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The most important thing is that there is a gap of at least what is specified, otherwise when the engine is hot the valves may not close fully, so causing the valve to burn and reduce performance.
Obviously there is not much that can be done with too wide a gap, as the adjustment is to grind the end of the valve! I’m my limited experience the valve lift is quite high so performance is less affected Though if tuning for performance you will have to fit new valves.

One issue with over gapped clearance is that many small engines have a decompression feature that involves lifting a valve ( usually the exhaust) to aid starting. Consequently an over gapped valve may reduce or nullify that feature. It is important when checking clearances that both valves are “ off cam”, particularly where a decompressor, which may be a “bulge” in the cam, is concerned; gap the valve when it’s still “on cam” and you will end up with a wide gap and an engine that snatches or kick back when starting is attempted.
In the absence of engine specific information, a good rule of thumb is that both clearances should be checked when the piston is a quarter of an inch down the bore AFTER top dead centre.

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Images will help, but when you pull the chain, are you pulling against spring pressure ?
Sounds to be a similar set up to my Wanners. Cold and dark out there now but I’ll take an image or two tomorrow.

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All well here thanks, just trying to make all the available work, take up all the available time.

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Love it; shades of metal stitching a cracked cylinder block.

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the one thread in use all over the world to this day is ¼ Whitworth. It is found in the bottom of very camera ever made and on every tripod

It has always struck me as strange that the square drives used in socket sets made in “metric countries” are quoted in quarter, three eighth and half inch sizes etc. They appear to be another accepted international standard for that application.

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The fact that you say the plug has a tapered thread suggests that its for a 14mm plug hole which surprises me as I would expect an 18mm thread. Also , my experience is that NGK plugs don’t suit old engines.
First you need to establish whether its 14 or 18 mm diameter plug thread; then possibly the Green Spark Plug company will be your best bet.
https://www.gsparkplug.com/?gclid=CjwKCAiA_eb-BRB2EiwAGBnXXrA6MUagTJCDRqav-3twFo1AOZ141swNZ4wHQICJQHg1AIafwv7jDBoCDG8QAvD_BwE

[wristpin]

Hi I have a M1 rotorvator with a Briggs engine starts and runs fine if you put petrol in the carberetta but it won’t start without putting it in???

Really need the Model (92908?), Type and Code numbers but being on an M1 Cultivator it could be from the early 70s and quite well worn . From your description the engine is not sucking up fuel at cranking speed . Simple things, the O ring between carb and manifold has gone hard and is leaking, ditto the two ends of the pulse pipe, the choke butterfly is not shutting / sealing properly, the carb is not sealing to the tank top ( warped carb or tank face ) there is a simple cure . Then it gets more serious, valves not sealing properly and finally rings.
I’ve just changed what’s probably a similar engine on a Hayterette from an iffy starter to a first pull wonder by fitting a cheap set of pattern rings.
Before you do any of the above, try it with a totally full fuel tank and with the throttle just off stop.

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Your broken shaft. Just opened my copy of Heritage Tractor and seen an advertisement that says “obsolete parts repaired and manufactured”. May be worth an ask. JJPrice. 01981 510522

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Do we understand why the shaft failed in the first place?

When I had my business you’d be surprised how many transaxle half shafts we sold or fitted. Not confined to any one ‘box manufacturer either.

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If it’s the shaft with the green line over it, it’s the gear selector / first motion shaft with the two sliding selector keys (37) that engage with the inner dogs of the pinion gears just off the right of the image.

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Briggs always used to recommend a straight SAE 30 and I still use it in earlier/ worn engines but they now say that 10/30 is acceptable. Synthetic ok but a waste of money.
Don’t be too quick to knock Amazon, I’ve just purchased a set of genuine BS piston rings via them for far less than the UK TRADE price – crazy!

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When I was selling Countax tractors in the 90s/2000s they were fitted as standard so there will be plenty around from scrap engines.
Something like this
https://www.gardentractorspares.co.uk/westwood-countax-tractor-engine-oil-drainage-valve-52851200?gclid=CjwKCAiA_Kz-BRAJEiwAhJNY74fL76-64GFH22ZU4c2M34aITO_XvXYQXWtZWMUhy7TEj0hLkZjm_xoCCJ8QAvD_BwE

Or

[wristpin]

Using a proper vacuum extractor with the machine tipped towards the base of the filler tube gets most of the oil out and if changed regularly what’s left is not worth worrying about.
Alternatively get a quick release drain valve. Tip the machine away from the drain plug and fit the valve . Then, when it comes to change time, warm the engine, push a tube onto the valve with the other end in a catch can, and twist the valve to release the oil.
A brick under each of the row opposite wheels helps in both cases.

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1. Atlas Chain Co,Derby
5. Stowmarket

No idea about the rest but it raises the question of what sort of flight. Hot air ballon ? Engine powered?

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Sounding good. There may be something here that’s of assistance

https://www.dropbox.com/s/qbzpnukk2kgc8p5/Villiers%20F150001.pdf?dl=0

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