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Author Topic: Building a Trike  (Read 241 times)
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« on: September 13, 2017, 02:26:17 PM »

So you want to build your own trike ?
Well the first two options we should look at are,
non SVA tested 'conversions' Vs full on custom.

If you are not confident in your abilities you may choose to go with some kind of bolt on conversion to a two wheeler which then does not require to be SVA tested.
Typically these are done by mounting a Reliant axle to an oversized swing arm,
where the base machine had the shaft on the left, the axle has to be inverted,
as is also the case for Ural.
You need to at least chop at least half a dozen inches out of what was the offside tube,
that will get the pinion shaft somewhere near lining up with the gearbox output.
If you are thinking of running some wide rubber, you probably want to take more off and shorten the other side a bit too.
Don't make the swingarm long, keep the axle line to within an inch or two of stock.
And try and get the pinion shaft to be as straight to the gearbox shaft at what will be the normally loaded ride height.
Prop shafts, joints must be correctly phased, and short enough so as to be one piece,
(not two bits welded together part way along, yeah really, scares me some days),
I would say get a new bit of tube, but no just keep it short, and straight.
if it clocks up at less than 15thou TIR it will not need balancing, and if it is worse,
cut it apart and do it again !

At the front end you can chuck in an AME trike kit which will sort the geometry,
for less bucks you could go for some slab yokes with another four inches of offset over stock to drop the motorcycle's trail down to something more suited to our threewheeler.
Or if the bike came with twin disc,
swapping the legs allows leading axle brackets to be bolted off the disc mounts,
and thus both trail and ride height be altered.
What ever, but you probably should think about doing something to the front end even if it's just fitting apehangers.

I would probably cut and drop the seat rails,
I know we were not meant to be cutting the stock motorcycle,
but this don't stop it being turned back into a bike, so I figure it's sort of ok,
and sitting a bit lower to me for sure feels that bit better than being perched way up in the air.

But yeah that and hooking up a couple of cables to a handle as a parking brake and you were largely there.

On the road without having to be checked out by the MSVA man,
however has to be said generally it don't ride well,
typically most don't bother sorting the geometry, so the steering is heavy.
too long a swing arm and too wide an axle are a bad idea off the stock swingarm pivot.
the driveline shockabsorber was in the bikes rear hub,
we now have none, and this makes the drive line feel rough,
again it's a minor thing, but all round it can combine to make the thing less than pleasant.

The alternative is the full custom built machine which requires MSVA,
Getting a machine through MSVA is not that scary,
a few basics would be that the man likes to see 'E' numbers on lights,
rounded edges, plastic mudguards and a lack of spikey bits,
glass fibre is your friend.

Obviously while having to meet a few requirements to pass the examination,
otherwise this did free one to build a better machine.

Certainly I think it is easier to build a machine without the flaws of the first option,
than it would be to fix them.
And there are some tricks which can save you a whole heap of work.

You are going to need a seat, often best to start with that.
here again fibre glass is your friend,
some mad king and queen with plenty of wrap so you don't slide out the seat,
go wild.
Motor wise there are far too many options to list,
to make life easy something which came with an automatic transaxle is gona save some grief.
but hey adapters can always be made if you got your heart set on a V8.
Fairly obviously an auto means no complex gearlink to be made, or clutch to hook up,
so that saves some work for sure.
Being a transaxle mounted engine means the engine/gearbox/final drive is all one bolted up unit,
so it's only one thing which has to be bolted into the frame,
making for simpler frame.
And if the motor sits ahead of the shaft outputs, it can become a chunk of the frame,
thus saving a bit more.

You are going to need a neck tube,
you can saw one out of an old motorcycle frame, but it's probably easier to machine up a couple of bearing cups to take 32005 bearings spigotted into a piece of two inch scaffold tube so the two bearings when assembled give a total length of 8 inches.
This then gives a 25mm diameter for the steering stem which suits available custom front ends, or something homebrew.

