So, I bought a new bare head from AMC to fit into my 2.5 DSE.
Just got a call from the mechanic that is doing the work saying that the valves from my old head don't fit the new one
Upon further investigation, the old valve stems have a diameter of 7mm while the bore in the new head is 6mm. Looking at Microcat and other parts sites for this BMW engine, the correct size for the stem is 5.97mm, so the new head is good.

My question is what the hell did the previous owner do to the old head and where did he find valve stems with +1mm!!

Standard bore of guide should be 7 mm valve stem should be 6.97mm. First stem O/S is 7.07 mm second O/S is 7.17 mm. The head is wrong. The guides need reaming.

PS suggest you ring AMC. It should not come like that if the reaming is done wrong the seats will need recutting. Guides should be done first then seats cut to suit them. 1 mm is a lot of meat to take out in one cut.

Wammers,

Where did you get that info from ? Microcat says that valve stem is 5.97mm, Rimmer Bros (Inlet Valve - Standard Size - Genuine Land Rover at www.rimmerbros.co.uk) states the same and the BMW parts catalogue from Valve Timing Gear ? Cam Shaft BMW 5' E34, 525tds (M51) ? BMW parts catalog also points to 5.97mm

I'm very confused now...

mcapinha said:

Wammers,

Where did you get that info from ? Microcat says that valve stem is 5.97mm, Rimmer Bros (Inlet Valve - Standard Size - Genuine Land Rover at www.rimmerbros.co.uk) states the same and the BMW parts catalogue from Valve Timing Gear ? Cam Shaft BMW 5' E34, 525tds (M51) ? BMW parts catalog also points to 5.97mm

I'm very confused now...

Click to expand...

Standard size of valve guide bore is 7 mm, first O/S is 7.10, second O/S is 7.20. Standard valve stem is 6.97 mm, first O/S stem is 7.07 mm second O/S stem is 7.17 mm. Range rover P38 BMW M51 engine specs. Think you need to be contacting AMC as i said, unless your mechanic has special tools he could knacker your new head up big style. If i was fitting a new head i would be fitting new valves and springs anyway. Microcat does indeed quote 5.97 but RAVE specs say 6.97 as your valves are 6.97 i guess Microcat is wrong. Rimmers also say 5.97 but you can only go on what came out. Which would make RAVE correct. Bit of an enigma.

This is madness. I found a technical data sheet from BMW that shows the valve stems as 5.97 or 6.97. So, right now, I'm guessing that the original valve stems for the M51 applied to Range Rovers were 6.97 while the original valve stems applied to the same engine but in BMW cars were 5.97. Does this make any sense ?

To complicate matters a bit further, my old engine was supposed to have already been replaced by one from a BMW 525tds wagon, so it should have had 5.97mm valves. Maybe I've been mislead by the previous owner and that was still it's original engine.

If the new head is machined to a 6.00mm bore size I'm guessing I'll be OK buying new 5.97mm valves, since the valve head diameter is still 36.00mm in both cases.