RichardW's Velocette rebuild

[moizeau]

I remember a while back reading that although the spark plug was dry the fuel mix was dripping out the crankcase. With a tighter ring gap upping the compression maybe that's why it is getting some fuel up there.
Without having seen the inside of this engine, but with it being a 2 stroke, the crankcases must be completely sealed surely. If a fuel mix can leak out, air can get in, weakening the mixture. Also the piston will pull air through the transfer port(s) instead of fuel from around the crank.
Crank case seals were always a neglected thing on little 2 strokes and caused starting and running problems without them actually leaking out.
If you put a small amount of compressed air down the spark plug hole where does the air leak out with the carb off and the inlet blocked?
One other thought, has it got some sort of reed valve between the carb and cylinder to stop blow (pulse) back. Race engines like a TZ350 Yam didn't have them as they were never on tick over but when I put the TZ350 barrels on my 350LC I got a bloke at work to weld some TZ750 reed blocks on.
I realise you have other issues at the moment with the crank that need sorting first or it will wreck itself.
Best off luck

[CitroJim]

I'll have a look in my old books on the subject Richard... I know some crank-wheels have tin covers riveted onto them to increase the crankcase compression ratio and these can come loose and rattle like a bag of nails... I'm thinking yours may be a bit early to have this but always worth a check.

I assume the main bearings are plain.... They're shocking for leakage and engines like this need a well sealed and crankcase to start fairly readily and run well... Loss of crankcase compression is a killer... Some engines of the period had leather packing glands to minimise leakage past the main bearings...

Also, at risk of teaching you to suck eggs here but have you got the piston installed correctly? I'm assuming again the piston is a deflector type and the engine has one transfer port opposite the exhaust port(s)...

Put them in backwards and the engine will run but not at all happily!

[RichardW]

I would not have expected a roller bearing in the big end of that engine, more likely a bronze bush or white metal running on the crank.

Definitely a roller bearing, Mike!

Then I dropped the cylinder on, so I could refit the rollers in the big end



Some of these are in better conditions than others....!

However, soon becomes apparent that all the rollers need to be fitted to the crankshaft before the con rod is dropped over, that's going to be difficult with the crankcase in, so out it came again.... Easy enough to fit the rollers and then the conrod once on its side on the bench

On that second photo you can see the different material on the inner ring of the con rod, which stayed shiny for 70 years, including 20 lying about in my garage, makes me think it's white metal!

I assume the main bearings are plain.... They're shocking for leakage and engines like this need a well sealed and crankcase to start fairly readily and run well... Loss of crankcase compression is a killer... Some engines of the period had leather packing glands to minimise leakage past the main bearings...

Also, at risk of teaching you to suck eggs here but have you got the piston installed correctly? I'm assuming again the piston is a deflector type and the engine has one transfer port opposite the exhaust port(s)...

Put them in backwards and the engine will run but not at all happily!

Yes, the main is just a long bronze bush, this an overhung crankshaft. I think this will be effectively sealed as the oil is sucked in on the far end of the bush. The other end of the crankcase has the spacer piece , and then the end cover screwed in. I don't recall any sealing washers etc when it was dismantled, but that was 20 years ago!! Sure the piston is in the right way, don't think the engine would turn over it wasn't as there is a cut out in the skirt at the back to allow the con rod to pass. I'll get the side off and have another look / think!

[CitroJim]

Watching this with great interest Richard She'll be running beautifully soon... How much work then before she can take to the road again?

[RichardW]

If I could get it run, just need to fix the throttle (I've put a twist one on, but it sticks, really need to figure out how to get the straight pull one apart and cleaned / lubricated) and the cable which is too long. Change the taxation to historic (it's on the DVLA under it's original number, but not registered or SORN at present). Insure it, and away we go (well, not quite, since I still don't have a licence!!) It also needs the lights / battery sorting, the clutch cable is a bit short, and no doubt there are other snagging items!!

[CitroJim]

A good weekend of work there Richard!

Have you got to start from scratch with obtaining your motorcycle qualification? I believe these days it's quite a process...

Sorting that and getting the bike onto historic taxation may be quite an epically long task given how glacial the DVLA currently seem to be these days...

[RichardW]

Tax just appears to be on the spot at the Post Office (ah, well, maybe there's an issue!) - but it has to be insured.

Licence, yes, treated as completely separate to Car licence, so have to do CBT, theory test - and since it is 250cc (even though only 2 HP or something), needs to be a full licence, so need to do the direct access course where you are accompanied on a bigger machine.

[CitroJim]

That's quite involved but for an experienced driver it should be a breeze for you Richard

I'd love to be a fly on the wall at your test so I can see the look on the examiner's face when you rock up on a vintage Velocette!

Happily yes, vintage VED is all done at the Post Office Looks to be very straightforward too...

[Gibbo2286]

It will be either white metal or rollers not both, I spent many hours in my youth using a bearing scraper to adjust newly re-metalled bearings to match the crankpins.

[CitroJim]

I spent many hours in my youth using a bearing scraper to adjust newly re-metalled bearings to match the crankpins.

Dad told me all about that Eric... Sadly, as much as I'd love to, I've yet to... One day maybe...

I believe it's a skill very much still alive on preserved railways running steam locomotives...

[myglaren]

My dad, originally a steam fitter, claimed he could scrape a surface to within ten thou.
Could have made Johansson's Passbitar* I expect.
He left the railways when they started transitioning to diesel, he hated diesel but like the Deltic when it arrived.
Took a job in a shipyard. Diesel fitter.

* Johansson used his wife's sewing machine to polish them to the fine tolerances he needed. Worked for Sverige's Gevärsfabrik and transformed production there. Adopted worldwide eventually.

[Gibbo2286]

Still got the scraper in my toolbox.