Not an expert really - I just like to get involved in my car where I know it is not right.

Your comments on the TRX tyres are same as mine. In the dry they are fine in the wet useless. Noise is pretty prominent with them but I haven't been in an M6 with a different wheel tyre set up. Best advice is to bin them at the next change and go for 17 inch with decent rubber. This is the same cost as replacing the TRX tyres for v rated items in the UK (£1000 plus UK VAT)

Compression readings - i assume your readings are in bar guage. If so they are not low. I got about 185 psi (12.7 barg) on all cylinders. My only concern for your readings is cylinder two which is low compared to others - perhaps needs more investigation/comments by others here.

Gearbox - fluid seems to make a lot of difference on the BM boxes. Changed my 5 series gearbox oil recently for the same spec (supposedly) and 1st to 2nd was very difficult until box was warm. I will be filling with proper stuff soon. Crunching gears points to worn synchromesh - box out job. Did the old oil have metal filings in it? Sump plug is magnetic so they will have accumulated here.

Rattle at 2500rpm. Surprise surprise so does mine and so does my friends (119k miles) but less so.

My rattle was two things - firstly missing roller on cam chain (scarey) this was sorted by changing chain sprockets etc.

However there is still a slight rattle present (this is a different rattle to my chain problem.) Noise comes from cam box and is due to what I think is a worn camshaft lobe. The lobe has a slight dip on the opening side. Can be felt with the finger so seems excessive. I have more than 1 worn lobe. Easy to check just remove cam cover and feel for wear on the lobes. My friends car has EXACTLY the same noise but less prominent. I also have low power at high revs so I suspect the worn camshaft is causing this. (lack of lift of valves)

Hope this helps

Ian

Hello, Both of you seem to be well informed about the M engines, and the M635csi. So here goes.
I have an 85 M635csi that is new to me. My ownership background is an 84 633 and two 87 635csi and have been driving the six series for some eight years. Now the M635csi.. Car has 109,360 kilometers bought it with 106,200 compression is in the measurment of BAR
Cylinder one 13.5 two 12.6 three 13.2 four 13 five 13.1 six 13.2
Never any oil loss or consumption and rear tail pipes are very clean no carbon. This is if I drive it hard or mild.
What I have noticed:
1- the car is load.. trx tires make a hell of a lot of noise. I also think that the headers are a part factor in the noise level? At certian times after inical start up the engine sounds like a dessel. and after a very short while the sound goes away. Could this be due too not enough oil entering the head at start up? Scares the hell out of me. Also at around 2500 to 3000 rpm I hear a little rattle vibration and goes away but only at that rpm. Checked the heat shield and all is thight.
2- After starting the car I must be very careful shifting from 1st to second. This means very slow engaging the gear until it is warmed up never any problems shifting up gears or down from 3rd to 2nd. After it is warm I still must be careful shifting from 1st to second. Direct north to south will result in grind. So I shift with lever after nutral gate a little left of center and it will go in smooth. But I still can't see how I could shift faster without having a grind problem.
Have chaged the trans oil to a 75 90w syenthetic and it helped a bit. The oil that was in there was old and dirty.
Any recomendations Please?
Thanks
Keith