Found cause of engine miss.

[bruce_launceston]

After cleaning out and resealing the fuel tank and carbs and checking ignition leads I still had what felt like a 'miss' on the left side.
Today I decided to start from basics and sort it out. I checked the left carb and jets again, still popping and banging.
Took off rocker cover and whola - one tight exhaust tappet - reset it to 0.2mm and it runs fine.
Now I understand the rattly popping in the left exhaust and the 'miss' at low revs. At higher revs it was not noticable as the valves are opening and closing so quickly.
Took it for a 20 minute test ride, came home and reset the air mixture and the idle speed.

Live and learn as they say!

[Hunsta]

So this was the cause of your miss after all, and not the balance of the carby? Interesting. When you say "One tight exhaust tappet" do you mean the gap between rocker arm and the valve stem?

[bruce_launceston]

Yes, there was zero valve clearance to the rocker arm.

[plc]

So Bruce do you think that zero clearance was caused by:
 1. Valve seat recession (I am told that usually doesn't happen to our bikes),
2. Valve deformation;
3. Something coming loose?

Hopefully number 3.

Best wishes,
Paul

[bruce_launceston]

Hopefully nothing more than not checking them for 18 months?
The adjusting nuts on the tappets were tight, so it's not a case of anything working loose.

The motor is original with 90,000km, the heads have never been off, I will check them more often and see if the clearance continues to tighten up.

[Bob_Roller]

So Bruce do you think that zero clearance was caused by:
 1. Valve seat recession (I am told that usually doesn't happen to our bikes),
2. Valve deformation;
3. Something coming loose?

Hopefully number 3.

Best wishes,
Paul

I had severe valve recession on my '81, at 45,000 miles (73,000km) .

Had to have the the seats and valves replaced .

The shop that did the work told me that I had at best 5-10,000 miles, before the valve would have been pulled past the seat, and into the port area .

[suecanada]

Remember my no clearance issue on LRB was caused by the other end of the valve...the keeper end. It was so close to failure and the fins/threads??on the keeper were super worn to the point of being knife sharp. I could not keep any adjustment. As soon as I started the engine, I am pretty sure the clearance was down to "0" again.

Ted Porter of the Beemershop in Ca did my work and I was very pleased. On Oak's advice.

[bruce_launceston]

Hi Sue, that sounds like an unusual place for a problem.

I have not seen a BMW valve dissassembled, OHV gear that I have worked with (Honda, Datsun etc) usually has a cap on top of the valve spring and 2 collets that fit inside this and lock under a groove in the valve stem.

Are you talking about the groove on the valve that the collets sit in or how does the BMW valve stay in?

Cheers Bruce

[Bob_Roller]

There are 3 grooves at the top of the valve, where the split collet sits, the 'lands' between the grooves on Sue's LS were worn so badly, they looked like barbs on a fishing hook !!!

[bruce_launceston]

Thanks Bob, I assume there would be no way to check these unless the head is removed.

If my problem returns I will have to remove the head(s) anyway, that will give me something else to check along with the valve seats.

If I get to that stage I will probably get all the seats and valves done and slip a new set of rings in.

I've got 25 years and 90,000km out of them so even if they don't technically need them new ones will see me out!

[suecanada]

Thanks Bob for clarifying the keeper/collette thing for Bruce. Sometimes my written descriptions confuse people!
I have kept those wrecked valves because they show more unusual wear.