Briggs and Stratton oddity (2023 Update)

[Tim+]

I happened to stumble upon an old Hayter electric start lawnmower chucked into the long grass by a road whilst out for a jog the other day so I?ve brought it home to see if it?s repairable or has any bits worth salvaging.

I started stripping it down and all the bolts were regular metric sizes until I came to remove the engine cooling cowling. 10mm socket too big, 9mm too small.

It did occur to me that they might not be the original bolts so I tried all the AF and Whitworth spanners that I have. No joy.

Eventually dug out a cheap 9mm open ender spanner that could be forced on with a bit of percussive persuasion.

I?m now inclined to think that they are original as they all match and my micrometer measures them up at 9.5mm. WTF is the point of that?? How many socket sets include a 9.5?

I can?t believe that a designer decided that 9 mm would be too weak and that a 10mm would be too cramped for space.

Tim

[alan_m]

A layer of rust making a 9mm bolt oversize

[Fredxx]

My 3/8" socket would be at least 9.525mm, likely larger for a little clearance. If this was a 3/8" bolt I would be surprised you squeezed a

9mm socket onto it, unless it was a 12 sided socket?

Briggs and Stratton has a US heritage so could well be imperial sizes.

[gareth evans]

The standard dodge is to use the larger spanner and then to fill the gap with the tapered end od a large flat screwdriver.

[Tim+]

Nope. Definitely 9.5mm.

Tim

[Paul]

Um, that is 3/8" ...

I keep both socket sets here.

Such an occurrence here, would not even result in an eye roll. We just alternate between the two socket sets, "until something fits".

With a lawn mower, the engine is made by one shop, the deck and handle by another shop, with thousands of miles between 'em.

You're lucky the engine block is not made of plastic. They tried that. Imagine how carefully you'd have to torque the bolts then. "Oopsy, <crack>, too much torque"

Paul

[newshound]

Is the right answer. Could even be BSF/BSW. Although Hayter is British (I used to work with a member of the family).

[alan_m]

I've just replaced the plastic carburettor on my Briggs and Straton engined lawn mower. The third party compatible carb cost around £10 (inclusive of postage). The only metal on the carb is the butterfly flap, the inlet needle to the float chamber, the pin that is the pivot point for the float, and the two bolts that hold it together.

I will strip down the one I took off but a can of carb cleaner recommended for refurbishment could almost be the same cost as the replacement carb. Also, all gasket kits also seem to be the same price as a the third party carb replacement - luckily the gaskets are robust and a replacement is not required for the carb I removed.

[Clive Arthur]

3/8" is 9.525mm

[Clive Arthur]

Ignore me. Been said.

[Tim+]

Found a 3/8? inch ring spanner eventually. It fits rather loosely but better than anything else so far.

Yeah but, these are bolts into the engine block. Everything else bolted to the engine is metric.

Tim

[Tim+]

I didn?t squeeze a 9mm socket onto it. Re-read my post. A 3/8? spanner fits rather loosely (but usably).

But that wouldn?t explain why all the other engine bolts are standard metric sizes. It?s just the engine cooling shroud retaining bolts that are odd.

Tim

[Tim+]

Yeah but, my micrometer measured at 9.49-9.50.

Tim

[Roger Mills]

What diameter and threads per inch are the bolts themselves?

[Fredxx]

Sorry! "9mm open ender spanner".

I have been known to hammer open spanners successfully too.

Sometimes it is useful to have a digital caliper. I fine 1/2" sockets and 13mm are often interchangeable down to tolerances.

You might get a clue from a thread gauge. The pitch on threads is more accurately defined.

[Fredxx]

11mm and 7/8" are interchangeable, and as I've said 1/2" and 13mm can be generally used interchangeably, so can 14mm and 9/16". It all depends on the quality of spanners/sockets.

[Fredxx]

I think the 3/8" - 9.52mm is treated like an upper limit. So 9.49-9.50 is a quality bolt. Shame about the 3/8" spanner!

[Roger Hayter]

That's 3/8" AF with pretty high precision.

[Brian Gaff (Sofa]

Its obviously an alien from the planet zob who dumped it there, and their socket sets do have that size?

Brian

[Brian Gaff (Sofa]

American stuff often seems to have illogical sizes, what about the thread itself? Brian