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Author: Subject: Si & Will's Tiger Avon based MX5 build
FOUR HUNDRED YEARS

posted on 12/3/19 at 01:54 PM Reply With Quote
Si & Will's Tiger Avon based MX5 build

Hi Everybody,

I acquired this chassis last year from a colleague who purchased it as a rolling chassis but for various reasons couldn't finish the build. I had to store it during a house move / renovation but finally am able to make a start.

This is a joint venture between my best mate and myself as a fun project in the garage. Neither of us have built a 7 style car before but I'm a CNC Machinist in vintage car restoration and he is an electrical engineer so hopefully we can work something out between us!

No doubt we will be asking for lots of help and advice!

This is what we purchased for a few hundred pounds:

2019011 3_173808 by Simon Longley, on Flickr

2019011 3_173537 by Simon Longley, on Flickr

At first we thought it was a locost chassis but after a bit of research into the front wishbone mod we realised ours is nothing like a locost, in fact the front and rear wishbones are most certainly Tiger Avon as they measure up correctly and also feature the weld marks for orientation. The chassis looks quite well made with an integrated roll hoop and is almost entirely bronze welded apart from the wishbone mounts, rad mounts and steering rack mounts which are mig welded.

Is there an advantage to a bronze welded chassis over a mig welded one? The tunnel has been modified by my colleague with bent round tube as he wanted a rounded look however we immediately ruined all his work after discovering that the MX5 box didn't fit as it was built around a crossflow and type 9 gearbox. We chopped out the tunnel just to see if the engine and lump would go in which it does thankfully though obviously we will need to make all new mounting for it.

The kit came with brakes, wishbones, steering rack & column, radiator, all bodywork (mainly aluminium apart from wings and nose cone), scuttle and dash, gaz gold coilovers, diff and driveshafts. Basically a rolling chassis in bits :-)

My colleague also decided the open Sierra diff was no good so he started modifying the chassis to fit an RX8 LSD, he was going to run a duratec engine. So the Sierra diff mounts are partially removed as is part of a crossmember at the rear to enable the massive mazda diff to slide in.

How that diff will work with a 1.6 MX5 engine and box is worrying me as the RX8 revs to 9k ish from memory, would anyone know if this combination will be usable on the road?

20190131_ 194302 by Simon Longley, on Flickr

2019013 1_194246 by Simon Longley, on Flickr

20190128_ 212331 by Simon Longley, on Flickr

2019013 1_194350 by Simon Longley, on Flickr

I have purchased the Aluminum casting that mounts the diff in the RX8 and have read up on the problems with mounting the MX5 diff using just that mount, we are hoping to utilise what's left of the Sierra diff mounts so that we can bolt the nose of the diff up solid as well. Gearbox mounts also look like some fabrication will be needed.

This is how the kit is atm while we finish stripping the donor MX5 of it's bits. We plan to use the loom, ecu and key etc from the mazda as the ME221 ecu is looking expensive at 600 quid ish. Anyone run an MX5 lump on standard fuelling / ignition like this or am I better off buying a standalone ecu?

Thanks Simon

[Edited on 13/3/19 by FOUR HUNDRED YEARS]

[Edited on 13/3/19 by FOUR HUNDRED YEARS]





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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kevyo89

posted on 12/3/19 at 02:59 PM Reply With Quote
Looks good bud. I am building my Locost MX5 Turbo at the moment and also currently exploring engine management. You are quite correct - the ME221 ECU is expensive at 600+. I have done a little research on a cheaper alternative and found the following:

https://lowcostracingsolutions.co.uk/pnp-standalone-ecu-s/20-6-mazda-mx5-standalone-pnp-standalone-ecu-all-models.html#/31-model_type-mk1_16_18

I believe it is a Speeduino-based ECU which is tuned using the same software as the Megasquirt ECU (a rival to the ME221). I have spoken to a tuner who believes it will do my trick perfectly but I am still debating whether this would be a case of 'buy cheap, buy twice'.

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miskit

posted on 12/3/19 at 11:58 PM Reply With Quote
I just stripped the loom and popped all the unused pins out of the connector blocks. Not especially difficult and mine was a Mk2.5 with all the bells and whistles.
End up with about 20kg of unused loom. Used the instruments but built my own loom for lights etc.





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Tiger Super Six

posted on 13/3/19 at 11:58 AM Reply With Quote
I am really not sure that this is a Tiger Avon - The Avon has fiberglass body panels and a raised bulge in the bonnet and nose. The Avon's body work is all in one piece, going round the car (including the rear wheel arches) and then having just the nose and bonnet to fit separately. Also, the chassis doesn't look right either.

