325 still knocking after valve adjustment,..

I posted earlier about my 325 with 145k miles that knocks for the first few minutes until it comes up to temp. Well, adjusting the valves didn't help any. They were fine except for two that might have been slightly loose by .01" or so. Could it be that one of the many sensors that control timing is defective? Maybe they kick out after they've done their job at cold start and the engine runs right after that.

Reply to
cosmo
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I can't remember whether you said or not (before) whether the knocking was in frequency with the cam or with the crank. There is such a thing as piston slap although I have no direct experience of it myself.

You need to try to find where the sound is coming from really and only someone experienced with the different failure sounds could probably tell you that.

I had a car once that was tapping and it turned out to be shapnel imbedded in the top of the piston. My dad's Saab had the little ends go. My GM sounded like the cam was on the way out but turned out to be water pump bearings.

Reply to
adder1969

I can't remember whether you said or not (before) whether the knocking was in frequency with the cam or with the crank. There is such a thing as piston slap although I have no direct experience of it myself.

You need to try to find where the sound is coming from really and only someone experienced with the different failure sounds could probably tell you that.

I had a car once that was tapping and it turned out to be shapnel imbedded in the top of the piston. My dad's Saab had the little ends go. My GM sounded like the cam was on the way out but turned out to be water pump bearings.

-----

Mine was Connecting Rod Bearings on #1 and #2 pistons in my '88 325is. It was heard the best when letting off the gas next to a wall or highway barricade/lane divider (to get the echo). That particular job was quoted as $2500 and the engine comes out. I did it for $60 including a new oil pump and bearings for all 6 pistons, and the engine stayed in the car (but I did have to lift it up about 3 inches off the motor mounts). Open to close took about 5 hours and a lift from the local auto hobby shop. Turns out the previous owner had a gasket failure and some coolant got into the oil. They fixed that, but the coolant ate little "worm tracks" into the Conn Rod Bearing shells. This created a low oil pressure situation and contributed to the "thunk" I was hearing. Oil pressure would be OK after a few extra seconds, but I knew something was wrong. After replacing the shells on all

6, it was fine.

Bill in Omaha '86 535i

Reply to
Bill

Your car uses HYDRAULIC valve lifters. These are thin devices that are rougly the size of a small stack of nickels. The lifters are prone to getting an internal build up that restricts the free flow of oil, OR the oil flows properly but the spring inside gets stuck in such a manner as the lifter is slightly collapsed when cold.

1.) There is very little you can do for this beyond adding a detergent product (automatic tyransmission fluid works here) to clean the contaminants out and hopefully regain full operation of the lifters. There are a variety of detergent-products you can add, automatic transmission fluid is what we used in the old days before the specialty products that may or may not work better. 2.) Before we got hydraulic lifters, valve noise was common. A slight tap from the lifters (where the rocker arm contacts the top of the valve) is not a problem. It is an annoyance, but it is not a problem. 3.) Cold weather plays into this trouble because the oil gets thick when it is cold, and thick oil does not flow through the very small orifices inside the lifters, causing them to tap until the oil gets warm. One of the available remedies is to use a lighter weight motor oil in winter. If you are using 10w40 now, try switching to 5w30 for winter use, then back to 10w40 for summer.

Hydraulic lifters expand to fill the space between the valve stem and the rocker arm so there is no noise coming from the valve train. When the cam lobe rises, the rocker arm presses against the valve stem, pushing the valve open. Because the valve has a very strong spring, some of the oil inside the lifter will get pushed out as the rocker arm pushes the valve. When the cam lobe falls, the rocker arm releases the valve which is closed due to the very strong spring mentioned earlier. There is a small spring inside the lifter to cause it to expand again to fill the gap that forms between the rocker arm and the valve stem. When the lifter expands, oil flows in and the valve train sits and waits for the cam to roll around again and start the whole process over.

The problem you are noticing is that the lifter is not fully expanding when it is cold, and the tap you hear is the result of the small gap between the rocker arm and the valve stem. The cause of not expanding can be dirt/sludge inside the lifter, blocked passages impeding the flow of oil, or thick oil that is slow to run through the passages. Of course, a combination of all of these is possible as well. One other possibility is a broken spring inside of the lifter, but this would make a sound that remains after the engine gets warm.

I said earlier that the lifter goes between the rocker arm and the valve stem, but this is not always the case. The lifter can go between the cam lobe and the rocker arm, and on a push-rod motor it will almost always rest on the cam lobe, with the push rod fitting between the top of the lifter and the rocker arm (the configuration of a push rod motor is not really germain to this discussion since your BMW does not use that design). The point being, the physical location of the lifter is not important, the job it does is what I wanted to describe. Once you understand what a lifter does, finding it is easy. The job of the lifter is to fill the small gap that exists between the rocker arm and the valve stem. There are engine designs where the cam makes direct contact with the valve stem through the lifter, in this instance the lifter will need some form of device to hold it in place. (Your BMW does not use this design either ... )

Bottom line, You worry too much.

