[briansansone]

Hello from Brian sansone . I just finished doing a partial engine overhaul on my 88 chevy tbi 350 . I had the heads serviced , replaced the rod bearings , piston rings , lifters , and two connecting rods - wich I had checked and reconditioned at a reputable machine shop . Now I seem to have an engine vibration . The vibration ONLY occures at idle in gear when I have my foot on the brake. As soon as I give it some gas , it runs as smooth and quiet as a brand new engine . The vibration is very fast , it makes the cab of my truck resonate like the inside of a bass speaker . When trying to observe the engine in this vibrating state I noticed that it was vibrating so fast that I could not read any lables on the engine or accesories . They appeared as blury as if I had been drinking all day -not the case - at any other rpm the engine runs perfectly smooth and steady . Could this be a failing harmonic balancer ? I put ALOT of undeserved stress on the balancer bolt during the rebuild ; especially when taking the old pistons out . Could I have damaged it . Is there a way to check it ? Or could the two rods from the foreign engine be the culprit . I realize a vibration could be from any number of sources . But I am tempted to think it is from one of these two sources. Truck ran fine before I did all this work . Any advice will be much appreciated . Any Chevy Guys ?

 

[MI2600]

From what I gather you put in two rods that were not from the original engine. If that is the case, you could have an internal balance problem.
I don't fully understand the "undeserved stress" on the balancer bolt. But, if you have concerns about it or the balancer, I would swap them out before going inside.

Added thought: Are all your vacuum sources connected or plugged?

 

[pro70z28]

If it was a balance problem, wouldn't the vibration get worse, the higher the RPM.

 

[USA1]

Motor mount or trans mount could cause this.

 

[briansansone]

no vaccum leaks , new trans and torque conv( from mr transmission- sure hope thats not the problem ) . I put alott of torque on the balancer - 6 ft pole - and had to bang on it . the pistons were very tight -jammed at one point- the engine was very hard to turn . Everything turns very easily now . should I try a new balancer , used balancer ? Is there an inspection I could do? I have never removed a balancer , and do not know how they work . This is my first american v8 . All my previous expeirience is with vw's , wich don't have harmonic balancers attatched to the crank . Thanks for the advice
Brian