Tapping sound from the engine?

Impreza 93, FWD, 72Kmi has developed strange sound couple weeks ago: Rather low-pitched, "tapping" or "knockng" that sounds like it is synchronized with the engine (as if a small hammer on a wood, fairly frequently and at some distance). The sound comes from under the hood (seems to be closer to the passenger side). It is heard only when accelerating (the harder, the louder the sound), and disappears very quickly as soon as I take foot off the gas pedal.

Oil level is OK, during the last weeks that the sound appeared milage remained the same, oil is not burned, other than this extremely annoying sound, the car feels normal.

Any ideas what this might be? Someone told me I might be killing the engine by driving it without fixing the problem. How likely is that? Unfortunately, I will not be able to get to the dealer this week, and maybe even next one...

Thanks a lot for any hints!

DK

Reply to
D.K.
Loading thread data ...

Sounds like piston slap. Do a Google search on that on this ng. There's been much discussion of that.

As far as the OP's '93, I'm not too sure. Piston slap appears to be more of a problem with some of the later engines.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

Reply to
Edward Hayes

Reply to
Ed Rachner

I had the same problem with a 2001 Outback. I thought that it was a bad lifter. Since the car was still under warranty I brought it back to the dealer. It turned out to be the idler pulley for the serpentine belt (bad bearing).

Reply to
Tony K

I've had a similar noise on my 02 Legacy. If the sound is worst when the engine is cold and tends to disappear when warm it could be the timing belt tensioner. That's what mine was. Replaced under warranty (UK warranty is 3 years/60K miles).

If this is what the problem is, it doesn't seem to do any harm to run the car with the noise present.

Regards

Doug

Reply to
Douglas Barr

Had a similar sound w/ 99 Outback. Thought it had something to do with the clutch/transmission. Took it to the dealer who discovered it was the heat shield on the catalytic converter. The shields are not stainless and tend to rust. They welded it back on since it was still somewhat solid and the sound was gone. The dealer said it is quite common and they often remove them completely.

Reply to
SpongeBob

I don't know how helpful this might be but one additional thing: the "tapping" sound only happens when the car is in gears. There is no such sound when I rev up the engine while in neutral. (Does that means it's not engine-related?)

DK

Reply to
D.K.

Reply to
Bill Putney

Thank you. I have replied to him in this thread asking couple more questions. Mind looking at it? Another thing I have noticed yesterday: that sound was gone for a while after the car was parked for many hours under sun during a hot day (>80F). In the evening, when things got cooler, it resumed again. Does this make any sense with regard to CV joint idea?

DK

Reply to
D.K.

CV (constant velocity) joint - its part of the drive axle - there's a left and a right - each called a half shaft. Replace the half shaft. Since you asked what a CV jopint is, I assume you don't do much of your own work - if that's the case, best take it to a shop. Haven't done one a few years, but I believe price (parts and labor) would run $125-$200. Careful - there are some junk aftermarket half shafts out there. You'd be wise to insist on one from NAPA - they seem to pay attention to supplier quality than some of the other chains.

I wouldn't expect temperature to affect it much - possibly grease got warm and filmed over the moving parts a little so it was quiet for a while, but I wouldn't focus on that too much.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

I know (on paper) what CV joint is, but Ed mentioned DOJ which I've never heard of. After some search I conclude that the Double Offset Joint is one of the possible varieties of CV joints. Correct?

Thank a lot! I did look under the car - the boot there is clearly torn badly, which I now understand probably resulted in some damage/wear off in the joint.

DK

Reply to
D.K.

Nice to see you've got your noise sorted. My boots look fine so I'll have to look further afield. The noise doesn't seems related to RPM more than vehicle speed so I'm going to try to get the car up on a rack this weekend and see if I can spot any cracks/holes in the exhaust. If not I'll let the dealer try and diagnose it.

Thanks for the input guys.

Regards,

Gerard...

Reply to
Gerard

Yes - there are actually two joints on each half shaft - the outer, properly called CV-joint, and the inner, called DOJ, or double-offset joint. It is called that because it offsets (1) angularly (like the CVJ) *and* (2) longitudinally (in-out - like a spline shaft) to compensate for geometry changes as the engine and tranny move around on their mounts and the wheels move up and down. The CVJ is usually the one to fail because it flexes a lot more (boot tears, grease flings out, dirt gets in, etc.) when turning corners, but the DOJ can fail too (it turns thru a much smaller angle so boot lasts a lot longer).

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

Well, I'd consider it sorted when it's fixed (and I don't go broke in the process) ;-) But yeah, it makes so much more sense than my original thought about engine... Besides, I have now listened carefully and there are definitely growling sounds when turning wheels, particularly at low speed - a sign of bad CV joint, according to everything I read on the web.

Good luck! Does the noise disapper practically the same moment you get foot off the throttle? That's my case - even though for few seconds RMPs and speed remains more or less the same.

DK

Reply to
D.K.

Reply to
Tony Hwang

If you do not KNOW that the boot has only been torn for a VERY short time, then it's impractical to think you can just clean, re-lube, re-boot the old joint. More so if it's on the right side (more dirt in the gutter, tighter radius turns). BUT if the boot has only recently been torn or the noise is only when you turn or very slight when going forward - MOST cars will drive for MONTHS like that.(wonder what percentage of FWD cars on the road right now have undiagnosed torn boots?) But save up quickly for that new CVJ (or rebuilt half axle) cause some day when you tromp on it you may not move and just hear-ZZZZZZZZZZZZZZZZZZZ!

Carl

1 Lucky Texan

D.K. wrote:

Reply to
Carl 1 Lucky Texan

Yep, thanks for the advice! Went to the nearest to work shop, explained about noises and when they called back they said it needs new half-shaft. I ended up paying $261 of which the part came at $119 from NAPA.

Amazing how powerful Usenet combined knowledge can be! I don't mind paying good money for good work, but I've been burned with car repairs more than once, and having some pre-existing knowledge really gives some peace of mind knowing that the problem was probably addressed correctly.

DK

Reply to
D.K.

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.