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rlobdill

Delay in gaining oil pressure / lots of smoke

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Hey folks:

 

I've made a few observations, maybe enough for the wisdom of the forum to point me in the right direction.

 

Background info:

 

'72 tii, owned for a year. Original block and head. Unknown amount of work done on motor. Running 20-50 wt oil. Located in SF Bay Area. I've had these symptoms since I bought the car but things seem to have gotten worse with the nights dipping into the mid 20's.

 

Two problems:  

  1. At cold start, the oil pressure light stays on for probably 5-8 seconds.
  2. Cold start produces a prodigious amount of grey smoke out the tailpipe. (in addition to the expected water vapor seen on colder mornings).

Things I've observed:

 

Measured oil pressure with a gauge. At cold start, pressure sits at near zero but when pressure does appear (in 5-8 seconds) it jumps to 75 psi and stays constant. Sometimes I hear a squeal at startup that sounds like a slipping fan belt. But I've replaced the fan belt. I think it might be coming from a rocker on a cam lobe that has run out of lubrication but then quiets down when oil from the spray-bar finally makes it to the cam/rocker interface.

 

Someone had suggested that the oil-spray bar might have sprung a big leak causing the delay in the build up of oil pressure and subsequently flooding the top-end. Which would  then leak down worn valve guides causing the big smoke.

However, this morning I removed the valve cover and cranked the engine until I got oil pressure to the top end. There was no evidence of the spray-bar hemorrhaging oil.

 

I've lately checked the compression (cold because at the moment I don't want to run the motor up to temperature).  All four cylinders were very close to 150psi. Not as good as I have measured on this car but consistent and suggests that I don't have one bad hole. Also each plug was badly fouled but, again, the fouling was consistent across the board.

 

Plan of attack:

 

It's clear to me that I need some head work. The smoke and the fouling of plugs tells me that valve guides and seals need help. I'm in the position of being able to remove my head and bring it to a local specialist (any recommendations? ideally in the North Bay). I'm comfortable doing the grunt work for top-end work.

 

What I cannot do at my home is pull the engine for bottom end work. I also do not have the budget to do a full-on engine rebuild. I need to spend my car-budget money judiciously.

 

On the other hand, it doesn't seem to make sense to do all the head work and still have sluggish oil pressure on start up. If the problem lies in the oil pump itself, then (as I understand it) access to the oil pump requires either pulling the engine or removing the front sub-frame (no?).

 

Malfunctioning check valve?

 

This just occurred to me.  Is there some sort of check valve on this engine that holds oil up in the top end when the engine is turned off?  That would explain why so much pumping is needed at cold start to get oil up to the valve train.

 

Thank you in advance 

 

Rich

 

 

 

 

 

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Hi Rich- the short answer on your oil pressure is that it's probably popped an o- ring on the bypass tube.

I've had it happen to 3 or 4 engines- the o- ring gets extruded, and that opens up just enough

of a hole to let air in, and your oil drains back to the pan.

 

The easy way to test this is to restart at increasing intervals- if I'm right, the longer you wait,

the longer it takes to build pressure.  The fix I've used is to not set the choke, and crank until I see pressure,

THEN set the choke.  It's a band- aid, but it makes me feel better.  On the tii, you could rig a cutoff

switch on the additional injector, or on spark.

 

The right way is to pull the oil pan and front covers, and re- seal the tube that runs from the main galley

back down to the oil pump. 

 

As to the smoke, don't jump right to guides.  Oil's usually whitish smoke with a distinctive smell, and if you're

over- choking (or overfuelling) at start, that'll be darker smoke that'll clear in a few seconds to a minute or two,

depending on what the warmup fuel circuit's doing.  Again, the test here can be to unplug

the warmup injector, and see what happens.  It probably won't start at first- but you never know- and then

if it DOESN'T smoke, that points at the warmup circuit.

Or pump adjustment.

 

hth. for starting thoughts,

 

t

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Toby:

 

Excellent help thanks.  Makes a lot of sense.

 

But as I understand it, removing the oil pan is no mean feat (?).  Sub frame has to come down?

 

Rich

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(edited)

Yeah, it's either subframe down or engine up a bit.

Fussy, messy, and not easy.

 

That's why I tend to live with it as long as I can.  I even

went to a smallish Accusump on the car I tracked-

it band-aided the startup AND the air pickup problems.

 

It's odd- some, like me, have had this problem recurringly,

and others, who have built far more engines than I have,

haven't ever had the problem.  I have not compared bypass

tubes yet (I haven't built an engine since I figured this one out)

but I suspect there is variation in them, and I further suspect that

maybe the 320 engines have shorter tubes.  But I've never proven it.

 

Oh, and as to the screeching, try starting without the fan belt on (don't run

very long this way!)  That rules out the alternator and the water pump.

 

As to the 20-50, I've run that in cold weather, and it doesn't usually make much

of a difference (maybe less than a second at 20f) .   What it DOES tend to do

is pop that o- ring, or the seal on the oil filter!  Done that at least twice...

 

hth

 

t

Edited by TobyB

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Don't forget about the anti-drainback valve in the oil filter.  It could be allowing the oil to drain back.  Seems easier to check than removing the pan which I don't think will get you to the o-ring on the engine front also.

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jimk:

 

Thanks for your input

 

I've had two different BMW (Mann) filters on the car since I've owned it. It would be a welcome solution if that were the problem but I think that would mean both filters had the same problem. Would there be any way of testing this idea other than putting in another new Mann filter?

 

The other point you bring up also causes me some indigestion. It would be a real drag if I went to the trouble of removing the oil pan only to find out that I still can't reach the problem O-ring(s).

 

Rich

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I think that would mean both filters had the same problem

If by design, then yes, but if by manufacture, then no. Spin it off and take a look. It can be reinstalled if you have to.

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I've never had a problem with Mann, nor Mahle.

 

The 3 engines I've had do this all did it at the o- ring that seals the pipe

to the oil pump.  Thus, technically, you can get to it with the pan down-

pull the oil pump, replace o- ring. 

 

The stinker would be if you needed to replace the pipe- then the lower front cover has to come off.

 

You know, you could get to it just by pulling the lower front cover.  Not that THAT is any fun to take off,

but at least then you're not having to monkey the engine around, and

the amount of cleaning would be more satisfying- as in, you'll have an easier time KEEPING it clean.

 

I wish someone else would chime in here and say 'oh, yeah, mine did that, too.' 

 

t

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