You just finished cleaning up a neglected kitchen exhaust fan on a first service, only to turn the fan on and find it shaking. You inspected every blade for grease buildup and the backs and fronts of the blades are spotless.
It wasn't shaking when you started, so now the problem is going to be on you. You most likely knocked one of the balancing clips off of the fan. These are factory installed using high tech equipment that you won't have on the job.
The good news is this can be fixed fairly easily with some sheet metal, tin snips and some channel locks.
The first thing you want to do is take the belt off of the fan. if it is a bowl fan, you want to tip it to 90 degrees, hopefully there are two of you on the job so you can tip it over. Spin the wheel and mark the bottom blade, you can scratch it or mark it with a pen, just make sure there is a way to mark it without adding extra weight to the fan.
Spin it a few more times and you will most likely see that the same blade is always ending up on the bottom. This is the heavy blade on the wheel and is what is causing the fan to shake.
Go to the blade that is directly opposite this blade and add a small piece of sheet metal to it. Cut out a small rectangular piece, fold it in half but leave it a little uneven, so that one half sticks out a little more than the other. This makes it much easier to add the clip to the fan.
Do the spin test again and see if random blades end up on the bottom after each spin. This will be the best way to know if you got it right. The real test will be turning on the fan to se if it running smoothly.
This is just a temporary fix so you don't have an angry customer in the morning, but we have done this several times in a pinch and it works great.
The fan will need to balanced properly by a company that specializes in this, but for now you should have a happy customer.