Worn valve guides (again)

[hzbloke]

1986 R65 200,000km, new pistons, valves, guides etc 30,000km ago.

Chasing why the compression was low on the left cyclinder I found that the exhaust valve was not seating properly. Perhaps because the guide has something around .080mm free play. The book says .055mm is acceptable.

What would make a guide wear so quickly? I've got the Swiss valves and high temp guides from Motobins. They were fitted by a pro who's done good work for me in the past. The right hand side seems fine.

It worries me that this is the same valve that broke about 15 months ago because the guide was very worn.

As far as I can see everything is OK with the rockers etc, and they were assembled correctly.

Any suggestions?

[George Ryals]

If your left cylinder is running rich at noemal your cruising range, the excess carbon in the exhaust stream can accelerate exhaust valve guide wear. Check the needle jet and needle for wear as a cause of rich mixture at cruising speed. Replace both if you think either is worn.

[Duane Ausherman]

I don't think that you have found the reason for the low compression, or at least I am not convinced.

The following paragraph was explained to me by my super machinist over 40 years ago.

If you spend some time doing very accurate measurements of a worn valve guide, you will find that they wear more on the ends and less in the middle. The wear is also making the hole oblong, not round. For this reason there is no easy way to measure the wear with accurate instruments. I think that there is, but it isn't important as it can be done by hand in seconds, but it takes experience. Remove the spring(s) and rock the valve back and forth in the guide in the same direction as the rocker forces it. This would be forwards and backwards as seen if the head were on the bike. You will find far more "wobble" in this plane than at 90%.

I assume that the head machinist did the grinding of the seats after the new guides were installed.

I would do a leakdown test and then you will actually know something. Right now you are guessing.

[mattcfish]

No problem with oil delivery through the top cylinder stud? This can ware out guides (and rocker bearings) very quickly.
Easy to plug the oil way by putting too much sealer on the cylinder base. You can check delivery by running the bike with the valve cover off.
Just a thought.

[hzbloke]

Thanks for the suggestions. The plug doesn't look as if it's running rich, but it's an option I hadn't considered. And I did run the engine with the cover off and lots of oil was pumping out, but I didn't look closely to see how oil gets to the valve & guide.

Yep, I did wobble the valve, but not having years of experience I wasn't sure how much wobble it should have. The inlet valve barely wobbled at all. So I measured it. Which seems to be a better way of conveying information than saying "It wobbles". Yes, the guide is oval. I'm pretty sure I'm not just guessing that it's a valve problem as it is clear from both the seat and the face that the valve is not closing properly.

Does anyone know about valve rotation? Do they rotate, what makes them rotate and why would they stop rotating?

[the quinner]

I did wobble the valve, but not having years of experience I wasn't sure how much wobble it should have. The inlet valve barely wobbled at all. So I measured it. Which seems to be a better way of conveying information than saying "It wobbles". Yes, the guide is oval. I'm pretty sure I'm not just guessing that it's a valve problem as it is clear from both the seat and the face that the valve is not closing properly.

Here is the party line on how to quantify guide wear:

[hzbloke]

Thank you Mr Quinner. That's excellent info.

[Duane Ausherman]

I can't read the page, but can see that they do measure across the maximum wear path. We just did it by feel. I wonder just how close we were. Some were so sloppy that I didn't know how the vavle could hold up and not fracture at higher rpm. It would have been interesting to see a high speed movie of the valve at rpm.

I might have to recall all of those jobs I did 45 years ago and fix them.

[Garnet]

I might have to recall all of those jobs I did 45 years ago and fix them.

That would be a nice retirement project. You could not start is tomorrow after you don't go to church.

[the quinner]

I can't read the page, but can see that they do measure across the maximum wear path. We just did it by feel. I wonder just how close we were. Some were so sloppy that I didn't know how the vavle could hold up and not fracture at higher rpm. It would have been interesting to see a high speed movie of the valve at rpm.

I might have to recall all of those jobs I did 45 years ago and fix them.

Most people who have experience will make the determination purely by feel. The OP specifically mentioned his lack of experience. The BMW bulletin simply shows how one can quantify the wear...regardless of experience (or lack thereof).