mx5cartalk.com

Hi every one,
I thought I would start a thread for this so that it will be easy to find for others who encounter the same problems, and so that it doesn't clog up my build thread.

I have got 2 sparco sprint jnr's which will both be put into my 96 NA8.





One of the seats came with an na6 rail already mounted and ready to bolt into my car (there are plenty of threads on this)

As most of us would know, the NA6 seat belt receiver (stalk) is not mounted to the rails, but to the transmission tunnel.
However, Na8's seat belt receivers are mounted to the rails like so.




After searching for info it seems that it it not possible to mount the sparco seats onto na8 rails without cutting off the seat belt receiver mounts (essesntially turning the na8 rails into na6 rails).
Therefore, the seat belt stalk (receiver) can no longer be mounted to the rails as they come factory if you want to run a sparco seat.
So, most people get hold of an na6 seatbelt stalk and bolt it to the transmission tunnel like this.



However, when doing this the na6 belt stalk sits above the opening of the sparco which is designed for the belt to go through.



This means that the belt will not sit snug over your hips.



This can cause 'submarining' in the event of an accident and I believe is very unsafe.


However, even if I wanted to roll like this ^ my na8 does not have the ability to mount na6 belt stalks in the same spot on the transmission tunnel.

I believe most na8's (up to '95 models) still have the mounting points for the na6 belt stalks.
However my '96 na8 does not.


1 = where the na6 seatbelt stalk mount should be. However mine is just a hole with no thread etc.
2 = where part of the na8 rail bolts to
3 = the rear left seat rail bolt thread.

If I was to mount the na6 seatbelt stalk to the threaded hole in my transmission tunnel i still encounter the same problem of not being able to utilise the seatbelt opening in the seat.

So, atleast for now I have mounted the na8 seatbelt receiver (stalk) to the rail mounting point (2) in my trans tunnel.




This means that the belt is able to go through the seat as such (fitting much tighter and preventing sliding out from under it (submarining)




I am fairly sure that the mounting point for the na8 seatbelt rails (2) (where my seatbelt receiver is now mounted) is the same as the na6 seatbelt stalk mounting point (1), but just in a different spot. Therefore, my logic says that it should be just as strong and just as safe. Certainly safer than not having the belt around your hips.

Maybe I am missing something? Maybe some one knows something I dont, or has a better way of going about things?

(harness problem to follow)

RileyR wrote:However, when doing this the na6 belt stalk sits above the opening of the sparco which is designed for the belt to go through.



This means that the belt will not sit snug over your hips.

Maybe I am missing something? Maybe some one knows something I dont, or has a better way of going about things?

Just poke the end of the seatbelt stalk through the belt opening in the seat before you bolt the stalk in..?

yeah it looks like some people remove the plastic cover off the belt part (not the locking mechanism) and do just that.
Would work great if I had the na6 mounting point.

Can any one confirm that the na8 rail mounting point (2) (where my buckle is bolted into) has the same structural integrity as the stock na6 mounting point (1) - (which mine does not have)

Here is a picture of the underside of the transmission tunnel where my seatbelt is currently mounted.
That bolt is the one protruding through #2
You can see a small diameter round backing plate there. I am wondering if the na6 seatbelt stalk mount (where #1 is) has the same backing plate. If it does then it would make my #2 mounting point the same strength as na6's stock seatbelt stalk mounting point (1)?





If not, I will have to get a backing plate like this one below and i would buy 2 new na6 stalks from mx5+ and take the plastic off the stalks so that it can be fed through the side of the sparco.

RileyR wrote:yeah it looks like some people remove the plastic cover off the belt part (not the locking mechanism) and do just that.

Think what Rascal's suggesting is before bolting to the trans runnel, try feeding the other end through from the inside of the seat, which might negate the need to remove the plastic cover if the stalk is long enough to still attach to the top rear of the trans tunnel, depending on how far you have the seat forward to drive.

93_Clubman wrote:

RileyR wrote:yeah it looks like some people remove the plastic cover off the belt part (not the locking mechanism) and do just that.

Think what Rascal's suggesting is before bolting to the trans runnel, try feeding the other end through from the inside of the seat, which might negate the need to remove the plastic cover if the stalk is long enough to still attach to the top rear of the trans tunnel, depending on how far you have the seat forward to drive.

