Low RPM "rap" from rear valve cover

[SleeperStyle]

I just picked my a '94 ATX for $350. (will post pic soon) Anyhow, I got it so cheap becuase it has an engine rap/rattle coming from somewhere in the back cams. It almsot sounds like the timing chain, but it comes more from the middle of the valve cover. You can feel it vibrate through the intake when you place your hand on it. The noise goes away after about 1700rpm's, and the car is still very strong. I plan on tearing it down soon to figure out exactly what it is, but would like some ideas from some knowledged people on what to look for.

 

[K-Dawg]

Don't rule out rod bearings.

 

[SHOtimer]

How many miles are on it? I would suggest not driving it much, untill you pull the VC, and the oil pan to examine everything and ***** the conditions of the rod bearings and the cam chain tensioners.

Doug

 

[SleeperStyle]

I don't think it's in the bottom end as you can hardly hear it from under the car, also I doubt the noise would go away as the rpm's went up if it were rod's. I'm just getting ready to do the tear down and see what I find. Hopefully its not to bad. I'll post back and let you know what I find.

 

[SHOtimer]

As, the RPMs go up the oil pressure builds so the knock would subdue, if it is the rods. It very well might not be. If you are not fimilar with the SHO motor the rod bearings are its major weakness. There was just a case of a motor spinning a bearing with 60k on the motor. He also orginally thought it was in the top end of the motor. Who knows what it is, hopefully it is something simple, however a knock is almost never simple. Anyway, just don't rule out the rod bearings.

Edit: How many miles are on the car? Even if the knock isn't the bearings it would be a good idea to do them anyway, only $100 parts, and an afternoon of work.

Good luck,

Doug

 

[Cobraii976]

SPUN Rod Bearing. Same noise the wifes 95 was making. I thought it was comming from the valve cover or the timing belt tensioner...... When I cracked it open it had 1 missing bearing. Ground into a fine powder. Ask SHOBILL what that looked like it took him 3 hours to clean the pan. Mine never sounded like the bottom end always sounded like the top. and it would go away when pressure built. I paid 500.00 for it so I kinda expected to do an engine swap.

 

[SleeperStyle]

Well, I tore the intake and valve covers off earlier tonight. Can't find anything visually wrong with the cam's or cam tensioner's. Only thing I noticed was that the back head is darker (more oil burnt than the front one).
Guess I'm gonna have to pull the oil pan and check the bearings. Sure was hoping I would't have to.

 

[SHOtimer]

SPUN Rod Bearing. Same noise the wifes 95 was making. I thought it was comming from the valve cover or the timing belt tensioner...... When I cracked it open it had 1 missing bearing. Ground into a fine powder. Ask SHOBILL what that looked like it took him 3 hours to clean the pan. Mine never sounded like the bottom end always sounded like the top. and it would go away when pressure built. I paid 500.00 for it so I kinda expected to do an engine swap.

Your probably looking for something like this.

Hope it goes well and the crank isn't hurt.

Doug

 

[Dr.Evil]

my $ is on a rod bearing. Sounds like a sticky spring tapping the cam cam or a shim fell out. Hopefully the crank / main journals are okay.

 

[SonicRiot]

Rod Bearing. Reground crank or motor swap time.

 

[SleeperStyle]

Well I've been busy lately so today was the first time I got to get back under the hood. Anyhow, I went to check the torque on the camshaft caps before I put it back together and found a stripped bolt. The car's top end had obviously been apart before, I presume for it's 60k, and maybe even the 120k. Knowing the way we tech's can be he probably felt it starting to slip, stopped, and just put it back together. Almost all the tech's work on flat-rate, so he must not have wanted to eat that days pay.
Now I'm going to fix that and put the top end back together before I take the oil pan off. Considering I only payed $350 for the car I just might use a Heli-Coil as a quick fix.

 

[Rockledge]

Drop the pan and check the rod bearings. That's how I'd be spending my diagnostic time if I were you.

http://www.shoforum.com/showthread.php?t=35455

If the bearings check out OK and are just worn, change them out with new ones and feel fortunate. If a bearing is spun, probably time for another engine.

 

[SleeperStyle]

Does the motor like any particular brand of bearings more than another, also does anyone now a cheap place to buy them? All the places I;ve found have been around $125 for the set.

 

[Rockledge]

Clevite rod bearings from Napa. About $50 for the set. You'll probably have to order them.

And don't forget the new Fel-Pro oil pan gasket (actually a set of two end pieces and some RTV for the sides) from AutoZone.

 

[SonicRiot]

When you get your set of Clevites, don't send them back because the blackened color looks inconsitant or the bearing faces look "burnt." It is perfectly normal and Clevite makes a good bearing. But $50 bucks? Last price I got was about $100.

 

[Rockledge]

When you get your set of Clevites, don't send them back because the blackened color looks inconsitant or the bearing faces look "burnt." It is perfectly normal and Clevite makes a good bearing. But $50 bucks? Last price I got was about $100.

$7.49 per pair.

6 cyl. x $ 7.49 = $44.94

Napa Part # CB1435P

That was the price a year ago (I'm looking at my receipt), and I just checked NapaOnline, and the current price is the same.

 

[Cobraii976]

Well my last NAPA reciept for bearings was Saturday and they were 42.00 out the door. Clevite CB1435P. I get them at a little over cost but I do know that they retail at NAPA for 7.49 a set and you need 6 sets. As for the blackened finish well I'm not real sure about that Saturday was the 6th set of 6 I bought and none of them were blackened. Although the CB1435P.75mm I bought was a tad discolored. but the .25 and .50 I bought were all nice.

 

[SonicRiot]

Ok, I guess they're not 100 bucks. But occasionally Clevite with have a "burnt" look to them. Good bearings, though.

 

[SleeperStyle]

What are the torque specs for the camshaft caps?

edit- n/m, I found it in another thread.

 

[SleeperStyle]

Any other ideas???

Well I changed the bearings out like everyone here said I should... what a bad idea that was! To start things off, every single exhaust stud snapped off. I spent about 5 hours repairing that, and it still isnt quite right. Beter yet the "rap" is still there, same exact noise, hasen't changed a bit. And to top it all off I've aquired a whole new taping sound that was'nt there before. What a nightmare this has been, mostly beacause of the exhaust, even more now because its still broken.