A Few Rod Bearing Questions.

[79pace]

Ok.. I have a 93 ATX. I just put all new upper gaskets on and checked the valves. The previous owner just did the 60K it looks like but put the old gaskets back on for some odd reason. New plugs and plug wells all clean. I fired it up and still had a nasty knock so its rod bearing time. I have never done this on an SHO and have read through a lot of back posts and get the gest of what I am in for. I also found the page with instructions for doing it so I am not worried about the actual process. My questions are as follows.

#1 Has anyone seen the crank damaged on one of these? I dont know how long this things been knocking but it sounds pretty bad.

#2 The car hs 115K miles and with the valve covers off is very clean like the oil has been changed regularly and was fairly well taken care of engine wise. What might have caused this rod knock in that case? The car had plenty of oil in it when I got it. Not real clean oil but I have seen worse so I dont think the previous owner through oil in to make it look better than it was.

#3 How hard is it to rod out the cats with the Y pipe off the car. I am sure they are wore out and we dont have emissions here. This wont cause any ill effects I wouldnt think since I have done it on plenty of stangs. Should make the car sound meaner though.

Thanks in advance.

 

[shojuan]

79pace:
#1 Has anyone seen the crank damaged on one of these? I dont know how long this things been knocking but it sounds pretty bad.

If the bearing spun then there may or may not be damage to the crank. Often there is but sometimes there isn't. Only way to find out is to drop the pan. Something you would rather find out about sooner rather than later I might add. I wouldn't drive the car until you can drop that pan.

 

[olympic]

It's almost impossible to hollow out the cats by smashing the material out. The easier way is to cut open the cats, remove the material and then weld them back up.

A good alternative would be an off-road catless y-pipe from SHOshop. You'll notice a nice mid-high RPM gain and it was only $199 the last time I checked.

 

[Off Road SHO]

79pace:
Ok.. I have a 93 ATX.

#1 Has anyone seen the crank damaged on one of these? I dont know how long this things been knocking but it sounds pretty bad.

Yes.

A knocking crank will ovalize the rod journals eventually. The bearing are much softer than the crank so they take the brunt of the hammer blows for a while, but eventually crank goes bye-bye.

Scott Patterson on this Forum did an excellent write up on how to change the rod bearings; find it, read it, know it, DO IT.

If you want to check your bearing clearances before you buy new bearings, you can, but they are so cheap to buy and it takes so much work just to get at them to check, to me it's just not worth it to NOT replace them.

As always, use plastigage to measure the gaps that you end up with when you install the new bearings.

Good luck

Tom

 

[79pace]

The car has not been driven since I bought it. Just on the trailor and off the trailor and started up twice to listed to the knock. I know engines well enough to not drive this thing. I was just curious as to how tough the cranks are on these.

Why cant you hollow out the cats? Are they made of something different than most engines? Or are they that hard to get a rod in there to do it?

 

[NotSoSlowSHO]

The cranks are VERY tough. But damage is damage. If you have spun a bearings, hopefully thte damage is repairable (while in the motor) and you can simply run larger bearings.

I am planning on gutting the cats on my factory y-pipe. Yes, it is dificult, and no, it isnt made from some mysterious compound

The bends in the pipe make it difficult to completely gut them. I am planning on cutting the nasty 90 degree out anyhow, so Ill probably just cut the other down pipe off temporarily anyhow. That should make gutting the cats much easier.

 

[Yamaha V6]

I've hollowed out a set once, with a custom-bent piece of metal electical conduit. It took forever, but it is possible. You MUST make sure it's totally clean though - nothing at all rattling around in there.

Wear a dust mask also.

 

[Ishodu]

http://www.kurtmetros.com/bearings.html
Is a good write up. Not a very hard job once the Y-pipe is off.

<small>[ July 04, 2003, 03:51 PM: Message edited by: Ishodu ]</small>

 

[Off Road SHO]

NotSoSlowSHO:
The cranks are VERY tough. But damage is damage. If you have spun a bearings, hopefully thte damage is repairable (while in the motor) and you can simply run larger bearings.

No, that's not how it works. To run larger bearings, the crank comes out of the engine and down to the machine shop. There it is put in an eccentric (sp?) lathe where the rod journals are the center axis instead of the mains. Then a powered honing stone is used to grind the rod journal down EXACTLY 1/4 mm or more.

Very light scoring of the journal might be able to be "polished" out with crocus cloth and a light mineral oil. Light scoring is defined as "not able to catch your fingernail on it".

Rods that have been knocking too long will cause the journal to deform into an oval instead of round shape. Crank is Toast, yeah....Toast.

Tom

<small>[ July 04, 2003, 10:47 PM: Message edited by: Off Road SHO ]</small>

 

[shojuan]

Off Road SHO:

Rods that have knocking too long will cause the journal to deform into an oval instead of round shape. Crank is Toast, yeah....Toast.

In other words at the first sign of trouble stop driving the car, get it towed, and drop the pan. SHO pan is EASY to get to (unlike my 4X4 truck. Sighs this weekend a-plenty.) Even a serious novice can at least drop the pan of a NON-OP vehicle to assess damage and determine if serious engine work (new crank + install....not really that serious if you have resources like shoforum at your disposal) or simply new bearings is required. New bearings = no problem. Sure, takes a bit of time for the DIYer but crap, what are weekends for?