Looks like a rebuild is in order...

[E30_Crazy]

Was on my way to work a few weeks ago on my 85 K100, when just after a gear change (2nd to 3rd I think), it started running very weak. Felt like low compression. Couldn't really hear or feel any misfire. If so, its missing on 2 opposed cylinders, with an even pattern. Been crazy busy with work, moving 7k miles, and a baby on the way. Only thing I've done so far is stick a flex scope down the plug holes. Couldn't get a look at the valves, but pistons look nominal. With the engine running, I got very distinct puffs of air from under the oil service cap, which tells me combustion is getting by the rings and into the crankcase/block/oilpan area.


So first to do, is a compression test. See if it's all cylinders or not. My guesses, in order, are rings, then valves, then maybe timing? In case it jumped a bit? Is that even a thing with these engines, or would it have gone "bang!" before that's likely?


There's going to be a degree of disassembly regardless, and I was already burning copious amounts of oil, along with a rear main and/or output shaft leak. So I figure while I'm in there, get the valve stem seals done (and possibly valves if I jumped timing. Didn't see any contact on pistons though) most likely rings. And that'll mean new rod bearings, too. Plus the rear main/output shaft seals.


And just because I like clean parts going back together, if I don't also buy new pistons, what are some of your pistons cleaning techniques/tricks?

[The Mighty Gryphon]

How many miles?  When was valve clearance checked last?  Could be a damaged valve seat.  Burning oil means bad rings.  I just did a valve guide seal job on my RS and it still burns oil.   I don't know how you can do a ring job with the nikasil when you can't hone the cylinders without taking the chance of damaging the lining.

Check with Safari Cycle in California.  They have a ton of used engines for less than the cost of a complete set of rings and a head gasket.  A later model engine with 40k miles is the way I would try to go.  Granted, shipping is going to be expensive, but that is offset by the machine shop labor and all the other bits you won't need to buy.  Trust me, they add up pretty quick.

It's the way I would go.

[E30_Crazy]

Crosshatching still looked very nice, as far as I could see with pistons still in. Shipping would be terrible from CA to VA.  Not as bad as AK, but still.


Mileage is around 40-45k I believe. No idea on any checks last done. PO was pretty mechanical, so he could have done everything ever needed... Or not. Who knows. I'm ok with burning a little oil. God knows these BMW engines do it. But I was burning/leaking a quart every 100-200 miles.

[Martin]

+1 Do a compression test and if you can do a leak down test. Is it blowing lots of smoke out of the exhaust it will be blue if it is oil, what do the spark plugs look like. I think members have replaced rings if the cross hatching is OK. But you need to cost it out, as second hand engines as per Gryph can be had cheap. Post the compression figures which should be done with the plug wires earthed and the throttle fully opened.
Regards Martin.

[The Mighty Gryphon]

You will find that most of the bricks around here don't use much oil.  My K75's get about 2000 miles or more of 75-85mph to a quart of oil.  My K100Rs is relatively alarming in that it uses a quart every 7-800 miles.  But then, it has 116,000 miles on it.

When I did the seals in my 4valve RS the job cost me about 300+ and I didn't do any head or piston work.  Add about $450 for rings and bearings, and you are looking at a used engine being a pretty good deal even with the freight. 

Speaking of freight, there seems to be a lot of bricks in the Seattle area.  Should be some breakers there with engines.  Might save a little bit on the freight.

[E30_Crazy]

Will a leakdown work the same on a horizontal engine? Most of my engine hands-on is old bimmer 6s. Been working on those for 10 years now in my own time, just never a horizontal beamer before

[The Mighty Gryphon]

Just reread your original post.  Have you checked the plugs for spark.  There are two weak points in your ignition system that will affect two cylinders when they fail.

First is the coils.  On the early model K100 they had issues and were replaced later with a better design.  There is also the infamous Hall Effect Sensors.  They typically give problems when the engine is at operating temperature but work when cold.  There has been a fair number of Hall Sensor problems over the years so I would definitely check them.

[Martin]

Yes no problem, but it looks like you haven't done many miles on it. Did it sit for along time, they don't like sitting and oil consumption often settles down after use. A high detergent oil used for about 1000 miles can sometimes free up the rings. Are you sure it is firing on all cylinders a laser temperature gun pointed at the individual headers close to the head will quickly  show up a non firing cylinder. They are now really cheap ( $ 20.00 Ebay) and are a handy diagnostic tool.
 Regards Martin.

[The Mighty Gryphon]

Also, I can't imagine a sudden loss of power due to a mechanical failure not being accompanied by a lot of expensive noise.  Unless there was a lot of clanking and so on going on, I would be concentrating on checking the engine management and ignition systems.

[E30_Crazy]

Plugs and wire are all firing. Didn't measure the strength though. Just a visual. Coil is good, and is a nodded/relocated coil, up behind the radiator on the righthand side. All 4 points firing. Recently did a hall sensor test, as I had a starting issue. Along with testing the hall sensor, I've replaces the ECU, AFM, and ignition unit with known good units (and it ran for 2 or 3 months on these, fine)


Been on it for about a year now, at least a couple times a week, if not every day, so not much sitting, and still high consumption. Heated garage kept over the winters while in AK.

[Martin]

Do a compression test and is it smoking? Have you checked the valve clearances? Have you checked, cleaned or replaced air cleaner and fuel filter?
Regards Martin.