I could probably give it a go, though I dont mind the current position of the seatbelt receiver, and by using the same mount point its much of a muchness. Im more concerned with whether the mounting point currently used is as strong as the na6 mounting point.

I have done the drill and spreader plate method on my NB so that I could use an NA6 stalk.
it works fine, and my theory is that if the plate (and the proper high tensile bolt, not just a random one) are able to support a harness belt at race speeds, it should work fine for a seatbelt at road speeds.

The submarining part can be solved by gaining weight until the buckle is on your lap.


But yeah, I had much the same issue (fitment) with my NB so I just drilled the tunnel and fitted the plate where needed. (NB has no holes at all there)

The stalk not fitting the seat hole part was something I just ignored, I now have a different fixed back which doesnt have the issue.

RileyR wrote:Im more concerned with whether the mounting point currently used is as strong as the na6 mounting point.

Yeah, been having a look at that. Also recalled hks_kansei posting about fitting an NA6 stalk to his NB8A & using a spreader plate, so also looking for that: viewtopic.php?f=28&t=68327

NA8 seatbelt receiver is attached to a bracket (that the side rail simply slides through), which in turn appears to be attached to the seat base. So it would seem to rely more on the seat floor mounts as anchor points. But given the type & size of bolt & captive nut used to secure the sliding side rail to the top rear of the trans tunnel, it's meant to take some force. Perhaps you could strengthen it by putting a spreader plate & captive nut behind it & if necessary using a slightly longer bolt.

I have an NB so I had that problem with the short, solid stalk.

I got hold of a pair of NA type with the fabric stalk and bolted them to the seat brackets. That allowed the stalk to slip through the belt holes on the seat, and it would move with the seat rather than be fixed to the transmission tunnel.

So with your concerns about "submarining", are you going to install/use those 4-point harnesses?

So the verdict is in about whether or not my current seat belt receiver mounting point is the same as the na6. A mate sent me a photo.

Here is the na6 mounting point - there is a spreader plate there unlike the #2 above.



So the answer is no its not.

I have ordered 65x65mm spreader plates, all eye bolts and new seat belt stalks. The seat belts that I have in there are next to new from seatsafe - and they make A LOT of different receivers. Im going with a shorter stalk than the stock na6 stalks so I can feed the belt rather than the stalk through the seat.

Steampunk wrote:So with your concerns about "submarining", are you going to install/use those 4-point harnesses?

Yes I certainly am when the belt isnt around my hips. Its so loose when mounted like that that I can slide under it to get out of the belt instead of unbuckling it.
The 4pt harnesses came with the seats, so I will use them. They will be very low and very tight when im on the track. That has to be a lot safer than the standard lap sash belt.

RileyR wrote: They will be very low and very tight when im on the track. That has to be a lot safer than the standard lap sash belt.

That's what I, and countless others before, thought, but when you cinch them up the shoulder belts pull the lap belt on or above your stomach.
Have a look around the net. 4-points are pure show, and considerably more unsafe than the standard lap-sash.

The Sparco harness on the left of picture appear to be authentic so check the buckle, if it has a provision for a 5th belt at the bottom then that's the fix, buy the lower "crotch" belt so it becomes a 5 or 6-point harness. This crotch belt is what secures the lap belt from riding up.

Steampunk wrote:That's what I, and countless others before, thought, but when you cinch them up the shoulder belts pull the lap belt on or above your stomach.
Have a look around the net. 4-points are pure show, and considerably more unsafe than the standard lap-sash.

The Sparco harness on the left of picture appear to be authentic so check the buckle, if it has a provision for a 5th belt at the bottom then that's the fix, buy the lower "crotch" belt so it becomes a 5 or 6-point harness. This crotch belt is what secures the lap belt from riding up.

I had read that 5pt harnesses were safer than 4pt harnesses, though I hadnt read that 4pt harnesses were less safe than lap sash belts.

The buckle has the provision for a 5th belt. However, the seats dont have the opening for the crotch strap. Could I sill run a crotch strap without the opening? I can see that some people do.

I could quite easily make a hole in the sparco jnr's in the same place that the sparco v's have their opening. I would not be cutting anything vital for the seat to function, just the very outer fabric. The crotch strap would pass in between anything vital (as pictured)

I would re-enforce the hole with a vinyl, canvass or leather patch underneath just so it wont tear or deteriorate from daily use. The GF is pretty handy these kinds of things.



Thoughts?