Why can't flywheel screws be re-used?

Mark42

Mark42

Fleet Admiral
Joined
Oct 8, 2003
Messages
9,334
Service manual for the 2003 90 hp johnson specifically states to use new flywheel screws when re-installing the flywheel. Wondering why? They are rather expensive at about $5 - $6 each. Five with shipping will cost about $45!

I'll bite the bullet if I have to, just wondering why they say to use new bolts. :mad:
 
Chinewalker

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Why can't flywheel screws be re-used?

I believe those bolts get "stretched" when they are originally torqued, much like a rod bolt. If you remove them, they get twisted back against the stress. Torquing them yet again weakens them further. I am by no means a metalurgist, but I have seen the results of re-used rod bolts in racing motors. Not sure how much more stress a flywheel bolt has as it is mostly shear forces, not tensile forces (like a rod bolt), but I believe that is the thinking behind it. That, and getting folks to buy $6.00 bolts...
 
J

Jim311

Petty Officer 2nd Class
Joined
May 31, 2011
Messages
169
Re: Why can't flywheel screws be re-used?

Yeah, some bolts are torqued to a pretty high torque and it's actually the stretch or tension of the bolts that holds everything together. Somehow I kinda doubt this is the case in this particular application, BUT I don't want to be the one to tell you that and have your flywheel shear off, LOL.
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Why can't flywheel screws be re-used?

What they said, Mark. Same reason you should never try to tension (stretch) previously used barbed wire. . .almost sure to break if stretched or torqued.
 
J

jonesg

Admiral
Joined
Feb 22, 2008
Messages
7,198
Re: Why can't flywheel screws be re-used?

Mark42 said:
Service manual for the 2003 90 hp johnson specifically states to use new flywheel screws when re-installing the flywheel. Wondering why? They are rather expensive at about $5 - $6 each. Five with shipping will cost about $45!

I'll bite the bullet if I have to, just wondering why they say to use new bolts. :mad:
Click to expand...

I did the water pump on my volvo, the 4 bolts that hold the cooling fan to the pulley have to be replaced everytime its removed.
So I re-used the bolts, they "looked fine" to me, it threw the fan on the highway.! :)
 
You must log in or register to reply here.
Top