R75/6 oil pressure valve leak (disk valve)

[Andey]

I’m getting oil run down the breather hose attached to the older disk type of breather valve...

It’s leaking into the carb intake which is a little worrying.

I thought it would be bad piston rings and blow-by creating higher pressures in the crank case being the problem.

But I’ve honed the pistons and installed new rings...

Then I thought it might have been the position of the disc spring circlip... (used the top position...) but that hasn’t solved it...

Any ideas anyone?

[schrader7032]

According to Snowbum, the top position is for the R75/6 (as well as R50/5, R60/5, R60/6). Do you know if the disk moves freely? Is it chipped in any way? You could convert to the newer reed style.

But if you just installed new rings, could be this is something you'll have to deal with until the engine breaks-in a bit more.

[Andey]

So I moved it to the top clip after seeing it on the bottom clip and reading about it on Snobums page...

The disk is in surprisingly good shape and it moves freely...

I kinda like it’s the original style and I don’t mind the noise it makes... I have a reed valve part ready on the sidelines, but I’m actually a little stumped on how to pull the old one out...

I’ve seen the video by boxer2valve, but I definitely don’t have that tool. I have a reverse hammer, but no appropriate adapter to put it out...

I’ve done 100 miles on it so far... maybe needs more time to break in?

[schrader7032]

I'd give it a bit of time. While with the old rings, you might have had blow-by, with the new rings, there is some added pressure build up when they go to BDC. Do you have the stock oil pan? Are you running oil at the very top of the dip stick? And just to be sure, you measure the oil level by putting the dip stick into the hole but don't screw it in?

You might see what happens when/if the oil level drops down to mid range. Often times an engine burns oil until it finds its "happy" level. If it remains steady at say half way down, don't keep topping it off...let it stay where it likes.

As for removing the old breather, I did it with some coat hanger wrapped around the spokes of the breather (after the disk is removed) and connected that some kind of rod, like something used as a battery hold down in an older car. That let me put a large socket and washer over the rod and created sort of a slide hammer. With a little heating around the perimeter of the edges, I was able to pull the old one out. Might want to see if you can stuff some rags in there as well just to keep things from falling through.

[srankin]

Not to be a smart ass. You said you honed the cylinders and then installed new rings.

Overall, when you started, did you measure the bore diameter of the cylinders? Did you check to see if they were cylindrical and not odd shaped? I am having a hard time trying to get my point across so I will use my 84 RT as an example.

Now I know the 84 has Nikasial (however you spell it) coated cylinders but my point I am trying to make is valid for cast or Nik cylinders. Anyway back to my point, my piston rings were shot. But beside that fact, over the miles of use, the cylinders became egg shaped or non cylindrical. This was found by using a dial bore gauge and measuring many points inside the cylinder itself.

Of course the ring gap was way out of spec but at the same time, the bores themselves were way out of spec, not cylindrical. In a cast iron bore, honing it would not have made it the proper shape. It needed rebored to the next size piston and ring combination to make it tight and right.

So, when you put in the new rings, did you use the same rings as you had OM or did you go to a bigger diameter size? What was your ring gap to start with versus what you finished with.

Sometimes despite going to a bigger ring gap, the added ring diameter cannot make up for oversize or wear in the cylinder walls. The walls may look nice and smooth but, they may not be a cylinder.

At that point, a bore to the next size and piston and rings are the one way to go. If I am recalling correctly, BMW stamps the cylinders with the bore specs and then you go from there as to if you can in fact bore to the next size.

On my RS I just purchased a used set of jugs, had them bored out so I could use my pistons but needed new rings. Why, because it was sucking oil and the rings were shot, the cylinders were at the max point for boring and could not be bored again.

Sorry, I am going on and on. I guess the point I am trying to make is just because the cylinders look good visually, does not mean they are good. Only by using a bore gauge can you determine the shape and dimensions of the cylinder to determine if it is the proper diameter for the pistons and rings being used. Also is it the same shape from top of cylinder to bottom.

I am sorry to say, I have never just tried honing and rings to see if compression or problems go away so I can't comment on the success of that method. Each time I have had to have one of my airheads rebuilt, it meant more than I expected.

Kurt will I am sure fill in some of my lack of knowledge and I am sure he knows where to find more information about this subject.

Now after my long boring write up, I would say ride the bike for now, give it a thousand or so miles to break in the new rings. If you still have the problem, over the winter you can pull the jugs off and measure things to see what you have. That would also be a good time to look at the heads and bits there.

Write to you later, St.

[Andey]

I'd give it a bit of time. While with the old rings, you might have had blow-by, with the new rings, there is some added pressure build up when they go to BDC. Do you have the stock oil pan? Are you running oil at the very top of the dip stick? And just to be sure, you measure the oil level by putting the dip stick into the hole but don't screw it in?

You might see what happens when/if the oil level drops down to mid range. Often times an engine burns oil until it finds its "happy" level. If it remains steady at say half way down, don't keep topping it off...let it stay where it likes.