Pick a sensible length of wheelbase,
seventy inches is compact, eighty to ninety is midsized, hundred inches is big, beyond that monsters lie.
If you keep things simple with a forty five rake you only have to comeback the same distance as the neck is off the floor to get the position,
so as a typical where the tubes bolt to the motor ten inches ahead of the axle,
for an seventy inch wheelbase using stock length forks at forty five gives a top tube length of thirty four inches ( 70 = 10 + 26 + 34 ) where the top of the neck is twenty six inches to the floor.
Keeping the neck low is good,
for a start it reduces the frame stresses,
and for a second it reduces the amount of tiller effect you end up with,
well that and the rake for sure,
if you want to do however many inch overs,
it's all do able, but for anything beyond ten inch overs I would stick another five degrees in the neck.

brackets cut from 6 or even 8mm section angle iron bolted to the motor,
spacers, brackets that span multiple threaded bosses,
top tubes should run as straight as reasonably possible,
lower ones limit the bend to forty five,
tube stock to connect the neck to the motor need only be 16swg, but use diameters of more than inch, go inch and a quarter or even inch and a half diameter.

At the rear end, upper shock mounts are probably easiest to do as plates off the ends of a piece of 40mm box,
so one piece of 40mm two foot six to maybe three feet long spanning the width,
just aft of the axle line, again bracketed back to the engine gearbox unit.
this bit will carry the greater part of the weight of the total machine,
so make it strong, bracing, webs, lots of weld.
probably should attach to at least six bolts of M8 or better.

Suspension arms need not be difficult,
semi-trailing arms are cheap to make,
four cheap rod ends in 5/8x1/2 does the job and allows for some adjustment of toe-in.
some more of that box section and angle brackets,
you may have to get a bit creative with some minor structure to tie the two bits of box to the motor/gearbox unit, but there are usually some threaded bosses or fixing which can double up with a longer bolt.
Again this bit is going to carry some larger forces, so make it strong.

The beauty of this game plan also came when we got to the front end,
typically with eighty five percent of the machines total mass being held up by the rear tyres, this only left a limited number of killos to be support by the forks,
even if you build a half ton monster V8 the forks still only have to hold up 75kgs !
So making a set of forks to hold up less weight than a stock motorcycle was less difficult.
Springer/leading link forks are easy enough, girders were worth the extra effort,
modifying an off the shelf custom fork was easy enough,
longer links, less bend back in the case of sidecar forks,
all certainly achievable,
Bring the trail right down, under two inches,
if you run a modern radial superbike tyre as a front you can take that down to zero,
the tyre will give you enough pneumatic trail to centre the steering.

I have typed enough for now,
feel free to pass comment
I will work on this further,
but for now am done.


« Last Edit: January 02, 2018, 10:58:20 AM by Thunderace » Logged
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« Reply #1 on: November 26, 2017, 02:18:10 PM »

I meet numerous people who seem to see the attachment of the neck as being an issue,
I have never figured what caused this,
whether it was strength or accuracy worries.

I will attempt to address both.
So as a start let's look at the strength of attachment,
typically the neck will be welded to the ends of four tubes,
the top tubes will probably be at least 1 1/4 dia,
while the lower at least an inch,
so going round the tubes we will have an easy fourteen inches of weld,
plus another eight or more with a nice big gusset plate ether side.
more than twenty inches in total.
An inch of weld is usually claimed to be able to hold a ton,
while the actual forces when multiplied up by the length of the forks,
are going to be a few hundred kgs,
even if you do a V8 with twenty four inch overs,
the load on the neck attachment is less than 3/4 of a ton.

So strength of attachment should not be an issue,
ok so what about accuracy ?
obviously it's going help if the neck is welded on nice and vertical to the longitudinal axis,
and somewhere near close to our fortyfive degrees of rake,
if the neck and thus the front wheel sits off at an angle,
the plot ain't going to track straight.
However you probably have to be more than a couple of degrees off before it really becomes a problem,
and as half a degree at twenty four inches is more than 5mm,
getting the neck accurately enough aligned is only a matter of stuffing a broom handle through it and achieving better than say a quarter inch.
again well within the capabilities of even non-engineering staff,
spirit level, plumb bob, string, marker pen and a long ruler !

