Author Topic: MkV Only working on one cylinder  (Read 539 times)

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Offline Pallijen15

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MkV Only working on one cylinder
« on: 25 May 2019 at 14:34 »
Hi, I've swapped over spark plugs, HT leads, cleaned slip ring with petrol rag but when running engine I take off the right side suppressor cap from spark plug engine still runs. Repeat operation on left side and the engine immediately stops. Been on a 30 mile run this morning but engine falters when ridden hard or uphill sometimes like there is fuel starvation. The fuel tank needs sealing as there is a bit of crap in there  but I've fitted a couple of glass type filters for now. Left side smokes very slightly(don't think this is a problem though, only seems to be on starting) right side doesn't. Any advice please? Just ordered new spark plugs although can't see this being the problem since I've swapped sides. Thanks, Paul J

Offline eddie

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Re: MkV Only working on one cylinder
« Reply #1 on: 25 May 2019 at 15:12 »
Paul,
        This sounds as if it started as a carburettor problem (an inbalance between the 2 carbs). It could be down to throttle cables not adjusted correctly - so that one cylinder pulls harder than the other, or possibly dirt in the bottom of a float chamber. The float chambers have a guide hole in the bottom for the float needle - they some times get partially blocked by dirt, thus restricting the movement of the float, thus ending up starving that cylinder of fuel.
  Please do NOT repeat your test of which cylinder is firing by removing a plug lead - this is the easiest way of ruining a Lucas magneto, as the spark will have no option but to short across the windings. (BTH magnetos had special spark gap screws to prevent this happening!).
  I would suggest you check out both float chambers, then set both slow running screws to 2 turns open, and the throttle stops so that they are just lifting the slides, and there is some slack on the throttle cables. Start the engine and get it running smoothly on both cylinders and down to a steady tickover. Finally, adjust the 2 throttle cables so that both cylinders pick up together.
  Also, engines that have the carbs out of balance often suffer from smoke from the cylinder that is running lazy, as that cylinder tends to draw oil past the rings.

  Regards,
                 Eddie.

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #2 on: 25 May 2019 at 18:47 »
Ok thanks Eddie, I'm sure there will be crap in the bottom of the float chambers as I didn't clean them out, I just fitted the inline fuel filters thinking that would solve the problem. I took the fuel tank off a while ago to rearrange the cable as the engine was racing when I turned the handlebars. There was no adjuster inline on the cable as I thought I was told there should be. The left carburettor I have dropped the needle a notch as the plug gets quite sooty. Both slides lift at the same time when opening the throttle. One of the fuel filters always has a little air in it, the other is always full with fuel.  Thanks

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #3 on: 26 May 2019 at 19:02 »
Hi Eddie, done all that, the right side(offside) cylinder (the lazy one) carburettor float chamber needle guide holes did have a lot of muck in so cleaned out, unfortunately still the same. There is no smoke at all from the offside exhaust but slightly from the nearside (whitish grey smoke). Would I be looking in the right direction if I were to check the points clearances in case the cam ring is worn? Could tappet clearances have an effect? If piston rings were gummed up would there be excessive black smoke? Any other pointers as to where I could look? Many thanks, Paul J (p.s. Throttle slides are 4/3, Left carb 274AK/4A, right carb 274/407R, needle jets 106, main 80, jet block30T. I know I already gave you this info a while back but just a refresher) 

Offline eddie

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Re: MkV Only working on one cylinder
« Reply #4 on: 27 May 2019 at 07:09 »
Hi Paul,
             First of all, check that the needle jets are both the same length - Amal made them in 2 lengths - your 274's should be fitted with the shorter ones otherwise the float chamber banjo bolt may be masking off the end of the main jet. You may find the bike runs better with 85 or 90 main jets (remember the sizes quoted in the handbook were for proper petrol - not the unleaded rubbish we are expected to use today!).
    Oil getting past the rings causes whitish grey smoke - black smoke is caused by too rich a mixture.
    By all means, check out the points gap - it wont be exactly the same for both cylinders, but should be within a couple of thou. If greater than that, check for slack in the armature bearings. Magneto bearings are mounted in paper cages and can work loose. If the outer track is loose, remove it and it's paper cage, thoroughly degrease it and re-assemble with a smear of Loctite.
  Tappet settings obviously affect how the engine runs - worn cams usually only affect the engine's high speed performance.

