Slight knock from bottom end.

UPDATE: This is no longer a slight knocking. It is a very loud knocking which comes and goes. Please ee the last post for more details. This is a 2.5L 5-chain boxster engine, but I figured since the architecture of the engine is the same as the 3.4L there may be more people in here who might have some insights to share. I have a slight knocking sound from the bottom end of the engine. It is clearly audible with my stethoscope and faintly discernable during idelig when standing next to the car. I found nothing in the oil, and nothing in the coolant. Any thoughts? There is a leak from the rear main seal, ims seal or both. It is an old leak and very slow. The oil is thick and crusty, no drips. I don't believe the IMS has been changed on this one. I have narrowed the location down to this area.

You sure the noise is not the usual clatter these engines make? I like to point out these are internal combustion reciprocating engines and there is lots of hardware spinnning around, moving back and forth, going up and down, valves opening and closing, injectors opening and closing, spark plugs sparking. These engines are by nature noisy. Add a stethescope to the equation and you'll hear nearly all the noise these engines make and they make a lot of noise. However, if the noise is discernible (with unaided hearing) over and above the normal din of the engine, has an interval to it, this is usually -- but not always -- a sign of sometihng that needs to be looked into. There is not much at that location of the engine. At the back of the engine on the right side is the camshaft drive for the right head. The drive for the left head is at the front of the engine. 'course, the IMSB is in that vicinity. But the oil and I assume the oil filter housing oil (and filter element) are free of any scary debris? If the noise were from the IMSB I would expect debris in the oil as the noise comes from the bearing disintergrating. If you have a Durametric you can I believe check the camshaft timing variation. If the noise is camshaft drive related, possibly a weak chain tensioner, the cam timing could be erratic and this is a clue. There is the oil pump. This is a rotarary gear pump and this is usually quiet in operatiion, as quiet as gear pumps can be. I'd be hard pressed to believe this the source of the noise. If the noise is present cold from a cold start you can remove the serpentine belt -- carefully note its routing and direction of travel you can install it correctly and in the same direction of travel -- and start the engine and let it run only long enough to confirm the noise is still present or gone. If gone the noise is from an accessory drive. If the noise is still present then this suggests the noise is within the engine. If the car is equipped with a manual transmission does depressing the clutch pedal fully and releasing it affect the noise? If so, the knocking can be the clutch disc rattling on the input shaft splines or even a bit of gear knocking from the transmission. My 2002 Boxster produces this although it is rather faint. (My 2003 Turbo is worse in this regard often the knocking is present after I roll up to a stop in neutral with the clutch pedal released. But pushing the clutch pedal down then releasing it has the noise gone.) Another source of knocking when cold is -- and my Boxster manifested this too -- is a loose converter brick. In my experience this was responsible for a dull irregular deep and subdued knocking sound. After everything was warmed up the knocking was gone and there was a buzzing that had me suspsecting (hoping) it was a loose heat shield. If the noise is from inside the engine my next step would be I think to connect a quality oil pressure gage to the engine -- might have to rig up a t-fitting at where the oil pressure sensor connects to the engine -- and check oil pressure cold, during warm up idle and after the engine is hot. Last but not least, I advise one in these situations to enlist the help of a professional tech one experienced with these cars. He will be at the engine and can observe and note things and get a pretty good idea of what's likely going on. Absent any nasties in the oil, absent a CEL, any untoward engine behavior, I'm thinking this is more your imagination than real. I mean this in a nice way. it is easy given all the talk about engine troubles to get overly anxious and one then starts hearing things. 'course, you are certainly free and I would recommend it to research this until you are convinced there's nothing amiss or until you find the source of the noise and what it means.

That area is the IMS chain tensioner. You can put the egine in tdc cyl #1, lock the bank 1 cams and remove the tensioner to inspect it.

Thanks for your informative answers. I have -6 and -9 camshaft deviation so I have to change the pads. I plan to pull the engine this weekend to replace the cam pads ++. The noise is a rytmic knocking in time with the engine. It's not a steady whirring or grinding friction-type noise which is heard in various forms all over the engine. The loudest point is where I indicated in the photo. Listening directly to the tensioner weakens/muffled it.

In that case, it's probably not the tensioner itself. Have you checked for bore scoring, especially in cyl #6, which is close to the area of the noise?

This is for my track car. I have lost the last six seasons rebuilding my 951 so I'm not giving up on this season. If there is a problem which is likely to kill the engine I'll just have to buy another to run until I can find the time for a complete rebuild. Track time is the only priority. I am going to get a cage installed. This requires the car to be with the builder next weekend, a 10h. drive each way. I can't afford to pull the engine this weekend and get stuck because the cage builder is going on holiday soon. The noise has made me think I'd rather chance leaving it for after the trip if I'm likely to discover problems requiring internal work. I need your help to decide whether to: 1 follow my original plan and pull the engine this weekend to replace the cam pads, inspect IMSB and RMS, remove AC, fix vacuum leaks, install a deep sump and generally prepare it for the long trip and the season. I'll do this if it is likely to last the season despite of the slight knocking sound. This is my preference. 2. Leave the engine in and drive to the cage builder as it is. Then spend time looking for a replacement for this season. I'll do this if it is likely to last a few track days until I can find a good replacement. 3. Consider it ready to blow and try to buy a new one for an immediate swap. I'll do this if it is unlikely to last a season on track without internal work.

