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Noise: started very low, once per rev, a sound sort of like the chuffing of an old steam engine, which led me to think it was an exhaust leak, but I couldn't find one so I let it go, thinking it would be easier to find if it got a little louder. The “chuffing” got a little louder, and a soft knock appeared also. I could now tell that the noise was louder on the PS, but still no evidence of where it was coming from, but now seems to be top end. The only other noticeable change from normal was a rich-smelling exhaust.
So now it's up on the lift, and here are the results of my tests and inspections:
First, the good:
Oil analysis from Blackstone good: “This sample looks good. Silicon was kind of high and that can show abrasive dirt in the engine, but with wear metals looking nice, we're not sure that's the case. Silicon could also be from some sort of sealer, and that's harmless, but check the air filter/intake for leaks or problems just in case [N.B. Recently installed silicone OP gasket]. Sodium was present, but we're guessing that's just an additive in your oil and that's fine. Averages show typical wear for this engine after ~4,000 miles and your metals all look fine by comparison. This is serviceable oil [Royal Purple HPS 20W-50].”
Both flexplates good per recent check.
Plugs: new and clean on each test (cold and hot)
Temp normal, needle on lower mark and steady
Performance: smooth idle, strong acceleration
No detectable WP leak
Coolant is relatively fresh, and clean- no trace of oil. No sign of moisture in oil fill neck.
Quick check of TB tension appears normal (at high end of window)
The not so good:
Compression: good on DS, 185-180-180-182, lower on PS, 170-167-165-170 engine warm, head temp at spark plug hole ~130, ambient 70.
Timing belt far forward on sprockets, almost to edge. Tensioner has “wept” a little but so far appears ok. The TB was replaced 9/14 at 196,717, current mileage is 204,441.
Very rich exhaust smell.
The only thing I have found here on RL after an extensive search was in this thread: https://rennlist.com/forums/928-foru...cam-cover.html In post #5 the OP wrote, “I took the car off the road a month or so ago when I started hearing a strange noise from the passenger side cam area. Based on suggestions here, I have replaced the oil galley plugs. They were all still in place but the rubber was not in good shape. It was all buttoned up today and started right up and no more mystery noise.”
Besides finding this problem and fixing it, I am using this rack time to install new cam sprockets (Roger's special ones- I think I got the last pair), a new belt, and the S4 tensioning roller support- that shoulder bolt has always bothered me.
I would like, actually I am almost desperate for, any hints, tips, insights or whatever. Although I will chase this fox right to its den, I don't want to run riot while I'm doing so (sorry, I'm surrounded by foxhunters...).
A mechanic's stethoscope is a valuable tool for finding noises. Beyond the obvious use for directly detecting mechanical noises, you can substitute a length of vacuum tubing to 'sniff' for those hissing and aond other 'leaking' noises. Mystery ticks in the head include lifters that are starved for oil, perhaps from failed oil galley plugs. Usually ticking though, as oil flow noise is pretty much drowned out by other engine noises in that area.
Exhaust gas leaks can usually be found with a combination of the Dexter Test and the 'sniffing' with the stethoscope and vacuum hose. You can do half as well with a piece of vacuum hose pushed into one ear, by the way. Just put the hose in your good ear. I SAID: "JUST PUT THE HOSE IN YOUR GOOD EAR."
The good news, based on your description of the source arear of the noise, is that piston slap at idle is normally lower in the block.
Those compression values you post are not something to get excited about, especially considering the miles on the engine. I'd be pretty proud of those! Guessing that you tested the driver's side cylinders first, while the battery had a little more available cranking current? Add a charger to help keep the abttery full during testing. All the plugs were removed, EZF fuse pulled (stops both spark and fuel delivery), throttle propped wide open during the testing? Ignoring these will give you lower and less consistent compression readings. How do the plugs look? Uneven combustion shows up readily at the plugs.
