Gen Set

[samcrimm]

My generator started make the scraping sound and come to find out two mounting bolts have sheered off. So I am in the processed drilling out at least one of the bolts. As pictured, I have figured out to get to the back one I would need to remove the Generator..... So one for now.

Should I use a grade 8 bolt for this? If not what should I use?

Thanks

Sam

[porky69]

Look at the other mounting bolts and get the same thing. Count the number of lines on the head if fractional or xx.9 if metric.

[samcrimm]

Originally Posted by porky69

Look at the other mounting bolts and get the same thing. Count the number of lines on the head if fractional or xx.9 if metric.

I was hoping to improve what I had. They both have broke.

Sam

[Bob86ZZ4]

I'd use grade 8.

[porky69]

Just because they broke doesn't mean they weren't strong enough...they could have been loose or other bolts may be loose elsewhere causing these 2 to be overloaded or the mounting holes are worn causing excess movement in the mount.

Also if the others are grade 5, going to grade 8 does not necessarily make them "stronger", while they have higher tensile(straight pull) strength they are are more "brittle" in shear load. Sometime (although rarely) going down a grade can work out better as the bolts have more give (stretch) to them.

[hot rod]

I agree with porky, I'd wonder why they broke and try to figure out what is going on to make it happen. Excessive vibration, worn out rubber isolators (or lack of) or something. No reason those should snap under normal use. Just putting in stronger bolts may let an ongoing issue get works. Also in some cases a lower grade bolt is used so that it CAN break if something bad happens, easier to replace a bolt than a mount or bracket.

[bushpilot]

I (unknowingly) lost a mounting bolt on our generator (electric) motor, not the engine...and i while I'm not certain it was related i had developed a short in the stator ($2k to R&R the gen and install a new stator)...now i check ALL those bolts a couple of times a year!

[samcrimm]

I will up date you guys maybe tomorrow, got my angle drive drill working and hope the rain is gone.

[samcrimm]

Well so far I have gotten the bolt drilled and soaking with penetrating oil, the eas out is waiting for the oil to work and so am I. Tried with out the soak and I was about the break the eas out so...... I also cked the stator bolt on the outside and it looks great. I also could not get my battery angle drill to charge so I just torn it apart and it worked great too.

Sam

[38Chevy454]

Just a FYI, grade 8 is not more brittle. It is stronger, and does have less ductility which is the amount of plastic deformation (permanent stretch) that occurs between yield and ultimate failure. But the shear strength, which is proportional to tensile, is higher for grade 8 vs grade 5, for the same size bolt. Grade 8 is heat treated after cold forming to give the strength, whereas grade 5 is just stronger due to cold forming. The ductility is not brittleness, they're different properties that are sometimes used as interchagable but should not be.

Just some info from a metallurgical engr (me). I would use grade 8 for that application.

[samcrimm]

The eas out never worked, I broke it so I ended up drilling out the bolt... I hate that job and I got a 3/8 tap and ran thru it. it's ok but I have done better, but not in such a pain in the ass position. I have used a normal 3/8 bolt for now, but I will up grade to the grade 8 I am sure. After 38chevy454 information.

sam

[samcrimm]

Update,

After 1590 miles my bolts broke and pulled thru my tap job. I got lucky and had a friend in Delta Co and we fixed two of the bolts on the outboard. The engine bolt had pulled the threads out and I had to drill up from bottom up, measured about 10 times eye balled the drill and stilled missed the hole about 3/16. We finally found the hole but it was only 100deg in the shade.
Went to the local tractor place and got a foot of baler belt. Cut a square put a hole in it and it made the rubber donut fill up the sleeve the bolt had to go thru. The extra rubber made it ride better. The sheared bolt on the gen end soaked in some wd40 and it backed out like a champ! Used another square belting and the donut. Used grade 8 bolts this time, lock tight on the one I had to drill all the way thru. Figured out that the rough roads and g forces bouncing down the road are the breaking force. Let hope I can get home and fix the other 2 bolts on inboard side. So 38chevy454 was right off the bat.

Sam