Good luck with the build though and enjoy it





Mark

Tiger Avon

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FOUR HUNDRED YEARS

posted on 13/3/19 at 01:25 PM Reply With Quote
quote:
Originally posted by kevyo89
Looks good bud. I am building my Locost MX5 Turbo at the moment and also currently exploring engine management. You are quite correct - the ME221 ECU is expensive at 600+. I have done a little research on a cheaper alternative and found the following:

https://lowcostracingsolutions.co.uk/pnp-standalone-ecu-s/20-6-mazda-mx5-standalone-pnp-standalone-ecu-all-models.html#/31-model_type-mk1_16_18

I believe it is a Speeduino-based ECU which is tuned using the same software as the Megasquirt ECU (a rival to the ME221). I have spoken to a tuner who believes it will do my trick perfectly but I am still debating whether this would be a case of 'buy cheap, buy twice'.


Thanks for the link I will bear that in mind as the project progresses.





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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FOUR HUNDRED YEARS

posted on 13/3/19 at 01:38 PM Reply With Quote
quote:
Originally posted by miskit
I just stripped the loom and popped all the unused pins out of the connector blocks. Not especially difficult and mine was a Mk2.5 with all the bells and whistles.
End up with about 20kg of unused loom. Used the instruments but built my own loom for lights etc.

Brilliant thank you, this is the route we would ideally like to take, how come u didn't use the lighting loom? Is there anything odd that you had to keep to enable the engine to run? Mine is also a Mk2.5.

Cheers
Simon





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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FOUR HUNDRED YEARS

posted on 13/3/19 at 01:54 PM Reply With Quote
quote:
Originally posted by Tiger Super Six
I am really not sure that this is a Tiger Avon - The Avon has fiberglass body panels and a raised bulge in the bonnet and nose. The Avon's body work is all in one piece, going round the car (including the rear wheel arches) and then having just the nose and bonnet to fit separately. Also, the chassis doesn't look right either.

Good luck with the build though and enjoy it


Excellent I was hoping someone with a proper Avon would tell me otherwise..... I have amended the header to 'Avon based' :-)

I purchased the How to build a Tiger Avon book and compared the chassis to the drawings, dimensionally it is practically identical (within 1mm) and there are similarities most obviously the steering column, radiator mounts and the webbing around the seat back area. The rear end section where the wishbones all mount is also very similar. There are differences, most notably a lot of square box section has been substituted for tube and there appears to be a fair amount of additional webbing/bracing in some areas.

The wishbones and uprights (front and rear) are definitely tiger.... these are identical to the book and also feature the weld orientation marks. The scuttle / dash is possibly different as it has been made in one piece and bolts on and off, it's quite nice tbh!

The body is also different as you say, it's all a bit puzzling tbh. Looks home made but whoever did the aluminium work was good, the side panels have lovely swaged holes for the wishbones etc.

I suspect this is a home built chassis perhaps based on the Tiger Avon but changed to suit the builders requirements. I stated it was an Avon as after much research realised it wasn't really anything but is more Tiger than locost.

I will post more detailed images of the chassis, perhaps you guys could give me some more thoughts.

Thanks
Simon

[Edited on 13/3/19 by FOUR HUNDRED YEARS]





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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Tiger Super Six

posted on 13/3/19 at 04:31 PM Reply With Quote
I agree, I think it is likely a home built chassis based on the Tiger Avon, changed to suit the builders requirements. Will be interesting to see if the Avon bodywork fits it.





Mark

Tiger Avon

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miskit

posted on 13/3/19 at 10:44 PM Reply With Quote
quote:
Originally posted by FOUR HUNDRED YEARS

Brilliant thank you, this is the route we would ideally like to take, how come u didn't use the lighting loom? Is there anything odd that you had to keep to enable the engine to run? Mine is also a Mk2.5.

Cheers
Simon


I had already replaced the lighting loom on the car using the MX5 column so just spliced into that (built the wiring box over the top of the battery, it has a lid to seal it up)

Yes! - The earth for the main relay is attached to the same earth as the wipers , indicators and other stuff I was not using. If you are not using the MX5 box you will need speed and N sensor, if you don't use the dash it needs a bit of extra work too

Oh I have wiring diagrams if you need them



[Edited on 13/3/19 by miskit]

[Edited on 13/3/19 by miskit]

[Edited on 13/3/19 by miskit]

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FOUR HUNDRED YEARS

posted on 15/3/19 at 09:41 AM Reply With Quote
quote:
Originally posted by miskit
quote:
Originally posted by FOUR HUNDRED YEARS

Brilliant thank you, this is the route we would ideally like to take, how come u didn't use the lighting loom? Is there anything odd that you had to keep to enable the engine to run? Mine is also a Mk2.5.

Cheers
Simon


I had already replaced the lighting loom on the car using the MX5 column so just spliced into that (built the wiring box over the top of the battery, it has a lid to seal it up)

Yes! - The earth for the main relay is attached to the same earth as the wipers , indicators and other stuff I was not using. If you are not using the MX5 box you will need speed and N sensor, if you don't use the dash it needs a bit of extra work too

Oh I have wiring diagrams if you need them

[Edited on 13/3/19 by miskit]

[Edited on 13/3/19 by miskit]

[Edited on 13/3/19 by miskit]


Miskit wiring diagrams would be amazing, any chance you could post a link to them on here?

