the speedo- early K speedos were notorious for "going on permanent vacation" during the first 50k miles of their lifetime.

[cjack]

10 bar would be around 145 lb/sqin. But 20 sounds goofy.

[lostboy]

Were those numbers leakdown numbers?

[beamercon]

Lostboy, I believe that was the test not a compression test. It was a couple of years ago, so some synapsis got juggled with some other up in the old noodle.

How would I go about performing a leakdown test again on all four cylinders? and what should I look for? What are the specs for the cylinders.
Appreciate all who look in and give advice. :thumb

[lostboy]

While most of us like to see 10% or less, 20% is quite normal in a healthy K motor. If you don't hear leakage past the valves, you have nothing to worry about.

[jobee58]

If I remember from when I was young and heard my mechanic father talk (which, sadly, I did not pay much heed to, way back when), ring problems invariably lead to oil burning in the cylinders, which makes exhaust extremley heavy and dark. I'm no expert, but would a simple spark plug check give some good indication as to what's occuring in cylinders? To me, fuel system faults seem to make the most sense.

[beamercon]

thanks for the replys. now that the weather is warmer I'm eager to break down the old k. The test I had performed was indeed a leakdown test with 3 of the 4 cyl's reading 15%-30% in the leaddown test.

What should I be looking for to replace/furter diagnose as I open the engine? rings? Cylinder bore?

thanks

[Dennie]

I cant believe (actually, I can) they didnt tell you where the leakage was from primarily . ( I cant spell either:laugh ) you can hear it while its being done. ask them to listen at the oil fill port, and exhaust. the intake is much harder to do, but can be done.

[lostboy]

Getting accurate leakdown numbers in a K motor is difficult; the pistons lying on their sides apparently disrupts sealing when the engine is stopped. When I see an above normal leakdown reading in one of these motors, but it is running well, I rotate the crank until that cyinder is back at TDC compression and check again. If the reading doesn't improve, I make a note of it and check it again after it has been run for some time-often not untill the next service. These motors last a very long time and it is rare to need to disassemble them.

[98lee]

Don't be so quick to tear it down!

The first thing that I'd do would be to check the valve adjustment (something that unfortunately rarely gets done on used K-bikes). This is the likely source of your poor leak-down numbers and could be the major cause of all your other problems.

It costs nothing to check and can be done in less than 1hour. DO THIS FIRST.

I will bet that you will find a couple of overly tight exhaust valves.


:dance :dance :dance

[58058D]

Just as an innocent bystander here....you seem very eager to tear down the engine. Maybe that is good for the experience and something you might need to do to occupy time, but the advice above seems pretty clear that it is unlikely to be the right approach to your problem. Sit back, have a brew and take your time.

[zoridog]

FYI
There is a K engine for sale in the classifieds for $125. Location is Florida.