Forum bmwbike.com

I have mentioned the probs with my R69S before-but its now worse than ever-in short a horrendous rattle, similar to a shot big end, from the right hand side of the engine especially when throttle is opened. I have checked-pistons-(71.90 original Kolben Smidt) have had two complete re-sleeving jobs done(last one sleeves set at 71.98mm)-checked big and little end clearance(perfect-crank was brand new less than 6000 miles ago)checked cam followers-perfect-push rods-not bent-carb slides-perfect-timingring;spot on; pistons rings-renewed last year with Deves ones-less that 1000 miles since-bike now unusable due to clanking /rattle being so bad that people look at the bike with a worried look.....and yet....when a screwdriver is played on the engine to act as a sounding device-the worst noise is from the RH barrel. Could it be defective old stock pistons-too oval or som ething?perhaps they are smaller than the stated 71.90 size stamped on them? I'm very reluctant to spend lots of money on new parts until someone can suggest what I should do!

oh and one thing I forgot to mention-I have got 5 ring R69 pistons in the motor-due to being advised to do so way back in the 1970s when i had the engine rebuilt originally-being told that they were superior pistons in all respects with the 5 rings giving rock steady smooth running in the cylinders.

I think you need to remove the cylinders and take some measurements and inspect. It appears that you do not know the actual clearance from piston to cylinder. It could be greater than you think, or there could be some other problem or damage. Probably we cannot accurately tell the problem from a description of what you are hearing.

Allan, thanks for the response-saw your mse on the other board as well-my bore measurement is 71.98-piston varies top to bottom or vice versa 71.85 to 71.90 the stated size on the top of it. There is no noise from the other side of the engine by the way and they are matching pistons.

"...have had two complete re-sleeving jobs done..."

Sleeving is an unusual procedure, and your noise coming from the sleeved barrel is unusual. If you rule out the new crank and the new pistons as a source, is it possible that a sleeve is loose?

It's not unknown for a valve seat to work loose. Have you checked these out?
Best of luck, Alun

John,

R50 pistons are de-axed by some 1.5 mm giving them a front end and a rear end. Hence it matters how you mount them on the connection rod. R60 pistons I think are in principle symetric. Are you sure these things are not messed on your R69S ?

Han Verhagen

In spite of the work you have done, your symptoms would still seem to suggest small end clearances or piston slap.

Steve

all I know is that having swapped the pistons and barrels from the right to left hand side-the engine starts and runs much better!!! but the rattle on the right hand side is there just the same-its got to therefore be crank, camshaft, or timing gears-hasnt it? Im mystified-because-A) the crank appears to have no play in big or little end, cam followers look perfect, and the camshaft was new 6000 miles ago, and when ;ast looked at the timing gears seemed ok-!!!

Here's your problem...............The slide in the right carb is worn to the point that at certain throttle positions it bangs back and forth in the carb cylinder. It sounds just like a real bad valve adjustment. Pull the right side intake tube off and look into the carb. when you here the noise you will see it banging back and forth. I dissassembled my R69s engine twice before I found the problem by chance. Take a look and see if its the same problem I had. Let me know. Peter