I ask because the sampling tubes are big exhaust leaks after they rot away. You can remove the connector and drop in a ball bearing (in place of the rotted tube) to close the exhaust port. Maybe around 6mm or 1/4"? Anyone recall?
I have been thinking about that. The only evidence against is the Blackstone oil analysis, which I had done long enough after the noise became apparent (I think) that anything the chain ground off- tensioner pads or heads - might be indicated in the analysis. What do you think? Good to hear from you, BTW!
"Chuffing" with a soft knock sounds like an exhaust leak to me. Dr. Bob's suggestion of a hose as a make-shift stethoscope is the best option for finding it, I think. If it sounds slow, like five times a second, then look around the exhaust connection to each cylinder. Tape the end of the hose to a stick and poke it around various places from above and below.
This could also be related to the rich-mixture smell. An exhaust leak will pull in fresh air as well as leak out exhaust, which will fool the O2-sensor into thinking the mixture is lean (excess O2), which in turn will fool the LH computer into squirting more fuel. Just a possibility...
At 204K miles the cam-chain tensioner is a possibility. That would also explain the lower compression numbers on one side, but not running rich. Can you post the full Blackstone analysis? I've got a bunch to compare to.
The more likely cause for lower compression on one side is that the cam timing is off a bit on one side or the other. Next time you are in there, check that the cam timing marks line up with the notches on the back cover, and that the rotor-mounting holes line up in the center of the slots. If you want to get precise about it, beg/borrow/steal PK's V32 tool and set the cams with that. But that is not likely the current problem-- unless the noise is the cam-chain tensioner...
"Chuffing" with a soft knock sounds like an exhaust leak to me. Dr. Bob's suggestion of a hose as a make-shift stethoscope is the best option for finding it, I think. If it sounds slow, like five times a second, then look around the exhaust connection to each cylinder. Tape the end of the hose to a stick and poke it around various places from above and below.
This could also be related to the rich-mixture smell. An exhaust leak will pull in fresh air as well as leak out exhaust, which will fool the O2-sensor into thinking the mixture is lean (excess O2), which in turn will fool the LH computer into squirting more fuel. Just a possibility...
Jim, that was my first thought and I hope you are right. I tried the make-shift stethoscope, but not aggressively enough. Your comments reinforce the need to do so.
Originally Posted by jcorenman
At 204K miles the cam-chain tensioner is a possibility. That would also explain the lower compression numbers on one side, but not running rich. Can you post the full Blackstone analysis? I've got a bunch to compare to.
Thanks! The report is below (I had originally edited out the comment about leaded fuel, it was just an error).
Originally Posted by jcorenman
The more likely cause for lower compression on one side is that the cam timing is off a bit on one side or the other. Next time you are in there, check that the cam timing marks line up with the notches on the back cover, and that the rotor-mounting holes line up in the center of the slots. If you want to get precise about it, beg/borrow/steal PK's V32 tool and set the cams with that. But that is not likely the current problem-- unless the noise is the cam-chain tensioner...
The lower PS compression seems to me to point to cam timing, and I am going to spring for Porken's gear- my new sprockets are too precious not to install correctly. I am worried about the chain tensioner, though. I would think something would have showed up in the oil analysis, but I don't see a data row for "yellow plastic bits"...
IIRC the tube is somewhere around 10mm OD, so a plug would need to be a little larger.
Meanwhile, a standard Porsche closed wheel nut threads on to the header fitting perfectly.
I'd heard about the wheel nut, I am not wild about aluminum in that role but I suppose it'd be OK. You are right about the tube, I located one and it is 10mm OD. Good memory.
A dime would have to be ground down a lot to fit, I recall a 16mm Euro cent is too big. Maybe a 1/2" ball or 12-13mm.
A 10mm or 3/8" button head cap screw or crown bolt is probably the cheapest/easiest to find option, dropped into the cap in place of the tube. Any decent hardware store should have them.
12-01-2015, 12:33 PM
In serious need of help diagnosing engine noise
but I'll look again!