  Regards,
                 Eddie.

   P.S.  I assume you have already done a compression check to eliminate a burnt out valve or cracked seat.

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #5 on: 27 May 2019 at 10:52 »
Hi Eddie, I measured both float needles with a vernier gauge when I cleaned out the guide holes and the difference in size of the needles was minute, if any. I also measured the height of the floats.
There is no smoke at all from right cylinder so must not be ring problems or mixture then.
I'll check out the points gap next.
When starting up starts straight away but is a little bit lumpy until I increase the revs, then it's fine. Opening the throttle and driving at high speed is when it falters on the problem cylinder, steep hills also
I did a compression test a while back and think it was roughly 45psi. What should I be looking for, is this okay? I'll do another one anyway. Thanks, Paul
 

Offline eddie

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Re: MkV Only working on one cylinder
« Reply #6 on: 27 May 2019 at 11:19 »
Paul,
        I didn't say measure the float needles - I said check the length of the needle jets (the .106 jets that the main jets screw into) - they were available in 2 lengths (274's use the short one). If you have one long jet, the main jet may be so close to the bottom of the banjo bolt that the petrol flow is being restricted - this will be more noticable at higher throttle settings (only the slow running circuits bypass the main jet).
 
Regards,
               Eddie.

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #7 on: 27 May 2019 at 19:21 »
Sorry Eddie, I misread that. I'll check them once the rain stops here. I mentioned a while ago the guy who sold me the bike gave me some push rods that he had made specially. They are 5mm longer because when he tried to adjust the tappets there was no more adjustment left. After checking the contacts gap and needle jet lengths, if nothing unusual found, do you think it would be a good idea to take the rocker box off and see why the rappers won't adjust any more? Thanks, Paul

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #8 on: 28 May 2019 at 12:05 »
 Should have read 'why the tappets won't adjust'

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #9 on: 28 May 2019 at 14:35 »
Hi Eddie, measured needle jets, both identical laid side to side. Carried out a compression test, readings around the 50psi mark for both cylinders. Used my Sealey tester of which the Test Results say the needle on the gauge should move on every kick but the right (lazy)side didn't.  I did the test twice about 10 kicks each cylinder and both times the right one, the gauge did not move. Although it only took two kicks and the gauge did move(the Test Results state if after several kicks the gauge does not move then this is indicative of a sticking valve) could a valve be sticking intermittently, only now and again? Thanks, Paul

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #10 on: 28 May 2019 at 16:29 »
Just been informed I should have had the throttle wide open when doing the compression test but as long as I got the same results both sides should be okay for what I was testing for. Points gap is 8thou and 15thou of an inch. Is this acceptable?

Offline eddie

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Re: MkV Only working on one cylinder
« Reply #11 on: 28 May 2019 at 18:34 »
Hello Paul,
                 That difference in points gap is too much - it will cause one cylinder to run in advance of the other, as well as resulting in a weak spark on one cylinder. The usual cause is a paper cage around the armature bearing breaking up and allowing the bearing to float in the magneto end plate. Magneto bearings are mounted in paper cages  so there is no electrical connection to the body of the armature - if there were, the spark would etch the bearing track causing premature bearing failure.
  You should be able to replace the cage yourself - with the points plate removed, undo the 3 screws (one incorporates the spring clip for the points cover) and pull the end plate off. The inner half of the bearing will stay on the armature - the outer half may also stay on the armature if it is very slack in the end plate - just gently lever it off. The paper cage is like a narrow washer with about 16 'petals' around it - the petals fold up around the bearing, so the cage keeps the bearing central in the housing, and it also acts as a shim behind the bearing to control end float. You will find the cages come in 2 sizes, and different thicknesses - I usually opt for a slightly thinner cage and then fit it with a smear of 24 hour Araldite (don't use Araldite Rapid as that is next to useless for this purpose). When set, the Araldite gives the cage extra support. When you removed the end plate, there was probably some thin brass shims between it and the mag body - you may need to remove one or more of them if there is still noticeable end float on the mag armature. Aim to finish up with just perceptible end float.
   Good luck with the repairs,
                                             Regards,
                                                            Eddie.

