Top-end rebuild - now I have a knock - Page 2

Rob 930 · 11-26-2007, 02:37 PM

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

gigem75 · 11-26-2007, 07:02 PM

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.

lucasdw63 · 05-22-2008, 03:21 PM

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.

Rob 930 · 05-22-2008, 03:52 PM

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

gabenheimer · 05-25-2008, 04:21 PM

Quote:

Originally Posted by lucasdw63

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.

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

lucasdw63 · 05-26-2008, 08:39 AM

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.

lucasdw63 · 05-26-2008, 08:42 AM

... 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!

Rob 930 · 05-26-2008, 09:38 AM

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

lucasdw63 · 05-26-2008, 10:18 AM

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!

alphie · 01:59 PM

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)...

matty74 · matty74's Garage

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.

fastfredracing · 08-16-2008, 05:01 AM

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.