Author Topic: Breather hole in 2 3/4hp engine  (Read 3664 times)

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Offline Lat Fuller

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Breather hole in 2 3/4hp engine
« on: 26 Jul 2016 at 23:24 »
Hello anyone who can help,
I am in the process of assembling my 2 3/4 hp engine and in doing so I have found the following:
The hole in the bottom front of the crankcase where the decompression cable goes in has a slight cutaway to enable the rod that connects to the decompression levers to fit through the hole.  Is this to act as a breather or to let the "total loss" oil out ?   Or must I somehow block this cutaway to prevent breathing through there ?
The reason I ask is because in an article about oiling and valves in this forum it is mentioned that crankcase pressure is required to allow the oil to be drawn into the engine through the oil feeder (and I am worried about the engine loosing pressure through there - and of course the oil leaking out of there).
I have 2 other crankcases and they both have this same cutaway..
Any assistance appreciated

Offline eddie

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Re: Breather hole in 2 3/4hp engine
« Reply #1 on: 27 Jul 2016 at 07:57 »
Lat,
      The crankcase breathing on the 2 only controls the breathing of the actual crankcase. The partial vacuum generated in the crankcase helps to draw the oil from the tank. Once the gases have reached the timing chest, they are free to escape to the air via the breather pipe, so the cutaway has little or no effect on the breathing. On my 2, I have fitted a copper washer to the decompressor fitting to reduce the oil loss (but some still escapes through the cable). Lubrication of the timing gears would seem to be by oil mist spraying from the breather valve in the crankshaft - the timing gears are set too high to pick up oil from the bottom of the timing chest.
 Regards,
               Eddie.

Offline Lat Fuller

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Re: Breather hole in 2 3/4hp engine
« Reply #2 on: 27 Jul 2016 at 23:28 »
Hi Eddie
Thanks for your prompt reply - and yes what you say makes complete sense.
I appreciate your assistance.   I am working in the dark here as there are very few 2 3/4 models in Perth.   My bike has not run for about 50 years.  Thanks Lat Fuller

Offline cardan

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Re: Breather hole in 2 3/4hp engine
« Reply #3 on: 29 Jul 2016 at 09:11 »

Hi Lat,

That looks very nice! I assume its a veteran (pre-1919 out here), but what year?

The National Veteran Motor Cycle Rally is being hosted by the VVMCCSA in the Barossa Valley in September next year (2017), See you there?

Leon

Offline steveale

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Re: Breather hole in 2 3/4hp engine
« Reply #4 on: 30 Jul 2016 at 01:02 »
my 1913 has a drain pipe fitting on the back side opposite the decompression opening.  My decompression opening has no vent or slot.

Offline Lat Fuller

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Re: Breather hole in 2 3/4hp engine
« Reply #5 on: 30 Jul 2016 at 05:35 »
Thanks for the comments and advice.   This is a 1917 - model "W" I think, frame number 32746.
I would love to go over next year - but will see how I go.   This is what it was like when I picked it up 2 years ago..

Offline cardan

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Re: Breather hole in 2 3/4hp engine
« Reply #6 on: 30 Jul 2016 at 06:14 »

Hi Lat,

Yes, correct on both counts I think. https://www.douglasmotorcycles.net/aa-files/html/identify-part1/veteran3.6.htm

Nice to have a complete-ish bike to start with, and one that looks close to original. You'd be very welcome at the Veteran Rally, and there will be a good contingent coming over from the West. Just to boggle UK forum members, it's about 3000km (2000miles) from Perth to Adelaide, with not too much population in between.

Does anyone know when the Lycett pan saddle - as on Lat's bike - became available? I think Brooks was the leader with its leather-covered-sheet-metal-pan saddle, but Lycett were probably not too far behind.

Cheers

Leon

Offline cardan

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Re: Breather hole in 2 3/4hp engine
« Reply #7 on: 30 Jul 2016 at 23:26 »

Nothing on TV last night so I can answer my own question. The first mention I could find of the Lycett pan saddle was on P&M machines for the 1913 season (i.e. late 1912), where they were described as "made specially for P&M". However at the 1912 Show there were several bikes (1913 models) with the saddle.

In short: a Lycett pan saddle is fine for a 1913-on Douglas.

Leon

Offline graeme

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Re: Breather hole in 2 3/4hp engine
« Reply #8 on: 30 Jul 2016 at 23:56 »
Hi Leon

The 1914 3 1/2 I own came with a Lycett saddle, so they were being fitted to Douglas bikes then, and likely in 1913 as you say

Offline cardan

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Re: Breather hole in 2 3/4hp engine
« Reply #9 on: 31 Jul 2016 at 09:22 »

Hi Graeme,

Yep, and the Brooks B170 - its leather-covered-sheet-metal-pan saddle - was available for 1912 Triumphs (announced at the Show in late 1911) and advertised from April 1912. Since Douglas sales were escalating in 1912-1913-1914 I assume they would fit either Brooks or Lycett saddles depending on availability and perhaps customer demand.

By the way, I have recently had some leather-in-tension (i.e. no metal pan) saddle tops done by Paul Watson in Melbourne. They are absolutely superb - by far the best I have ever seen.

Cheers

Leon


 

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