Author Topic: OVER-OILING CYLINDERS ON T35  (Read 6040 times)

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Offline Brian

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OVER-OILING CYLINDERS ON T35
« on: 10 Dec 2008 at 15:39 »
This is a query posted on behalf of a Forum Member ( PULLON) with a pedestrian interenet-link.
I quote from his message:

"I have still got persistent over-oiling on the r.h. cylinder of my T35. I have again stripped the engine because the r.h. cylinder continued to oil up despite the rings having bedded down to some extent. I am concerned that teh cause of the problem was a blockage in the oilways to the left-hand big end thus causing most of the oil supply to the b.e.'s flowing to the r.h. big end. Once the crankshaft was out of the engine, I used compressed air to blow out the oilways and no blockage was found and the air flow at each big end felt about the same.However, I previously ha dthe crankshaft main shaft ground true before fitting a "made to size" main bearing bush. This entailed pressing the front end section of teh crankshaft off for grinding and the company that pressed it back on aligned the end of the crank pin with the front face of the web.The side clearance of the front big-end now measures 12 thoiu compared to 6 thou on that of the rear cylinder. Would this perhaps be the cause of the over oiling of the front cylinder ??  "

Ok guys, what do you think about them apples ?

Cheers

Brian  p.p. Denis (PULLON) obe,vc, ma, mrcvs

Offline eddie

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Re: OVER-OILING CYLINDERS ON T35
« Reply #1 on: 10 Dec 2008 at 22:51 »
Brian,
          From the handbook for the T35 Mk1, the endfloat on the conrods should be .004". Any increase in the endfloat will allow more oil to escape from that bigend - thereby reducing the share going to the other bigend. This is not normally a great problem on the Mark series crankshafts because the oil is carried to the centre web before splitting to feed the two bigends. On Plus and Dragonfly cranks, the endfloat needs to be correct because the crankpins have oil holes that feed the oil direct into the bigend bearings. With excessive endfloat on the front rod, and a high revving engine, most of the oil gets thrown out of the front bigend by centrifugal force - leaving precious little oil to defy the centrifugal force and get back across the centre of rotation to feed the back bigend. Back in the early fifties, Eddie Withers did a lot of crank modifications in attempts at preventing the back bigend from 'drying up'.
        Getting back to 'Pullon's' crank - the excess oil may be overworking the piston rings. Also, he reports that he has had the front journal reground and a new bush 'made to size'. These front main bearing bushes should have .003" clearance on the crank to allow for any flexing. Reduced clearances usually cause the bush to 'nip up' on the crank and turn in the cases - distorting the flange as it rides over the locating pin. The result - a total strip down to rectify the problem!!
       Sorry, if this is not what you wanted to hear!
                                           Regards,
                                                   Eddie.

Offline David H

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Re: OVER-OILING CYLINDERS ON T35
« Reply #2 on: 12 Dec 2008 at 06:27 »
Hi
A couple of questions come to mind

1 What type of Oil control rings are fitted
             Piston to bore clearance ?
             Ring end gap?

I have found several engines with segmented Oil control rings which actually measure OK but have no wall pressure what so ever. and don't work to well.

2  What is the Inlet valve guide to stem clearance like, They will suck oil through there like no tomorrow if it sloppy.

Cheers
David H

Offline eddie

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Re: OVER-OILING CYLINDERS ON T35
« Reply #3 on: 12 Dec 2008 at 08:24 »
On the T35 (Mk1), the scraper rings were of the slotted type, whereas later Mks employed stepped scrapers. The standard reccommendation for ring gaps on air cooled engines is .003" per inch of bore - which equates to .007" on the postwar Douglas. Measurement of this gap may not be easy on the Mk1's as some of them had scarf joint rings.
      The fit of the inlet valve in the guide will obviously affect oil consumption, but should not result in enough excess to oil up plugs, etc. After all, the Douglas engine relies on mist lubrication for the valve gear - there is no positive feed to the cylinder heads.
      As has been stated before, the right hand cylinder always suffers first - because it has better lubrication due to the way the oil is thrown from the rotating crankshaft - up into the right hand cylinder and down into the left hand, resulting in the top of the left hand cylinder being somewhat starved of oil (prewar engines had a small hole drilled in the front barrel to provide an auxiliary feed to the piston skirt).
     Another avenue that might be worth investigating - is it the oil rings that are at fault or are the compression rings allowing too much blow by - thus creating crankcase pressue and forcing oil past the rings (and guides).
    To relate my personal experience - since rebuilding my Dragonfly (about 13 years ago) the oil consumption has gradually got worse, but has never resulted in fouled plugs, and the bike has proved to be utterly reliable. Eventually, of course, it started to leave the dreaded 'blue trail'. On inspection, the pistons looked OK, so new rings were fitted, along with new valves and guides - no improvement whatsoever! Then a well respected club member said "Stick an old set of pistons in it - you may be pleasantly surprised". With this in mind, I raided my junk box and sorted out a pair of well used, but serviceable pistons, fitted them and, hey presto!, no smoke and the oil consumption is reduced to about a quarter. Maybe the moral of this story is " Don't rebuild for rebuilding's sake - leave well enough alone!"
                                             Regards,
                                                    Eddie.

Offline Brian

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Re: OVER-OILING CYLINDERS ON T35
« Reply #4 on: 13 Dec 2008 at 18:53 »
Denis ("Pullon") thanks Eddie and David H for their replies and has now been able to decide on a course of action while things are still apart.  The piece of string between the 2 bean tins (in S Africa and Scotland) seems to work quite well as long as we remember to keep it taut.

Cheers

Brian