Time for new bottom half??

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When I first start it up after sitting for a day or so it has a really loud rattle....Not a deep knock.... but a rattle. The sound is a little too much imo to be the valve train (I have however gone over all of the valves and checked lash). The rattle lasts only a second or two then stops.

When I get on the gas hard the sound starts to come back at about 3500-4000rpm..Its no way near as loud as it is at start up but its there.

Otherwise the engine runs fine....no pinging or oil consumption...no sound or problems under normal driving

I posted a while back about the cam chain tensioner.

I cleaned that out and put it back in, but the problem I have is still the same. I have not looked at the chain guide.

Someone suggested a piston pin??

Would the cam chain make this kind of noise if its to loose?




:)
 
Are you certain the rattle comes from the engine?
Have you checked the exhaust system or the prop shaft?
If the sound comes back around 3500-4000 rpm it could be the engine 'rotating' under load (worn engine mounts) and thus something touching the body.
 
My experience with piston pins is that they are more load dependent than speed dependent.

I have a VW Jetta VR6 that got a hole in the oil pan. The engine ran OK, but on startup it rattled something awful, and when I would let off the gas it would rattle, but under load it was OK. I belive this was a piston pin issue since it was load dependent, and also since the piston pin bearings would be the first to get really hot under low oil conditions.
(State Farm replaced the engine...$7K).

I'd check other things in the engine bay, and also check the tensioner. on the M30, there is an oil filled piston (not sure if it was used on the coupes or not), that damps the tensioner. If for some reason that is not working right, or is crudded up, it might be doing a poor job of damping the tensioner.

S
 
Thanks,

Im pretty sure its not hitting anything outside the engine. The sound changes in frequency. But I will look around.

Scott, thanks for the words of hope.

I have cleaned the chain tensioner and it was really filled with some gunk. I called the local bmw dealer here for a new one, but they said it needed to be special ordered and was going to cost me 80 bucks.
 
Bottom end IMHO. Bearings are bad and the noise is worse when oil pressure is low. Occasionally this can be caused by a stuck pressure relief valve in the oil filter cannister, but if you get the same noise at higher RPM too, it is not that. You need bearings, probably a crank regrind and all else that follows.
ps/ck
 
You said you checked the valve lash, did you also check the banjo bolts that attach the valve train lubrication tube? They have a habit of coming loose and falling out. BMW updated them with a Loctite type of coating on the threads
 
I did not check the valve train lubrication tube....I do know that it was there :)

I will check.

Pressure relief valve??

What does this look like and what does it do??

I keep on thinking how hard its going to be to take off the front pulley.....so.... Im trying to exhaust all options..... hoping its something small that Im missing...

The inevitable might be upon me.

I like this Forum...lots of helpful and knowledgeable people!!!!

Thanks!

Im slow to work on these things but I will revisit with new information when I get some.
 
Ok....I had some time just now and pulled the valve cover. The spray bar is tight...

The chain.....well....

How much slack is acceptable?

If I reach in with a screw driver the tensioner side will deflect about a 1/4"

The other side will deflect a bit more....say 3/8 of an inch.

I started it up and let oil spray a bit...checked the chain slack and its a bit tighter but still able to move around a bit.

Is this normal?

The guide opposite the tensioner is there....the guide on the tensioner side looks just like a metal bar, I cant really tell if there is any kind of plastic on it or not.....should this be readily apparent?

:)
 
Ok....I had some time just now and pulled the valve cover. The spray bar is tight...

The chain.....well....

How much slack is acceptable?

If I reach in with a screw driver the tensioner side will deflect about a 1/4"

The other side will deflect a bit more....say 3/8 of an inch.

I started it up and let oil spray a bit...checked the chain slack and its a bit tighter but still able to move around a bit.

Is this normal?

The guide opposite the tensioner is there....the guide on the tensioner side looks just like a metal bar, I cant really tell if there is any kind of plastic on it or not.....should this be readily apparent?

:)
 
It's very difficult to diagnose any noise without actually hearing it but if you are correct when you say the noise isn't a deep knock but more of a rattle then I would lean towards the timing chain and tensioner. If the chain is stretched and the tensioner and guide rails are worn you will get lash in the chain on start up and again as the revs rise. If you take the cam cover off grip the chain at a point along the centre line of the engine and try lifting it away from the sprocket you shouldn't be able to move it more than say 20 thou (0.5mm) and ideally less than that.

Just read your last post. Get a timing chain kit It sounds worn out to me.
Don't go to the main stealer try sourcing one from a engine reconditioner or motor factor I'm sure you'll have some where in the U.S like this (just done a quick search) http://www.eurocarparts.com/ecommerce/Search_Results.asp
 
I didnt try lifting from the center but I sure can pull the chain away from some of the cam teeth off center.

I will try changing the tensioner, piston, chain and guides, before I abandon hope of maintaining the original block. Time is so tight lately (joys of parenthood), so you all probably wont hear from me in awhile.

I will definitely buy the parts over the internet using sources other than the dealers. Thats the reason why I chose to clean the piston out first...I couldnt justify the extra 60 bucks the dealer wanted to charge over what I saw on the net.

THANKS!
 
You can do a quick check on the bottom end by doing a simple test. Remove the plug wires one at a time, and see if the knock goes away. If it does, then it is a bottom end issue. You may find that removing one wire reduces the sound. If so, then go along removing and replacing the wires until the knock goes away. Typically only one or two bearings are bad, so this test is usually pretty effective.

In addition, try to guesstimate the rate of the noise. Timing chain noises will happen at crank speed. A rod or piston pin bearing will happen at half crank speed, and a valve noise will happen at 1/4 crank speed (I think...)

S
 
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