As for removing the old breather, I did it with some coat hanger wrapped around the spokes of the breather (after the disk is removed) and connected that some kind of rod, like something used as a battery hold down in an older car. That let me put a large socket and washer over the rod and created sort of a slide hammer. With a little heating around the perimeter of the edges, I was able to pull the old one out. Might want to see if you can stuff some rags in there as well just to keep things from falling through.

So yes, stock oil pan (I’m thinking about getting the siebenrock extending adaptor to add more oil) and oil the level is right at the top of the dip stick (noted on the way to measure the level...). Weather has been really hot so I imagine having max oil would help out with that... I’m thinking now it might not be the best idea... what you’re saying about mid level makes a lot of sense...

Thanks for the tip on pulling the old valve out, will give it a try when I have the bike stationed for a while.

Looks like I’ll try lower the oil level and put a few more miles on the bike first!

[Andey]

Now after my long boring write up, I would say ride the bike for now, give it a thousand or so miles to break in the new rings. If you still have the problem, over the winter you can pull the jugs off and measure things to see what you have. That would also be a good time to look at the heads and bits there.

Write to you later, St.

More than happy to be reading insights from folks who have looked at this in the past..! That’s the reason for the forum, right? Always good to hear more...

I’d imagine having oval cylinders doesn’t help anyone, so when I had the cylinders off the bike, first thing I measured was the piston ring gap, and they were super worn out, I think the gap was something like 0.8mm on the first ring (the new ring ended up at 0.4mm).

I managed to get an inside micrometer and measured 3 points in the bore (near the faint marks of TDC and BDC) and at 90degrees from the first reading. I have a bunch of notes written down on it, but having never done it before, it took me what felt like forever to take the readings (second guessing my measuring and imagining angled readings)... from what I saw it seemed within the 0.010mm tolerances of being cylindrical...

The honing was to smooth out a lot of pitting from what I imagine from the bike sitting around a long time... the bike just blew a smoke on each start up and peering down the spark plug hole, I could see oil build up at the bottom of the cylinder... at that point the head gaskets were leaking too... it was just impossible to get good idle setting the carbs...

[schrader7032]

You might consider doing a leakdown test. I bought a kit at Harbor Freight a number of years ago. Each cylinder is brought to TDC on the compression stroke and held in that position. Then air is pumped into the chamber through a fitting. The dial shows the level of leakage. Less than 10% is considered good. You can also tell where the leak is...if air is escaping through the carb, the issue is the intake valve; through the mufflers, the exhaust valve; or out the dipstick hole, the rings.

[srankin]

I concur with Kurt in regard to doing a leak down test. It pinpoints not only cylinder problems but head problems as well.
So, you know more than you think, you did take the time to measure out the bore for condition. Good show.

Now, Back to the honing job: You don't mention if you did a hand held hone job or a machine shop job? Hand held is fine for light touch up but if you had pitting from rust, honing by hand might mess things up more than you think. The reason is of course our hands. We are not fixed in one position as we move the hone in and out, the angles and such vary. I am not saying you caused more problems but it is possible. A proper machine shop job will give you a smooth perfect cylinder from top to bottom free of any imperfections due to our limited anatomy. So ball honing or light honing by hand is fine but for serious honing, only a machine can do the job properly.

So, where am I at, ride the bike, see if the rings do break-in. If they do, no problem, if they don't sorry back to rebuild.

In the mean time, Kurt suggests a leak down test. I would advise you do this. I just hope you don't get burned and find something wrong with the heads.

My friend at my local airhead shop tells me if you want to get rid of the bike you are working on, he knows of an older fellow who is no longer able to ride who has a 71 one owner low mileage bike in very good condition for a fair price.

As I say often not to be a jerk but beware the cost of things versus what the bike is worth. In my case, I have way more into repairs, rebuilds, modifications to my two airheads than if I were to sell I would ever recoup. However as I told my Mates at the shop, I don't plan on ever selling my two bikes, my estate will have that task and I won't be worried about how much they get for them. LOL.

Keep the faith, and enjoy the ride, St.

[Andey]

Thanks guys, definitely getting a leak down test kit... I see how it can help find out more whats going on inside.

Seems like a worthy investment.

Ah, mine was a handheld honing job... I wasn't expecting to to take a lot of material off, the pits were definitely from rust, which was in patches at the bottom and sides. I totally can see how a machine hone would've been the most ideal and granted my work would have been a bit amateurish (I did manage to get some decent 45deg cross hatching and on a microscopic level, i imagine it wouldnt have been completely flat...), it did improve the bikes starting and running though.

I do hope the heads are in good shape, I did do a crude leak test with some gas down the ports to see if it would pass through the valves, and both sides all managed to have a good seal in that sense. Problem is there are no head machinists in my neck of the woods, so having new seats and guides is off the cards.

Looks like i'll be doing more test riding to break in the rings