To seal or not to seal. Refitting of subframes

[Ropariva]

Well, its time to refit my subframes back onto the tub.
When they were removed there was quite a lot of sealant (dum dum?) around the joints at the fire wall
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Not only was the dumdum around the edges, but it also looked to be between the frames and the bulkhead. This appears to have done a reasonable job of keeping dirt and moisture out of the joints.
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Side by side pic. Trial fit of sub frames minus sealant.They weren't particularly careful back in 1970 :-)
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My question is this, should the sealant be replaced with a modern equivalent, or should the sub frames just be bolted direct to the firewall dry? I haven't seen this mentioned before so am hoping to get some consensus on what is considered best.
As a supplementary question, what is the general feeling about flat washers under the bolt heads? A number of the bolts screw directly into captive plates and so could likely damage paint when being tensioned.

Appreciate any feedback,

Alan

[christopher storey]

I would not use any sealant under the frame mating surfaces - it will seriously affect the fit of the frames and possibly the front suspension geometry

[Heuer]

Agree with Christopher - you need metal to metal contact. Also the DumDum gasket will creep under driving conditions leaving the frames loose. The E-Type is not a particularly rigid car any way so this is going to make things worse!

[rfs1957]

Shame to p--- on Alan's bonfire. Nothing wrong with the principle - sandwiched areas like these often reveal horrors later - just ask Mini-owners about the gussets next to the front cone bolts. A semi-soft gasket cement like Hylomar will be squeezed to zero in a context like this, and keep water out. We use a big dollop of Waxoyl or similar soft oily wax, and wipe off the excess. Bolt head; every single one should have a flat washer under the head. And every bolt on the car should be greased before assembly, just ask us motorcyclists ..............

[KingRichard]

Mine also had the sealant between frames and bulkhead as OP showed. I put some Sikaflex 221 between them when refitting. I had some left from rebuilding the bonnet, and thought wise to put some sealant to prevent rust.

Better to remove it when engine is out, I guess :? ?

Regards,
Richard

I would not use any sealant under the frame mating surfaces - it will seriously affect the fit of the frames and possibly the front suspension geometry

[Moeregaard]

I used some non-hardening Permatex when I reinstalled the subframe on my '65, back in 1991. I figured that paint-on-paint contact would soon lead to steel-on-steel contact, with corrosion being the eventual result. Jaguar's use of sealants must have come along later, because I don't recall finding any when I dismantled the car.

[norman m. macleod]

Christopher and David are correct. The frame end connection plates to the bulkhead should be virtually metal to metal, as is good structural practice. Anything more than the metal primer is not recommended, in fact the end faces should be masked off if painting or re-painting. Anything between these faces will encourage movement over time.
As for washers, these should not be used under the bolt heads. If the correct class 5 (or better) bolts are used, there is a narrow machined circular step below the head. It is there for a reason. The only washers used are on the inside of the bulkhead (for the through bolts), and under locknuts. Anyone still unconvinced should check with:-
(a) The Jaguar Spare Parts Catalogue, or
(b) Uryk at E-Type Fabs, who makes the best replacement frames on the planet, with bolt kits.....
If anyone, despite the foregoing, insists on putting washers under the bolt heads, the use of hardened and tempered structural washers is an option. Expensive, and quite unnecessary, but it may help them to sleep at nights..

[rfs1957]

Great to find so much useful and innovative information all in one place - shades of the famous PTFE-on-brake-fittings debate !

Where I live, the machined step under bolt heads is insufficient to keep the corners of the rotating hex from chewing up paint.

If it is acceptable to use washers (that are neither hardened nor tempered) under nuts, then, could someone explain what objection there might be to using the same washers on the other end, under bolt heads ?

[PeterCrespin]

The purpose of the frame clamping system, however configured, is not primarily to protect paintwork. The fasteners are designed to ensure maximum rigidity over long service life with significant flex loadings..

I would prefer the round machined collar under the head of the bolt to bite through paint (eapecially over-done modern resto paint jobs) than for the paint to fret away over time. I back Jag's spec, although it has to be said that this did seem to change sometimes between painting assembled frame/tub and painting separately.

