Originally Posted by
scott 4991
Several years ago I had a valve job done, ... removed the head, timing chain,... the head was trued as part of this service. I did all repair work with my son, and it was a good learning experience. The car is running fine, but if I were to guess, it's low on power - but since that time I have been driving newer cars, with more power, so hard for me to compare. I recently checked my vacuum, AT IDLE, and at the manifold, it was 19in hg - not bad. When I connect up the vacuum line to the carb intake, the vacuum drops to about 7.5in hg. In reading about the vacuum on these 535i's, it reads..
Procedure:
1. Take your Bmw for a spin to warm up the engine. Turn the engine off and use a tee to tap a vacuum line. Connect the gauge to the tee.
2. Start the engine and take a close look of what the needle in the vacuum gauge will do.
3. The ideal reading would be a rock steady 17-22 in.Hg (inches of mercury) @ 1000Rpm. (I DID NOT CHECK MINE AT 1K RPM YET)
Possible readings:
- Low steady vacuum reading (15-20in.Hg) at idle:
This could indicate a problem with an external vacuum leak, late ignition or valve timing, low compression or stuck throttle.
I have checked all compression, 165 on each. So, I'm wondering:
- what would happen if I slipped 1 tooth on the timing chain when I disassembled the motor?
- Would the car still run?
- What if I connected a timing light up and looked at the timing marks at 600RPM? They should 'line up' I would think - I have not done this yet, but plan to this next weekend.
I may just have a compression leak? Will try to isolate this also.
Any other ideas, just to check out, could be appreciated.
Thanks
Scott
Your engine compression sounds kind of low to me. Did you check it with a hot engine and the throttle plate held wide open while cranking it? I would re check it once dry and then squit some oil in the Cyl.'s and do it again,to see if it goes up.
The 19" Hg. sounds OK at manifold Vac. (down stream of throttle plate), and the 7.5 Hg sounds OK too, if it was Venturi Vac. (reading Vac. up stream of the closed throttle plate)
You can check and see if everything lines up at TDC (on compression stroke) in regards to the timing chain ? I'd assume motor would run like crap if it was off 1 tooth.
You should not need to run motor at 6000 RPM to check total timing advance.
You can look in a good shop manual to find out what RPM total timing advance comes on. The easiest way to check it with a timing light is to have a timing light with +/- timing advance wheel or LED readout on it. Set timing light to what ever total timing advance is, bring up the RPM's where total timing advance happens, and the timing mark on the crank should line up at the 0 TDC mark.
I'd redo the compression check like I said above first though.
1991 525i M50 5 Sp.
N.California
America is all about speed. Hot, nasty, badass speed. -Eleanor Roosevelt