Knocking from cam tower

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05-08-2007, 08:02 PM

MM951

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Knocking from cam tower

Sounds like one of my lifters is f'ed up. I was under the hood w/ the engine running and noticed a rpm related knock.. Did not sound like it came from the bottom end, oil pressure has always been perfect (5bar on startup...2/2.5bar at warm idle) but it dropped down to approx 1.5bar with the AC on.

Sounds like a failed lifter to me.. Anyone agree/disagree? Anyone ever experience this .. about how many miles till you replaced it?? I can imagine bad things happening if it were to compleltly go and I would hate to do that to 6K miles on a completely new top and front end.

In any case looks like I'll have to order a new cam tower gasket..

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05-08-2007, 08:13 PM

TRP951

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its not that bad of a job to check them at least I would just pull the cover to check them but thats me

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05-08-2007, 08:21 PM

SoCal Driver

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Several things can sound like they are coming from the top of the engine. Water pumps are one as well as rod bearings. Lifters clatter not knock.

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05-08-2007, 09:39 PM

KuHL 951

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Do a search on BradCam + Wentworth from about two years ago. We were on a run in the mountains and he started hearing a knock that sounded like a bad lifter or valve hitting. Oil pressure had dropped some also. We had no less than 6 heads under that hood and thought the noise was in the cam tower. Turned out he had to nurse it home on a spun#2 RB. When he started the teardown he also found a broken inner valve spring but he doesn't think that was the main culprit making the noise. If you have a mechanics stethoscope give it a try, those things are amazing in pinpointing noises. Hopefully it's just a lifter.

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05-08-2007, 09:50 PM

early85944

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Bad lifters make the same sound as when your car has sat for a while and it takes a bit to get the oil back to the lifters. The only difference is the sound does not go away.

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05-08-2007, 10:02 PM

MM951

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Damn... Not what I was looking to hear

Guess I'll have to look more into it tommorow

Last time (approx 2K miles ago) I changed the oil it looked good with no shavings.. The bores looked perfect when I had the head off 6K miles ago.

Anything you suggest to check the waterpump? For what its worth I stuck my head down under the car when it was running and did not hear anything near the oil pan.

Steve- did your friends car have any symptoms before spinning #2??

thanks guys
mike

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05-08-2007, 10:42 PM

KuHL 951

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Quote:

Originally Posted by Mike Markota

Damn... Not what I was looking to hear

here's a few old posts by Brad that might help.

Quote:

Originally Posted by Brad-Cam

My 951 started to knock above 2500 rpm, lightly at first, then it got worse. I wanted it to be anything but the rod bearings, but eventually I tore into it and the #2 rod bearing was totally disintegrated.

Check your magnetic oil pan plug for fine gray stuff stuck to the magnet. And check to see if your
oil pressure is lower than normal. These are signs of a rod bearing failure.

Sorry the scare you - not much information above to diagnose from, but be prepared...

Juan, I've kept you in suspense long enough

I think the previous owner of my car ran it low on oil - actually, I know they did since when I got it, it was down 3.5 quarts !! Anyway, it sounded like a lifter but got worse on the ride as Steve says, and was banging loudly by the time I was at the top of the mountain. Drove it 140 miles home, knocking like an SOB. When I pulled the motor apart, the #2 rod bearing was in little pieces. This says something about the durability of these motors. A lessor motor would have thrown a rod through the block. Moral of the story is to just keep it topped up all the time with good quality oil and don't worry too much.

If anyone wants to turn this into a #2 rod bearing or "what oil is best" thread, "take off, eh?" (a tribute to my Canadian heritage).

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05-09-2007, 01:06 AM

MM951

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Thanks for digging that up for me..my brother was itching to get back on the computer so I didn't have time to search

"started to knock above 2500 rpm" thats where mine knocks

I have a rod bearing set (and every gasket for the engine) but thats for my turbo...I'll see how it goes over the next day and then decide what to do..

thanks!
Mike

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05-09-2007, 06:52 PM

MM951

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OK, I checked it some more.. Oddly I was somewhat low on oil?? I wasn't last week.

There is NO knocking on cold startup.. I only noticed the knock after approx a 10 mile drive (no high rpms etc but it was at temp.) but my oil pressure is still perfect. This being my only car on the road is making me worried..

What do you guys suggest I do to narrow down the problem? Keep in mind it is my daily and I work/school alot. Also have a tight budget

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05-09-2007, 07:31 PM

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early85944

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If it is a rod knock you can unplug each cylinders spark plug and listen. If the noise gets quiter or dissapears when you unplug a certain plug wire then it is more than likely a rod bearing issue.

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05-09-2007, 07:45 PM

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If you have access to a dial indicator, you could use it to measure piston movement through the spark plug hole against the top of the piston. Rotating the crank in opposite directions for any minute distance (away from TDC or BDC) with no piston movement would indicate a spun bearing.

One other thing would be to do a compression check. If I remember, that's what I did before pulling my engine to replace number 2, and number 2 was reading low. Actually, I did try to cheat by just pulling the oilpan, removing number 2's cap and polishing the journal.

Never could get it good enough, so it was engine pulling time for sure then.

Good luck....

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05-11-2007, 10:32 AM

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MM951

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OK, all cylinders are at 170-175 except for #4 which is 150

changed the oil (it only had 1.5K miles on it

) and it looked great with nothing on the drain plug etc.. oh yeah it went from 15-40 to 20-50

The noise is still there when warm..hmm

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05-11-2007, 10:59 AM

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Quote:

Originally Posted by Mike Markota

Steve- did your friends car have any symptoms before spinning #2??

A few weeks leading up to my 944S burping up #2, I heard what I thought was the release bearing in my clutch going. I was wrong.

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05-11-2007, 11:20 AM

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KuHL 951

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Quote:

Originally Posted by Mike Markota

OK, all cylinders are at 170-175 except for #4 which is 150

changed the oil (it only had 1.5K miles on it

) and it looked great with nothing on the drain plug etc.. oh yeah it went from 15-40 to 20-50

The noise is still there when warm..hmm

From your compression numbers I would say that problem is independent of your knocking sound, unless it's a cracked ring which can cause accelerated oil burning. A broken valve spring will always make noise and a seized or collapsed lifter usually is louder when cold. The low oil level isn't good though. Try the method suggested above of disabling the cylinder and see if the noise changes. Not to be ignored is a loose spark plug or exhaust leak, they can make a hellacious noise but it's usually worse when cold, at least mine was. Does the noise seem worse under load? I've found that a bad rod bearing will usually knock more if you try moving from a stop in 2nd or 3rd gear, especially when it's warmed up. I hope you find the problem. If you do pin it down to a rod bearing stop driving it before it does anymore damage.

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