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 1 
 on: February 11, 2018, 12:28:34 PM 
Started by Thunderace - Last post by Thunderace
When it comes to available powerplant configurations,
theer are various to choose from,
the most common arrangement available tends to be Giacosa style side mounted gearbox.

This is largely the industry standard for FWD platforms,
first off it probably looks less than useful, with the engine offset to one side,
however it's often quite a compact package which would fit in the Servi car's rear box.
(with space to spare).

The smaller cc units are typically only about twenty two inches tall,
while larger are often canted as stock to achieve similar,
which means the cam cover sticks up some thing a little over six inches higher than our upper front frame tubes.
As long as passenger(s) are sat a little further back,
this need not force the rear seat to be insanely high perched (chicken on a gate),
big wild swoopy king and queen seat and you can hide the little bit where the engine sticks up in the hump between the two seats.

As I say the engine being offset does make for some interesting bracket making,
you may have to come out a little wider on the bottom rails,
or head towards a semi-punt chassis style thing,
but main thing would be huge choice of donors.

Less common are the longitudinal mount,
My Subaru is of this type, as are many Audi's, Bigger Renault's, various Italian,
and a few others.
First off while at least more symmetrical (to a degree),
the engine sticks up right about where you want to be sitting.
options are to run the shafts at a slight angle forwards (often how it was in the car),
and extend the wheelbase a little so you can sit sit low ahead of the motor.
This is a real easy way to go for sure,
however the other option is to angle the shafts a little aft,
and thus sit behind the engine,
It's a bit tight for space for sure, but as long as you and your passenger ain't too fat,
typically pilot is sat on axle line, passenger at little behind,
you may have to come up an inch or two on the seat and pegs so legs miss hot stuff.
but yeah probably the most fun design.

Other configurations,
AP four speed and Saab BW35,
Leyland, Austins, A series, Maxi, Allegro etc,
Gearbox bolts in place of sump.
Does make the thing tall, but less wide, split rear seat is probably good.

GM's THM425, & 325,
bit rare this side of the pond, but not impossible to find,
these are a 'folded' longitudinal mount,
with a Morse chain driving a reverse running GM Turbo 400,
It's the 'Lego' block of building weird stuff,
bell housing is Buick so Rover V8 will fit.

       
 

 2 
 on: January 21, 2018, 04:22:23 PM 
Started by Thunderace - Last post by Thunderace
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).

I tend to construct around the engine/gearbox unit sat on the bench,
it's easier to work this way, and I have a bad back.
 
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 13 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.

Similarly when it comes to footrests,
particularly if you are doing 'forward sets'
typically it's useful to come up a few inches,
footrests don't need to be right down low,
it's more comfortable and practical on a trike to bring the pegs up,
measured off the bench top six to a dozen inches is not unreasonable a height.
This allows plenty of space for linkages,
and avoids master cylinders hanging bellow frame tubes and other horrors.   

  
  

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