Douglas SV54

Sadly, although there is a picture of thumb nut on villiersparts website, he has no stock.
Back to square one. I wish I could work out what thread it is. OD is about 0.156" and 30 TPI so far as I can see.

Duh, I always forget BSC! I reckon it might be 5/32 x 32 TPI BSC. Back to the shed

So the barrel came off fairly easily - once I discovered the two studs inside the valve chest.  (Must take the time to study manual BEFORE starting disassembly)

Piston rings all present and correct and moving freely.  Couldn't believe the size of the tappets.

On to the valves. The lip on the valve chest made it a bit tricky to get the spring compressor in which resulted in a certain amount of foul language.  Got there in the end and inlet looked pretty good but, of course, exhaust was quite pitted. Stems were a bit 'gummy' but cleaned up fine. Seats re-cut and valves lapped in. Much easier to get them back in as I could fully compress the springs.
Should get it all back together in next day or so and hopefully will have better compression

Decided to have a go at taking off the flywheel.
Got the starting handle 'boss' off okay and found big bolt holding flywheel on. Didn't have a 11/16" socket (now on order) but 1-1/4"AF was close enough.
Looks as though it's keyed and doesn't want to come off yet. Any suggestion?

rusted on, tapered shaft, lots of heat but try to heat just the flywheel, make a puller to load the flywheel whilst heating. Can you get the crankshaft out and put it under a hydraulic press.

Maryalice

Find somewhere you can get a pry bar behind it, put nut back on loose and while pushing on the pry bar so it is pushing the flywheel off belt the nut.

blue cat wrote:Actually three types of thread were/are used for spark plug thumb nuts, 2BA, M4 and 8/32 UNC.

I buy a few M4 thumb nuts from the green spark plug company and if they don't fit the sparkplug threads I just tap them out to 8/32 UNC, being brass they tap out easily (these taps are dirt cheap on fleabay) I've never had one that did not fit afterwards.

maryalice wrote:rusted on, tapered shaft, lots of heat but try to heat just the flywheel, make a puller to load the flywheel whilst heating. Can you get the crankshaft out and put it under a hydraulic press.

Maryalice

Bless you Maryalice  I'm just a retired IT consultant (fancy name for someone who tinkers with other peoples computers ) with no access to that sort of esoteric weaponry - just hand tools and a pillar drill.  No formal training , can't weld, never touched a metal working lathe. I did restore i.e 'bodge' a few Minis and MGs in my youth.

Despite the lack of experience, whilst working in KSA, I did help repair a 400 horsepower Ingersoll Rand air compressor because the factory engineer was on leave. With the factory totally shut down through lack of air the MD said "Paul,  it is broken now. When you have tried it will not be any more broken"  Turned out one of the hoses had delaminated and there was a dirty great lump of rubber stuck in one of the rotors.

Paul,
Sorry I just assume that everybody has a workshop like me.

Maryalice

maryalice wrote:Paul,
Sorry I just assume that everybody has a workshop like me.
Maryalice

No apologies necessary  Just 'cos I'm green with envy doesn't mean I don't enjoy seeing all the skill and expertise shown on this forum - anyway I love making busted stuff work. Goodness know what's going to kick off when I start on the Petter!

Well setting the gap between tappets and valve stems was a right faff! Two dirty big spanners and a piece of metal rod to stop the tappet rotating all inside the valve chest. The air was blue!

Finally put it back together and put a squirt of petrol down the plug hole. A few cranks and.... nadda.
Compression still seems low despite re-cutting seats and lapping valves in. I whipped the head off again and a poured a dollop of oil on top of the piston - there is no slap when I try to move the piston. Head back on and when cranking compression seems improved.  So, despite appearances maybe rings are duff. Barrel off again and they look fine.
Any suggestions as to what else I can do before shelling out for new rings on the off chance?

Woodsman wrote: <snip> So, despite appearances maybe rings are duff. Barrel off again and they look fine.
Any suggestions as to what else I can do before shelling out for new rings on the off chance?

Gap the rings in the bore?

Robotstar5 wrote:
Gap the rings in the bore?

Brief explanation for numpty please.

Paul, I believe this means you should ensure there is the correct gap between the ends of the piston rings when they are sitting correctly in the bore. The usual way to do this is to insert the rings , one at a time, into the bore at a point where the rings will have swept the bore. This means not right at the top or bottom of the bore, using the piston , if it is a flat top one, push the ring into the bore. This ensures the ring is sitting square in the bore, then use feeler gauges to measure the gap between the ring ends. There is usually a manufacturers recommended gap, which allows for the different expansion ratios of the various materials that have been used to produce the cylinder, pistons and rings. If this is not known, then there is a rule of thumb which can be used. This calculates the gap as a ratio of the bore size to gap in thousands of an inch. Off the top of my head I cannot remember the formulae, hopefully someone else will be able to let you know, if not I will try and find it for you.

Neil

Thanks for the instructions Neil. I think I can manage that but not sure what to do with the info. My limited understanding of piston rings goes as follows:

Bottom 'oil control' ring allows oil to pass up from crankcase to lubricate cylinder.
Middle 'scraper' ring returns oil to crankcase.
Top 'compression' ring does what it says on the tin - maintains seal on compression and power strokes.

Given that the gap is to allow for expansion as the engine warms up how do I determine that the compression ring is worn and leaking when it's cold?

All advice gratefully received.

All rings are gaped cold.
Remove the rings from the piston and carefully place each one in the piston bore square to the bore, check that there are no gaps showing between the ring and bore, if there is the bore maybe oval or the ring maybe oval either way it will need new rings, the bore can be honed with a three legged honing tool in your drill, this will help the new rings bed in. Also check the ring gap if its outside its spec then new rings required.

Maryalice

Rule of thumb for ring gaps is 4 thou per inch of bore on water cooled engines and 6 thou per inch of bore on air cooled engines.

Well done Stuart, I thought there would be someone with the knowledge. I knew there was a difference between water and air cooled but I couldn't remember what the actual figures were. Hopefully your information will help Paul to assess the wear, to determine if new rings, or worse case a re-bore is required.

Neil.

Thanks men. Will try to get the feelers gauges out later today.

Woodsman wrote:Thanks men. Will try to get the feelers gauges out later today.

I had to smile recently when my local garage was sold and the owner was getting all the tools etc ready for auction. He has had the place for almost fourty years so a lot of stock to dispose of. Anyway he employed only one mechanic in the end and he was helping to sort things, and Dave (the owner) came across a set of feeler guages. His mechanic, who is in his thirties, didn't actually know what they were! Well of course they are rarely used nowadays, plugs come ready gapped, contact breakers don't exist in the motoring world, nobody checks valve clearances and the garage stopped doing engine overhauls years ago as they were too time consuming so they contracted them out while they got on with more profitable servicing etc.
Actually I bought two sets from ebay recently as I could never find mine, our motor factor didn't stock them as 'nobody uses them nowadays' but last week a neighbour was sorting his old toolbox out and gave me set of pre-bent feeler guages that he had in the early sixties. At least I no longer have to bend ordinary ones to get into tight spots!
Apologies for going off topic!

Pete.

Measured bore as best I could (no stick micrometer) as 3.227"  Nominal bore is 3.250" so that fits nicely, if you'll excuse the pun, with the 0.030" OS piston.

Stuart's rule of thumb gives me approx 0.020" gap. Measured gap is approx 0.040" so I guess that settles it.
I emailed Cox & Turner a few days but no reply as yet.
Thanks to all concerned.