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MG MGA - Help - seat belt mounting dimensions
|Hi all. I am designing an upper seat belt mounting that will bolt directly to the wing mounting bolts. |
I did not think about welding the MKII mounting before painting the car!!
I know others have done this but these typically have the fixing point too low. The modern international standard is that the fixing point is a minimum of 450mm above the seat. This distance ensures that the belt does not slip off the shoulder. It is hard to get the mounting that high and the original MKII point is only just higher than this. Mounting on the wheel arch is much too low and would not meet modern safety standards.
I have designed a mounting and have had it stress analysed and have tested its strength in a laboratory. I will give Barney the details for his site. The current design withstood 30KN which is 3 tons, before one of the bolts sheared. The standard test is 13KN and it is therefore a bit over engineered and I plan to make another one with slightly thinner steel and see how it performs.
Where I would like need your help is getting a better knowledge of the position of the bulkhead behind the wing mounting bolts on various cars. I expect there will be quite a variation in the tolerance on different cars.
Could some of you do a little exercise for me? Could you measure the distance of the bulkhead behind the 2 wing fixing bolts centreline. This is a bit tricky to do with a tape measure. The best way to do it is to use a piece of card, cereal packet top is ideal. Push the card over the two bolt heads and through the gap at the end of the bulkhead. If they are pointed bolts its easier. Then draw a line up the bulkhead inside the cockpit on the card.
You can then take the card away and measure it on a desk. I would like to know the distance from the centre of the rear wing fixing in the cockpit and the bulkhead along the centre line of fixing bolts. If you can measure the angle of the bulkhead to that centre line as well that would be great.
The picture shows a piece of card I have used for the right hand side. On my car 'the distance is 16.5mm and the angle is 71 degrees, see picture.
Chassis no. 95194
N/S 17 +/- 0.5 mm 68 deg
O/S 16 +/- 0.5 mm 72 deg
Measurement tolerance on angle probably 1 - 2 deg...................................Mike
|Mike thanks. Can anyone else help with this simple survey. Thanks|
Left side 23mm, 75 degrees
Right side 9mm, 75 degrees
Chassis No. 55600
Car was rolled racing in California which could account for the variation. Never noticed the difference before. Could it have come out of the factory with that difference?
The 9mm is very small! That would foul the current bracket design. Does the circular weld nut for the wing mounting go past the bulkhead. It is about 20mm diameter?
I will have a look in the morning.
I also have been working on an upper mount for the shoulder belt for my MGA roadster, #73029 which is an earlier 1600. I decided not to use the Mark II mount as it interferes with the side curtain pouch and instead, opted to check the fender bolts to see how the angle across the shoulder would work out with that upper mount position. Also of concern was to check the top (hood) frame for belt interference with the frame up and when folded.
I found that locating the upper belt mount on a vertical plate attached to the two fender bolts provides a very good position across the top of the shoulder. The lower out-board belt does need to be disconnected and the belt "threaded" over the top frame when folded and under the frame when the top is erected. The "original-style" quick release outboard belt mount makes this repositioning very easy. Very high quality reproductions of the lower outboard mount and the frame attachment are available through Todd Clarke at Clarke Spares in the U.S.
Per your question, I made a template for comparison (actually three templates - photo included). The measurements and angle are as shown. This car has had no body damage to that area and is as original.
One cautionary note. The seatbelt latch will be attached to the inboard mounting anchor and it is very important that the length of the inboard belt is adjusted "short" so that the latch and lower attachment point for the shoulder belt is as low as possible. For the lap and shoulder belts to secure a passenger properly, the upper belt needs to come across the top of the shoulder, cross the chest and abdomen and attach to the lap belt as close as possible to the hip bone. It is a good idea to check the passenger to see that the lap belt is low and tight and that the shoulder belt attaches as low and far as possible to the side of the hip.
In summary, the upper mount location will work very well and should provide an extra measure of passenger protection. The only drawback is that a sudden rain shower will leave the occupants exposed a bit longer while the belts are relocated around the top frame!
I hope this helps you!
|The wing slots are quite long at 7/8" so with a 5/16" screw there could have been a +/- 7mm spread on the positioning of the welded nut. If the 'correct' point is 16mm from the bulkhead then this would give a spread of 9 to 23 mm which covers both of Steve's positions. All this assumes no variation in bulkhead positioning...................Mike|
All measurements of the captive nuts are symmetric so any problems are with the bulkhead positioning, either as fitted by the factory or as a result of accident repair from being rolled - which is possible.
I can find no evidence of previous welding marks. The only thing I can see is perhaps a slightly distorted bulkhead upper attachment bracket. If I straighten it I may be able to pull the top of the bulkhead back a smidge, but that will do nothing for its attachment to the floor.
You can see my present arrangement. Barry Gannon welded a strengthening plate in position for me - covered by the carpet. There is also a plate on the other side of the inner wing. If I have the lap strap (anchored to the tunnel wall with similar plates) short enough I do not suffer too much with the diagonal slipping off the shoulder, but it can be an issue from time to time. The biggest problem I find is that I have to release the tonneau turnbuckle securing point and fold the corner of the tonneau to enable routing of the diagonal strap. This problem goes away if you remove the tonneau when driving. I always keep it attached, folded behind the seats.
Piccy attached of the bulkhead.
I have been doing some more measurements. The bottom edge of my bulkhead is square. i.e. the right and left bottom ends are equidistant from the front edge of the battery box vertical (wooden) bulkhead.
Therefore, all the errors generated in the measurements I previously supplied to you are caused by the 2 angle brackets that secure the bulkhead to the underside of the rear tonneau panel - the brackets are welded to the top struts but secured by bolts to the bulkhead. In my opinion, any variances given to you by other users could be down to these 2 brackets being bent/distorted or having elongated attachment holes. I will have a go making good and let you know the result.
This thread was discussed between 27/03/2011 and 30/03/2011
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