MX5 Donor, Using as a Donor/problems/solutions/advice Info
 

A great suggestion has been put forward by forum member "Johno" to have a dedicated MX5 Donor page on the forum, as the Sierra is getting a little thin on the ground & as the current "Book" is written around using a Sierra then this thread will hopefully be a source of information for any current or future builders using the MX5 as a Donor.

There are currently some great builds in progress using the MX5 & all have their own "Build Threads" so, this thread will be a source of helpful tips / advice / solutions of using the MX5 which may hopefully help all current builders & hopefully encourage any future builders of a Roadster that may possibly think twice about a build due to a shortage of Sierra,s to take the plunge & build with an MX5.

So......Over to you guys who are or will be using this alternative Donor .

cheers
andy

Hi Andy,
Looks a bit quiet on here so I think I will start the ball rolling... (come on guys form an ordely que)...LOL
I asked Andy to put up a page to help out new members going down the MX5 route (plus ongoing builds) so lets not let him down.:D
Sometimes it's hard to pick out the info you need from this forum for specific related builds so lets put together information on this page for sound advice for new converts to the MX5.

Well here's my first two pence worth.
A good place for information regarding the MX5 for a Haynes/Locost build is Keith Tanners Seven build.

Just Google the above and you wil find over 1400 entries of all aspects of his build.
Well worth a look....:D

Johno

Brilliant, can you sticky this then please.?
I'm going the mx5 route so will need all the help I can get and would need to find it easily. ;)

Some pointers about donor choice, or things to look out for if you're buying parts piecemeal rather than a complete donor.

All the 1600 and 1800 parts are interchangable to an extent. For example, you can run a 1600 engine and gearbox with a 1800 diff. You would need a 1800 prop and drive shafts to suit the diff. A 1600 engine will fit a 1800 gearbox.

Apparently (I don't know if this is true or not) but the 1600 gearboxes and diffs are slightly weaker than their 1800 counterparts.

A common upgrade for the 1600 engine (especially if tuned) is to fit the 1800 flywheel and clutch.

You can tell the 1600 and 1800 apart by looking at the cam cover - the 'Mazda 16V DOHC' lettering is raised on a 1800, sunk on a 1600. The 1800 has 'BP' cast into the block on the exhaust side.

The 1800 comes with bigger brakes as standard all round. Mark 2 Sport brakes are bigger still.

Early driveshafts are bolt on (and the PCD is different between the 1600 and 1800). Later driveshafts are push on (and I believe are still different between the 1600 and 1800).

There were several wiring revisions over the course of the mark 1's life.

Early 1600s ('short nose') engines had crank problems. Later long nose engines are fine. They can be identified by counting the number of slots on the crank pulley. The short nose has 4 slots, the long nose 8.

Any imported (Eunos) 1600 engine will be 115bhp, as are UK engines of the same era. The JDM 1600 was discontinued when the 1800 was introduced. The UK 1600 was then detuned to 88/90bhp at this time, so any later UK spec 1600 would be the 90bhp version.

The OEM alloys are very light for an OEM wheel. You would need to spend a significant amount of money to get lighter aftermarket ones.

A mark 3 MX5 gearbox will fit the Ford Duratec apparently :)

The mark 2 6 speed box is rumoured to be stronger than the mark 1 5 speed.

Little can be swapped between 1600 and 1800 engines but they do both fit in the same 'hole' and fit on the same gearbox.

1600 diff up to 94 is 6" crown wheel from 94 all diffs 7" crown wheel and essentially the same as RX7.
7" naturally stronger than 6" but both are stout. 6" are open or the unpopular VLSD, 7" available as open or with Torsen type 1 or 2.
Three different types of driveshaft depending on the diff you have so get the driveshafts at the same time to go with the diff.

MK2 gearboxes are 'better' than mk1 in that the mk1 is intentionally noisy but this proved unpopular and the leaky remote change was redesigned but both are equally stong as they came from the B1600 pick up.

Clutches - If running a tuned 1600 N/A engine then avoid the heavy 1800 flywheel better to use a H/D 1600 clutch. I'm using a 1600 flywheel and clutch on my nearly stock 1800 with no problems.
If turbo'ed then use the 1800 flywheel and MX6 clutch unless running mental amounts of power

5 speed boxes have better ratios that the 6 speed and in something like the haynes roadster first in the 6 speed would be pointless. Just extra weight to carry around and as its bigger, more of a squeeze on footwell space.

