How tight does a belt need to be?

[Jdwilli]

I removed the belt in my Mercruiser to change out a pump impeller; I have put it back on now but do not know if it is too tight. How do you know how tight to have your belt? Do you go by feel or is there a measurement you can use? Thanks

 

[bobeast]

If you have twins, just do the thrum test. Pluck the belt on the opposite engine like a guitar string and listen to the sound. Then do it on the newly installed belt. If the tone is higher the new belt is tighter. If the tone is lower, the new belt is looser.

If you only have a single you may have to thrum someone else's belt. But be warned, you may get slapped.

 

[achris]

Serpentine or V-belt? Engine, year, model, serial number.

Please add engine information to the initial post of all your threads. People can't remember each engine that each member has. (Or do as many of us have done, add it to a signature file that appears on the bottom of all your posts.)

Please Read This Before Posting...-> How to Ask a Question....

Chris......

 

[Jdwilli]

Sorry, 2014 Mercruiser 5.7 350 MAG Bravo, Single serpintine belt

 

[achris]

From the Merc service manual (manual #31, section 1B, page 55)

• Proper tension - 6 mm (1/4 in.) deflection, with moderate thumb pressure, on the belt
at the location that has the longest distance between two pulleys.

Chris....

 

[H20Rat]

That really is in the manual? What is 'moderate' thumb pressure... It isn't like many boats have a fairly well-designed tool to measure belt deflection! (fish scale & ruler)

My personal standard is TLAR. That Looks About Right. For the most part, I usually error on the side of too loose and tighten it up if I here it slipping or see the belt is glazing. Too tight can cost you bearings.

 

[achris]

Yes there is a special tool... I'll dive back into the manual tomorrow and post it (it's currently 10pm, so 'not tonight Josephine')...

 

[achris]

Ok, here's the way it's done with the 'special tool'... (BTW, I don't know anyone who owns one of these.)

The gauge part number is BT-3373-F (from Kent-Moore). Correct tension is on the gauge face.



Chris.........

 

[DouglasW]

There's a used one on eBay for $75. I think I will keep using my calibrated thumb ;-)

 

[achris]

There's a used one on eBay for $75. I think I will keep using my calibrated thumb ;-)

:thumb:

 

[Scott Danforth]

standard belt tension gauge.......

 

[dingbat]

standard belt tension gauge $15.

Write “for marine use” on the side and your good to go.

https://www.amazon.com/Gates-91132-B...78047065&psc=1