My trailblazer is now making a rattling noise when I gun it and a slight rubbing noise is this the piston??? How much will a rebuild cost??? will a weisco prevent this???

 

Will; Chances are if you are hearing a "scrubbing " noise it may be coming from your clutch housing. Try moving the housing with your hand when the sound is being made see if it makes any diffrence. If that is where it is coming from you may need to try and adjust your housing to where it will not rub. I have in the past tie strapped the housing by its intake neck to the upper frame to quiet down a belt rub. Normally these noises are the result of someone stepping on the clutch housing and causing it to be pushed down onto the clutch.

 

Rattling on acceleration could be the piston, but not likely the scraping sound. Check the belt housing first as suggested. If that doesn't do it, maybe get it checked out because it will be alot cheaper to rebuild in running condition rather that waiting for the piston to break the skirt and send metal pieces all over the insides of the engine. I have heard of the skirt wedging inside somehow, cracking the case & bending the crank. Hope I didn't scare you, but it has happened.
Farmr

 

The Wiseco piston will cost you $69 from Chaparral Racing and $13 for a new wrist pin bearing. Boring over .020 will cost @$50. I did my piston job for $170. The Wiseco seems quieter.

 

the noise sounds like it is metal on metal not constant but alot of the time it will do it in neutral when I give it a little throttle and let off.

 

My 400 a rattling, squeaking noise when the piston was scored. Pull the carb and / or the pipe off and look into the ports at the piston.

 

what do I look for???

 

Vertical lines or discolorations on the piston skirt, or broken off areas in the skirt. Some small lines are normal, but the ones that will cause noise will be VERY noticable

 

You probally need a new top end. Luckly for you (unlike me) yours is a single cylinder not a twin. Air cooled, should be REALLLLY easy to tear it apart. I had never worked on a wheeler before I tore my banshee apart and that was peanuts. Buy a book, piston/gasket kit, and go to town. The only special tools you should need is a torque wrench to torque the head back on right. One of my friends has a 2000 trailblazer that he has beat the living h#ll out of and now its got alot less "ummph" and "slaps" pretty hard. Even if you need to replace the crank/pistons/ get the cylinder bored and head machined Id say around $400-600 and it would be better than new.

 

the noise you hear is normal,EVERY trailblazer i owned and rode,made a clicking noise from the head.i found if your running lean it gets more noticeable.i think being an air-cooled engine and not having the coolant ports surrounding the piston ampifies just normal engine noise.my 98 has been doing it since day 1 and im still on the original piston & running great.