The mount is in, trimmed and holds the weight well. It also has been cured, so there should be no issue with the heat from the engine softening the resin. I am having some custom fasteners made to secure the mount to the aramid chassis – similar to these but to my own dimensions and specification of metal. I can then hard mount the engine mount to the chassis. I’ll also need to make a torque-control bar that attaches to the engine and stops it yawing when it spins up.
So, here it is in the current incarnation.
The mount now bolts nicely to the dry-sump. It’s actually quite a complex part, made in multiple separate stages:
- print the part, make the mould, lay and infuse the part. I’ve already written a lot about this, and you can get to it via the ‘engine mount’ tag.
- make the cross-bar. This needs to be very strong in compression and accommodate the hard points of the engine Bolting through it. To do this, I made a 5mm thick sheet of woven glass, infused with hig-temp epoxy. I chose glass because it’s strong in compression, and of course a good insulator: there is no galvanic response issue to be had which would happen if I made the plate out of carbon.
- I then made a jig from the front of the dry-sump to capture the wiggly up and down bit and the bolt holes. From the Jig I transferred this to the glass fibre plate, cut and fettled until the plate fitted the sump-front nicely.
- Next came the problem of attaching the plate to the cross-member. I had a plan … successful, as it turned out. I bolted the plate up, and lowered the engine down to the mount, onto a bed of the easy-composites two-part structural adhesive. This accurately located the plate on the cross-member. I let that set. All this would give me is accurate location. I couldn’t trust the adhesive to hold the plate in place in the rigours of the engine bay.
- Once set, I extracted the mount, and set about fixing it in place for good. I created some 45 degree chamfered foam corners to act as an interface between the plate and the cross member, meaning not only would the cloth not have to go around any extreme angles, but it would also gain some strength in a rocking front-and-back motion.
- Once the fillets were in place (a smidge of hot-glue), I then layered CF between the cross-member and the plate (3 layers of 300 either side) and then one layer of woven glass on the outside of each side. Again, I’m using glass as an insulator between the bold heads and the CF – it’s easy to work around galvanic response issues, so why not do it?
- Finally, I bagged it in a tube-bag and infused high-temp epoxy over it again. Then a curing cycle in the domestic oven and viola: an engine mount.
There’s still stuff to do though.
Firstly, the bid coloured in red on the mount needs to go – it is too tight against the left chassis rails. Once gone, I have more room to finally position the engine before I bolt it down. To bolt it down into the floor pan and I have to make some hard points for that. Watch this space. I have a tested technique which I’ll share next.
So, the first engine mount is now nearly a mould. I thought I’d share the prep process I’ve been going through in taking a 3D printed part to a CF part.
There are elements of the printing process I’ve had to compensate for – mainly that a part is many thin layers of plastic. For a non cosmetic part, this doesn’t matter on the the top of the part, but it does on the side. The gel-coat will go into the very fine layer lines there and lock the part. Also I made the part in a few sections and they had a visible seam where they bonded together. I had made it in sections for a couple of reasons – firstly because I only have a bed of a certain size. Secondly making it in a modular fashion means I can correct a small part of it, rather than waiting 10+ hours for a full print. Saying that, what you gain in flexibility you lose in post-prep time.
The post-prep phase is summarised as fill, flat, and flange.
So, I used some Dolphin-Glaze liquid filler to take care of the most obvious demands (such as the seams):
Once I’d got the filler in, I did some rough flatting. I also made a mistake here that can just be seen on the red piece on the side. I made the parts with a biscuit cut on each mating surface, and used printed biscuits to help lock it in whilst I bonded it with 2-part fast setting epoxy. On the red part at the mating surface it curled up a little. This wouldn’t have happened if I’d clamped it to the bench when the glue was setting. No biggie – when I flanged it later, I clamped it and bonded some carbon to the back to stiffen it and hold it in place.
After this I sprayed it with high-build primer and briefly flatted it. I used a rattle can rather than mixing up some two-part just because it’s a pain to spray. I have the correct mask and so on, but it’s just a lot easier for a small part to use a rattle can, even if it’s not the cheapest.
So – one flatted 3D printed complex part to make an engine mount.
I’ve created the front engine mount in CAD (another post to follow) and now I need to test the engine height with the mount and the bonnet fitting – it’s no good having a beautiful mount if the engine then doesn’t clear the bonnet. I’ve gone for a trial fit of the mount (several hours of CAD and printing) to be sure it works before I go through the process of moulding and making the CF part. What I wanted to do was put the mount in place (it cradles under the front of the sump and bolts on to the front of the dry-sump). It also needs to curve around the awkward external dry-sump pump which seems to get in the way of everything.
Having fitted it, here are a set of photos that attempt to show the bonnet in place, and the engine having about 30mm of clearance between the top of the engine and the bonnet. One of the other interesting things about doing this is it’s the first time in a couple of years that the car has had any bodywork attached. It’s gone (in my head) from an abstract chassis concept back to something that relates to being a car again.
From a reference point of view, the sump will sit between 115 and 125 mm from the floor, and my suspension is height adjustable so on a track I can lower it a bit more. Right now, I’m safe to go over a house-brick without writing off the engine.
Here you can see the bonnet resting on a clamped large table-mat as a reference line. (Clamped to the top chassis rail). The mat and clamps weren’t strong enough to handle the weight of the bonnet, so I needed another idea. So, what you can see sticking down is a piece of (cut to size) wood that represents the chassis rail height to the floor as a relative position. The table mat is now just sat there without any vertical load – it works well as a reference point.
With the bonnet properly propped, this a bit of a scrappy shot down the bonnet. There’s loads of clearance here, and you can see the CF footwell and gearbox.
More of the same here and you can make out the 3d printed blanking plates I made.
And again – hopefully you can see the oil filler cap at the front a good 30mm below the bonnet.
Here it is from the top down. It looks a tiny bit like a car again.