belt relocation

[John Robinson]

Looking for some advice here, I need to relocate the mounting location for shoulder harnesses. According to the formula that came with the new hans/Schroth belts. I need to move the locations closer to each other. The original mounts are sleeves welded to the cross braces coming from the roll hoop to side bars. Will it be ok to drill those tubes and weld sleeves inside them? Otherwise it will require pulling fuel cell and all sheet metal from rear bulkhead in order to get access to weld tubes to back side like original.

TIA
John

[Mike Scanlan]

John
That's exactly what I did on my DB-1, it worked well and cleared tech no problem. We just welded a sleeve to the existing mount in order to lower it into position.

[John Robinson]

Mike,
After re-reading my post it might be unclear as to what I need to do. I need to bring the mounting points closer to each other as well as lower them. I want to drill the brace and weld sleeves there. I think this will be ok, but just wanted to throw it out there and get other opinions.

Thanks,
John

[SteveG]

John,

This exact discussion took place in FF:Chassis under the topic "Drilling crossmember for belts". (I should take the time to figure out how to post a link to another topic)

Steve

[cliff]

John, not sure where you are on this deal, but I had a second set of sleeves welded on that cross brace inside the original, as in closer to the center. I had used a HANS and the belts were slipping off. I remember asking someone and their advice was to not drill that tube and at the time I remember why and it made sense.

[John Robinson]

Cliff,
I would be interested in hearing why not to drill those tubes. I was just about to drill and weld in sleeves, as this seemed the most logical thing to do. If I remember correctly, in order to get the belts close enough together, I would have to place the tubes as far back as possible and wasnt happy with how it wopuld be welded in.

Steve,
I re-read the previous post and it isnt exactly the same situation. I cant add the piece in like Dave was refering to.

thanks

john

[cliff]

John
Too many brain cells have been lost since then, I just don't remember. I know the car was stripped down at the time and maybe it was just as easy to do it like the original. I looked last night and they are about 1.75 inches further back on that chassis tube towards the center on each side. I know I had to whittle into the tin that surrounds the fuel cell as the top is right in the way.

[DaveW]

The obvious problem with putting new mounting holes closer together in the original tube is increased bending moment on the tube. If the tube is only supported at the ends, then mounting closer to the center (further from the ends) puts more bending stress on the tube. If the tube had enough safety margin originally, this could be OK. However, if the original tube is not strong enough, it could bend or tear in an impact if the new mounting points overstress it.

[cliff]

In this case there is a diagonal chassis rail on each side that angles back to an upper chassis cross member, so all we are doing is moving the mounting back on its respective rail, either the left rail or the right side rail, not closer to the center of one rail, and further back is closer to the center of the car, which is the goal. If there is no rule against it, you would actually be drilling closer to the point at which that tube connects to that rear upper frame rail and further from the center so it would be stronger than the original location, had they
done it that way. The original mounting is a small vertical tube welded to the back side of this angled-back chassis rail, that you drop a bolt thru and bolt up the metal end of the belt. What John is asking is can he drill a hole thru that same chassis rail and weld in a sleeve instead of welding a new vertical tube in the new position.

[DaveW]

If I remember this correctly, a possible problem with that may be a rule clarification (came out this past year?) that I think said that belts could not extend into fire-prone areas outside the cockpit where they could melt or deteriorate from the heat. You may have to make the firewall extend back to cover them.

[John Robinson]

Dave,
the tubes are cross braces that goes from the center of the brace between the roll hoop legs to the top frame rail members. The down tubes from the roll hoop also attach on these tubes near the frame rails. The mounting brackets for the harness are sleeves that are welded to the back of the cross braces. They are located approx center on the cross braces. In order to move the mounting points closer together. I need to either move the sleeves back almost against the fire wall or place them thru the cross braces not as far back. I would think that placing sleeves thru the tubes would be stronger then welding them behind, but maybe not...that is why I asked.

Thanks

John

[DaveW]

Since the frame tubes are supported in the middle, I see no harm in welding the belt attachments through the tubes as long as they are structurally sound (welded all the way around on both ends and sides if necessary). As you state, it might be a more structurally sound belt anchor.

[John Robinson]

thanks Dave, I also sent some pics to Richard Pare and he agrees. Should be acceptable and maybe even stronger.

John