‘87 K75S Failed compression test - burned valve

Wow !

Thanks, lots of info here !

I got mines from Moto Bins, $22 Cdn, don't know if they are oem. I will check that mold line tomorrow.

This breather and the big hose were my problem, maybe with a too tight valve too...

Here are the picture of these culprits !

Ignace

Nice clear pictures! I can tell you that this is harder to achieve than it would appear. The depth of field with such macro photos is small. Plus, having dirty, greasy hands from retrieving the part and holding the camera is usually awkward for me. Nice job!

Failed compression test K75

jagarra said:

Sometimes it is best to stick with an OEM supplied part, in this case you know there is engineering to back the specifications that the product was built upon. In many cases with third party suppliers, they make what appears to fit an application, but the materials and construction don't meet the original OEM specs, fit and durability suffer. As long as BMW is willing to supply an original item that is the best choice, they see demand, they continue to supply.

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OEM?????
This might answer some of the questions.......
https://forums.bmwmoa.org/showthread.php?12060-BMW-parts-made-in-China-WTF!

It's bad when the Germans are outsourcing to the land of 'Good Enough'.

Failed compression test K75

robsryder said:

Next shown is the top air cleaner housing. Perhaps the hose, shown as item #1, would need some attention?

View attachment 87283View attachment 87284

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The hose between the intake plenum and breather box is crucial in the scheme of things with the early 2v. I bought a K100RS for peanuts because the PO could not get it to run right. After going over the bike for a few weeks, I found the hose clamp had not been properly tightened and the hose not seated correctly and let air in at the plenum. The MAF was not getting the right signals to the computer .
Boy was the PO ticked at his mechanic.

As Lee pointed out the crankcase breather hose is a major culprit to always keep an eye on. Can't say if the 'OEM' are outsourced or not as opposed to the aftermarket ones, but just sent EME a bunch of money for parts and these were in my order. Time will tell.

With these older bricks, ALL of the rubber components should be considered suspect, especially if the bike is 'new' to us. I usualyl take 3-4 weeks to fondle, caress, and talk nice to my new 'other woman' as the wife calls them. It pays off in the long run.

Thanks guys ,

There seems to be no thin mold line on the ones from Moto Bins. Time will tell if they last !

Thanks also for the comments on the pictures, it effectively is not that easy to take nice closeup picture, specially with greasy hands !

Take care,

Ignace

I believe the ones from Motobins are from BMW. The ones from Beemerboneyard and Euromotoelectrics are reproductions.

I have obtained my vent hoses from BMW, EME, and BeemerBoneYard. Photos and data from my examination follow. In short, all of the hoses were similar in appearance. None appeared to be "weaker" than any others. It is my plan to use all of these (over time) in my K75S bikes.

It took a week for the BMW vent hoses to arrive at my local dealership. The EME hoses arrived in 2 days, from BeemerBoneYard in 3 days. Shipping for EME was $10.99 with a $4.44 discount. Shipping for BeemerBoneYard was $7.95 with a 10% discount (BMWMOA member). Prices for each vent hose are shown below. End thicknesses were measured using a caliper at the 12, 3, 6, and 9 o'clock positions (i.e., 90 degrees apart). Each end was measured. For the two photos showing vent hose ends: top was from BMW, middle from EME, and bottom from BeemerBoneYard [BBY].

Rob,

Since you have a couple samples of each, do me a favor.

Take each one and put your thumb and index finger on opposing sides of the hose, where it narrows down, with your fingers on the mold lines. Lightly squeeze each hose. Do you notice any difference?

I had noticed a definite difference between the BBY ones and the BMW ones. The BBY ones felt thinner along the mold line. You could feel the flexing at the mold line more than the rest of the hose. This was a couple years ago, maybe they have improved the process.

The BMW vent hose "felt" a bit stiffer, but I have no way of making a quantitative assessment of the stiffness. The EME and BBY vent hoses were only slightly more pliable in the mid-section. I have a BBY hose from a few years back that felt similar. The other BBY vent hose purchased a few years ago has been on my 92 K75S and is due for replacement. I will also replace the vent hose on my 88 K75S that was replaced several years ago with a BMW hose. I've noticed no difference in apparent wear (or leaks) from either. But, I replace the vent hoses every couple of years as a matter of course. A feller suggested this practice back in 2010 when I purchased my first K75S in California.

This is information !

You'll be good for a couple of years with this stock !

I'm the OP of this tread, just got a used top condition complete valve train from the Motorcycle Guys. So it went jn with new valve seals and new exhaust studs. I seated the valves with the proper paste. I just replaced the 3 exhaust valves (but all the seals). The valve guides were within tolerance.

I'll keep you posted on the next compression test !

Really thanks to all for the invaluable info !

Ignace

Nice work

It’s been a long time since I have been that deep on an engine repair.

OM

Thanks OM !

Ignace

Nice photos and looks like a good job by a competent mechanic. Enjoy riding the K75.

Thanks Robsryder ! It's a fun.venture. When the bike will be totally restored, I will post pictures of the whole process!