Slow morning in Ann Harbor, Norm?

M.

My mind's made up - don't bother me with facts!

 

 

this is a great thread.

Ha ha ha ha ha, get it?

man, I kill me.

Norm

Buttress threads are used on toothpaste tubes.

Cheers,

Kelley

"If you can afford the car, you can afford the manual..."

I think Lowenherz is German pre metric. Buttress is used some time on hydraulic lines to keep fluid in and on some moving parts where strength is important.  Don’t hold me to the Buttress thread though.

I did notice that the threads were really tight when putting some of the parts back on my mini; I just taped and dyed every nut and bolt before I put it back on.  That seemed to make up for any defect in the new parts.

(Insert snide comment here)    

There are entire books on thread forms and classes of fit.  Before you run a hardware store thread chaser into or onto a thread it probably makes sense to find out why it's tight.  Assuming everything is SAE coarse or fine is not a good assumption.

Since so many people have mentioned the trunnion/subby/body bolts it's safe to assume they were designed that way either by drilling the hole smaller than usual before tapping or using a tap with a lower or truncated crest to provide a tighter fit so they wouldn't loosen over time.  When Minis were designed it wasn't common practice to use Locktite or Nylocs - intentionally making interferance threads was.  The acknowledged off the shelf standard for thread fit in steel is 70-75% thread contact. Anything more than that provides a tighter fit.  Chances are the original designers took that into account.

Just flipping through an old machinist's practical guide I keep in my desk I found a page that shows 12 standard thread forms.  SAE (technically called American and Unified Standard) and Whitworth are only 2.  Ever heard of Lowenherz or Buttress?

No, the formula for the original Whitworth bolt head is D x 1.75 and gives pretty weird hex sizes.
Later, they modified this to save material and then called the spanners `BS', the formula became (D x 1.75) -1/16. Hex size is still weird.
The Yanks had the right idea with their UNC and UNF- "let's just use standard imperial size hex bar!!"

Kevin G

Sears - I picked up a thread cleaning set there back in Feb for next to nothing that included UNF, UNC, Metric and assorted thread files.

Metric is for people who can't do fractions.

zip,  where did you find a "thread restoration tap" ?  I have heard of chaser taps, but can't find anyone who has them.

I'm no machinist, but I would have thought that a quality, fresh tap would do the job.

He designed head size by what hex bar stock was readily available!

M.

 

My mind's made up - don't bother me with facts!

 

 

I read once that the Whitworth thread was about as close to a perfect thread form that could ever be designed. If only he wouldn't have picked some arcane method of determining the hex head size, it would probably be the standard today.

Declanm, I've noticed some tight threads also on my '67. Didn't think about it much and just cleaned things up with a thread restoration tap. Maybe BMC suppliers back in the day let tooling go past it's sell by date to save cost.

 

I referred to internal threads in immovable parts, not jam nuts.

I had to find some BA bolts for a Lucas dizzy and found some at an English firm named Model fixings: http://www.modelfixings.co.uk/

They are one of the few firms willing to sell in small quatities. 

His grandson taught me Applied Mechanics at the University of Birmingham!

Wait until you need an extra, extra fine 5/8" Whitworth jam nut for the chutch or brake hose!

Now I'd agree that B.A. (British Association) is hardly worth mentioning, although I believe the float chamber top on the S.U. is from that stable!

Back to the question, I have not experienced any noticable tightness compared to USA or metric threads. But I do use 'Never seeze' everywhere!

Martin.

My mind's made up - don't bother me with facts!

 

 

I have worked on a lot of different cars and race cars since the 70s, but I have never had problems with

threads being so tight as on Minis.  To be specific, I am referring to chassis parts, not engine parts.

I always had a simple view of the thread world.  There are coarse threads and fine threads as well as

metric threads and some hardly worth mentioning such as Whitworth.  This simple belief worked pretty

well until I started removing chassis and suspension parts from Minis and then trying to reinstall those parts

with new bolts into threaded holes.  So many of the new bolts are a really tight fiit into the front and rear subframes

and where the trunnion bolts attach the rear subframe to the shell, for instance.  I have also found the some of the gearbox

case and drop gear case are threads also quite tight.

I have assumed that all bolts are either SAE coarse or fine, with no metrics or other weird threads used on these early Minis.

Anyone else had these problems?  Am I missing something?  These words are for 1960-ish shells and apply even after

I have chased threads with a normal tap.