Reply to
Jeff Strickland

"Jeff Strickland" wrote

Jeff, you're completely off on this. If you go back and actually READ the previous thread, you would discover that this is an '88 325i with M20 engine, which does not have hydraulic tappets.

FloydR

Reply to
Floyd Rogers

Well, except for that tiny problem, my explanation is good ...

I find it odd that there are no lifters though.

Reply to
Jeff Strickland

Umm, didn't Floyd say no hydraulic tappets? That generally means the valves are actuated by solid (mechanical) lifters, unless it's a rotary or 2 stroke motor.

Tom K.

Reply to
Tom K.

Reply to
Michael Yeager

Well, in that case if there is still a tapping then either the tapping is not the rockers OR the rockers are still out of adjustment.

I haven't seen the inside of an M20, but I was thinking that pretty much all motors used a hydraulic tappet or lifter in the valve train somewhere. I've owned old cars and trucks that did not have hydraulic lifters, so I get the idea. But, I just thought that engines came with hudraulic parts to avoid the noise that comes from valve lash. I guess I was wrong on this one ...

Reply to
Jeff Strickland

I was going to post the same as Jeff, however although big sixes in the

1980's had hydraulic tappets, I was not sure about this model.
Reply to
R. Mark Clayton

Get a long screwdriver and put the metal end on the cam cover and your ear to the handle end (make sure your hair/necktie etc are well away from belts and pulleys) and listen. Then put the metal end on the block and listen. That should tell you where the problem is - ie tick or slap.

On an '88 M20 at that mileage I would expect a pit of rocker wear which would put a slight groove in the underside of the rocker so even getting the clearances 'spot on' there would still be a bigger gap than the feeler guage suggests - flat feeler v grooved rocker. Learn to live with it. I had the same with an M20 320i - UK 6 cylinder E30 coupe.

Piston slap - well time for another engine or car!

John

Reply to
Ranger

The big 6's in the 80's also had rockers with eccentrics.. no hydraulic lifters. And several current BMW engines use "solid" lifters and rockers.

Reply to
admin

Believe it or not, most performance engines up until just a few years ago had solid lifter or rocker arm type arrangements. Hydraulic lifters were designed for ease of maintainance and as mentioned to quiet the valvetrain (and stop the customer from complaining). Ferrari and Lamborghini I believe are the holdouts on hydraulic lifters unless they've done it in the past year ot two...

Reply to
Michael Yeager

I know all of that, and I thought that BMW motors -- while performance is very good -- were essentially luxury products where noise (or the lack of it) would take precedence. I assumed, wrongly I've been told, that BMW motors would employ tappets to reduce/eliminate valve noise.

Reply to
Jeff Strickland

Honda likes their mechanical valve adjustments, at least on their

4-bangers. I haven't kept-up with them in recent years, but I'd bet they, and others, still do...
Reply to
dizzy

Well, you think the Earth is like 10,000 years old, too. Dumbshit.

Reply to
dizzy

On Dec 19, 9:44 pm, Michael Yeager > quiet the valvetrain (and stop the customer from complaining). Ferrari

..and BMW. My 2001 has no hydraulic tappets.

Reply to
adder1969

Sorry - wrong.

Ferrari has had hydraulic lifters for about 10 years that I know of - and that's on engines that turn > 8K RPM. No valve adjustments, but they did use timing belts - which require engine removal to replace at

15k intervals (which is why you see Ferrari's available cheap at around 15K miles.. people don't want to pay the money to have the belts replaced.)

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There's a nice 10 year old with hydraulic lifters and recently replaced timing belts.. :)

Haven't looked at Lambo's..

Just looked, hydraulics:

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Hmmm..

99% of the facts on USENet are made up on the spot..
Reply to
admin

"adder1969" wrote

You must have an M car; BMW I6 engines since the M50 in 1990 have had hydraulic tappets, and the V8's do, too. Only the engines in the M cars have solid lifters.

FloydR

Reply to
Floyd Rogers

That's nice to know, not sure I care for the arrogance of "Sorry - wreong" but that's the way it is. There have obviously been a few advances in hydraulic lifters over the years. The last time I dealy with them they tended to float and subsequently fail at RPM levels over about 6500. This was a pushrod motor as well, I'm certain that makes a difference.

Reply to
Michael Yeager

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