Isuzu Chassis Bolts- What Size to Use?

[steve66]

G'day All,

I need to source bolts for attaching the spring mounts to the chassis.

The OEM bolt holes are 11mm. OEM bolts are 10mm.

My concern is that the OEM bolts are a sloppy fit. I know a thousand engineers must have ok'ed it but seems strange. OEM bolts/nuts are flanged as well which plays into it.

What bolts does everyone else use? 11mm bolts don't exist.

standard HT 10mm?

7/16" and drill out the holes slightly (not strictly allowed but it's only 0.11mm)

I know I'm probably over thinking this

Cheers Steve

 

[SkiFreak]

7/16" and drill out the holes slightly (not strictly allowed but it's only 0.11mm)

Why can't you drill out the holes?

Not only did I drill out my holes to a M12 clearance hole, I also replaced a few of the rivets in the step section with bolts, as that is where some of my mounts needed to go.
Also, if you think that mixing metric and imperial bolts on anything is a good idea then we are definitely not on the same page when it comes to building things. Personally, I think this is a very bad idea, but each to their own...

 

[steve66]

Hi Ski,

11mm is the max hole size allowed by the Isuzu body building manual for my truck and drilling to oversize is prohibited so trying to stay within that.

Would prefer not to have to use 7/16 bolts but in theory once installed they will never need to come out so I don't feel it's the end of civilisation if I go that route.

I'm sure other Isuzu builders here must have struck the same issue.

cheers steve

 

[Amesz00]

Standard to have 1mm clearance, pretty much always has been, that I've seen. Apparently allows for chassis movement without binding the bolt or something like that.
Like skifreak said don't mix bolts, please.. m10 10.9 is fine.
Pretty sure the VSB on chassis mods changed, now there's a whole lot of rules on drilling holes. So hence all the builders manuals just say don't do it.
Of course we had to have a tightening of the VSB codes to stop the country wide epidemic of breaking truck chassis' that's been happening ever since... ummmm... yea.

 

[steve66]

Thanks, I did wonder if it was something to do with chassis flex, drilling extra holes is no problem, the manual says were, what size etc, just not allowed to enlarge any that exist already.

The gov guys that issued my pre-approval to modify permit said to treat the Isuzu manual as the highest authority on what is ok or not.

Cheers steve

 

[Spanna 53]

When I did mine on my NPS the engineer was happy with 10 mm bolts and nyloc nuts but wanted high tensile washers under bolts and nuts , 60 odd bolts once it was all finished including under the springs definitely a 2 person job,just as well all he wanted was decals on gas bottle locker and the tag back on the tow bar just what we needed the week before Christmas

 

[steve66]

Thanks Spanna

 

[javajoe79]

I'm in the USA and I have been upsizing to 7/16" bolts. Breaking all the rules