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #12 on: 28 May 2019 at 19:35 »
Ok thanks Eddie, I'll get onto that tomorrow. Do I get this gasket from the Spares club or can I make one myself? Is it worth buying the book Spannerama? The BMS manuals seem to miss a lot of stuff out. Thanks, Paul J

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #13 on: 30 May 2019 at 11:00 »
Hi Eddie, removed end cover, prised off ball bearing cage from armature which came off easily, the cage had quite a lot of movement, before I prised it off moved it up and down. Behind the cage is, I presume, the armature shaft. A brass plate about 2" in diameter with four holes in at 90 degrees from one another. There are no shims or paper cages. Thanks, Paul

Offline eddie

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Re: MkV Only working on one cylinder
« Reply #14 on: 30 May 2019 at 12:29 »
Paul,
         I dont think Club spares stock the paper cages.  The Spannerama book has a lot of helpful information, but I dont know whether it covers mag repairs. The BMS manuals were basically a reprint of the Douglas owners handbook (that was supplied with the machine when new). In those days, it was expected that owners would contact their nearest Lucas depot for these types of repair - sadly, they no longer exist!
         When you took the end plate off the mag, the inner half of the bearing would have been left in place on the armature (with the brass cage and balls on it). If the outer steel track of the bearing was slack in the end plate, it may have stayed on the inner half of the bearing. The paper cage that normally gives trouble is in the bearing housing of the end plate and is sandwiched between the end plate and the outer half of the bearing. If you can turn the outer half in the end plate, it is too slack and has probably allowed the armature to drop (thus making the 2 points gap settings different). If the outer is firmly held in the end plate, leave well enough alone. While you have the end plate off, check out the cam ring and it's fit in the end plate. Also, check out the condition of the ramps on the cam ring - they should both be the same height (Lucas cam rings are usually pretty good for height, but they are often not quite 180 degrees apart, and need tweaking with a small grinder to get precise timing on both cylinders - not a job for the average owner!).

Eddie.

Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #15 on: 30 May 2019 at 14:41 »
Hi Eddie, cam ring, both sides 147thou one side and 148thou other side roughly the same and are 180 degrees to each other. Outer bearing ring in housing is tight fixed, won't move at all. Behind the bearing I can see a shim and a worn ring inside the bearing where the balls are in contact with.  Feeling with my hand there is no noticeable play with the cage in place. There is quite a lot of up and down play on the armature shaft but this is with the housing off. Any more ideas please. Thanks,  Paul  J

Offline Neville Heath

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Re: MkV Only working on one cylinder
« Reply #16 on: 30 May 2019 at 18:41 »
There are five pages on mags and dynamos in the Spannerama book. They include details of special tools that can be made to assist work and how to convert anti clock to clockwise (Douglas) if you have the need to. Go on treat yourself, it's only 7 going to charity.
Neville


Offline Pallijen15

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Re: MkV Only working on one cylinder
« Reply #17 on: 31 May 2019 at 07:35 »
Ok thanks Neville, I'll order one today. Think I'll check the timing as well. Only runs best on full advance all the time. It's difficult to check the points gap with a normal set of feeler gauges so I am going to check them again.

 

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