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banditxmike

Can a pilot bearing sound like a rod knock?

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I know this is a dumb#%$ question but here is why I am asking.

Yesterday morning, I went to get on the freeway and put my foot into it a bit. The car kind of stalled for a split second then ran normally but an audible ticking/knocking was going on. It was engine speed dependant. I really thought it sounded like an exhaust leak and I was really close to work so I kept driving.

Once to work the noise was a bit louder. When I went to my car to go home, I checked to make sure I had enough oil and it was fine. No noise when I started the car so I am still thinking exhaust leak that might come back. Sure enough about half way home it came back. It got worse the closer I was to home.

Once home, I let the car idle in the driveway hoping I could pinpoint the problem. The noise got REALLY loud and was making sounds that led me to believe something major failed.

I did a quickcompression test and did not find anything specific. This seemed reasonable as the car was basically running fine other than the knock.

Right, wrong or indiffereent, evertything pointed toward a failing rod or main bearing so I decided to pull the engine after looking through some posts here. Engine removal went pretty well except there is nothing obviously wrong in the bottom end. The only thing I have found so far is a bad pilot bearing. Is it possible for that to make that much noise or am I just looking in the wrong spot.

Sorry for the long post but wantted to get you as much information as I could. I have done some searches on th esite and have found nothing specific to this so far. Thanks in advance for the help.

Mike

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Can't really help much with your noise but thought I would chime in to ask if it made a difference with the clutch in?

In theory the pilot bearing (in the end of the crank that the gearbox input shaft runs in) only does something when the clutch disconnects drive from the gearbox. Clutch out, accelerating - I doubt it is your pilot bearing as this should be stationary unless the clutch is slipping.

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The noise did not change if the clutch was in or out. When the knock really got loud was idling in the driveway. However, it was bad enough that I could hear it in the car while driving.

The reason I asked about the pilot bearing is that is the only thing found so far to be a definite problem. I have not removed the timing cover or looked at any of the main bearings to see if there is anything else definite. The sound definitely seemed to be related to one cylinder and the engine was running pretty normal too. Thus the idea being something other than a valve/timing issue.

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Did not think so either but just wanted to check in case I missed something else.

I will start breaking things down more later this week.

Would it be an accurate statement to say that nothing initially visible or audible in the bottom end while rotating the crank means the issue I was hearing is either mild or in the wrist pin area? Again, the motor was generally running no different than it was prior to the gawdawful noise.

Thanks again for the replies. I can't tell everyone how much I have been able to learn from this FAQ.

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Remember, rotating by hand cannot simulate the forces developed when running so you are not likely to feel it (unless it is a massive fault).

Conventional wisdom is a knock that gets more obvious at idle and less under load is a wrist pin / gudgeon pin / small end issue but without a fine mechanics ear you will have to examine (check bearings for unusual or uneven wear) and measure (check main and big ends when assembled and torqued for ovality or tapering) each part in turn against specs. There will be one failure.

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First- Thanks for the help and thoughts around this problem.

As it turns out- I pulled a bonehead move when working on my Weber. I removed the choke shaft to reattach the actuator arm. When I put it back together I THOUGHT one of the screws that seemed to be stripped would stay put. Well, it did not and THAT is what the horrible noise was. So, the head is good enough to clean the welded on screw from and reuse. The valves look fine although I will do more of an inspection.

The problem now is I don't feel good about reusing the piston.

My question now is can I use a used piston or set of pistons without any problems. I checked the bore and it looks like it is not overbored. So I would be looking for a used set of standard sized pistons.

Should I install used pistons?

Any help would be great.

Thanks,

Mike

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