Mk 5 plugs & caps.

[Hampshirebiker]

Sorting a few things out prior to starting the MK 5, I've removed the plugs (Bosch RO 545); which are well sooted & past their best. The NGK caps are stamped 5k ohms & I thought that resistor caps were not best suited to magnetos.
To cut a long story short, what plugs & caps should I buy? I assume new copper cored HT lead wouldn't come amiss either.
Thanks, Dave.

[Hampshirebiker]

I decided to stop fannying about, cleaned up the old plugs, fresh petrol & gave it a kick. It started OK but only ran well on one cylinder. The other was backfiring through the exhaust. Not easy to tell which side with the waffle box; but think N/S. I gave it a gentle rev, but it didn't clear. Both exhausts were hot & the O/S was slightly hotter (?).
I'll clean out & check the carbs; which I should have done in the first place. I just hope it's not a sticking exhaust valve.

[Hampshirebiker]

One blocked main jet - silly beggar. Now fires on both & idles beautifully. Thought about a quick run up the lane & by the time I'd faffed about & got it off the lift it wouldn't start - not a glimmer. I've had enough for one day, Im puffed out. How I wish I was 25 again.

[AndyH]

Haha you seem to be having about as much fun as me. I have been working really hard to get my comp into good usable roadworthy condition. So this evening after, cleaning the carbs out, balancing them perfectly, fitting a new petrol tap and filter plus more. I set off on a forty mile round trip, first 30 was good, but still tapping a lot from the top end, I am thinking the little ends haver gone, then the clutch started to slip..hmm a bit worrying so I adjusted cable and took it easy, started finding more and more false neutrals in the box, then it blew a head gasket which I had just fitted. I tell you what a Douglas 350 on one cylinder is hard work, especially up 1 in 5 hills. Finally got it home though

Oh well back to the drawing board. I didn't really want to do it but I guess its engine out and lets sort this properly once and for all. PS The head gaskets in the Douglas gasket sets on Ebay are lousy.

Andrew

[Hampshirebiker]

Andrew, that's a great help I must say, but it's cheered me up no end. Good luck with your grief. It sounds like you've got a bit more to do than me.
I've fitted a set of NGK B6HS & gave it another go. OK but a bit spitty from the carbs. Time to dismantle the carbs & put in the ultrasonic cleaner. I will ride it before winter.

[AndyH]

If your still having trouble starting the bike once the carbs are cleaned out it's more than likely the condensor that's built into the magneto that's failing causing a poor spark, I think it's quiet a common problem on old magneto's. I had the unit on my comp rebuilt by Brightspark magneto's and a more modern condensor installed. I know my bike has lots of issues but starting is not one of them It always starts first or second kick.

Well that's my best guess.

Andrew

[eddie]

Hi Andy and Dave,
                             When you strip and clean your carbs, carefully check and clean the choke blocks. On the engine side of the choke block there is what looks like a blind drilling with 2 holes coming in at the sides - there is also a very small hole (about 30 thou) in the bottom of the drilling - make sure this is also clear. While the carbs are dismantled, also check out the float chamber bodies - in the bottom of the chamber, there is a 1/8" guide hole for the lower end of the float needle - clean this out with a small drill. It often gets a build up of rubbish that either makes the float movement sluggish or limits it's movement.
  With regard to a weak spark - if the condenser has failed, there will be considerable arcing at the points. If this is the case, try backing it up by wiring an external condenser into the cutout lead, to see if there is any improvement.
  Blown head gaskets - this is becoming much more common now that we are forced to use asbestos free materials - I am still re-using the old original head gaskets I fitted to my Dragonfly in 1976. If the problem persists, go back to the copper gaskets (even fit 2 if you are worried that one may be too thin). Also, if you have the heads and barrels powder coated, make sure you tighten the head nuts several times during the first few cycles of heating and cooling - the powder coating is a plastic and it squeezes out from under the head nuts, thus releasing the pinch on the gaskets.
  Spark plugs, etc. - NGK B6HS plugs with non-suppressed caps on copper leads is the favoured setup.

  Hope some of this helps,
     Regards,
                   Eddie.

[eddie]

Andy,
          Regarding the clutch slip - try riding the bike again to see if you get a repeat of the clutch being OK and then suddenly slipping. I had a similar problem on my Dragonfly - I could start off on a cold engine and everything was fine for the first 12-15 miles, then clutch slip would set in to the extent that about 20mph was the limit. Stop for about 5 minutes to let things cool down, and everything was fine again for the rest of the day. Go out again the next day and the same would happen! On stripping the clutch, I found that the coupling on the gearbox was worn. This is wider than the centre boss of the clutchplate, so was trapping the plate and preventing any axial movement. Fitting a better secondhand coupling cured the problem.
      Also, oil on the clutch plate will give rise to clutch slip (and also drag - which can result in poor gear selection). If you suspect oil to be the problem, block the drain hole in the bottom of the bellhousing and pour about 3/4 pint of petrol in through the clutch inspection plate, then lift the clutch and operate the kickstart about a dozen times. This will wash the oil from the plate. Then remove the bung and drain the petrol. Before starting the motor, give the clutch release a couple of shots of grease (to make sure that hasn't been washed dry). Finally, check that the breather hole in the gearbox filler plug isn't blocked (this usually results in oil being pushed past the mainshaft seal into the bellhousing).
  Regards,
               Eddie.

[Hampshirebiker]

Thank you for the tips on the carburettors Eddie. When you say the "choke blocks", do you mean the big blocks in the main bodies that the slides rise & fall on?

[eddie]

Yes, Dave. the main brass block inside the body. If the carbs haven't been stripped for some time, the blocks may be stubborn to move. I usually undo the bottom cap nut about 1 turn at a time and with a suitable sized socket on top of the block, squeeze it in the vice to get the block on the move (don't try drifting it out as the blocks can be easily damaged). With the blocks out, you will find the 'blind' drilling centrally just below the main bore (it picks up with the drillings to the pilot air screw).

  Eddie.

[AndyH]

Hi Eddie

 Yes thanks very much for that information, like you said I should have probably re-tightened the heads after a heat cycle. I stripped them off today to do the blown head gasket and like you say, they weren't exactly tight. Good info and I will use the copper gaskets next time.

Re the clutch yes it was grease and oil on the plate, good tip for next time re the petrol and I will check the gearbox breather although it looks like there was an aweful lot of grease on the clutch operating mechanism and also a small leak from engine oil seal.

How do I know this, because I thought I better check the crank and sure enough the noise that I thought was detonation under full advance load was actually the big ends, one has about 10 though of up and down play and the other 20 thou, hence the metallic tapping noise I was hearing, especially under load.

I have pulled the crank out today and could really do with some advice as to what to do next. Does the club stock the parts to repair these? Will the rods be okay do you think? Do you know anybody that would be able to repair the crank for me.

The rest of the motor looks okay, barring a broken ring, some scuffing on one of the pistons but it doesn't look recent and there is no alloy pickup on the bore. However the cam followers are slightly dished.

Any help would be appreciated.

Regards Andrew