A10 won't start.

[a10 gf]

With plugs taken out, and well fixed against some engine part: "Spark seems reasonable.... its yellowy white....", I'd say that's strange. No sign of any blueish spark even with a solid kick? And one should be able to 'hear' a small 'tick' when sparks occurs.

After some good period of kicking + various throttle action, does the plugs get wet (they should), does it smell petrol from the silencers (it should).

If petrol for sure getting into the cylinders: not even the smallest sign of any explosion, some kickback, some carb spitback? absolutely nothing whatsoever? Unless timing is completely havoc (still could ignite some fumes), then imo no spark occurs when plug is in position in cylinder.

[Ewen]

Trying to get crankshaft pinion off..... pretty bloody tight so maybe it has moved. Good news really.... if it has. Thinking about heat now. I'm tapping it around with a drift while it's under load from the puller. Problem can only get very thin puller blades in the grooves. I have had to grind my puller down.

[Ewen]

Was some moisture on plugs. Bit of blue in spark when I check in shadow.

[Rocket Racer]

What sort of plugs? There have been issues with the NGK's that once flooded wont clean up and chime in. A number of people I know struck it, with new NGK's and I've reverted to champions.
With a correctly timed spark, a motor with a blocked pilot wont idle well but should still be capable of being started and ridden. But the pilot screw will not be responsive when you try and wind back the idle
I recently had a problem with my ZB33 where after changing a slide to a less worn one, I managed to block the pilot hole (a 289 carb) with a poor gasket, around the same time my mag started packing in. the overlapping problems :popping and banging due to the blocked pilot, then cutting out after a few miles due to the mag did cause some head scratching.

[Ewen]

The original plugs had seen very little use and then I tried brand new ones so it won't be the plugs. Does anyone know if the pinion on the crankshaft is usually very difficult to pull off?

[Ewen]

It does fire..... got a very short burst ONCE.
How do I check valve timing precisely?

[Rocket Racer]

It does fire..... got a very short burst ONCE.
How do I check valve timing precisely?

Ewen, I'm a bit confused why you are thinking about cam timing or the crank pinion. Is this a recent build? those things dont typically change. The mag gear might shift on the taper or be set on the wrong cylinder. What has been changed since it last ran well. is it a k2f mag with auto adv retard set up? You say you had a burst, so better than a single bang. sounds promising for ignition you're unlikely to get a burst of firing from an incorrect ignition setting. Fresh fuel? did it sound like both cylinders, does suggest fuel side if you got a burst or a weak spark. Also indicates timed on correct cylinder.

[Ted_Flash]

Modern plugs have no glaze on the nose as they run under computer control/ very lean.  Once wet with "fuel" that's soaked in, the nose is conductive.  Have you access to a couple of old plugs with glazed noses?

[Ewen]

Swarfcut cracked it... thanks a lot. Incredibly the key sheared on the crankshaft. The intake valve starts opening when the piston is at the bottom of its stroke and continues to open fully as the piston rises... I think we all know that ain't right. Of course the ignition timing was right because I set it off the piston but the valve timing is way out. I can see the section of key in the pinion and can just make out, with a magnifying headset, the keyway in the crankshaft about 80 degrees around from it anti- clockwise. Surprisingly this means that the crank has rotated a full 280 degrees within the pinion since the key sheared.
Now gotta get the bloody thing off..... it is tight. Any ideas gratefully received. I ground down my puller legs to get them to go in the grooves in the pinion and clamped them in place but no joy. I guess heating the pinion is the only option??  Has anyone taken one of these pinions off? How hard are they to get off usually. Thank you for all contributions.

[RDfella]

Usually they come off easy. Clearly the sheared key is binding things up. Heat may help (shouldn't affect the temper unless you get it to blue heat, and then heat transfer to crank will be a worry) but best to somehow - without damaging the teeth - rotate it back and forth to free up the sheared key a bit.
After you've sorted that, a compression test will be useful, in case timing that far out has bent valves.

[Ewen]

For those who came in late... I mention a piece of metal jammimg in the gears on 1st page.
How do I get this bleedin pinion off??

[RDfella]

How do I get this bleedin pinion off??

See post above yours. Good 'ol Percy Verance required I'm afraid.

[Ewen]

Thanks RDFella. Just seen your post. So the valves descend far enough to potentially hit the pistons. Fingers crossed.

[Ewen]

As I think about... quite amazing that the valve timing was way  out and yet both tappets were rattling free when I did the ignition timing. Rather unlucky.... if even one of them had been under load I would have been alerted to the problem much earlier.

[Swarfcut]

 Ewen. Reading thro' from the start the evidence was there, just a little obscured. So, how to get it off?  Firstly the crank nose is relatively soft, so avoid violence if you can. All that is needed is enough brute force and guile to draw the pinion off the crank. As RD suggests, rotating the pinion back and forth so the keyways align again is worth a go. Locked on solid? Heat and a puller.

 Worst case is to sacrifice the pinion, either by cutting it off piecemeal, or welding lugs on and use a big takes no prisoners puller, or preferably a slide hammer. If you go down the welding trick with Mig, TIG or Arc, put the earth on you new lugs  otherwise everything will end up as a solid lump......

 Don't forget the cam drive key. When the keyway on the cam is uppermost, the timing side inlet camlobe points down to roughly 5 o'clock viewed from the drive gear and the inlet valve should be closed as the follower approaches the back of the cam. You can't see this on a built up motor, but that's what's going on inside.

 Good work finding the problem.

 Swarfy