Can you reuse bolts

[Stryped]

No Loctite, and most head bolts are grade five, partially threaded. Just make sure they are clean, dry and in good condition. Also make sure the holes are clean and dry.

There were six marks on the bolts so I assumed grade 8….

 

[Rivets]

You are correct.

 

[sgkent]

unless the bolts are corroded, look fatigued or crystalized, or they feel like they are stretching when they are tightened I would use the old ones. As to rod bolts it is a crap shoot. I have seen new ones stretch below the recommended torque, and I have seen the old ones fail. Anyone remember the Jesus bolts on the L1011's where the engines fell off? Not all bolts are created equally.

 

[bertsmobile1]

Before you stretch the bolts on an alloy mower engine you will cause the hole to collapse in on itself, which is the way you know if they have been overtightened in the past .
As for thread length put the bolt through the head / rod .
If the thread is better than 1 full turn inside the head / rod then there is sufficient thread to torque the head / rod .
A mower head is roughly done up till the parts have touched & the bolt stops turning easily ( finger tight if you like ) then 1/3 a turn in 2 x 1/6 turn increments