Top-end rebuild - now I have a knock
 

Over the weekend I finally managed to get the engine back in the car. During the past several months I have replaced the P/C and had the heads done at a reputable shop. All of the parts were OEM. I did not split to case as the engine *only* has 125,000 miles on it.

On Sunday I started the car for the first time and broke in the engine for 25 minutes of moderate medium to medium high revs (2,000 - 3,500 RPM). Everything went like clockwork. The engine fired right up, ran smoothly, and sounded normal.

After changing the oil and filter, I took the car out for its first drive. After about a block of driving, I noticed a knock in the engine. No smoke was visible and the engine was still running smoothly with plenty of power. I parked the car overnight and had nightmares of what could possibly be wrong.

Today I started the car again and there was no knock. I carefully drove around my neighborhood while the engine warmed up. Sure enough, after 2-3 minutes of driving the knock was back. After lifting the car on jack stands, I crawled under the engine to see if I could tell where the noise was coming from. I believe it's originating on the passenger side. Could this be a valve out of adjustment? Please tell me everything is going to be OK. Right now I'm too scared to look.

Randy

uh o

valve out of adjustment is usually a loud tapping sound. Cut off a broom handle to about 2-3 ft and move it around the engine while holding other end against your ear. you should be able to isolate the loacation of the knock that way.

It didn't knock with the origingal filter, and it started after you changed the oil and filter (that's what is sounds like) 99.9 percent of the time when a trouble arises it's from what was most recently changed.

Does anybody else care to weigh in?

Randy:

Tapping/clicking sounds come from loose valves, worn guides, and worn rockers/shafts.

Knocking sounds come from the bottom end; rod bearings, wrist-pin bushings, wrist pins, intermediate shaft gears and bearings.

I would recommend using a stethoscope (either a broom handle or a long screwdriver) and listen all around the engine; top and bottom to isolate where the noise is coming from and what it sounds like.

Subscribing for information purposes.

While under the car, I used a piece of hose to try to isolate where the noise is coming from. Maybe I should try the broom handle as well. I'm pretty sure the noise is from the #5 or #6 cylinder near the head. No unusual noises were detected in or around the crank case. What's alarming is that it sounds more like a knock than a rocker arm tap.

Is there any way I could have messed up the cam timing so bad that I have piston to cylinder contact? The engine runs very smoothly and the noise only becomes pronounced when the engine warms up. This weekend I'll pull the valve covers and check the clearances.

Thanks
Randy

You said new P/C is the piston hitting the head??

If it was the other way around and would quiet up when hot I would say you had some piston slap. I have had exhaust leaks that made some very strange sounds before too.

Randy,

I'll second what Steve said above. To add a little detail from my own experience, I've seen the result of what can happen when a wrist pin circlip is not fully engaged in its groove. Don't ask me how I know. :)

The wrist pin can wander out and contact the cylinder wall. It definitely makes a knocking sound. It did not do so immediately; the knocking sound occurred after a few minutes of warm up. And the sound was not clearly from the top end, nor from the bottom end. That lesson, learned 25 years ago, still sticks with me.

It sounds like you have some diagnosis to do. I'd consider draining the oil and looking at it very carefully. Maybe open the filter and look inside. And as you had planned, you should remove the valve covers and scrutinize the valve train, valve timing, rocker shafts/arms and whatever else can be seen from there.

A knock is a very bad sound, though. I'm afraid you're going to be doing some disassembly.

Good luck and please keep us posted as to your findings.

Rob

Hose is only useful for tracking vacuum leaks,..........:)

If you didn't get the cam timing correct, you might get piston-to-valve contact. If the deck heights are off, one can have piston-to-head contact. Generally speaking, neither condition makes a "knocking" sound.

After you confirm valve clearances, use a long-handled screwdriver and place it all over the engine (top & bottom) while its running to listen. Have someone rev the engine a bit while you are doing that.

Rob's suggestion is excellent and I'd strongly recommend that you pull the oil filter and cut it open with the special tool (keeps the steel casing material from contaminating your efforts) and unfold the paper all the way out on a clean bench to look for bearing material. You may need someone who is well-versed in this to help perform the forensics.

Great question, but I don't think so. The P/C are stock Porsche and nothing hit when the engine was breaking in. In addition, when I turned the engine over on the stand, everything moved freely.

I'm going to try to further diagnose the problem this afternoon with the screwdriver as suggested.

Thanks to everybody for the advice.