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Not yet. I can get a scope tomorrow. Would that cause a knock? I guess this the easiest plug to get to so could be worth doing before I decide whether to pull the engine or not.

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Yes, it will sound like a noisy lifter but more solid. https://youtu.be/GRjBQB6XKXY

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Would be better to pull the sump plate and go in with a scope that way.

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Agree that would be ideal.

I was going to say it sounds like a lifter only more solid. It seems to be once per revolution. It's looking like I've bought another lemon ;( Won't the scoring likely be at the top of the cylinder. If so looking in from the bottom won't the piston skirt cover it? I'm asking cause I don't know these engines yet. I only know the inline 4s in the 944. If the cylinder is scored it will be a waste of time changing cam pads and doing all the other work. If it is not too bad I might consider the drive to the cage builder. If the the engine is toast I have a gigantic problem.

Jake always says the scoring starts at the bottom of the bore hence goimg on from the sump. However, since it's a lot easier, maybe just go in from the spark plug first. Also, cyl 4, 5, 6 are more prone to scoring.

Thanks. I really thought I had done my homework this time....I guess it could turn out to be something else, but I can't come up with any reasonable sources....anyway, it's definitely from cylinder 3. I'll know tomorrow.

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Without being able to hear the noise it is impossible to make a judgement call regarding continuing to drive the car. Even if I resigned myself to an engine R&R (with an intent to address the noise) or to swap out the engine I'd be reluctant to continue to use the car. The old engine might be salvageable or at least suffice as a core. I'd certainly not want to track the car. If the noise progresses to something catastrophic you could lose the engine in a spectacular fashion and oil the rear tires and the car could leave the track. Or another car could encounter the oil/coolant from your engine and leave the track. I think you owe your fellow enthusiasts some consideration. What are you prepared to do if you pull the engine for new cam pads and such and upon opening the engine the problem more serious? I doubt it is bore scoring. This is not a common problem with the 2.5l Boxster engines. You could do a compression test or leak down test of the #3 and #2 cylinders, using the #2 as a control. If the #3 cylinder/piston/rings were compromised I think one of these tests/checks would let you know. With a leak down test you could experiment with moving the piston downward on its power stroke to test the integrity of the cylinder/et al from TDC down to just before the exhaust valves open. Might add regarding a bad chain tensioner usually -- but not always -- o-ring or seal material from the tensioner are found in the oil filter housing oil and filter element. If the chain pads are bad usually -- but again not always -- one finds pieces of the composite plastic chain pad in the oil filter housing oil and filter element.

BTW, just to avoid future confusion for the discussion, the red circled area in your photo is cyl #6, not #3. Cylinders 4, 5, 6 belong to bank 2. M96/97 cylinder numbering

Yes. But since this is a boxster engine it is installed the other way round, so the red circle is cylinder 3.

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I appreceiate your thorough answers. I just had a look in the cylinder using a bore scope. I get limited FOV but from what I can tell the cylinder walls look good. The plug looked perfect. I will try to get a leak down test done too. If this were a problem with the rod bearings I should be hearing it in both halves of the engine case, right? Since I only hear it on the 123 bank I'm ruling out a rod problem. The noise is not double crank speed, so I'm thinking it can't be a wrist pin problem. Could a broken chain tensioner rail cause a knocking sound?

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ml I realized you have a Boxster but look at my diagram again. It's cyl 6, not 3. Cyl 6 is always the cylinder that's closest to the oil filter, Boxster or 996.

You are right. My memory was playing tricks on me. I have had another listen and this time I think the sound is definitely coming from the lifters. I'm going to check them thoroughly when I change the cam pads.

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That would be the best time to check the lifters. You may find some are jammed solid.

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Yes you need to address this issue. 1st drain the oil & remove the tensioner where you hear the noise. Inspect the chain & "paddle tensioner" that should keep the chain in place. Also inspect the wear button that the removable tensioner contacts for excessive wear. Since the engine is a 2.5L there is no reason to check for bore scoring. Scored or not you will race the engine as long as it works for you & you don't repair a 2.5L engines bores you find a better engine.

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If if were a rod knock the noise would be more pronounced on one side but the nature of the beast is the noise would detectable throughout the engine. There are always exceptions and I'm no expert on broken chain tensioners but a knocking sound is not what I'd expect from a failed chain tensioner. The chain would run with excessive slack and there would be some noise. Along with this you'd have the tensioner trash (o-ring) in the oil and filter element along with shortly composite plastic debris too as the chain slapping the guide rail would soon beat this up. If (big if) the timing didn't jump due to the loose chain.