Worst case if the neck ends up a little bit out of true,
if the rear end is independently sprung,
a little tweak of spring platforms and maybe tracking can usually sort,
so the thing still goes down the road straight when you take your hands off the bars.
which is nice  trike.gif

Hopefully that has put all worries regarding neck attachment to bed,
but if I have not understood the imagined problems,
both forgive and better still explain what the nature of the problem was !

If you are worried about appearing dense or foolish,
and don't wish to add to this thread, for goodness sake PM me or something.

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« Reply #2 on: December 17, 2017, 03:44:32 PM »

In a similar way I meet many who are reluctant to narrow an axle,
which rather than saving work tends to result in more.

Accepting the need to chop the shafts allows greater freedom in both track width,
and if need be wheel station stud PCD and brake,
so if you want to use Ford Sierra rear discs on a Peugeot powered trike,
you can,
It just means hacking the shafts, and then doweling or muffing the ends,
while prop shafts turn fast enough to be scary,
CV jointed drive shafts only go round at wheel speed,
which makes them more forgiving of accuracy and alignment.

The beauty of this as a game plan is that once you accept chopping the shafts,
it means they can be removed out of the way,
a couple of pieces of bar stock turned down to fit through bearings at one end while the other end is turned down to fit a suitable length of tube,
turns the two wheel stations into a dummy axle,
with the track adjustable by sawing bits off the tube,
this way you can get the two rear wheels pointing about the right way,
I tend to favour a pair of dirt cheap home brew semi-trailing arms,
all cars use parts which are too big, too heavy, too complicated,
trying to integrate them is harder than making something more suitable.

Semi-trailing arms give a good amount of camber increase in compression,
which is useful for a trike rear end,
It's harder to design and make multi-link systems to give as much.

If you make your suspension arms reasonably short (14 to 18 inches seems work),
have the two pivots at least half the length of the arm apart,
and use at least 30mm with a 5mm wall it won't bend none in use.
It's best you gusset everything,
I speak from experience here, I did not gusset the underside of the two tubes which are the N/S suspension arm on my Subaru,
and after about eight years I noticed the wheel had kicked over at an angle and the weld had cracked, had to limp home a bit careful with the nearside wheel on an angle.
(Still drove ok !)

It does not seem to make enough difference for it to matter,
what sweep angle or relative height pivot centre one uses.
possibly thirty to forty degrees with at least two inch below axle pivot centres,
but what ever angle you do, you still get a combination of the good bits of both trailing arm and swing axle.

It is cheap since each arm only requires a couple of heavy 'Rose' joints,
or four nylon top hat bushes,
I have been using 5/8 x 1/2 male rod ends,
again tried lighter rated M12,
only had one failure, and that was extreme abuse,
but if you only have to buy four might as well have a heavier rated and be sure.

Nylon bushes work well, but you have to like machining nylon.

While the stock shocks that came with might look attractive as a cost saver,
it is better to forget them.
Don't be tempted.
It's a whole heap easier to work with the idea of using a rather more expensive race shock.
Springs of what ever rate you need will be available to fit the race shock,
the racing item is available in any length we want from nine to nineteen inches,
comes with adjustment of spring platform and damping, and is always the same 1/2 x 1 1/4 fitting.

That last bit is worth grabbing on to,
so if you make yourself a pair of 'lockup bars' from 1 1/4 tube or 30mm box with a washer.
and put the hole centres at what ever is mid travel for your chosen shock,
so typically I use a thirteen inch shock which has three inches of travel before the bump stop,
so I drill my lockup bars at eleven and a half centres,
and this allows me to build the suspension without having bought the shockers yet.

