How many bonnet shims?

I am fitting the bonnet on my S1. I replaced the center panel and both wings, so I will need to cut some off because they are all different lengths. I am planning to shim the bonnet forward enough so I can get the bonnet seated without fouling the bulkhead, which I am calculating at around 3/4" of shims. Then I can just mark the bonnet across for cutting.

So is there an “ideal” number of shims to be left with after cutting? The difference in length between the two fenders is 7/16 so that’s the minimum I must cut off the longer fender, then I could use 5/16" of shim to create the gap between bulkhead and bonnet. I could go to zero shims, if that were desirable for some reason. Maybe I need the most shims I can get to give me more room, like for the radiator or something.

Any other considerations?? Cutting this thing is going to be a stress event!

John North
S2 Coupe

Use the number of shims needed to line up the wheel well arc with the end of the sill panel and them trim from there.


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Curious if you left on board the shimmed brackets when removing bonnet.

'66 fhc

the rear of the wheel well on the wings must line up with the sill, a nice smooth transition,
I would want to end up with at least 2 or 3 shims so you have some adjustment. also shims come in different thicknesses. remember the front of the bonnet height is also adjusted by shims. and the wings must be level with the sill. and the horizontal gap should be established.

the top of the bonnet must also be level with the top of the bulkhead, I would install the rubber seal on the bulkhead.

I layed a 6 ft straight edge along the side of the body and bonnet on both sides to make sure the bonnet was sitting straight to the body, adjusting with shims to get it straight.

on cutting the back of the bonnet to fit the bulkhead, I used a tape line for a cutting mark

and never tried to cut it in one go. but eased into it and readjusted the bonnet, and then cut again, watching all the alignment points, when it was close I chose my gap width and put tape down and rechecked all alighnments again. I used a small air powered cutting wheel . and made my cut just shy of my desired line, then finished up with a file and a orbital sander to really dial it in, gaps must be all nice and even for it to be e type worthy Roger

Here’s how I tackled it. I was working with a restored tub, new frames, old bonnet frame and a new bonnet assembled from donor bonnets. None of these components had ever been fitted together before so I was in for a challenge. I purchased 1/2" of shims for all 4 shim areas. That is; QTY 8 X 1/8" of one type and QTY 8 X 1/8" of the other. They’re not too expensive and I figured it was a good starting point. I also purchased QTY 4 X 1/16" of each type to fine tune. First I found and drew a center line down the tub, then the same on the bonnet. I figured it should all start with the bonnet in the center and going down the road in a straight line with the car. When I first mounted the bonnet it was off about 3/4" toward the LH side. I worked at adding shims until I centered it. In my case I needed 1/4" more shims to raise the LH side than the RH side. I think that happened because my bonnet frame was the only old part I reused and I think it had been bent slightly down on the LH side. Nevertheless it worked out and I only had about 4 shims left over. When I was satisfied with the alignment of the wheel wells and the wings to sills, I temporarily installed the landing rubber gasket and only then did I do a slight amount of trimming (slowly) to dial it in. I hope that helps.

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John Wrote:

I am planning to shim the bonnet forward enough so I can get the bonnet seated without fouling the bulkhead, which I am calculating at around 3/4" of shims. Then I can just mark the bonnet across for cutting.

Hello John,
You wont be able to fit 3/4" of shims. There is a finite amount of shims you can fit, as the bolts securing the bonnet screw into plates that are held inside cages. Accordingly, you can only fit shims to the extent that the cage and the holes in the component of the lower valance through which the bolts pass, will permit.

You want to have some shims to allow final, fine adjustment. When fitting a new bonnet, I aim for around 6mm of shims, which will allow give and take should it be required in the future.



Easy answer, NO!

Bonnet builds and bulkhead/firewall dimensions are not consistent 50 years on, most of the people here, have had their car apart and tweaked in some way, so much as not go be a stock example.

If per chance, you do find a half a dozen low mileage examples that haven’t been involved in a shunt, I’d wager they wouldn’t have the same amount of shims. There are just too many variables.