Brakes - Mk1 1800's have bigger front brakes, Mk2 1600 and 1800 had the MK1 1800 brakes and bigger rears, MK2.5 had bigger fronts again and then there were bigger rears for some special editions.

Wheels MK1 all 14" MK2 15" MK2.5 16" mk3 17"

Mk3 MX5 does indeed use the duratec engine as it was part developed by Ford and Mazda. (Well Ford does own part of Mazda)
So a Mondeo engine can be used but a mazda flywheel clutch and starter will be needed. I have a MK3 6speed if anyone wants to make me an offer?

MK1/2 parts Hardly anything interchanges with the MK3's. The MK3's all different, being based around the RX8.

The 1.6 inlet manifold is bigger making it harder to fit it under the bonnet, but people on here have managed it.

+1 on Johno's point about Keith Tanners book How to Build a Cheap Sports Car, it's just about how he managed to overcome all the problems in his build. And his contact details are in the back, there's not much he doesn't know about taking apart an MX-5 and he will answer you if you send him an email.

:) Consider it done :)

Great to see some very helpful info being posted, I,m sure this thread will be a great source for all MX5 donor builds....:cool:

cheers
andy

Hi all,
Some good info there guys...;) . Thanks for helping out with the page to get it going and thanks to Andy for making it a Sticky.
Well I'm going to keep it short and sweet. Here's a guy from the good old US doing a Haynes Roadster the American way.
http://www.locostusa.com/forums/view...hp?f=35&t=8967

Some very interesting ideas there for a different approach to the car.
Have a look and see what you think...

Johno

Here is a question
 

Got the rear subframe dropped down to the floor today but the front subframe has got caught up on the threads

As far as I can tell all the groundwork to removing the subframe has been done

Have I missed anything why even bashing the subframe with a length of wood and a sledge hammer it just wont budge

Have you undone the 2 14mm bolts right at the rear of the subframe? There's 8 bolts to undo IIRC in total including the 4 around the strut tops.

That was the 'to an extent' bit that I mentioned ;)

The front is bolted on in 4 places I think, once on each side inline with the wishbones, then some more further back and in towards the middle of the car.

I did the back ones first, then held it up with a jack while I undid the fronts.

Can't remember if that rear bit uses 3 or 2 bolts though.



Does that help?

Yes got the 2 rear most ones and 2 each side at the top of the subframe behind the strut that makes 6 where is the other 2

His build log was my inspiration to start my own build! Sadly, the book is out of print and unavailable on the online booksellers for a reasonable price.

Have you undone the damper mountings? There's 2 bolts on each side. You won't be able to separate the shell from the subframe if you don't undo these.

Yeah got them too spent most of the last 4 hours head scratching and double checking next step is going to be the gas axe I think

I know it's a bit late now, but it might help someone else - the bolts you mean are a bit hidden.

If you look at the front lower wishbone from the side of the car, you'll see an indentation in the bodyshell just slightly further back from the rearmost wishbone mounting. That's where the bolt is hidden, one on each side of the car.

These 2 bolts should be immediately obvious if you have either a pit or a lift.

Solution to steering rack clearance issue. Turned alluminium tapered insert fitted into control arm on upright reamed to take standard ford rs2000 track rod ends from the top as opposed to underneath. Picture taken without rack in place but gives an idea how much clearance there is now. Its yet to be seen if there is any significant change to the amount of bump steer as the instant centre position is changed from the original setup, but either way its safer than having contact between rack and wishbone. I did toy with the idea of changing the upper wishbone to induce some negative castor, both to help lift the control arms and help with self centering, but it would be no consellation to those who have already made their wishbones so i think this is the best solution, although iirc talon was talking about using the bent bmw track rod ends- thats another solution well worth playing with, i dont know if hes tried it might be worth a mention.

