Bench Seat Plywood Dimensions

[s2europa]

Recently acquired a 1964 Seven S2 race car that came with vintage type racing seats. I do not fit in the seats and would like to reinstall the stock bench seats (which will allow me to fit down in the car), which the car did not come with. Does anyone have the dimensions for the seat back and seat bottoms plywood blanks? I am planning to buy the bench seat vinyl kit from Redline Components and want to make sure I have the correct size pieces. Thanks.

[11Budlite]

I'm not sure where I got this drawing from, but it could have been from a member here. I'm thinking it could have been Al N when he was restoring his old S2.

[s2europa]

Thank you. This is great. I'll cut out some cardboard versions and try it out.

[EdWills]

Hi.  I think you'll find that those measurements came from Mick Beveridge at Xtra Special Sevens (now sadly out of business).  Tony Ingram was importing the seat covers in the U.S. sewn up by Mick's wife, but Tony notes on his website that he is out of the covers.  Tony would be able to confirm measurements for you though, as he has rebuilt his own Series 2.  

 

Cardboard cut-outs are a very good idea, as in some cases Caterham specified slightly different prop shaft tunnel widths from Arch depending on the chassis.  In one case the prop shaft tunnel was 6 inches wide (seats were 15-1/2 inches wide + 6 inch tunnel width, and 1 inch x 2 lower side tubes to produce 39 inches wide total chassis width (Imperial Lotus measurement chassis built on original Lotus Seven jig).  Arch (Bruce Robinson) advised me that the tunnel could be 5 inches wide (old Lotus chassis measurement) and therefore the seats could be 16 inches wide.  Bruce provided another possible measurement that 5-1/2 inch tunnel width had been used, so there seems to have been enough variations for the need to make up a good template for your particular chassis.  Don't forget to allow for the thickness of the seat material all around (to fit inside the chassis snuggly) when cutting out the plywood.  5/16 inch thick ply seems to be good, but perhaps 1/4 inch would be o.k.?  In Canada we can get nice Baltic ply and also waterproof ply (not just for boat use) but expensive these days.  I've asked on another Lotus Seven forum what comes first (not the chicken or the egg!), but does the seat back fit over the seat squab, or does the seat squab go in last to secure the bottom of the seat back in place?  If the seat back fits over the seat squab, it might sit too high for seat belt mounts behind the seat back. (61 centimetres in the drawing equal to 24 inches - 60.3 centimetres drops 1/4 inch off this measurement). Mick's 91.5 centimetres seat back width equals 36 inches, so with the chassis rails of 1 inch each side for a total of 39 inches (this measurement was confirmed on my 1969 Lotus Seven chassis as well on various Seven diagrams on the web), there is a slight gap of 1/2 inch each side of the seat back which is o.k. with the seat cover material taking up the gap.  Mick used double stacked foam to produce the raised front section of the seat squabs.  Lotus had their seat manufacturer produce a one piece wedge for the front, but unless you happen to have a hot wire cutter (or can make one?), stacking 2 foam pieces may be easier.  Good luck with your upholstery project.  Check Tony Ingram's site as it shows the seat covers that Mick produced for the Series 2. Cheers EW

[IamScotticus]

Too thin a backing wood will warp and bow from the cover when it shrinks, or if covered to taught.  I estimate my back squab wood to be 3/8", 10mm.  The back seat is very warped from age and bad storage practices.  Fortunately it didn't bow laterally and is usable as is.

 

I measured my Cat squab back to be 24" tall.  I measured my rear seat bulkhead to be 24" from top of top square chassis tube to top of bottom square chassis tube. 

The bottom seat squab sits afore of the seat back cushion.  I would suggest some Velcro to keep the top secured.

 

61 cm = 24", very close to the Lotus spec.

Edited December 24, 2024 by IamScotticus

[EdWills]

Your choice of course, but 3/8 inch thick ply may be a tad too thick, and can still warp. To avoid the possibility of warpage (wood has a mind of its own as we have all experienced probably?), you can use varnish or paint to seal the ply, on each side and the edges.  No guarantees it won't warp, but worth doing.  Water based varnish or paint will raise the surface structure of the wood, so sanding may be required after treatment.  Lotus used a black painted thin ply sheet for the boot top also.  On my old seats, 1/4 inch ply was used by the Lotus seat manufacturer.  The previous owner discarded the wood boot top, and used sheet aluminum instead.  

 

I used a hand stapler to reattach my seat covers as the original wooden base was starting to rot and develop mold (mould?).  I used 3/8 inch staples through the seat covers into the varnished ply.

 

Scott, on your chassis, and on my new one, Arch welded in a 1 inch square tube at the bottom of where the seat back rests, but Lotus never included this in the Series 2 or 3, so if this extra tube it fitted, it may force the bottom of the seat back forward a little bit.  If refitting used seats to a chassis that has this tube added, it will mean that the length of the seat squabs may require adjustment (slight shortening) either at the front 'tabs' or in the total length starting at the back.  For all of the suggested 5.7 cm inside radii, a 2 inch hole saw does the trick. EW

[MV8]

Also a good idea with vinyl to use a hole saw to port the wood backing here and there, to prevent damage from a person jumping in so the air in the foam has an exit versus ballooning the cover.

 

For a more secure back, there are nut inserts for wood that go in from the foam side to accept a #12 screw and fender washer. Just need to ensure the screw is just long enough for the threads to be flush with the nut when tight.

Edited December 24, 2024 by MV8

[IamScotticus]

GT40 grommet covers will fix that.  Trying to find it for squab builds

Edited December 24, 2024 by IamScotticus

[EdWills]

On 12/24/2024 at 1:11 PM, MV8 said:

Also a good idea with vinyl to use a hole saw to port the wood backing here and there, to prevent damage from a person jumping in so the air in the foam has an exit versus ballooning the cover.

 

For a more secure back, there are nut inserts for wood that go in from the foam side to accept a #12 screw and fender washer. Just need to ensure the screw is just long enough for the threads to be flush with the nut when tight.

Hi MV8.

A very good idea if the seat cover manufacturer has not included mesh vent ports in the sides of the seat squabs.  A few years ago, a very helpful Seven owner in the U.K. (via the lotus@se7ens forum) introduced me to a U.K. seat manufacturer called Aldridge, who also produced manufactured seat covers for Europas and Elans. After producing the seat covers for the U.K. Seven owner, and myself, the company advised that due to the time it took to produce them, and the labour involved, they politely advised that they would not be doing it again.  But - perhaps they may be persuaded to reconsider?  They sourced the identical vented basket weave vinyl as used by Lotus, and hot melted the exact same seams into the material.  Round brass vents were added to the squab sides.  Failing Aldridge, the Caterham U.K. seat manufacturer - Oxted Trimming - may be a good choice. EW

[EdWills]

Just a P.S.  Not sure why Mick drew the Series 3 seats without the front wooden seat 'tabs' (and produced them 1 inch shorter) as my Series 3 certainly had the wooden plywood extensions on the front and exposed to the elements.  I have seen an alternative type of seat squab on later produced Series 3 cars, so obviously the seat manufacturers at the time made slight design changes.  EW

[wobblyweb]

I asked Mick if he could miss out the large cut-outs for seatbelts. I drew a small taper to the rear to  make room for them.

For comfort I also went for the longer S3 type but don't think it makes any difference. 

The foam is also a bit squashy and flattens after a few hours driving, I would try memory foam if made again.

On mine the rear goes down to the cockpit floor with the squab in front.