Bolt length?

[Tree Trimmer]

Not having any engineering background, what would be the results of using a 5mm shorter bolt (same hardness) on front drive members. Also same for 5mm longer on upper swivel pin, (which by the way works out to be the same bolt) as long as it does not go all the way through the housing.

Tim

 

[D Chapman]

Technically, when you have a 90% tread, three (3) full treads hold all the weight.

I'm not 100% what your talking about, but 5mm seems like it could be a lot.

 

[RichardS]

Longer should not hurt as long as the extra length does not get in the way of anything.

Shorter is more difficult to say without more information. Is it threaded into something or does it pass through something and secure with a nut? If it is secured with a nut you are safe as long as there is a thread or two visible after the nut is installed.

If it is threaded into something I would err on the safe side and find the correct length. Or find one that is too long and cut it to length with a hacksaw, then carefully file the threads on the end into the right shape. A small triangular file works fine for this purpose. All of this takes more time but a bolt that breaks or pulls the threads our because it is too short could end up taking a lot more time and money.

In both cases pay attention to whether or not the original bolt has an area that is not threaded. If so try to find one that is the same - the area without threads is stronger and sometimes the extra strength is important, especially in shear loading situations.

 

[Tree Trimmer]

That's interesting. The shorter bolt in question and the original have the unthreaded area. The bolt I mentioned above is to bolt the front drive member into the hub. If I heard the guy at the fastener store right the original was a 45 mm and he only had 40 mm in 10.9 as the original. The other bolt also has the unthreaded area and is the one I really need to replace a broken one. The one for the top swivil pin. Again IIRC the original measured 35 mm. I knew I could cut the 40 mm if necessary. I was just going to replace the drive member bolts for the heck of it. I still have all the originals to use back.

All call for loctite and specific torque. Holding the bolts side by side, the length difference seems small, but since I know everything is engineered to certain specifications I just wanted a "learned" opinion.

Thanks,
Tim

 

[RichardS]

The bolts that hold the drive member to the hub are pretty much in a pure shear situation so the length of the threads, or number of threads engaged, is not going to be as critical there. The presence of an unthreaded portion of shank is important - for best trength there should be no threads close the the interface between the drive member and hub, that's where the shear load is the greatest.

Since you have the stock bolts I'd say reuse them. If you were in a bind you could get by with pretty much anything close since there are 5 bolts there sharing the load. You could even just leave one out for a while. But I would not replace all of them with something of different spec than the stock bolts and leave it that way long term.

The loading on the top swivel pin bolts is not so clear to me. There's definititely some potential shear but IIRC the parts are flanged where they fit together and that would greatly reduce the shear load. I think in this case the tension load may be more important, and therfore the number of threads that are engaged would be more important. I would go with the 5mm longer 10.9 bolt there to be safe. Shorter might work but could really make for a bad day if it failed.

 

[Tree Trimmer]

Thanks for the advice.

Tim