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Messages - OneManAndHisBike

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British Bikes / Re: kick starter slips

« on: March 22, 2009, 02:06:03 PM »

Take the clutch cable of, first of all. You want to get that out of the equation. If it still slips, you could have a bent clutch pushrod that's holding the pressure plate off (unlikely, but possible). You could have lost compression in the engine somewhere, and that would give the feeling of clutch slip. You could have oil that's too "slippery" in the primary case (have you used an additive?). You could have too much oil (suggest you drain the primary and try it for a while; it won't hurt to run it with oil in the primary for a day or two). You also want to check the clutch operating mechanism inside the gearbox end cover. Ultimately, you'll just have to drain the primary oil, take the primary cover off, and look at what's going on when you kick over the engine. The main thing is that none of these problems are particularly difficult to sort out. You just have to be methodical and work your way through them one by one. If the engine is running okay, you might try putting the bike on the centre stand, running the engine and using the back brake to see if the revs drop when you brake (MAKE SURE YOU KEEP THE REAR WHEEL OFF THE GROUND!!!). Better still, just ride the bike and snatch at the throttle. That will soon tell you what state the clutch is in. You could simply have worn clutch plates, of course.

British Bikes / Re: Rebuilt Engine Start Up Advice Needed

« on: March 22, 2009, 01:48:30 PM »

People worry too much about starting a freshly rebuilt engine. Inevitably there will be some wear (a cold engine is where most of the wear really takes place, after all). The trick is not to let the engine labour at low revs. Far better to get the revs up to around 2000-2500rpm and get that oil splashing around. If the bike has been standing for a while, I'd take the top end off and would directly lubricate the valves. I'd probably squirt some oil down the bores too and would leave it for a couple of hours to drain past the rings before starting. Then just fire it up and accept the wear as part of the natural life of the engine. The next most important thing is to keep that engine in service, which means running it as often as possible and always letting it warm thoroughly. Just remember to keep the revs up a little, and then run in the bike carefully by using all the gears and varying the revs; never too high, and never too long at any fixed revolutions. Sorry if I'm telling you the obvious.

British Bikes / Re: Help - rebuilt bonnie engine is smoking horribly

« on: March 22, 2009, 01:24:33 PM »

Regarding your smoking Bonnie, you say that you had it rebored, but what about the honing? People often forget how important honing is to get a good oil "shield" on the inside of the bore. Without honing, you can have either a dry or an overwet bore depending on how the rebore was handled. Also, you may have sticky piston rings. Replacement parts aren't always accurately made. The rings could be tight in their grooves. Either way, if it's smoking as bad as you say, you'll have to take the top end down and measure things. Take nothing for granted. It sounds like a vernier and micrometer job. Remember that if it's smoking continously, it's the bottom end. If it's the valves, you'll probably get smoking only on the overrun; i.e. when you open the throttle and then shut it off. Of course, you might just run it for a few miles. It just might need settling in. Lastly, Bonnies usually smoke on the left cylinder if they lean over too much on the centrestand. I think you said that the right side was really the problem. I assume you haven't got the bike on a slope or something when you're running it up? Hope this helps. Almost forgot, are you sure it's oil smoke and not just running rich?

British Bikes / Re: bsa m20

« on: March 22, 2009, 03:07:59 AM »

Regarding your M20, you can check compression and/or clutch slip simply by standing on the kickstarter. It should hold your weight easily unless you're unusually heavy. You don't say whether or not the bike starts easily, which can be a good indicator of various things. Next, check that the valve lifter has some free play. You could be inadvertently holding the exhaust valve off its seat and losing power. Next, check the float in the carburettor. You could be starving the bike of fuel, although you'd probably have other indications of that (coughing, banging, etc). A weak mag could be your problem. The spark might be adequate under a low load, but might fail under a heavy load - but this is unlikely to be the cause. It could also be the exhaust valve (common fault). It might have a burnt seat, or some carbon grit holding the valve off its seat, or might need lapping in. Either way, get the head off (after you've stood on the kickstarter and tested that for compression). Check your points too. Worn points will put the ignition timing out. Maybe you could post some more details about general starting when hot and cold, tickover, performance, etc. Also, this site has some good information on M20s: www.sump-publishing.co.uk. The comment about clutches on military bikes is correct. WM20s have single spring dry clutches behind an ally drum. If you overfill the primary case, you'll wet the clutch plates and the clutch will slip. But you should notice that on starting (you can easily clean off the plates after dismantling). But some WM20s have later 6 spring clutches fitted, which are designed to be wet (but still won't want over-wetting). I suggest you try a hill climb experiment with different plugs just to rule that out. I hope some of this helps.