Pete

[Ropariva]

Thanks guys for your advice on this. One of my main concerns was keeping rust at bay where the inevitable chips in the paint are likely to occur from the bolts. I kept the paint very thin on the mating surfaces of the frames, but with the paint on the bulkhead there really is no option. It was obvious from the strip down that the original paint was very thin but I doubt many restorers would try and emulate this feature on purpose.
In regards to an alternative to the originally used sealant, I thought perhaps spraying the contact surfaces of the frames with some Dynax S50 left over from rustproofing the insides of the frames. This I feel should give the minimum product between the surfaces and the rust prevention I am after. Another thought was to just lather up each bolt with Copper Slip and clean up the excess when its all tightened up.
The bolts that came in the kit from XKs appear to be a good match for the original, though the bulkhead setscrews are a little longer. The replacement bolt is on the left. The re plated original on the right. Note the machined steps on both bolts are similar, but slightly more pronounced on the new bolts.

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Again, the original on the right. Replacements are grade 5.


By the time my car hit the production line, E Types had been around for 9 years. That's a long time for the engineers to review their design, so I guess if they still thought washers weren't needed, then so be it. My frames will be bolted up just as god designed it.:-)
As for the truckload of Dum Dum throughout my car... ? I wonder if they had to change the weight on the brochure for the 1970 Series 2??
One last thing, can anyone advise me how many foot pounds the various subframe bolts should be tightened to, or do they just need to be VBT (very bloody tight)
Thanks again
Alan

[Heuer]

From our Knowledge Base:

Torque Values (Word version): http://dl.dropbox.com/u/8496016/Torque%20settings.doc
Torque Values (HTML): http://dl.dropbox.com/u/8496016/Torque% ... 281%29.mht

[Steve Marshall]

What a helpful and informative thread, and I will be torquing mine up quite soon, so it will be good to have the official figure.

Seems to me that metal-to-metal contact, or very thin primer coat would be desirable.

I wouldn't think that the 5/16 screwws actually need to be that tight, the upper ones will be in compression most of the time, and for the lower ones the only criterion is that the axial tension created by the bolt tightening remains higher than the stretching force applied by the frame under suspension shocks. As the bulkheads are reasonably flexible the loads on a certain plate should share out fairly equally between its bolts. Even if the lower subframes were to part company with the bulkhead momentarily, that would have to happen repeatedly for fatigue and screw failure to occur.

Reaching for the fag-packet:- each screw would have a maximum theoretical clamping force of about 1?tonnes, it's a 1?tonne car, maybe 65% down the pointy end (that is massively generous as in reality the function of the frames is to hold up the front of the tub, which is itself partly counterbalanced by the boot) shared 50/50 side-to-side, shared between 8 bolts, say a force of 2G (which if actually applied to the tub would be noticeable!) geometry of frame gives a leverage factor of maybe 3, fudge factor of 2 for not equally sharing the load - gives about ? tonne per bolt. Obviously a simplification, the bolts in a combination of tension and shear.

Controversial conclusion, mild steel would do! Firm rebuttal anticipated ...

[RogerM]

Not wishing to be a pedant on this argument but we are discussing SETSCREWS not Bolts. Setscrews are threaded all the way to the head, bolts have a plain shank below the head.
One other point of debate regarding washers is whether to put them between lock washers and the metal. I have always said NO but I see many cars with washers, lock washers and nuts.
:?

[abowie]

Personally I see no great problem with either sealant (I don't use it) or washers (I do.)

While no engineer, I really can't see a micrometrically thin layer of sealant is going to affect the integrity of the engine frame joints to any significant extent. From Ropa's original pictures his "dumdum" only extends around the rim anyway; the centre of the mated surfaces under the is just paint. This might actually be beneficial as 50 years of rust developing under the plates can't serve to make the joint more stable.

Similarly, I see no difference between the face of a nut or bolt head or a washer in terms of the hold on the frames. The washers get squashed evenly into the paint. Nuts and bolt heads chew unevenly into the paint. In both cases there's still some paint layer in between the surfaces which could theoretically come adrift and loosen the bolt's torque. If Jaguar really thought that there was a need for solid metal to metal contact they would have assembled the frames first then painted them after. I suspect that saving 1/6 on washers was by far the stronger motivator.

[PeterCrespin]

One other point of debate regarding washers is whether to put them between lock washers and the metal. I have always said NO but I see many cars with washers, lock washers and nuts.
:?

Jag spares book showS numerous uses of plain and lock washers together.