David bolam was asking about wingstays, if you make them like mine, just be sure to make sure the return angle at the bottom clears the wishbone plates at full hight of travel otherwise if there is any interference it could cause an accident whilst flying over the brow of a hill not being able to steer, probably best to use the dust cover holes as mounting points as suggested, something i never thought of duh

Mx5 Based Choice
 

Hi,Im joining you guys ,just bought an MX5 based chassis off a guy on e bay that was never started and came complete with all running gear,1800cc
need to start looking at the brackets necessarry for the sterrring column ,pedals etc
I think its a better choice than a sierra based model nowadays
cheers
Gary

Hi Gary welcome aboard....:)
Plenty of people on here more than welcome to help you out..
So don't hesitate to ask.....:D

Welcome Gary :)

Was this the chassis you bought? http://www.ebay.co.uk/itm/290779639242

e bay purchase
 

no the seller was Reading based
what caught my eye was the MX5 dodr option as I believe it has more character than traditional Sierra choices, and also the less availability of Sierra parts currently which will only get worse I guess
I am trying to go the route of clam shell wings as a preferance and wondered why most go cycle wings,hopefully this is personal choice rather than influenced by IVA approval!
cheers
Gary

Only prob is when you've built it you'll need to get a perm :p

I hope i never bump into Skov at any point! :)

Clam shell wings are very "old skool" and cycle wings are more modern really but its personal choice .At the end of the day its your car do what you want V6,V8,turbo,nitrous,jet engine, whatever takes your fancy really :D

Clamshell wings give an early, iconic look but are not regarded as very aerodynamic. Caterham started to fit them (mid 60's KAR120c etc ) but then changed back to cycle wings and stayed with them.
I may get a pair of clamshells sometime if some come up at the right price but would need to mount them so the car could be easilly swapped back for long trips etc

Clam shells have a lot of lift at high speeds!

oi!




Thinking about fitting a blower to mine post-IVA, not sure which one to go for though, this:



or this:



:D

Kiwi MX5
 

This is the way I will be going.I have the steel and a MX5 donor. Once I tidy up my work area and make a build table I'll be into it!! It is great to have a MX5 area.Sierras are Dodos here in New Zealand.

Stupid question
 

What size and grade bolts have people used to hang the diff

Need to know before going and ordering my nut and bolt set

Using the saturn plans and want to get the diff mocked up this week

Can I ask how you are planning to mount the diff?

I will pop some photos up of my modified mount in the next few days

I have made sure it won't budge

David

Dunno about size, but you'll want 8.8 grade at the very least.

Just to add to this; I've been researching both locostusa and Keith Tanner's build site.

The vast majority of people Stateside have had issues with the track rods fouling the lower wishbone. There are several reported ways of tackling this...

1 - straighten the steering arm so that it's horizontal, then ream to take a TRE from the top. Don't like the idea of this as you'll probably have to heat the arm, so the upright could be fatigued as a result of this.

2 - a mark 2 MX5 upright has raised steering arms compared to the mark 1 (7mm difference). The TRE would fit as OEM. There should be enough adjustment in the steering design to remove any bump steer that this might dial in. The 7mm may be enough to provide sufficient clearance. This is how Keith Tanner did it after trying rose joints on mark 1 uprights.

3 - remodel the front edge of the lower wishbone to clear the steering rack completely. This is how it is on a MX5.

Looking at the way Nathan has done it, I would be tempted to try a MX5 TRE instead of a Ford item in that situation. The cranked end of the TRE would bring the track rod down a bit, should still provide sufficient clearance for the lower wishbone and might reduce the amount of bump steer introduced by doing this.

Here's an article I found on bump steer - http://www.longacreracing.com/articles/art.asp?ARTID=13

Any thoughts?

Same way as the donor bolt through the mounts then rigidly mount the doughnut rubber to a plate welded to the diff cage

Then I was thinking about solid mounting the diff nose to take the place of the ppf on the donor was also going to work out a shield to protect me should the diff break

Have you thought about making a bracket out of some 5mm plate that looks like this at all? Remove all the blocks/brackets around the nose fit some 3/4-19mm round stock with 12mm through holes in the 18-19mm holes in the nose and use M12 bolts.

That was the kind of thing I had in mind

Was worried about vibration from the diff till I remembered the book build diff is hard mounted to the chassis

That seems like an a lot of machine work for a home builder to do why not just make the whole thing more simple like this:

So there is an option 3 available :D; my problem is I've already got the front wishbones to SSC spec.

I really don't like the SSC front lower wishbone design it realise on people's ability to weld those adjusters a little too much for my liking, they make the wishbones overly complicated with no apparent need for them as there is an adjustable drag link at the top.

I've got the ssc ones and there is no fouling of the wishbones and steering arms. I have put a limit on the amount of lock available but there is still more than my passat has.

David

How much lock did you take off David (how thick were your stops?).