So I just picked up my Evo 8 from getting a timing belt job and a Cobb 3 inch downpipe install. I got all belts replaced, all pulleys and ancillary bits, and a new water pump. New spark plugs installed and an oil change to boot. Transmission fluids were done a week ago.

Now when I drive it there is a funky resonance coming from the exhaust. The car starts up fine and truthfully drives fine. I can hear a different quality from the exhaust when the resonance isn't happening and it's pulling hard most of the time.:

When I ease past 3000rpm, most often in 3rd gear, the exhaust gets a strange resonant burbling quality to it. It goes away as soon as I lift, but if i go to WOT the exhaust's resonant quality continues, plus the normal roar of the exhaust, and it doesn't seem to pull as hard. What the heck???? And it will continue into a 4th gear shift at WOT. So confused.

If the exhaust pulses were hitting the resonant frequency of the Cobb downpipe, wouldn't the resonance go away as the rpms go higher/lower? And why would it continue through a shift? It's happened in 1st gear too while pulling out of a driveway.

Unfortunately, I don't have a boost gauge so I can't tell you if boost is being affected, but I have a Depo electronic gauge on order, so that might be able to tell part of the story.

Help!

 

Balance shaft out of time.

 

Uh oh, have you had experience with something similar? Am I going to have to have my mechanic tear it back apart? That might explain some of the vibrations and rattle that I can hear from my engine at idle now when warm.

 

No personal experience, I do my own belt work and avoid this gotya.

Do a search and read of other peoples symptoms with a balance shaft out of time. The happening is not uncommon. Search on strange vibration or something similar.

 

Your mechanic has reassembled the balance shaft out of phase. I know from personal experience becasue I made the same mistake. Even though all the dots are lined up, the balance shaft can be out of phase. The solution is to follow the shop manual and stick a screwdriver blade in an inspection hole on the front of the engine while setting the timing. The problem is that this is impossible to do unless you take the radiator out first so most mechanics skip this step and then it's a 50-50 chance that the balance shaft will be out of phase with the crank.
Take it back and tell them to do it right

 

Changed the thread title for you.

 

If the BAL shaft behind the oil pump is out of phase you will know it. **p did a timing belt job on my car prior to me getting it and had it out of phase... you will get a bad vibration around 3k or so if it is out of phase. Maybe a tight BAL shaft or tbelt.

 

Whatever it was I think it is fixed. The thread is 4 months old.

 

Just had my TB changed and its doing the same thing. High frequency vibration, feels like when your watching the scene in star wars where they are on speeder bikes, that high frequency buzz in the pedals and seat.

I did one 3rd gear pull and logged it and there was no knock, so i bet its the balance shaft out of phase.

My guy said he'll look at it when I bring it back, he didn't sound to happy on the phone, not angry just disappointed I guess.

It also has a slightly meaner exhaust note when revving it.

Athanasios

 

You can lose the balance shaft and take out your entire engine if you continue like this. Park the car until it can be addressed.

 

Easy trick. Line the oil pump sprocket mark up at 12:00 and let go, if the sprocket wants to turn...

-CCW its in phase
-CW out of phase turn it 360* and you'll see that it'll want to fall CCW now

 

I printed out a few reposes here and the "trick" to show him. He insists he followed the Screw driver step in the oil plug hole. I bet the screw driver didn't go in all the way(60mm) and the pulley turned on him. He didn't seem to happy , he should take this as a learning experience, and so will I. Next time I'll do it myself.

I'll post back when I get it back.

Athanasios

 

I would get it looked at asap, as if your timing belt goes so does your valves and a lot of head work to boot. You could go for a balance shaft delete or just have it redone. The sound could be of your t-belt getting chewed up, being loose or rubbing though. Please post your resolution to the matter.

 

Its at the shop now, Hopefully they'll get it all sorted.

I don't think the timing is out because I did a 3rd gear pull and there was no knock at all and the log showed similar timing numbers in certain cells as before when using EvoScan. From the original responses in this thread for the original posters problem i would agree its one of the balance shafts.

Is there a way to put the Shaft back into phase with out removing the entire TB and starting over? Just curious.....

 

You'll need to at the least un-tension and slip belt off the oil pump sprocket in order to turn the oil pump