[Brad-Man]

A modded/relocated coil?

All K's have two coils.

[The Mighty Gryphon]

A modded/relocated coil?

???? 

Is this another cafe/scrambler mod?

[E30_Crazy]

A modded/relocated coil?

All K's have two coils.

Unless they dont, and it runs on one 2x2 coil.

[E30_Crazy]

???? 

Is this another cafe/scrambler mod?

Yes, it's somewhat a conglomerate cafe/naked/street fighter build.


But again, it's not a "what did I do wrong" post. It ran for some 2+ years as is. It's a new development, if you would. I can filter through the suggestions for what may apply to me. The engine and management are really all still standard, minus a come filter, and a different coil/cables.

[The Mighty Gryphon]

Ok, so how much new clanking are you getting from the engine? 

Can you fire it up for a couple minutes and see which exhaust headers are getting hot? 

What did you say the compression was?  Compression is unrelated to oil consumption.  My RS uses more oil than I like, but still has good, uniform compression across all cylinders.

How old are your spark plugs?  I have seen a fair number of plugs over the years that would fire in free air, but misfire or not fire at all when dealing with the compression in the engine. 

What are your valve clearances?  When were they last checked? 

[E30_Crazy]

Ok, so how much new clanking are you getting from the engine? 

Can you fire it up for a couple minutes and see which exhaust headers are getting hot? 

What did you say the compression was?  Compression is unrelated to oil consumption.  My RS uses more oil than I like, but still has good, uniform compression across all cylinders.

How old are your spark plugs?  I have seen a fair number of plugs over the years that would fire in free air, but misfire or not fire at all when dealing with the compression in the engine. 

What are your valve clearances?  When were they last checked?

Not a lot if clanking. A little noisy from the lower idle, but nothing alarming.


I'll have to get back later with a compression test and checking the exhaust for heat. Still getting settled at my new place. Spark plugs have maybe 500-800 miles on them. Haven't checked the valve clearances yet either, and unknown last checked. If anything, I doubt they are loose. Don't get an excessive amount of tapping. Just the good old sewing machine tick BMW motors are known for (rockers and injectors) But it definitely wouldn't hurt to cross that off the list by doing it. I'll have it all apart anyways. What are the clearances for intake/exhaust cold/hot?


But really, if the rings have got a chunk blown out, that would allow blowby, causing the hot puffs of air from under the oil cap.

[Laitch]

Have you checked your crankcase vent tube,E30_Crazy? How did you adapt that bit to your current setup? Have you posted a picture of this critter on here yet?

[Martin]

+1 on crankcase  venting, is it stock?
Regards Martin.

[E30_Crazy]

Have you checked your crankcase vent tube,E30_Crazy? How did you adapt that bit to your current setup? Have you posted a picture of this critter on here yet?

I don't thinknthe crankcase vent had been changed fromm stock? I'll search the diagrams to make sure I'm looking at the right one, but isn't that the zigzag one that goes to the inlet/filter box?

[E30_Crazy]

Just broke her open tonight, thinking I'd check out the top end, and prep for a clearance check, and found I'd snapped the inlet cam! So now I can begin the process of replacing that. Are there any options for upgraded/better power curve cams for the K100? Without needing a standalone ECU?


Looking at it here, it seems pretty easy to swap in situ. Held in by caps, like a crank. My old M20 powered E30 (and many other car engines) they slide out the front of the head after beadbolts are loosened and rocker retainers removed.

[Martin]

There must have been a reason for the camshaft to snap. Check for a seized bearing due to oil gallery blockage, the breakage point should indicate which bearing has possibly seized, pictures would be helpful. When fitting a new or secondhand camshaft, it would be better to renew the bearing. Also check the tunnel alignment and bearing clearance using Plastigage.
Regards Martin

[E30_Crazy]

I looked all the faces over pretty well. Didn't see any damage, burns, shavings, etc... I was looking for bearings, but didn't see any? Are they not bearing half-shells? Just the first cap? All other caps and journals looked fine, regardless.


Sorry for the lack in pictures, can't seem to get the link once I upload them, since I'm using my phone. And the direct upload is too large of an image. It broke right before the #4 intake lobe, leaning just the lobe and final bearing

[Martin]

Sorry the shaft runs in the head no bearings. It is extremely rare to break a camshaft and I have only ever heard of this when a bearing nips up or head warping from overheating. You might also consider a complete second hand head.
Regards Martin

[Laitch]

Sorry for the lack in pictures, can't seem to get the link once I upload them, since I'm using my phone. And the direct upload is too large of an image. It broke right before the #4 intake lobe, leaning just the lobe and final bearing

Photos showing the condition would be beneficial to others who might encounter similar problems later. There are applications that allow resizing of photos taken by phone. Images must be downsized to load well here. The use of these applications is infinitely less complicated than working on an engine.

So far, I don't know if this is all theoretical or if there really is a bike in Eagle River that really has a camshaft problem; furthermore, it's not really important that I know either. Questions are being asked here that can easily be answered by consulting a workshop manual available on this site and a BMW parts fiche like the one at MAXBMW so clarification of why that doesn't work would be helpful.

Contributing is part of being a community member. You've got something to contribute, E30. Upload your photos from your computer, or your friend's computer or the Chugiak-Eagle River Public Library's Internet computer if you can't master your phone's functions.