Author Topic: Ignition timing MK5.  (Read 8154 times)

0 Members and 1 Guest are viewing this topic.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Ignition timing MK5.
« on: 09 Feb 2016 at 12:46 »
I have now had my magneto rewound & overhauled. I propose to retime it from scratch. By reference to the manual the static timing is 36deg BTDC (lever fully advanced). Is this the correct figure?
I will have to remove the timing cover at the front & use a disc. Are there any marks that will indicate TDC with accuracy, or any further advice in connection.
Many thanks in advance (no pun intended), Dave.

Offline douglas1947

  • Master Member
  • ****
  • Join Date: Feb 2014
  • Posts: 385
  • Location: Germany
Re: Ignition timing MK5.
« Reply #1 on: 09 Feb 2016 at 15:47 »
Hi Dave,

there are no marks and you have to check tdc through spark plug hole (if your engine is not dismantled).
I have no measures in mm before tdc for the piston, so the disc is the way to do.
I have also to do it in the next time!

Michael


Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1724
  • Location: Hampshire, UK
Re: Ignition timing MK5.
« Reply #2 on: 09 Feb 2016 at 17:19 »
Hi Dave,
             Some years ago, I worked out that 36 degrees BTDC on postwar Douglases equals .276". On Mark machines, the mag gear will go through the hole in the back of the timing chest, so you can set it up before fitting the mag. I would suggest making sure the taper is clean and dry, then fit the wheel with a spring washer under the retaining nut. Just lightly tighten the nut so that the wheel drags on the taper, fit the mag and turn the armature until it is correctly timed. Carefully remove the mag, give the wheel a sharp, light tap to seat it on the taper, remove the nut, swap the spring washer for a plain one, then fully tighten the nut and refit the mag. Remember that Mark mags are set up with tight wire advance (unlike most British bikes). When messing about with mags on a Mark, it pays to remove the 2 HT pickups so that you can fit the 2 ¼BSF bolts after the mag is lined up.
    Regards,
                  Eddie.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #3 on: 09 Feb 2016 at 17:33 »
Thank you both, but another question; resulting from Eddie's post. The gear wheel is already on the mag securely. I assume that (under these circumstances) I will have to mesh the cogs as close as possible when mag & engine are set. Will this be close enough, or should I loosen the cog from the mag & get it spot on?

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1724
  • Location: Hampshire, UK
Re: Ignition timing MK5.
« Reply #4 on: 09 Feb 2016 at 20:00 »
Dave,
         If the mag wheel is already firmly fitted, I would turn the engine to 36 degrees BTDC, then turn the mag until the points are just about to open, and see if the wheel will mesh. If it is a couple of degrees over advanced (points already opened), I would settle for that - correctly set Mark engines tend to run sweetest just off full advance, so if yours is slightly over advanced, you will just need to retard it a little more on the lever. Of course, you will have to make sure you are timing the mag on the correct cylinder. To do this, remove one of the rocker covers so that you can check that the piston is coming up to TDC on the compression stroke (there will be some valve clearance on both valves), then remove the HT pickup on the same side and turn the mag until the points are about to open and you can see the brass segment of the slipring (the mag turns anti clockwise at the points).
  Regards,
                Eddie.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #5 on: 09 Feb 2016 at 21:14 »
That's exactly what I was hoping to hear Eddie. Very comprehensive and I'm now clear on how to proceed. I'll let you all know the result after the first kick or two. I hope it was two hundred quid well spent.
Out of interest, a 1952 road test I've got, states that Douglas retarded the ignition to give a "softer" engine with better low speed torque. Unfortunately, no figures are given.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #6 on: 05 May 2016 at 16:45 »
Well, to my shame, I've finaly timed & fitted the magneto. I glued the disc to a socket & used a mark on a piece of batten (see pic). With luck the cogs meshed perfectly.
Amazingly, one prod and it burst into life. It revs cleanly, so it's back with the dynamo etc. tomorrow. I've also fitted a new tyre to the front & had the spokes nipped up. Lets hope that may have sorted the wobble.
One happy bunny here and thanks again for all the help.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #7 on: 17 May 2016 at 11:22 »
Having some other jobs to do, I've left the bike until Saturday. Off the lift for a short run. It flatly refuses to start now. Not even a cough. I disconnected the cut out switch; just in case. Nothing. New plugs; not a carrot. Big fat spark with one of the leads wedged between the fins.
I'm now thinking that the cog on the magneto drive has slipped. I tightened it as far as I dare; before fitting the mag. All I've done since fitting the magneto & starting (first kick) is refit the dynamo.
Any other clever ideas, before I recheck the cog & timing (not a five minute job)?
Thanks in advance. Peed off of Liphook.

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1724
  • Location: Hampshire, UK
Re: Ignition timing MK5.
« Reply #8 on: 17 May 2016 at 17:49 »
Dave,
          My initial thought is that the extra drag of the dynamo has caused the timing to slip. This can easily be checked by removing the plugs, then, with the bike on the centre stand, engage top gear and bump the back wheel round until the points are just about to open, then check whether the piston is around .276" before TDC. The next question is: Have you got a reasonably thick washer under the mag pinion nut? If not, the nut may be thread bound on the armature without actually putting much pressure on the pinion.
Regards,
               Eddie.
P.S.  Have you remembered that the Mark engine has tight wire advance? Full retard would make it almost impossible to start!