Randy

I checked the valves this afternoon and they are all set correctly. Using the "long-handled screwdriver" method I've isolated the sound to the #5 cylinder. Looks like the engine is going to have to come out. :(

Randy

Bad news, sorry to hear. It is every home mechanics nightmare. But, look at it this way, you already have the experience and tools. It will go quicker than you think the second time around. Take some pictures and let us know.

Rob, you called it. Either the circlip came out or I never put one in. I haven't tried to fish around in the crankcase with a magnet to find it. Now I need to evaluate the rod, piston and cylinder and see what damage has been done.

I really can't imagine how this happened. When I assembled the engine, everything was triple checked. Somehow this one got by me. I reckon, I'll remember this for the next 25 years. Thanks for the good advice.

Randy

It is always nice to find and fix a problem before it turns into another project, huh?

Any thoughts on what will be re-used and what will have to be replaced with new parts?

Randy,

Bummer. Well, at least you know what it is. Actually, for a knocking sound, it's probably the least bad of all possible bad reasons for a knock. The big question, as you have already asked, is where-o-where did that circlip go. If it's in the engine somewhere, then you might feel obligated to fish it out. You might worry that it may do more damage as it goes through the engine's digestive tract. Can you tell if it was ever there? If it went between the piston and cylinder and into the crankcase (the worst case), then it may have left telltale swirlies. Likewise, if it went up into the combustion chamber, it may have left little hammering marks on the head or piston crown before it got spit into the exhaust (a better case).

The next question is whether there's significant damage to the piston and cylinder. In my case, it damaged the cylinder, though not as badly as I expected, and as I recall, the piston looked okay. Back then, when I was on a stricter budget, I replaced the P/C pair with a used one from the same cylinder height group. And it worked fine.

Good luck. My guess is that you won't have to split the case.

Rob

The circlip did not make it into the combustion chamber. If in fact it was installed, it's somewhere in the crankcase. I'll be fishing for it with a magnet tomorrow.

The irony is, I had marked this piston as suspect because although it was in spec, there was a gouge in the wrist pin journal. On the top of the piston was my black magic-marker "x" right above where the wrist pin slid out. It really makes me wonder if I ever installed the circlip.

I'll keep everyone posted whether or not I find the clip.

Randy

Most likely I will replace the piston because the wrist pin journal is a bit messed up. The Cylinder will clean up with a quick hone job. Other than the $50 in gaskets I'll have to replace, I plan to reuse everything else.

Randy

Well, the engine is back together and in the car. I never found the circlip after fishing around the engine case with three different magnets for hours. I really don't think I ever installed it. I'm not sure what makes my ego feel worse - not installing it at all or just installing it wrong.

After consulting with the local Porsche shop, they suggested I reuse the piston, cylinder, wrist pin and rings. Aside from a small grove in the cylinder from the wrist pin, everything looked OK. So far so good. The engine runs fine and there is no smoke or expensive knocking sounds. I guess the real test will be after 200 miles or so when everything finally breaks in.

My thanks to everyone who offered up suggestions and shared past experiences.

Randy

Well done to you and the posters that helped. If it makes you feel better, I just had to remove and reinstall my left side P&C's after I figured out I had installed them upside down. :eek:

Randy,

Glad to hear the resolution.

When I was assembling my latest engine a couple years ago, I foolishly thought I could install the circlips so expertly that I didn't need to cover the cylinder holes. Wrong! Well past midnight one night, I was pushing the circlip into the groove with my thumb when it somehow slipped out and went "ping." I thought the "ping" sound came from close by, but the more I thought about it, the less sure I was. I looked in the cylinder hole and saw no circlip. No circlip nearby on the floor or amidst the huge pile of tools that resided there. It wasn't in my clothing. I started to get worried. Out came a bright light, a mirror, a magnet, and quickened pulse. I *thought* the circlip must have gone into the engine, but I wasn't absolutely sure. I rotated the engine every which way, listening for the sound of a circlip rattling around inside. Finally, after an hour and a half of rotating the engine around, and just as I was about to give up and tear the engine back down, the circlip fell out of the engine and onto the floor with a "ping." Whew! My biggest worry was that I'd tear the engine apart looking for that circlip, only to discover there was no circlip (and that five years later I'd discover the circlip under the workbench in the corner). I still have nightmares about that. Needless to say, I covered the holes the during circlip installation the next time...

Good luck with your engine.

Rob

If it makes you feel any better the first Alfa I bought was at a shop with all the hoses disconnected. No book, nada, It was one of those deals where, well this looks like it goes here, that looks like it goes there, and not ever really having seen an Alfa before things just went back. Well I got it running and made it about two blocks before steam started comming out everywhere and when I pulled the dipstick it was like Old Faithful. Turns out I had hooked one of the heater hoses to crankcase breather on the back of the block. (looked like a water hose outlet/inlet to me!) That was a long long time ago but I'll never forget it.