This also ensures that at mid travel the upper and lower shock mounts are reasonably in line,
Which is more difficult to achieve using the actual shocker in your hand,
and it's loads easier to set your axle centre to scrub line height,
again here I am working with typically five to six inches as being a reasonable figure.
for a normal sized tyre of around twentyfour rolling diameter,
lowest profiles I can find are about twentytwo rolling diameter, while biggest you want to be looking at are twentysix,
so variation in the axle to scrub line height is only an inch ether way.

So our temporary tube axle (remember that bit) can be positioned,
hell if need be welded with a few tacks to stop it moving while the rear suspension comes together.
The centre of the wheel stations do not have to be in line with the diff outputs,
If it helps the design to have the wheel stations a couple of inches further forward, backwards, up or down relative the joints will cope.
Typically the limit is more about the life span of the rubber gaiter,
(Aero-style CV gaiter if available)

If there is any slop,
pull the arms in at the front a little,
hopefully when welded it will be ether straight or slightly toe-in.
If you are doing threaded in rod ends as joints you will have adjustment,
but at least you are starting off on the right side of things.

Once it's all welded the temporary tube gets removed and the drive shafts can be chopped to suit.
Again here not that tricky, typically one if not both ends will be plunging type joints,
so there is a good range on the length accuracy.
Typically the shafts while often hard on the outside have a softer unheat treated core,
so boring them to take a 10mm dowel, chamfering, building up with weld and then machining down to size was doable.
Or if the shafts turn out to be too hard to machine, a muff can be machined as a nice tight fit on the cut shaft ends, welded and machined back to a nice look.
(I have one shaft doweled and one with a muff on my Subaru, both have lasted years, miles and wheelie popping antics).

Ideally check the welded shaft between centres,
but unlike a prop where we would be looking to get under 15thou,
anything better than a full turn on the dial gauge was probably fine to be honest,
hey do your best, but don't panic if it's got a bit of run out,
there is a bit of a trick to welding the shafts so they end up straight,
some rate the weld a third skip a third three weld method,
while others favour the straight round in one,
which ever I have a big hammer and can get em close enough.

One further note,
European cars tend to all use GKN drive components,
so there is a vast amount of mix and match possible between makes and models.    
« Last Edit: December 29, 2017, 01:13:13 PM by Thunderace » Logged
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« Reply #3 on: January 07, 2018, 04:20:51 PM »

It's probably true to say that all car derived power plants to be used in a trike,
will benefit from some prep and minor modification.

Typically the car will have come with a whole load of stuff we don't need,
fairly obviously air con and steering pumps ain't needed,
cab heater take-offs need to be blanked,
trans cooler pipes looped,
stock alternator is probably rated to run a heated window and a load of other stuff,
so that can be down-sized to an Iskra (2CV) replacement,
Typically the radiator which came with the donor will be rated to dump the heat from pulling a ton plus of car,
lightening the load reduces the waste heat,
so you only need a radiator to match,
the Valeo unit from a late metro will do even for a V8,
my own 1800 Subaru uses a late model BMC (1300i) Rad.
probably less than half the size of the stock rad which came with the donor 4x4.

Iron exhaust manifolds should go in the weigh-in pile !
The stock rubber mounts are best binned,
very few engines with four or more cylinders vibrate that bad,
(Ford Essex being the only real notable exception that sprung to mind)
and where typically there where three maybe four rubber mounts,
eliminating the rubber allowed us to bolt to more places,
and more usefully distribute the frame loads.
Engine/trans is quite a big thing,
rigidly mounting it not just to the frame, but as a major chunk of the frame,
is where it's at for sure.

I see many who will try to assemble a massively complex frame,
in effect trying to create the whole shape of the finished vehicle in tube.
I would stress that it's useful to keep in mind that the frame was connect forces.
Or the heavy bits to the suspensiony bits !
Keep it simple,
back end where the major part of the weight is going to held up,
heavy box, thick walled tube, no bends other than purely ascetic,
good and strong, and braced to the engine/trans in multiple places,
brackets out of heavy section angle.
Like I say try to focus on connecting the forces, so for instance the rear upper shock mounts can be joined by one transversely mounted piece of 40mm box,
and then that piece of box bracketed and braced to the unit,
thus wise the weight of the unit can be connected to the shocks by relatively short paths.
Ie less frame that has to be built massive.

