Are you a good mechanic? A few questions

[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

[Chris'91'525i]

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.

[bill g]

Are we talking about spark timing? I doubt that you will get any marks sensibly lining up under a timing light because even in a system running normally the ECU is adjusting the timing for all sorts of reasons like for example to speed up idle, and to adjust for varying engine load and revs.
You could possibly get an idea of approximate total timing by revving the engine but you would need to put degree marks on the front pulley.
Do you suspect something wrong with spark timing?

Bill G

[scott 4991]

Thanks for the replies -

Chris 91 - I checked the compression when cold, as it aids me getting the plugs out and the compression tester in, w/o burning my hands. No the throttle valve was not held open - is this necessary? The motor did turn very slowly - perhaps this was the reason? I refernece compression readings: "10-11 bar (142-159 Psi) - Maximum difference between cyl: 0.5bar (7Psi)" on the BMW e34 site.


The vacuum was checked upstream of a closed throttle plate. This post is why I am somewhat concerned:
http://www.bmwe34.net/e34main/troubl...e_diagnose.htm

- they appear to check the vacuum in the same place I am checking mine.

I did check the timing last night, seems to be at the 0/T mark when idling. but very hard to see. If I check my valves again, I will check this manually. The timing was checked at 600 rpm, not 6000, perhaps a typo on your part? My understanding of this RPM (600) is that before the advance starts to kick in is when you want to check timing. At 600 RPM is before the advance kicks in.

Bill G - I'm not sure I understand Spark Timing. I suppose if I was off 1 tooth on the timing chain, this would effect spark to the plug, and perhaps the Spark Timing you are talking about.


Thanks

sc

[Ross]

There is nothing wrong with 19in vaccuum. One tooth of would make a considerable enough difference in valve timing that it would be obvious if it ran at all.
The compression #'s seem okay too.
Why the concern after several years?

[Morgenster]

Maybe not so relevant to BMW but interesting nonetheless.

http://www.fordf150.net/howto/diagnoseengine.php

this page has a little more intel on the vacuum gauge methods of reading engine performance.
I might just do this myself.
What's the cost of a vacuum gauge and assorted tubes and tees?

[Boom n Zoom]

Just to clarify,

A one tooth difference in timing of the cam will still allow it to run no problems the only difference would be as follows:

If the timing was advanced one tooth you would find that it has better bottom end power (accelerates of the line/from a standing start better)

If it was reatarded one tooth it would have power further up the rev range (I am not familiar with the 3.5 Litre engines but I would hazard a guess that it would begin to make good pulling power from about 3500 - 4000 rpm maybe even higher, all the way to redline/spark cutout/rev limiter.

It will run fine with only a tooth advanced or retarded, you would need to refer to the figures for the engine in question to see how your match up.

Back when I was working for Toyota we would (depending on what the major use for the car was either city or country driving) advance the intake cam and retard the exhaust cam one tooth for city and a tooth the opposite way for country driving from the original timing specifications. This was on the 3GS-E fitted to the Camry's (not sure of the model name in the States)

Note: one tooth either way was 7 degrees of crankshaft rotation from 'normal'

As the 3GS-E engine originally began to make usable power from 4400 rpm (came onto the cams) it would in the city driving set-up bring the usable power down to 3600 rpm, With the 'Country' set-up it would push it up to 5200 rpm before the real power came 'on'

Mind you this was the 3GS-E 2 litre, twin cam, 16 valve Toyota engines where you had a single toothed belt running each camshaft (they are sperately adjustable).

What I am trying to say is that if it is only one tooth advanced or retarded it will still run fine it just moves the 'on the cam power' up the rev range if it is advanced or down the rev range if it is retarded. This will also be bourne out if you 'Static time' the engine, the timing mark will either be advanced or retarded from where it should be. In any good manual it will probably tell you what the number of degrees of crankshaft rotation a single tooth at the camshaft will give you. Remember always that the camshaft run at half crank speed i.e 6000 rpm indicated on you tacho will mean that the camshafts are running at 3000rpm (for example only).

Sorry I am pretty pissed right now, and it has taken me a long time to get this readable............or mayby not. my apologies if it doesn't make much sense, willl check back tomorrow (oh wait it is tomorrow) later today

Cheers!

[scott 4991]

Great comments guys ! Thanks.. my concern stems around the vacuum being 9in Hg or so, when the expected measurement is 19in Hg. and ONE conclusion based on, "Low steady vacuum reading (15-20in.Hg) at idle:
This could indicate a problem with ...late ignition or valve timing....."

I think I need to check the timing marks when I have the valve cover off to be sure I'm OK. A bit of a pain, but at least I will know.


This from the Clinton book on 'cars' - which seems to be where the BMW site took the info from - this is why I want to look into this.
· A gauge reading low (15-20 in Hg) but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking carburetor or manifold gasket.

Thanks

sc

[bill g]

Scott - spark (or ignition) timing and valve timing are two separate things - a tooth off on the timing chain/sprocket will not make any difference to spark timing.
As the other guys have said a vacuum reading at the manifold of about 18 to 20 in Hg is healthy. A further test is to briefly but quickly rev the engine at idle - if vacuum drops to around 2 in Hg then rebounds to 24 in Hg or so, before settling back to 18 to 20 then it is looking pretty good.
A reading of around 15 in Hg steady at idle would indicate poor compression.

Bill G

[scott 4991]

Thanks again - just connected the vacuum gauge to the car at the connection shown here:

http://www.bmwe34.net/e34main/troubl...e_diagnose.htm

I ran the vacuum gauge out to the window so I could watch the changes. Here are my observations:
- at idle, when cold, about 9in Hg
- as I would accelerate slowly, the vacuum would drop to about 5, or 3 if I accelerate harder, and instantly to 0 when I step on it.
- letting off the gas would cause a reading of 10 - higher than at normal idle. I did not see a reading of over 10in HG.

If I connect the vacuum gauge right to the manifold through this same tube, but plug the "T" off, the vacuum reads 19" Hg. It's when I plug the other end of the "T" into the valve cover / intake tube, the vacuum drops to the reading above. If I plug the valve cover connector, still keeping it connected to the carb intake, the vacuum goes from 24 - 10 or so, and to zero when I step on it. The vacuum seems to be 'perfect' when I do not connect it to the carb/valve cover connector and keep that connection plugged.

You have all been a big help - I'll play with a few things over the next months and see if I can't find anything else.

Appreciate the help.

sc