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #9 on: 17 May 2016 at 18:32 »
Thanks again Eddie. A/R cable is fully tensioned, so I'll do an approximate check as suggested. I can't remember about the washer as the mag. man left it loose & I just tightened. Hopefully that's the answer & then it's back on the lift again for a proper redo.
I might get there by christmas. :lol:

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #10 on: 06 Sep 2016 at 14:40 »
Finally got round to it. Too many bikes & only one lift. The timing was OK & hadn't slipped. Finally coaxed it into life.
It only runs on the N/S pot. If I put my hand over the O/S carb intake (reasonably tight) that one kicks in & both run fine. I've only done this for a short time, but it will cut in & out instantly with hand on & off. I've checked to see if the main jet is blocked or if the needle has dropped. Both fine.
Before I strip the carb again (I'm an expert now) has anyone got a magic suggestion. I might just have to bite the bullet & get adaptors made to git the Chinese carbs that are sitting on the shelf.
Thanks in advance, Dave.

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1724
  • Location: Hampshire, UK
Re: Ignition timing MK5.
« Reply #11 on: 06 Sep 2016 at 17:18 »
Dave,
          Take the brass choke block out of the O/S carb. On the engine side of the block there is a shallow drilling about 4mm dia. There should be another 2.5mm drilling at 4 o'clock. If it is at 8 o'clock, you have the wrong hand choke block. Assuming it is the correct hand, check out the 4mm drilling. There should be 3 other drillings intersecting with it - one that connects to the 2.5mm drilling, another smaller drilling that goes up to the main bore of the block, and there is an even smaller drilling (about 25 thou) in the bottom of the 4mm drilling. All these must be clear. There is also a small drilling in the carb body - from the slow running port to the main bore of the carb (on the engine side).
 When the carbs are set up correctly, you should get a smooth regular tickover with the pilot air screw undone about 1¾ turns.
  I make a point of turning off the petrol and letting the engine run until the carbs are empty, if the bike is going to stand idle for any length of time. If the petrol is allowed to evaporate from the carbs, it can leave a sticky residue that easily blocks the small drilling.

  Regards,
                Eddie.
« Last Edit: 06 Sep 2016 at 17:33 by eddie »

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #12 on: 06 Sep 2016 at 17:53 »
I appreciate Your continued patience Eddie. I will go right through it again tomorrow. It should be the right block as I've had it running fine several times.
It amazes me that I had one of these in the 60s & it started & ran fairly reliably with the minimum of attention. To be fair, it was only about 13 years old then. I was a little bit older. :lol:

Offline dragonmk5

  • Full Member
  • **
  • Join Date: Jul 2009
  • Posts: 39
Re: Ignition timing MK5.
« Reply #13 on: 06 Sep 2016 at 18:35 »
I bought a pair of the Chinese carbs, made the adaptors  and they're now on the bike.  I need to rig something up re choke operation, and I'm awaiting a pair of plugs to give it a try. I've had it running on one cylinder ( one plug, and all my old ones naffed), so it'll be interesting to see how it goes with new plugs.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #14 on: 07 Sep 2016 at 06:54 »
I've got a pair sitting on the shelf; all 33 quids worth. When I take the 274 off today, I'll have a serious look at what's involved in adaptors etc. If it's possible to stiffen up the black choke lever there would be no need for cable operation. It's only needed for cold starting. I'll post any progress.

Offline dragonmk5

  • Full Member
  • **
  • Join Date: Jul 2009
  • Posts: 39
Re: Ignition timing MK5.
« Reply #15 on: 07 Sep 2016 at 09:02 »
I certainly won't be fitting a handlebar mounted choke control but will be working with a view to providing a friction type resolution on the carb itself. Plugs yet to arrive so not able to proceed at the moment. Will also post results.

Offline dragonmk5

  • Full Member
  • **
  • Join Date: Jul 2009
  • Posts: 39
Re: Ignition timing MK5.
« Reply #16 on: 07 Sep 2016 at 16:30 »
Sorted choke lever friction by removing the cable holder bracket and placing a couple of small washers 
on the bracket location projection on the carb, replacing the plate and screwing up tight.  Bit of a bodge but it'll do for now.  Should get plugs tomorrow, then we'll see!

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #17 on: 11 Sep 2016 at 12:44 »
Two days soaking of the jet block in thinnerts & a good blast through with the CA nozzle. All now seems to be OK. The tiny hole in the middle of the shallow recess was the culprit. I wouldn't have thought it would make that amount of difference.
Thanks Eddie & everyone else who offered advice.

Offline Hampshirebiker

  • Full Member
  • **
  • Join Date: Aug 2015
  • Posts: 149
  • Location: Liphook, Hampshire
Re: Ignition timing MK5.
« Reply #18 on: 11 Sep 2016 at 15:50 »
Just to cap it off, my chief test pilot (no 2 son) after a brief test run. A tad spluttery, but probably needs a good thrash to get the cobwebs out. I've also fitted wider handlebars & no tank slapper reported.

 

motorcycle