i recently built the bottom end and since then its been making a hollow tap noise from the bottom end. it ran for three weeks and spun a rod bearing. (thats what i get for using the old ones) i replaced the crank and bearings and it idles smooth, but the noise is still there. only at idle and while deceling, i can kinda hear it while crusing but anything over a couple k-rpm i cant hear it. no noise under load either. has anyone experienced this? when the motor was stock, i heard a similar noise seldomly, but it was so quiet that i figured it was just oil sloshing around, but now it seems to be too loud for that.

If it is a rythmic tap that follows RPM, loud when cold, and quieter when hot, I would say not to worry. That would just be the extra clearance you put in for the forged pistons (assuming you used forged). The skirts are just slapping the cylinder walls a little. If it is a random tap or happens under heavy load, then I would worry. Already spinning one bearing is certainly a bad omen though. You are really a cheap bastard for re-using bearings during a performance rebuild. That's called stepping over a dollar to save a dime.

Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire

yup, spent a few hundred while trying to save 75. i know that now. the noise is not random at all and yes, forged pistons.i kicked my own ass about this allready. well, i drove it today and its not going away but its not getting louder. before i spun the bearing i was running 11psi and it made the same noise but it seems a bit louder this time around. well i'll try to get more oppinions about it till i feel confident to run it hard. thanks for the input.(and the criticism) sometimes we all need it.

Originally posted by eclipserst3
yup, spent a few hundred while trying to save 75. i know that now. the noise is not random at all and yes, forged pistons.i kicked my own ass about this allready. well, i drove it today and its not going away but its not getting louder. before i spun the bearing i was running 11psi and it made the same noise but it seems a bit louder this time around. well i'll try to get more oppinions about it till i feel confident to run it hard. thanks for the input.(and the criticism) sometimes we all need it.

like Corbin said, its probably piston slap. Try searching for piston slap, I posted a sound clip of mine a long ass time ago because I didnt know what it was, the video may still work.

Yeah, forged pistons slap. Loud when cold, and still audible when warm. Kind of diesel sounding when warm. Likely nothing to worry about.

Mine always did the same thing ... and I built two forged motors. Piston slap. Some say it goes away when the car is warm, but that's not really true ... it's always kinda there. Cast aluminum doesn't expand or contract, it cracks. Forged aluminum expands and contracts and so manufactures allow for a extra thousandth or 2 of clearance which is where the slap on the clyinder wall comes from.

cool, thanks guys. this engine building is all new to me so i really wasn't sure about it. its still running better than ever and the sound is still exactly the same now as it was the first time it ran. thank you much.

sound anything like mine in this video I took?

http://videos.sovadsm.com.vidiac.com/video/fc57a2a7-f571-4f3c-ac27-171031ec7280.htm

prety much but not as loud and rough

Did you remove your egr? Sometimes you can get this type of sound from a egr block off that isn't sealing right! Even a dead lifter could make the sound you are referring to as well.

yeah the egr is cut and blocked.it's sealed up tight. and as for the lifter, it apears to be a "hollow tap" sound, seems imposible to get that from the top end. i've had a handfull of sticky lifters in my day and it doesn't sound the same. (two hours after i pulled the car off the lot in 2001 a cyl#1 lifter got stuck. then again four days after they finished the topend job)

Piston slap almost certainly.

What brand of pistons, and where did you get them?

What did the machine shop clearance your pistons to?
And I don't mean what overbore (.020/.040) I mean clearance.

Does this amount of piston slap always occur with the low compression overbored pistons?? If the machine shop does add clearances will it ever be possible to eliminate it completely if done properly??

well I dropped some hicomp standard pistons into my block and honed the bore and like a dummy didn't measure it and it piston slapped pretty loudly it sounded almost like a diesal engine.

I'm on my second rebuild and I did it right this time and go oversized pistons and tool the block to a shop and had it bored out. I don't notice nearly (if any) piston slap than I did before. But I've only driven it like 2k miles so it may get louder O_o

yeah, i have about 1k mi. on this motor and it doesn't have me concerned anymore. i hopped on it one hard time to kill a maxima-ser and it felt good. i'm boosting on a reg. basis but dont really rev it out yet.