Thanks
Simon

[Edited on 15/3/19 by FOUR HUNDRED YEARS]





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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FOUR HUNDRED YEARS

posted on 25/6/19 at 12:43 PM Reply With Quote
Spent a few weeks stripping the MX5 of all its decent parts, managed to sell what I didn't need and ended up with an almost free engine and box! Not much progress on the kit as I've been busy at home but in the last couple of weeks I managed to find some time in the garage.

First thing was to cut out some of the tunnel as matey had built it around a type 9 box and my mx5 box was wider in certain areas. Got the engine and box centralised in the chassis, its sitting about 7mm lower than the book states, this is because I am trying to use the bodywork provided with the kit and the aluminium bonnet and GRP nosecone I have don't have the raised bulge like the Avon does, time will tell if I made a mistake here and should have cut a hole in the bonnet and fabricated a bulge......

Therefore my box is going to sit slightly lower than the centerline of the diff in its correct position, from talking to guys at work it should not be an issue as the prop should be at a slight angle anyway, its better for the UJ's on the prop I'm told.

So with the position sorted I made the engine and gearbox mounts, I have used 6mm thick plate and 4mm wall tube, possibly a bit overkill but certain to last and not fatigue. I cut all the plates and tubes on my CNC mill so all the angles were accurate. I didn't like the standard way of mounting the engine as it seemed to me with the rubber mounts bolted perpendicular to the engine the forces would be pushing sideways through the mount, therefore I copied the dimensions from the MX5 subframe and made some angled plinths to bolt the rubber mounts to, a bit fiddly but I'm quite pleased with the result.

20190507_ 190817 by Simon Longley, on Flickr

20190327_ 194533 by Simon Longley, on Flickr

20190601_ 142137 by Simon Longley, on Flickr

20190601_ 142203 by Simon Longley, on Flickr

20190601_ 142232 by Simon Longley, on Flickr

For the gearbox mount I took inspiration from the MX5 mount sold on Kit spares but I milled it from solid rather than fabricating it, just easier for me. I need to remake this as although it works I am going to beef it up quite a bit.

20190505_ 155243 by Simon Longley, on Flickr

20190505_ 155318_001 by Simon Longley, on Flickr

20190505_ 162446 by Simon Longley, on Flickr

So with the engine and box mounted I turned my attention to the diff, I know this is back to front as you are supposed to build a car from the rear forwards but I decided quite early on to ditch the RX8 diff so I knew the ford one would go back in its original place as most of the mounts were still in place. The RX8 diff was easily twice the weight of the ford one, and the mounts were looking complicated and weighty so although it was an LSD I decided the 120bhp mx5 lump really didn't need it, the bonus with going back to the ford spec is the driveshafts I have will slip straight in and I can always fit a Sierra LSD in the future if I want to. As you can see from the pictures quite a lot of the NS mount had been cut away, the Tiger book shows 4 separate plates to mount the diff but this chassis had two long plates instead, I am going to add some mounts using the two threaded bosses at the nose of the diff and also a mount at the rear on the cover, again probably overkill but peace of mind and all that.

20190615_ 154235 by Simon Longley, on Flickr

20190615_ 174207 by Simon Longley, on Flickr

20190615_ 174222 by Simon Longley, on Flickr

20190615_ 174240 by Simon Longley, on Flickr

20190616_ 155205 by Simon Longley, on Flickr

20190616_ 155229 by Simon Longley, on Flickr

20190616_ 155218 by Simon Longley, on Flickr

Then I took the weight of the engine and box on jacks and cut the rest of the tunnel away, hoping here the chassis hasn't moved I am going to have to measure up before I finish welding the new tunnel. I bought some box section and am copying the dimensions from the book and returning it to the standard design to make my life easier. That's it for now hoping to make some more progress soon.

[Edited on 25/6/19 by FOUR HUNDRED YEARS]

[Edited on 25/6/19 by FOUR HUNDRED YEARS]





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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Mazdaboy

posted on 24/8/19 at 06:37 AM Reply With Quote
Tunnel

Looking good, did you have to mod the tunnel much and do you have any pictures? Cheers
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FOUR HUNDRED YEARS

posted on 29/9/19 at 06:50 PM Reply With Quote
quote:
Originally posted by Mazdaboy
Looking good, did you have to mod the tunnel much and do you have any pictures? Cheers


Not really I think it's basically ended up the same as the original but with the front uprights positioned slightly further back. This is it for now once I've done the handbrake fixings and a few other brackets I'll add some more bracing.

20190928_ 200941 by Simon Longley, on Flickr

20190928_ 201010 by Simon Longley, on Flickr

20190928_ 201017 by Simon Longley, on Flickr





23hp 650cc Fiat 126 De Ville - Daily
Forward control Toyota Hiace LWB - Camper
1974 RWA MG Midget - Fun for the GF
Tiger Avon - Not built yet!

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