Can anyone provide me with the basic dimensions (A, B & C below) of the floorboards for an OTS XK120? Thank you in advance!
I measure:
A 20 7/16"
B 48 1/2"
C 14 3/4"
Board thickness measures 5/16".
All measurements taken from a new pair of floorboards sold to me sometime after Moss took over XK Unlimited’s parts business. They were advertised as being made of Baltic birch.
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I would say board thickness of 3/8 inch 8-9mm
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Agreed, but that’s what Moss is carrying.
5/16” is definitely light. 3/8” is better, but still light. I compared my replacement floorboards with the ratty originals when I acquired them 30 years ago and remember them to be ringers. They are made from 9-ply, 12 mm Baltic Birch plywood. That’s just shy of a half inch thick. They do sit slightly proud of the sills, though, so it could be 7-ply, 9 mm plywood was standard.
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Since local availability is going to play a large part in the decision, I think this is what I am leaning towards. Roughly 7/16" thick.
You will be better off with Baltic birch rather than fir plywood, Mike. It’s extremely strong and stiff and resistant to delamination, which is what you want for floorboards. A quick Google search indicates Distributor Service Inc. in Louisville carries it - they’re a wholesaler so may not be keen on selling a single sheet, though. The other thing you’ll have to figure out is the pattern, allowing for the gearbox/driveshaft tunnels to be bolted down accurately (tee-nuts on the underside), placement of the jackhole covers and clearance for the handbrake.
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The original plywood panels on my FHC floor are 7 ply 3/8" thick.
Same with my original trunk floor panels.
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The current problem with Baltic Birch is that apparently most of it was made in Russia. Not sure if it can currently even be imported into the US? Can it be that much better than Marine Grade? They seem share a lot of same technical attributes.
Do the floorboards have a clear span from the sill to the tunnel flange, or do they bear on the frame rails? 1/4" battens standing in for floors here.
Where they pass over the frame rails clearance is so close that there’s supposed to be thick strips of felt between rails and floorboards keeping them sandwiched in place. I’m guessing 1/8" to 1/4"? Someone here may have a more exact answer. Regardless, felt wicks up moisture leading to rust so it’s your call whether to remain authentic or not.
BTW, if you don’t already have this Mike (thanks to whoever originally posted it) you may find it useful for when you finally secure the floorboards with fasteners:
And don’t forget the heat shield that’s secured to the underside of the driver’s (LHD) side floorboard above the exhaust.
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I would not hesitate in using marine plywood but would suggest that you coat it with 2 coats of marine epoxy before painting. (Westwood makes a great one). 40 years ago I fabricated a third pontoon for a 20 foot derelict pontoon boat that I bought from a neighbor. Money was short back then so I built it out of construction fir plywood and spruce dimensional lumber. It was then epoxy coated on the outside and tar coated on the interior. We used the boat for a number of years and then sold it to a relative who then sold it to a friend. To my knowledge it is still water tight and rot free.
If you do a careful coating of a marine spec plywood the floorboards will still be good when that car is next torn apart and restored.
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I bought a couple of sheets 2, 3 years ago that came from Finland. I didn’t notice your link was to marine grade plywood. It should be a very good substitute, though it costs more. I checked my boot boards and they are as Rob describes - 3/8” (9 mm) thick 7 ply. I expect my 12 mm 9 ply floorboards are over spec - very solid, though.
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I was thinking North American marine grade would be keeping some Canadian lumbermen employed! 
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Well, then, that’s very considerate of you. My first job for a couple of years on graduating from university was logging, so I can appreciate the sentiment! 
3/8 inches = 9.525 millimeters
there are 3 grades of ply with various face qualities for cabinet making
basically interior
exterior and marine grade marine grade on floors given its specification is it won’t delaminate if immersed in boiling water for 24 hours.
It appears to have been painted at the factory with a black wash type fluid not paint as such maybe turps with bitumen in it ?
Locally, I’m finding 2 levels of marine grade, standard and Lloyds BS-1088 Certified. The standard marine grade available off the shelf in 1/2" (12mm) and in 3/8" by special order. The BS-1088 is 7 ply, but only available in 1/2" and is special order.
I’m not exceptionally concerned about floorboard water resistance. For one thing, they are easy to fabricate and easy to replace. I have an 07 E86 BMW Z4 coupe that’s only been driven in the rain twice in the last 15 years.
Mike, how deep is the floorboard recess along each of your sills? Something to factor in for if your boards then end up being too thick along with the addition of carpeting and chrome strip – making for a possible clearance issue with the underside of the doors (?)
Almost exactly 3/8". I’m leaning toward just ordering a 4x8 sheet of the 3/8" standard marine grade plywood. It’s less than a hundred bucks.