Front section of the frame,
again should not be too damned involved,
round tube looks nice,
I tend to prefer twin top tubes, inch and a half diameter in 16swg,
these get welded to another piece to heavy rolled section which is bolted to the engine,
typically somewhere around a dozen inches centre to centre,
with a something like a ten degree bend inwards to the ends meet at the neck.
lower tubes look better a quarter inch smaller (1 1/4),
and on slightly wider centres at the engine end,
I tend to go with a forty five degree bend to bring those up to the neck,
you have to get fairly inventive with the spacers and angle iron sometimes,
but there is always something to bolt brackets to,
The lower tubes will be in tension,
so a good attachment is important, minimum of two M10 sized bolts per tube would be good.
It can tend to look real naff if you build a frame with a space which looks like there should be an engine in there when there ain't !
Limiting the vertical distance between the top tubes and lower rails plus the forty five bend largely solves this.
a dozen to maybe sixteen inches max means the space stays looking 'less empty'
and by the time some pipes and odd bits and pieces are routed and located there in,
(battery, radiator, oil cooler, brake master cylinder, twin turbos and intercooler etc)
It fools the eye completely and don't flag 'there should be an engine there' !

Again as I say sitting the engine/trans up on the bench,
striping everything off and giving it a good clean,
typically you find loads of places you can make your brackets to fit,
sometimes you got to get creative with spacers and longer bolts,
but it's amazing how many usable bolt fixings there can be,
my own Subaru has twenty two bolts which attach the various 'frame' parts to the engine/gearbox unit.
Probably more than needed in truth,
but hey still going dozen plus years on,
I think I would try for at least ten being a minimum,
As long as they were all at least M8,
ten would give plenty enough strength of attachment,
but it's still a minimum number, more should be an aim,
more is better,
(well it is when it's bolts holding your trike together for sure).

Sometimes when making your engine/gearbox unit 'ready for trike',
you have get creative with relocating a few things,
oil filters may need relocating, alternators completely re-bracketed,
filler necks chopped or relocated, gearlinks fliped,
It's worth putting in the effort,
a few modifications can save you loads of sweat further on down the build.                
« Last Edit: January 08, 2018, 01:22:34 PM by Thunderace » Logged
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« Reply #4 on: January 21, 2018, 04:22:23 PM »

Another issue I meet repeatedly is that of 'ground clearance',
ether too much or too little and often different at the two ends,
(so the frame don't sit right).

The Yanks have a concept they call 'scrub line' ,
which is a line bellow which nothing must hang.
So an easy way for us trike builders was to make the top of the bench be the 'scrub line'.

Measuring off the bench top gives a fixed datum,
allowing seat, neck and axle heights to be more accurately determined.
Five to seven inches was probably reasonable as ground clearance/scrub line,
So go middle with six for now,
I subtract six from any vertical measurement and that gives me distance above bench.

So seat (19 to 26 inches ) becomes 14 to 20 as measured off bench top,
top of the neck comes 19 inches for stock length forks and a 'normal' (24" rolling) wheel/tyre combo,
and the centres of the two rear hub bearings 6 inches above the bench,
again for normal 24" rolling diameter rubber,
(subtract or add one for low profiles or old tall tyres).
add 1.4 to neck height for every two inches over on forks*

There probably is a limit to the usefulness of going longer on the forks.
Ascetically it's sometimes fun,
but it needs not to be at the sacrifice of increased neck height,
lower neck reduces torsional forces and makes it easier to reach the bars.
(well given some risers and apehangers it was gona for sure).

If you are making your own front end anyway,
there probably is some justification to shorter forks,
four under (26inch) forks is as far as you can go without swapping to a scooter wheel,
but this drops the neck nearly three inches,
which probably allows for six more in the length of the spine,
with the bars still ending up 'reading newspaper comfy chair' no problem.

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