Dropped Valve.

Steptoe

What a waste.
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This came up on my Facebook page from 6 years ago. 1200GS had dropped a valve. Needed a cylinder head, piston and barrel. All replaced with used parts. What is interesting is the bike was delivered to me from France, even with delivery cost it still worked out far cheaper than having it repaired over there. I wonder if that would be as easy doing the same today after brexit :D .... in case it’s confusing some people that’s a screwdriver in the picture pointing at the valve head embedded in the piston.
 

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I remember you posting about his before. Made a mess of the head and piston.
 
Everyone I have ever seen has failed in the same place

Just at the lower end of the sodium pocket !

Bad design or Cheaply made valves ??
 
Everyone I have ever seen has failed in the same place

Just at the lower end of the sodium pocket !

Bad design or Cheaply made valves ??


The wall of the valve stem looks very thin, particularly on part of the stem that's left in the cylinder head.
 
The wall of the valve stem looks very thin, particularly on part of the stem that's left in the cylinder head.

That's a Sodium filled pocket, apparently to both lighten the valve and aid cooling of the valve head by drawing heat away as the molten sodium sloshes up and down inside that pocket

Personally I call an "inadequately thought out" design as with quite a few things Chez BM these days
 
How common is this problem on the S/C Hexheads and what causes it please?

it happened more frequently in the early days and less and less as the models developed

Bad materials is the most suspected option but it nearly always seems to be the right hand side exhausts that let go
 
it happened more frequently in the early days and less and less as the models developed

Bad materials is the most suspected option but it nearly always seems to be the right hand side exhausts that let go

Better hope my Late 07 GSA will Escape Unscathed then!
 
I often wondered if this was due to a worn fuel pump delivering low fuel pressure.
On my TC at 50k miles the full throttle performance became week, first thought was a coil but decided to check the air fuel ratio at full throttle it was 18 to 1 .
Checked the fuel pressure it was 30 psi at WOT instead of 60 psi.
An AFR of 18 to 1 will soon overheat the exhaust valves and the fuel management in these conditions is in open loop so there is not any feedback to the ECU to correct the AFR.
A new pump and all is well and I now have a little fuel pressure gauge mounted in the dashboard.
 
Hi Mistacat

Can you let me know which pressure gauge you have and how you fitted it please?

Dave
 
The permanent fit gauge that I used was a 40mm dia 4 Bar gauge from ebay about £5 with pipe and fittings about another £5.
I fitted the permanent gauge as I used a cheap replacement fuel pump from ebay and wanted to keep an eye on it, 20k miles on and still good.
It is also handy to give it full throttle up hill every couple of weeks just to check the pressure.
The twin cam runs at 4 Bar and the pre twin cams run at 3.5 Bar.
For normal testing I use a universal fuel pressure test kit with pipes as in the photo, only use genuine BMW quick disconnects as the cheap ones available are 0.5 mm different and will not work with the BMW QD`s.

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valves giving up is an occupational habit of any engine - my (limited) understanding is, it's normal failure around 100k miles on a TC, so what's the usual rate on a Hex?

and of course if one uses the upper end of a bikes performance 100k miles on a bike averaging 4k rpm isn't the same as one doing an ave 6k rpm during its life

Someone should make a set of titanium valves and could make a nice living extending the life / reliability

and in case you're worried - mate at work with a mint laverda montjice (on apprentice wages) did his at 15k miles, but then it was Italian....
 
next point is it only ever the exhaust valves? if so just pop 4 in at 60k alongside a cam chain, the valves have to be the easiest job on the bike?
 
next point is it only ever the exhaust valves? if so just pop 4 in at 60k alongside a cam chain, the valves have to be the easiest job on the bike?

On the old 80/100 airheads it was recommended new exhaust valves every 70k miles, 55k on the R45/65.
 


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