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Haynes chassis measurement errors????
FERRARIST - 4/10/18 at 08:18 PM

Will start to build a Haynes chassis and i heard that there was some errors in tube measurements. I'm concern only for chassis itself, not suspension.
Is that true and is there any summary of it. Did a search here, it forwards me to Haynes forum, but registrations disabled.
Any help?

AdrianH - 4/10/18 at 09:13 PM

Which version are you considering building.

I built the Sierra option there was also a later MX 5 version although when I got a copy from the Haynes forum I do not think it was complete.

The changes I remember were to the rear wishbones to keep the original sierra drive shaft lengths.

There were also a drawing for left hand drive, an explanation of the front frame and position of the steering support, changes for the MT75 gearbox and a few other bits.

U2U me your email and I will send over a zip file with them all in.

Adrian

alfas - 4/10/18 at 09:43 PM

i know that for the crush-tube, the one inside the suspension bushes, was mentioned with a wrong measurement in the manual.

manual says 12,5mm, whereas the bolt has "only" 12mm...so too much play.

and unfortunately most of the (poly)bush manufacturers have followed this wrong measurement.

mikeb - 5/10/18 at 12:16 PM

This crush tube issue may explain a few things on my build.

Any idea which polybush insert manufacturers have it right?

Charlie C - 5/10/18 at 12:49 PM

I had a simular problem with the rear upright (sierra design) the upright made by Talon had a 1/2inch tube RU6 where the rear lower wish bone bolt on to the hub instead of a m12. I only notice because of the rotational play in the upright after using it for a few hundred miles.

jps - 5/10/18 at 01:04 PM

quote:
Originally posted by alfas
i know that for the crush-tube, the one inside the suspension bushes, was mentioned with a wrong measurement in the manual.

manual says 12,5mm, whereas the bolt has "only" 12mm...so too much play.

and unfortunately most of the (poly)bush manufacturers have followed this wrong measurement.


But an M12 bolt doesn't have an 12mm external diameter on either the threaded point or on the unthreaded part anyway.

Surely the crush tube should be torqued up with the weight of the car sitting on the wheels/suspension - at which point the crush tube will sit perhaps slightly off centre from the bolt holes - but likely less than 1mm - once it's torqed up the faces of the suspension bracket should be clamping the crush tube in place and the only movement will be the polybush rotating around the crush tube as the suspension arms move up and down.

An off-the-shelf bolt into a 'round number' mm hole/crush tube will never be a flush fit... If it was supposed to be flush fitting it'd be a machined tube inside the crush tube.

jossey - 5/10/18 at 02:58 PM

Have you seen the laser cut pieces that keep appearing on ebay on and off.

There used to be a post on here with page numbers and corrections.

I haven't looked but I recall scanned images of the book.

alfas - 5/10/18 at 03:00 PM

theoretically the crush tube is clamped by the chassis brackets...and the force to squeeze the brackets is done by the (m12) bolt.

in theory it doesnt matter if the crush tube has 12.1mm or 12.5mm...but under heavy loads i would not trust that the crush-tube stays in exact the same position inbetween the chassis-brackets, hence the bolt should keep the crush tube guided.

the non threaded part of an M12 bolt has 12mm, means the inner bore of the crushtube needs to be just slightly biiger than 12mm...12.1 is more than enoguh.

there s jsut 1 ebay-suplier selling poly bushes who also states the correct measurement (12.1 or 12.2) in his advert.

Slimy38 - 5/10/18 at 05:14 PM

There's a set of four documents that are 'fixes' to the Haynes book, if you haven't got them already send me a PM and I'll see if I have a copy somewhere.

The main one for me was the front part of the chassis, the D shape. The way it's built up in the book puts the suspension brackets at a slight angle, whereas the alternative approach puts a twist in the bars and lines the brackets up.

AdrianH - 5/10/18 at 07:18 PM

The sections I have emailed to him are as follows:

BYOSC_amendments_1.4.pdf
front_frame_guide_part1.doc
front_frame_guide_part2.doc
front_frame_guide_part3.doc
Left_Hand_Drive_Chassis.doc
MT75_Gearbox_Transmission_Tunnel_Mods.doc
Mx-5_Build_Guide-rev3.pdf
Roadster_Rear_Lower_Wishbone.pdf
Roadster_Rear_Upper_Wishbone.pdf
Seat_Back_Diagonals.doc
Shorter_Pedal_Box.doc
steering_support.pdf

Thought they would be a good starter for 10.


Adrian

jps - 6/10/18 at 07:36 AM

quote:
Originally posted by alfas
the non threaded part of an M12 bolt has 12mm


As standard they have manufacturing tolerances that mean the non threaded part could be as undersize as 11.7. If you're bothered about .5mm 'gap' you should be bothered about .3mm. (or not be bothered about either!)

Slimy38 - 6/10/18 at 08:17 AM

quote:
Originally posted by AdrianH
The sections I have emailed to him are as follows:

BYOSC_amendments_1.4.pdf
front_frame_guide_part1.doc
front_frame_guide_part2.doc
front_frame_guide_part3.doc
Left_Hand_Drive_Chassis.doc
MT75_Gearbox_Transmission_Tunnel_Mods.doc
Mx-5_Build_Guide-rev3.pdf
Roadster_Rear_Lower_Wishbone.pdf
Roadster_Rear_Upper_Wishbone.pdf
Seat_Back_Diagonals.doc
Shorter_Pedal_Box.doc
steering_support.pdf

Thought they would be a good starter for 10.


Adrian


Yep, they're the ones I have. Out of those the MX5 build guide is the main one I use, it's printed and pinned up around the garage. The first four are the main ones that apply to the book, I've actually pencilled in the amendments into my copy. The others didn't apply to my build although I did look at them for reference.

alfas - 6/10/18 at 08:38 AM

quote:
Originally posted by jps
quote:
Originally posted by alfas
the non threaded part of an M12 bolt has 12mm



11.73mm is the min. which is allowed by DIN-ISSO 4014 for bolts from class A...allowed does not mean that quality manufacurers will go onto this limit.

its like a bottle of shampoo...the target weight is 100ml...and the allowed tolerance is e.g. 98,5ml..... but the average of bottles must come close to 100ml...

and the tolerance accepted on bolts is minus measurement (the max. measurement is 12mm)....this means, the nearer you stay with the hole of the crush-tube at 12mm so less play you have. ideal would be a snug-fit, which you will not achieve in pratice .






[Edited on 6/10/18 by alfas]