Author Topic: Mark oil pumps.  (Read 5219 times)

0 Members and 1 Guest are viewing this topic.

Offline ChrisS

  • Member
  • *
  • Join Date: Dec 2005
  • Posts: 15
Mark oil pumps.
« on: 29 Dec 2005 at 08:46 »
All,
Interesting discussions on what oil to use in Marks prompted me to add my bit of info.
I have a Mark 3  [ 4002]  which is fitted with Hepolite period pistons and runs on a modern semi synthetic  from Castrol. Whilst modern oils keep the contaminants in solution so did the old oils otherwise there would be no sludge problem with the cranks, the secret is regular oil changes. It doesn't smoke it doesn't use very much oil and whilst I work it hard it's never shown any signs of nipping up when hot.
In my collection of parts I have a large selection of used pistons and everyone has pick up marks on it. This must have been a very common problem with the cast pistons and this is supported by the fact that Douglas used Loex pistons in the 80+ and Y alloy in the 90+ in an attempt to overcome the problem. I would imagine that the modern oils do a better job of lubricating and cooling the pistons.

In some of the litrature Douglas talk of uprated oil pumps fitted to the Pluses, but I havn't seen one of these. The Dragonfly has a similar pump to the Mark but its body is cast in alumimium instead of bronze it has 50% more capacity as the vanes are deeper and are fitted with two springs. However its possible to increase the output of the Mark oil pump by machining the offset chamber out by 0.050" this gives a greater stroke to the vanes.  However the tight clearance between the suction and discharge ports must be maintained ( that is all the material must come from the pumping side of the chamber). This will increase the pump output by about 50% and help to better lubricate the crank. Also on assembly the  end clearance of the pump must be maintained at a minimum consistant with being free, (gasket thickness is important here), otherwise the leakage rate wil substantially reduce output. Once the engine warms up the end clearance will increase slightly anyway due to the differing expansion rates of the steel spindle and the bronze body 

ChrisS

Offline trevorp

  • Master Member
  • ****
  • Join Date: May 2005
  • Posts: 502
  • Location: Australia
Re: Mark oil pumps.
« Reply #1 on: 31 Dec 2005 at 01:51 »
i have a spare oil pump i may give it a go
has anyone toyed with the idea of fitting a pcv valve {positive cranckase ventialtion}
i have bought a very small one and am going to try and fit it to a modified crank breather
basically they are a one way valve allowing pressure out but not back in and at 9 dollars australian sounds cheap to me also i have read about drilling small drain hole in front of crankase to stop oil pooling and climbing the gear train
what size hole a large one may cause it to drain to quickly so im going to try 1/8 th

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 4246
  • Location: Glen Mills, PA, USA
Re: Mark oil pumps.
« Reply #2 on: 31 Dec 2005 at 03:05 »
Trevor,

I have heard of a PVC valve fitted to a modified oil fill cap, with a hose then leading away to the rear of the subframe.  I made a one way valve and fitted it to the inside of a modified timing chest cover on my Mark 3 Sports early on, with a new larger vent tube down to the road.  I also know of a DT sprinter in the UK using a PVC valve with some success. 

I have not had trouble with oil leaks at the magneto joint face (thought it seems a common complaint), so have not drilled a drain hole in the timing chest.  There should be a hole already to allow the oil level to rise up just so the bottom train of gear teeth (camshafts) dip into the oil, before draining back into the crankcase proper.  You should not go lower than this.  The only leak on the engine I have is a slight dampness at the bottom joint edge of the rocker covers.  And probably because I do not trust to tighten down on the screws really hard, as the covers had been cracked once before. 

So I would try the PVC valve first before drilling drain holes.  It may be all you need.

-Doug

Offline ChrisS

  • Member
  • *
  • Join Date: Dec 2005
  • Posts: 15
Re: Mark oil pumps.
« Reply #3 on: 02 Jan 2006 at 17:14 »
Two common accepted mods to the crank case castings are:-


1] two holes around 3mm to drain the oil from the timing gear space back into the sump, as it appears there is quite enough oil from mist and front main leakage to lubricate the timing gears


2] Two holes drilled from the camshaft bushing bosses at 12 o'clock in the timing chest (behind the timing gear) at an angle to pick up the space between the bushes or if its a single bush, which was reverted too latterly, then the relieved groove in the back of the bush. This improves lubrication to the front camshaft bearings considerably. Once drilled the holes are countersunk to aid collection of the oil.

Douglas ran a timed breather on some of the 90 pluses, but I havn't found any info on this other than it fitted into the tacho drive casting. The T6 engine has a timed breather which works very well.   

ChrisS