Valve Seats

[MikeP]

Okay, what is the collective wisdom?

Do they need replacing for unleaded use or not?

I read adverts for Two-Valve Twins of a certain vintage and it's often stated that they have had the valve seats replaced to "run unleaded."

There's talk of valve seats becoming "hardened" by use and of "lead-memory."

One engine specialist, to whom I once took a pair of two-valve Boxer heads of uncertain provenance for "unleaded conversion" said that they didn't need to be changed (the valve seats were in good condition).

He said that aluminium heads have to have steel valve seats and that such valve seats are hard enough. He said that it's cast-iron heads where the valve seat is cut into the cast-iron that need steel inserts to safely use unleaded. (The fact that he turned-down the potential earner suggested to me that he wasn't telling porkies).

 

[cookie]

you can just leave them and see what happens. fixing damaged seats won't be any more trouble than the precautionary changing of originals.

might depend on how many, and what sort of miles you are going to be doing. sustained high speed running on motorways will accelerate the problem.

 

[(RIP) Proff]

1 of mine [80g/s] is unmodified and shows no sign of valve seat recession
100cs closed her valve clearance up in 2000 miles so was converted by City engineering Exeter £60 the pair
New valves from Sherlocks and 10,000 miles later no or negligible valve clearance wear

So I'd recommend>> set valves, run for at least one oil change period and if clearances have closed up by more than 003 thou inch get 'em done

 

[MickDB1]

I was told that g/s engines had unleaded seats fitted 82 on - but get better info than just my hearsay
My old un never needed adjusting while I had it (g/s)
The ST800 I had definately didnt have un-leaded seats - that would loose the gap in 2 thousand miles and sooner/ much sooner if thrashed
HTHY

 

[(RIP) Proff]

Late 1984.[ 85 models] Unleaded heads were made standard on all aircooled Beemers.
You can tell by the blue dot indelibly painted on underside of head
No blue = old stock in 1985

FROM BMW Gurus
Unleaded Fuel

R80 (UK) unleaded from chassis number 6440512 (1985)

R80RT (UK) unleaded from chassis number 6470498 (1985)

R80G/S (UK) unleaded from chassis number 6283306 (1985)

All unleaded head have a blue paint spot near the bottom head nut.

I have no information regarding the exact time that the other R Series machines were changed to unleaded. ALL twin shock machines were designed for leaded fuel and MOST monoshock machines are built for unleaded fuel.