johntorg

I just started my 951 and am hearing a very load valve train noise, which seems to come from around the no. 1 cylinder. The only thing I did recently was to jack the car up one side at a time to change the front rotors.

After I lowered the car and started it, the noise began. Tha car had been sitting for a day. oil pressure is 5 bar and the oil is full and not contaminated.

I checked the timing belt and its in time.

The knocking goes away when I rev the engine slightly, but comes back even louder when I let off on the throttle, but settles down to the original volume when the engine returns to idle.

I am very new to the 951 and could use some help in diagnosing the problem. If it is a collapsed lifter (cam follower) can I run it a while and see if it pumps back up. The noise is very loud and I'm worried about doing more damage. The head had a recent valve job but I just drove the car 1000 miles with no problem.

Other thoughts are a sticking valve or broken valve springs.

Chris White

Dead lifter. You can run it with out damage - just don't get to rev happy!

Chris White

Jeremy Himsel

If I let my car sit for a week or so I have one lifter that bleeds down (# 4 exhaust) and have a hard time pumping it back up while the car is running and cold. I usually pull the DME relay and turn the car over for 20 seconds or so (mainly until I build full oil pressure while cranking). It works every time for my issue so give it a shot.

johntorg

So the consensus is a bad lifter. If I pull the cam and cover and remove the lifters, will it be obvious which lifter is bad? If not, how can I check them? I assume new lifters should be bought from Porsche and not aftemarket.

Thanks again for the advice

Zero10

Use a stethescope to pin down the noise.
If it's a ticking, then it's probably a squished/collapsed lifter. Strange that one would fail suddenly like that, but not impossible. If it's a knocking, I'd be more worried.

johntorg

Thanks for the input. Its really loud and is definitely coming from the area of the number 1 cylinder. It appears to come from the top end, but noise can travel. I used a long breaker bar held against the cam cover and my ear to localize it. I have had bad lifter on other engines, but nothing this loud. I am gong to remove the cam tower over the week end to check it out. I will also do a compression test to see if its a piston related problem.

How do I check the lifters once they are removed?

johntorg

The more I think about it the more I suspect its a No. 2 rod bearing failure. I guess, I'll pull the plug out and see if it goes away. Does anyone know if just pulling the plug wire should make the noise diminish or do I have to take the plug out?

Zero10

If you took the plug out, you would have no compression on that cylinder. This might quiet the noise a little bit. However, you will then be spraying fuel everywhere through the sparkplug hole. I am not sure that test will tell you anything.

Unfortunately the only 2 signs are low oil pressure, and once the bearing spins, a nice loud big-end knock.

As for the lifters, which are definately the easier thing to check, remove the cam tower, then take each lifter in your hand. The little button on all of them should be hard, as in you shouldn't be able to push it in with your fingers.

johntorg

Oil pressure is fine, but the noise is much louder than any bad lifter I've ever heard. I may try to pull the injector plug on number 2 and see if the noise changes. I read somewhere on Rennlist that pulling the plug was a good diagnostic technique to determine if a rod bearing is bad.

johntorg

Here's the post from Todd911 that got me thinking it may be a rod bearing. The remark about pulling the plug is near the end of the page. Link

brad-cam

I worked for days trying to track down a bad lifter, with a bad "lifter noise" around cylinder 1&2. I even pulled the cam box and found a broken outer valve spring on cylinder 3, which I fixed. I changed a couple of questionable lifters and buttoned it back up. It still had a knock. I drove it some more, the knock got worse, then really bad with oil pressure issues - result = spun #2 rod bearing. I could diagnose this by pulling the head - piston #2 had about 1/8" of play longitudinally in the bore. That is, when I turned the crankshaft by hand to push piston #2 up the bore, I could then push the piston back down the bore about 1/8" by pushing the piston itself... This was handy as I was able to confirm the rod bearing issue without pulling the bottom end apart.

I hope for your sake this is not your problem, but be prepared for it...

Chris White

“Completely” collapsed lifters are rather rare –they normally just stick. When they are ‘completely’ collapsed it sounds almost exactly like sever rod knock. It will make you shut the engine off from fear…
Usually rod knock is accompanied by a reduction in oil pressure – if not then I will stick with the lifter diagnosis.

Chris White

johntorg

Brad, the car has just had a valve job and new headgasket. I really don't want to pull the head to diagnose the bottom end.

Chris, I hope you're right. The engine has 5 bar pressure when hot.

If I unload each cylinder, one at a time the offending cylinder should show a reduction in noise if its a rod bearing. I can try this by unplugging each injector plug and perhaps taking out the corresponding sparkplug. I would appreciate it is anyone can confirm that this method of diagnosis has a chance of success. If not, is there anything else I can try?

johntorg

Good news (I hope). I pulled the oil filter an dissected it. There is no metal paricles at all in the filter, so I guess the noise is coming from the valve train after all. Thanks for the advice, I guess I'll pull the camshaft module and see what's going on.