Author Topic: Dry 2+3/4 big ends ...  (Read 4682 times)

0 Members and 1 Guest are viewing this topic.

Offline phil_h

  • Full Member
  • **
  • Join Date: Aug 2009
  • Posts: 74
  • Location: Pulborough, W.Sx, UK
Dry 2+3/4 big ends ...
« on: 07 Mar 2016 at 18:12 »
I've finally put everything back together and run it up and down the road, only to get the dreaded squeal of dry bronze.
After head scratching over what I could have forgotten, I remembered the oil drilling in the front needed to have a matching hole in the gasket and I definitely hadn't checked that on reassembly :(
So a strip down has ensued, and the gasket hole is missing... but BOTH the big ends are as dry as a dry thing on a dry day - so I want to check if I'm missing something else.
Is the drilling down into the front barrel the only lubrication mechanism i.e. how is the rear big end expected to get its fresh lube ?
(and I would think it needs more than the front ?)
There looks to be plenty of oil in the sump, but perhaps not enough to give a good splash effect ?

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: Dry 2+3/4 big ends ...
« Reply #1 on: 07 Mar 2016 at 20:23 »
Phil,
       The small drilling in the front barrel is to aid lubrication of the upper side of the front piston. Due to the flinging action imparted by the crank, the oil gets thrown down into the front barrel and up into the back one. The small drilling does virtually nothing for the big end lubrication.
 If it is assembled correctly, the lubrication system draws oil from the tank and meters it through the sight glass. From there it is piped to a non return valve on the top front of the crankcase. From there it runs into a gallery inside the top of the crankcase, and drips onto the revolving crankshaft - and spread around the engine, aided by another non return valve in the timing side of the crankshaft. This valve also provides an escape route for crankcase gases, as well as providing mist lubrication for the timing gear. The gases then escape from the timing chest via a pipe that is usually routed so that any remaining mist oils the primary chain. The valve in the timing side of the crankshaft is a ball and very light spring behind the timing pinion retaining bolt. With the timing cover removed, the valve should 'fart' as the engine is turned by hand - if it doesn't, the spring is probably too strong, and the build up of pressure is preventing the oil from draining to the engine. If you have just rebuilt the engine, it pays to open oil regulator and allow one pumpful of oil into the crankcase prior to starting. Any excess of oil will be discharged through the timing chest, onto the primary chain and eventually the road! Also, bear in mind that these 2 engines have a very crude oiling system, so bigend clearances need to be fairly slack to allow oil to get into them - 2 or 3 thou should be fine. Also, make sure the ends of the bigend shells are flush with the surfaces of the con rod and cap, so that the keep plates are sandwiched by both the shells and the halves of the conrods, otherwise the shells will move or the bigend bolts will eventually slacken and undo. I usually tin the outside of the shells, then fit them over a suitable sized end of bar, and fit the conrod halves without the keep plates, then heat the whole assembly so that the shells end up soft soldered into place - the ends can then be accurately trimmed flush with the joint face of the conrod. With the keep plates reinstated, the shells can then be scraped to obtain the correct running clearance on the crankpins.
  Hope some of this helps,
      Regards,
                    Eddie.

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1191
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: Dry 2+3/4 big ends ...
« Reply #2 on: 07 Mar 2016 at 23:31 »

That's a good tip about soldering the bushes Eddy - I can think of another engine where I will try that.

I forget the details of the 2 3/4 big ends, but a general tip for splash-lubrication motors (no drilled oilways in the crank) is to make sure there are places where the oil can actually enter the big end and get between the bush and the pin, and once there spread out along the length of the bush. I'm a bit of an old-lady rider (with apologies to racy old ladies everywhere), so I use less than the 2-3 thou Eddy mentions, but always make sure there are appropriate entry points (some end float, or at least a V on the face of the rod/bush) and spreading mechanisms (a straight groove parallel to the pin is usually OK if you're not going racing) for the oil. If the con rods are drilled near the big end eye, drill through the bush and match up with your groove. Just think of how hard it is for the oil to get in there and spread itself along the bush more-or-less by accident! (Maybe Eddie's 2-3 thou is a good idea after all...)

Leon

Offline phil_h

  • Full Member
  • **
  • Join Date: Aug 2009
  • Posts: 74
  • Location: Pulborough, W.Sx, UK
Re: Dry 2+3/4 big ends ...
« Reply #3 on: 08 Mar 2016 at 20:34 »
Many thanks chaps, you've got me looking at all the right bits now.

