Timing cams on the BMW K1100 conversion options
Turbo Mini Forums

Hi all

I have slowly been restoring my old mark 1 mini cooper and pulled out the original 1380 engine that was running 296 cam big valve head and 45 DCOE. This made very good power but was a pain for my missus to drive so I bit the bullet 2 years ago and started a BMW K1100 head conversion on a new block bored to 1380 with all the usual niceties that will be needed for this type of engine.
Most of the work has been done and the engine is in however I am having big issue in setting up the cam timing (or getting a consensus on what so of lift on overlap the inlet and exhaust valves should be set to).

I have spoken with Specialist Components and based on the 38 mm BWM throttle bodies and RS cams they have indicated 2 mm inlet and 1.8 mm on the exhausts but there seems to be additional information here that indicate more lift i.e. 2.8 mm on inlet and 2.4 mm exhaust on overlap (leading to around 104 degrees full lift on the inlet and 110 degree full lift on exhaust). Specialist Components have acknowledged that the RS inlet is a bit sensitive to cam timing and is worth tweaking on the dyno (when I finally get it there)!

Looking at the BMW motorbike manual for the K1100 and K1200 both the inlet and exhaust are both 285 degree duration? If you take some base line figures for a typical overhead cam running 285 degree profiles and split timing figures we should see the following as an example only.

Let’s say for a set of split timed cams:

Inlet 37/68 and exhaust 68/37

Therefore:
Inlets (37+180+68) = 285 degrees
Exhausts (68+37=180) = 285 degrees.

If you check out Kent cams site they do a set of BDA L14 profiles that are not a million miles away from these figures and lift is in the right ball park on overlap.

L14
Inlets 35/64 and exhausts 64/35
Therefore both at 282 degree duration
Inlets 2.8 mm and 2.4 mm on overlap or 106 degrees full lift after TDC inlets and exhausts 106 full lift before TDC.

Any comments would be most welcome as this will save me some time mucking about on the dyno if I get it somewhere right in the first place.

106 degrees sounds like a good figure to me as a starting point,

easiest thing (assuming vernier pulleys) is to get a few good runs in on the rollers on 106 deg, and then move a cam 1 deg either way at a time and run it and see what it does,

Thanks Joe C
I will try to set lift at 2 mm inlet and exhausts and see what sort of timing I get at full lift inlet and full lift exhaust.

I have Vernier pulleys that should allow me some adjustment in terms of advancing or retarding the cams when setting the static overlap. I would like to see what overlap lift I will get when the cams are at 106 degree full lift.

Hope to have a look tomorrow and give is try then

for NA I think you'll need more overlap than 2mm,

on a freinds 8V ( which has similar duration cams) SC said to set it to somthing like 1.8mm to start with iirc, and it was flat as a fart over about 4 k.

we ended up retiming it to the standard BMW figure and it was much much better.

I think the std BMW figure is about 2.6mm, but I'm not sure on that,

BMW factory figures.

LT 106/106 at full lift
RS 102/106 at full lift

Since it is easy to work from those back to a lift on overlap figure 2.4mm is equivalent to 106 degrees with every 0.1mm either way aproximately worth 1 degree within the range we are interested in

This is at least somewhere right for the 16v cams rather than the 8v cams.

I have timed engines up the long way and the short way and both tend to represent the other pretty well. I have in the past also set the cams by eye after marking all the pullies when set first using the long way.

At the very least the least the BMW figures should be used as a sound starting point with timing sweeps on the dyno if funds allow.

Also worth pointing out that there are a couple of miss prints in some BMW documentation regarding valve timing so be careful. Its easy to use the valve timing data to work out the full lift degree.

I also forgot to say that Brumski asked me to change the timing belt on his Morspeed built engine to find that the cams where hugely advanced such that they were somewhere around 90 degrees at full lift. No surprize then why it idled like a bag of shit. Timing was set to factory figures and there was a healthy improvement in idle quality, but better still a fair chunk more hp in the useable range.

Edited by Sprocket on 4th Jul, 2014.

good info above,

your on rs cams from the sound of it, so you definalty need to go higher than 2mm

2.4mm on both seemed bang on for mine: 1380 k1200 on rs cams