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VIBRATION AFTER PROP CHANGE

Big Guy

Big Guy

Active member
I changed the belt drive on my SBC from a 1.774 to a 2.5 unit. I also put a set of WW Sirius blades on set at the factory mark. When I started the motor I felt a viboration I did not have before. Any Ideas?
 
Don't worry that's common. You need to set it by a protractor or clamp something onto your transom and us it to set the tips exactly the same!
 
It's a 2 blade hub. As for the Belt Drive, it was made by Century in Pa. I called and asked about this unit, they made it in 1990 on a short run. It is a CH-2. I picked it up here in Florida. I will update as to how it works for me.
 
I've got a three blade prop that I've used a digital protractor on. I got all blades spot on by measuring the angle at the tip as well as the center of the blade. Then I clamp a guide to my cage to make sure they're all tracking the same. They look dead on. I've done this at a variety of pitch settings and still can't rid of all the vibration at certain RPM. I even took my hub and blades to a aircraft propeller shop and had them balance the entire setup.

It isn't real bad, but it's enough for me to notice. I guess that I have to accept the fact that it's not going to be a smooth as silk so I try to keep the RPM up or down a hundred or so as to avoid that spot. Is it possible it's in the gear box?
 
make sure the serial #s on both halves of the hub are togeather thats how there milled if there not on the same side there out of balance
 
I feel sure its in the belt drive. I have a 2:1 ch 2 I'll trade. This should make your vibration go away. :D

Josh
 
Your prop vibration could be something as simple as harmonics between the engine and the prop, although harmonics are not simple. The short and simple in the aviation world the prop and engine have to be certified to work as a unit, and on the 4 cyl. lyc. you have a prohibited area in RPM that you can not run for long periods of time, due to harmonics, I'm not saying that's your problem ,I'm saying that's possible. I run a 6 blade 80" turbo Warp and I have a vibration in a certain RPM range of about 300 RPM and I set my blade angle with a digital protractor. I hope this info may be of some help, ZZ.
 
It looks like I solved my prop problem. I took all the advice and tried to change . First I took off the prop. Than matched the hub halves. I also set the pitch and tightened all the bolts. No more halves. Now I need time to run the boat to see if I have an improvement.
 
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