First find was that I'd forgotten the breather ball and spring in the crank, which will probably slow the suction from the sight glass.
(Incidentally, how do you check that the plunger is drawing oil up correctly ?)
Second find was that the timing side oil gallery has a big hole in its bottom - prob from the blowup at the graham walker some years ago when I first got it, and the oil for the rear big end will have been running down the front of the crankcase wall instead of dripping onto the bigend over the lip of the gallery... and that was probably what caused the rear seizure last year. I'll be aralditing up the hole in the gallery to fix that one.
So many thanks again Eddie for the most excellent description of the oiling system.

Next on the list will be a stripdown of my big ends (again) and I think I'll be adding a v at the side of the joint to allow the drips better access from above, and I'll check the scalloping on the cap's shell.

Offline Alan Cun

  • Master Member
  • ****
  • Join Date: Feb 2007
  • Posts: 431
  • Location: Qld Central Burnett District
Re: Dry 2+3/4 big ends ...
« Reply #4 on: 09 Mar 2016 at 09:02 »
Hello Phil,

One thing I have learnt about Douglas motors is never rely on what oil is delivered to the crankcase by the manual or if fitted drive pump. There is usually a plug where you can pour about half a cup of oil directly to the crank and big ends. We all know that the modern oils dont burn on a total loss system. After a long ride the oil may be coming out the main shaft or followers. The temptation may be to drain the cases. You can drain some but leave some. What does the book say 25 drips per minute at the sight feed hardly enough to cover a postage stamp.

Yep and like i have said before 3 things, good quality oil, right heat range of plugs, premium fuel with additive.

regards Alan

 


Offline phil_h

  • Full Member
  • **
  • Join Date: Aug 2009
  • Posts: 74
  • Location: Pulborough, W.Sx, UK
Re: Dry 2+3/4 big ends ...
« Reply #5 on: 12 Mar 2016 at 10:19 »
The voyage of exploration has also discovered that the oil pump has probably never been working properly !
I decided that had to come apart and get cleaned, and that led to the oil tank being emptied... and degrunged :(
Now that its all clean and back together, it's really easy to set the drip rate - for the first time ever, the plunger pulls up oil without huge resistance and gurgling of air, and then sits obediently at the top of its stroke, slowly letting oil into the sight glass, instead of giving a quick squirt of airy oil.
(That would also contribute to the many problems I've had, as I've obviously never been oiling as much as I thought !)
Seeing/listening to it idling in the drive, its the best its ever sounded (touch wood :o )
When the fog clears here, the test ride is hopefully going to be a revelation of proper oiling :) as the performance on the last test run was as good as its ever been.
Keep everything crossed for me, as I'm doing the Pioneer next week !

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: Dry 2+3/4 big ends ...
« Reply #6 on: 14 Mar 2016 at 22:26 »
Hi Phil,
           Glad to hear you are making progress toward having a sweet running and reliable 2. Once you have got it fully sorted, I'm sure you will have many hours of enjoyable riding. Hope all goes well on the Pioneer Run!
  Regards,
               Eddie.

Offline phil_h

  • Full Member
  • **
  • Join Date: Aug 2009
  • Posts: 74
  • Location: Pulborough, W.Sx, UK
Re: Dry 2+3/4 big ends ...
« Reply #7 on: 19 Mar 2016 at 19:44 »
Look out for number 171 on Sunday - I might need help if it all goes pear-shaped !

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1191
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: Dry 2+3/4 big ends ...
« Reply #8 on: 19 Mar 2016 at 21:51 »

Sunday morning here already. My wife and I are off to a poultry sale to bolster the back-yard flock - not half as much fun as riding in the Pioneer Run. Good luck!

Leon

Offline phil_h

  • Full Member
  • **
  • Join Date: Aug 2009
  • Posts: 74
  • Location: Pulborough, W.Sx, UK
Re: Dry 2+3/4 big ends ...
« Reply #9 on: 20 Mar 2016 at 21:38 »
Hoorah ! All the work paid off and it ran better than ever for a faultless ride... although I held my breath the whole way ;)
Unfortunately my wife's royal enfield 2 3/4 made up for that by playing up for half the time, although it did settle enough to get her to madeira drive in the end !

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: Dry 2+3/4 big ends ...
« Reply #10 on: 20 Mar 2016 at 22:18 »
Well done, Phil.   When a 2 is running well, even the Brighton traffic seems less fearsome!!!

  Regards,
                Eddie.

 

motorcycle