Exhaust manifold studs

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Originally Posted by aussiebushman

Hi Phil

Afraid you fell for one of the oldest tricks in the :threads" book - Chasers are NOT taps. The latter cuts a thread and that is the reason you ended up with excess play. Conversely, a Chaser does NOT cut the thread - it reforms it

Of course you needto know what the thread is because BSF, Metric and UNF are not the same.For that you need an inexpensive thread guide tool

Attachment 180912Hare & Forbes should know better than to sell a tap & die kit without asking what you wantedto do with it.

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Hi Aussiebushman, Perhaps I should explain myself more clearly.
Some years ago I was restoring a Morris Mini 850, and as all the fasteners are imperial, I bought an imperial tap and die set that included both UNC and UNF taps and dies.
While refurbishing the gearbox I decided that I should be able to run a tap through the holes to clean out any debris that may be in there.
To my surprise when running a 5/16” UNC tap through a previously tapped (by BMC) 5/16” UNC hole my tap was removing metal.
If I screwed a bolt into one of the old holes, the bolt was a nice fit.
If I screwed the same bolt into the “cleaned” hole the bolt was a loose fit.

I then went to Sydney Tools and bought a 5/16” UNC tap and ran it through one of the adjacent holes and it did not remove any metal, just some grime from the threads.
Clearly, there are some differences in the diameter of some taps and dies.
Perhaps some of the cheap sets are made to greater tolerances than “quality” ones, or are of a different size grade.

Based on the above experience where I have two different size taps for supposedly the same thread, could there be a similar variation in thread chasers, where a “cheap” set may not be manufactured to accurate size compared to a “quality” set.

Im not sure if you opened the Hare & Forbes link but their discription is for Tread Chasers but also refers to them as taps and dies.
The images of the kit clearly shows thread chasers. Perhaps it is just the way their IT people describe them on the website.

Regards
Phil

Hi Phil
I read your pm thank you. As said before, Hare & Forbes should know better than to cause confusion between taps and chasers- unless you have had prior experience of this it is very easy to be confused.

I can't see why there should be any noticable difference between budget and "high-end" chasers, though the latter would likely last longer. These are not tools any average vehicle owner will use more than a couple of times.

Unfortunately, now your threads are oversize, you will have to either use inserts (helicoils) OR tap the holes for the next size up and use bolts. The latter will be much easire to do than inserts unless the heads are removed. Retapping with UNC or UNF would probably be best but Whitworh is a coarser thread.

Rather than Hare & Forbes, I suggest you go to Lee Brothers at North Parramatta - very knowledable and helpful

Aussiebushman, the threads on my engine are fine as I haven’t touched them to fit the studs.
The issue I had with different sized taps was on a Morris Mini 850 gearbox as stated in my previous post.

I’ll check out Lee Bros as I didn’t realise they still existed.
I used to buy fasteners off them when they were in Church St, Parramatta !

Phil

And you had to use studs and nuts because you can't get bolts into the heads past some header bends.

DL