Engine knocking, but not at idle

[KTM300]

I did some searching and came up empty, so here goes. I am looking at buying a '95 GSX. It said in the ad that the engine is knocking. Car supposedly has 127,000, but the owner says he changed the cluster when it quit working and the cluster reads 94,000.

I went and looked at the car. Fired the car up and it sounds perfect at idle. Owner says it burns oil and only knocks above idle. I check the exhaust and it is burning some oil (blue smoke and you can smell it). Not bad at all, but noticeable. I jump in and rev it up a little. I can hear a faint knocking sound. I get out and reach under the hood and rev it up. You can hear the knocking a little better, but still faint.

Any guesses? Wouldn't a rod or crank bearing knocking be noticeable even at idle? I wish I would have a video phone to record it for you guys.

 

[killer_eclipse]

its really hard to give any good advice without actualy hearing it but it could be lifters because ive heared some so bad it sounded like a rod knock and would sound fine at idle... but if you could find a way to post a video it would help alot...

 

[haswesley]

There are two types of "knocking" people talk about here. One is pre-detonation knock which the knock sensor picks up when you are running too lean. The other is rod knock. Clearly, you are talking about rod knock. You usually cannot hear rod knock while idling because the engine isn't under a load. However, rod knock is usually the loudest when you rev the engine and then let off the gas and listen. The rods will knock when the engine is decreasing rpms rapidly. The only way to fix rod knock is to change out the rod bearings. Since you have the oil pan off, its a good idea to also change the main bearings. It doesn't sound like crankwalk, yet. Crankwalk causes the rod bearing in #2 or #3cylinder to spin and you would definitely hear more than just a faint knock. Good luck.