UPDATE: After working on the engine the problem has gotten ten times worse. I had trouble bleeding the cooling system. After about 2 gallons the system wouldn't accept more coolant. To avoid overheating I shut down the engine to let it cool a bit. When the engine was either idling or switched off to cool down I heard a loud crack, as if something had snapped or cracked. After this it runs and idles smoothly, but as soon as I even think of releasing the clutch to pull away it sounds like a piston skirt has collapsed. The noise happens also when pulling away down hill. It is very loud and extremely disconcerting. For the short time I've had the car there has been a loud knocking sound the first second or so when cranking. This was there at the first startup after resetting the timing also, but went away immediately after the the eninge fired. However, for each subsequent start it has taken longer and longer for it to go away. The sound is similar to the sound I get when I try to pull away. It could even be the same sound I did a full leak down test today. All cylinders are in excellent shape throughout the stroke. The cams ar opening and closing the valves as expected. Could a bad tensioner really cause such a loud and rythmic noise, sounding like a severly damaged piston? This is what I've done to the engine:

An audio clip would probably go a long way toward helping people understand what you're hearing.

I agree, but I'm reluctant to start her up and possibly do further damage.

Would not a collapsed piston skirt damage the cylinders enough to show up on the leak down test? Plan of attack . 1. Weld loose heat shield on catalytic converter. I'm pretty sure it is not the responsible, but who knows. 2. Remove and inspect all tensioners. I have ditched the AC so there is access to the top one. If the tensioners seem OK I'll have to pull the camshaft plugs and check the timing again. UPDATE: I checked the remaining tensioners. One was sticky and lots of metal flakes came out of it when pumped in white spirit/ mineral spirit. It remained sticky after pumping/cleaning, so I'm throwing this one out. The others are not sticky. They do leak however. When pumped in mineral spirit they leak a lot through past the piston seal. When pumped in engine oil they firm up well, but still leak past the piston seal. Is this normal or should they be replaced? 3. If I'm still uncertain I'll have to pull the transmission and check the DMF and the IMSB. Any comments anyone?

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It is so important in these situations to make the most of any engine run time to accurately/correctly ID the location of the noise. Given your lated report I would lean towards something amiss in the bellhousing. Unless you can confirm the tensioners are bad and then replace these I think removing the bellhousing is your next step. In fact, unless the cost is prohibitive I'd be tempeted to just replace the chain tensioners. As an aside: The flakes from the tensioner could be just the normal trash that can collect in things like the tensioner (and lifters). Dirty oil goes in and the bigger particles tend to stay as the oil then leaves again. The mineral spirts being a much lighter fluid was able to stir this stuff up and flush it out. It is my opinion that whatever you do you are going to have to do it without any more engine run time.

Thanks for trying to help. I have arrived at the same conclusion and will drop the transmission today. I need to check the IMSB and change the RMS so might as well get stuck in. I removed the aux belt and spun the water pump using a small drill and a short belt. It is completely silent. I thought it spun very easily, I expected more resistance, but the pulley is quite large compared to what I'm used to. The bad lifter was for the IMS chain. Since I found no metal flakes in the two others I believe them to come from the lifter itself. This lifter was very sticky. I could still have a bad piston or a cracked cylinder. Since the leak down test is done using very low pressure it may not uncover small cracks.

Today I finally finished dropping the transmission after finding the last bellhousing bolt hidden in 18 years of RMS or IMS seal seepage gunk. Checked DMF - fine but worn. Checked throw out bearing - smooth, but will be replaced. Checked IMS flange - some seepage but nothing serious. Checked IMSB - absolutely smooth and no play at all. Checked leak down - as good as I've seen. Checked cylinders for signs of striking valves or the top. The only things I've found so far is a bad tensioner for the IMS chain, a rotten catalytic converter, a worn clutch release fork and a slightly sooty spark plug. Nothing wich should cause such a racket. I'm looking for suggestions on what to do now. I'm a bit lost. Is there anything else I can check before I give up and pull the engine? I am of course going to buy new tensioner to replace the sticky one, but not if the engine is toast. Should I pressure test they cylinders at a much higher pressure to see if this reveals any cracks? I will do another inspection with the camera to see if there are any marks, but the camera has no fisheye lens so I can't really see the cylinder walls. I will also need to re-check the timing to see if it has slipped. Should i pull the oil pan to check the bottom end? Is it even possible to inspect the bores and pistons from below on the boxer engines? I find it very unlikely that this is a rod bolt problem since there is almost no knocking at idle. The knocking really only becomes evident when the engine is trying to transfer any load to the rear wheels. My fear is that I have a collapsed piston skirt, but since the things seem to check out fine what else can cause such a loud knocking sound? Tips are appreciated.

You can see the bottom of the cylinders by going in through the sump with the camera , this is where scoring occurs at the bottom of the cylinder also you can look for debris when you take off the sump pan. Also could this problem be related to the gearbox if it only happens under load, could be the carrier bearings just inside the gearbox, they hold the load from the driveshafts and I've heard they can go, anyone else got any thoughts on this ??