Question
 

When you had the knock problem was it audible at all RPMs? I have a similar/same problem with my 81 SC. She runs beautifully except for the knock coming from the #4 cylinder (top end); it is not audible above 1000 rpms. Thanks.

lucas,

My recollection of the time I heard the knock from a loose wristpin is that it was most noticeable at idle or low speed. I don't think it necessarily went away at higher RPM, it was just harder to hear and distinguish from other noises that overwhelmed it. In your case, was the engine just assembled? If not, then I'd doubt that a loose wrist pin because of a missing circlip is the problem. If the engine has been together for a long time (and you're sure it's a "knocking" sound, as opposed to a rattle from the cam chains, for instance), it's more likely a connecting rod bearing, a bad wrist pin bushing, piston slap, or some other mechanical problem. Have you ruled out the rocker arms and valve train?

Rob

As Rob noted in his response, unless your engine was apart, I doubt you have a wrist pin issue. In my case, however, the knock was clearly noticeable all of the time. Using the "screwdriver method" I could clearly identify which cylinder was making the noise.

By the way, to this day I have never found the circlip. Yes, it does keep me up at night.

Randy

Rob,

At this point I have not ruled anything out. I am a novive at this stuff. I am trying to do whatever I can before I take it to a professional. Are there any tests I can do to further the problem down? Thanks.

... The car has not been apart recently- well I've only owned it or a year and the problem just became evident after I sealed a massive air leak around the pop off valve. So, to tell you the truth, it could have been there all along- just not audible because the car was idling very high because of the air leak!

Lucas,

To further diagnose the problem, be sure to read the comments made my Steve Weiner, me, and others earlier in the thread. Without more information, it's hard for anyone to give specific guidance. The process is an interative one; eliminate what you can by testing or deductive reasoning, and whittle away at the remaining possibilities.

The worst news (and frankly, one of the more common reasons for a knock) is a bottom end problem like a rod bearing. How is the oil pressure? Often (but not always in the early stages), a bearing problem will result in reduced oil pressure. Have you drained and carefully inspected the oil and the oil filter? In most cases, a knocking rod will have shed bearing material that you can find. Even though you've described it as a "knock," unless I heard it myself, I'd suggest you pull a valve cover and look at the rockers, cams and valves. Is there excessive valve lash? If you can eliminate valve train and cam drive issues, the unfortunate news is that the engine will have to come apart.

There's lots you can do to get closer to identifying the problem. But until you figure out what the problem is, you'd best not run the engine very much or you may have a catastrophic failure that will be even more expensive to fix.

Rob

The adventure begins!
 

Thanks Rob. I'll start with draining and inspecting the oil. BTW- Knock, Tap, Slap... I would say it sounds more like a tap or a slap. I'll dig into it next weekend and keep you posted! :rolleyes::rolleyes::rolleyes:

My first engine rebuild I installed p&c (mahle max moritz). They had to be machined to create larger intake valve pockets. Even though I marked exactly what had to be machined my machinist randomly picked valve pockets, I ended up with 3 machined intakes and 3 machined exhaut valve pockets.

When I found out I wasn't happy but in my brilliant mind I figured it wouldn't matter. I could install them upside down and all would be well. The only diff I could see was the dome of the cylinder difference in relation to the plug. I was twin-plugging so I didn't worry about it.

Well during break-in I noticed a knock at idle after warmup. I was very upset. I talked to Steve Weiner and he immediately told me about the upside down pistons. They have an offset on the wristpin that if not installed in the right orientation will cause a knock.

I ended up distmantelling and upgraded to mahle 10.5:1 p&c. I'm in break-in now and all seems well (knock on wood)...:)

Yeah I had a sim ilar thing in my 2.7 it was an exhaust leak, now I have the same sound in my 3.0 but much quieter, this I believe is piston slap.

Dont beat yourself up too bad . If it makes you feel any better, I recently assembled a customers 5.4 ford motor, and somehow dropped an 8mm nut down the intake. Ran real good for about 30 seconds, and then BOOM!!!. I have been doing this for years, and have built hundreds of motors. We all slip up once in a while. I will also never forget this mistake. It was a very expensive learning experience. My mistake destroyed the piston , rod, crank, and put a huge hole in the cylinder wall. Your situation is a lot better, glad that you caught it in time. Good ear.