Engine knocking at 2500 rpm

[Wicked96GS-T]

Hey everyone, I just bought a 95 GS-T from a local guy. I bought it knowing that it had some type of knocking in the engine. The motor only has 60k miles on it, because it was replaced after the last one developed crankwalk. Anyways... at idle the noise is non-existant, but as i bring the rpms up, it starts making a knocking sound right at 2500 rpm. Any higher, nothing. Any lower, nothing. If i lean down so my ear is level with the exhaust ports more or less, it seem s like the sound is coming from the head. Sounds much too high up in the engine to be rod knock. I checked the compression, 170 across the board. I plan on draining the oil tomorrow and checking for metal fragments ( to see if it has spun a bearing), and one of my father's friends who is the head tech at Richmond Mitsubishi should be coming over to listen to the sound. Any help is greatly appreciated.

 

[Defiant]

First suspect is a balance shaft bearing, then a rod..

 

[huafist]

I agree with Defiant. Either the block puked out a BS bearing, or a rod is knocking.

 

[Wicked96GS-T]

Is there any way to check the balance shaft bearings without actually pulling the balance shaft out of the block? I guess i'll be draining the oil today to check for metal shavings.

 

[huafist]

Drop the oil pan and check for bearings in the pan
That's the easiest way, and if it's not the balance shaft bearings, you've already got the pan off to pull the rod caps and check your rod bearings.

 

[gsxtacy]

Another "I agree with Defiant".

BS's or a Rod.

Either way its a 7 bolt and 7 bolt cranks are non-turnable due to their shallow hardness.

At a minimum your looking at a Engine R&R, a tear down, a replacement Crank and Bearings, while your there might as well replace:

Water pump
Timing Belt and associated components
All Gaskets
Piston Rings.

OR

Talk to Mark at www.Overbore.com He sells complete 7 bolt short blocks, with a full rebuild kit, WITH a warranty.

BTW when my car started knocking, it was exactly like you described, and I found out that my thrust bearing had turned and scored the crank.

gsxtacy

 

[Wicked96GS-T]

Okay, i drained the oil today through a paint strainer to check for any metal. There is zero metal fragments/shavings in the oil. Just to be sure, i even cut apart the oil filter to check for metal. Guess what. There's none in there either. So, I'm guessing it's not a rod bearing. A mitsubishi head tech should be coming over tomorrow to tell me what he thinks the issue is. Could it still be a balance shaft bearing, even without any evidence of metal in the pan?

 

[huafist]

Okay, i drained the oil today through a paint strainer to check for any metal. There is zero metal fragments/shavings in the oil. Just to be sure, i even cut apart the oil filter to check for metal. Guess what. There's none in there either. So, I'm guessing it's not a rod bearing. A mitsubishi head tech should be coming over tomorrow to tell me what he thinks the issue is. Could it still be a balance shaft bearing, even without any evidence of metal in the pan?

Just because there wasn't any in your oil doesn't mean there's not any in the pan. Drop the pan. It's a common failure for the rear balance shaft's rear bearing to be completely spit out of the block.

 

[Syndicate13]

Another simple check for the rod bearings is to bring the car up to the RPM point where it knocks and pull the plug wires off each cylinder. When the load is taken off the offending cylinder it will stop knocking audibly.

 

[Wicked96GS-T]

Alrighty, I finally got around to dropping the oil pan today. Found some metal, and also found that the number 2 rod bearing was spun. You were right Defiant. Anyways, I measured the crank journal, and it came out to 1.765". The manual says that 1.771 is the factory size. Do you think the crankshaft is okay? I plan on going with a set of eagle rods and wiseco pistons. Tell me what you guys think.

 

[Defiant]

Anyways, I measured the crank journal, and it came out to 1.765". The manual says that 1.771 is the factory size. Do you think the crankshaft is okay?

7-bolt cranks aren't supposed to be serviced, just replaced.

Now everyone's going to be telling you about switching to a 6-bolt motor. Bear in mind if that one bearing has been beaten to death, it's in a motor whose whole assembly has been treated to the same beatings.