How do I lift the curse from my R75/5?

[166926]

Adjusted valves

Adjusted the valves, and all were tight. No free play at all, just loose enough to allow you to spin the push rods. Got them into spec, and started right up. I'll check again tomorrow, so many thanks for all the advice!0

 

[44006]

If tight valves were in fact the problem and the engine was run any serious distance
that way there may be carbon and other crud residue built up on the valve sealing surfaces.

The newly adjusted valves may now hammer this crud out of the way and close up
again faster than normal wear

Recheck the valve clearance again about 500 miles out from here

 

[happy wanderer]

Aren't valves tightening up over time sometimes a sign of valve seat recession?

 

[lmo1131]

Adjusted the valves, and all were tight. No free play at all,

These old machines are too simple not to run.

Whenever anything odd occurs, I always drop back to the basics on mechanical issues, regardless of what's going on. It never hurts to confirm that what is supposed to be occurring, is. The side benefit being that the more you do chores like adjust the valves, pull the front cover, check the points, etc., the easier and less intimidating they are. There won't always be daylight when you may need to check something.

 

[44006]

"Aren't valves tightening up over time sometimes a sign of valve seat recession?"

There are airheads and then there are real airheads like the /5 which was designed and built by old school folks
to last and be owner maintained.

The RAPID valve seat recession problems did not come along till the bean counters in the front office started to
compromise a good design with poor choices of materials to cut costs in the 1980's

 

[PGlaves]

"Aren't valves tightening up over time sometimes a sign of valve seat recession?"

There are airheads and then there are real airheads like the /5 which was designed and built by old school folks
to last and be owner maintained.

The RAPID valve seat recession problems did not come along till the bean counters in the front office started to
compromise a good design with poor choices of materials to cut costs in the 1980's

Not entirely accurate. The pre-1980 models relied on lead in the fuel to lubricate the valve seats to prevent the seats from wearing away (recession). Then folks stopped putting lead in the fuel. So for the 1980 models BMW changed the seat material to a very hard material that did not need lead in the fuel to prevent wear. This was an engineering - not cost - choice.

The problem was that the specific hard metalurgy transferred heat poorly. The heads of exhaust valves would overheat, especially on the 1000cc engines. Then the valve heads would deform, also causing gaps to close up but this is deformation of the valve, not recession. Early on dealers would replace the "bad" valves and leave the pristine seats alone. It took a while for BMW to figure out it was the seats that were causing the problem.

By the 1985 models BMW changed to the second generation hardened seat which solved the valve head deformation problem but remained resistant to seat wear and recession.

Blaming the bean counters is convenient and kinda fun, but it is wrong in this specific case.

 

[166926]

Final verdict

So it started up, took a bit of cranking, but not terrible. When it started, ran beautifully. I'm thinking that at this point, I will rebuild the carbs next rainy day (the gaskets on the idle jets seemed suspect), and a full cleaning of the carbs is likewise in order.

Many thanks, and ride safe!

 

[KillerBee]

If it really is cursed then there's only sure one way to lift it, trade it in!

 

[lmo1131]

If it really is cursed then there's only sure one way to lift it, trade it in!

That would just be foisting the beast onto some other poor unfortunate soul. Really, the only ethical thing to do would be to haul it out to the curb and leave it for the scrap iron guy.... . who comes around Bloomfield Hills on what day???

 

[166926]

Trash day motorcycles

I've gotten several motorcycles that were on the way to the trash. As my wife said upon bringing home the last bike, "you just made some other guys wife very happy."