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DUD Conversions

Old 05-02-2005, 10:10 PM
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David Owen
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Default DUD Conversions

Here's a few 2.5cc engines modified by a local Aussie firm, 'Down Under Diesels'. Also shown is a diesel head for a .21 powerhouse.
regards

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Old 05-02-2005, 11:05 PM
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fiery
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Default RE: DUD Conversions

Looks like real nice work there! What engines are they?

Unfortunate acronym though .... [X(]

fiery
Old 05-02-2005, 11:27 PM
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Default RE: DUD Conversions

I see there are bronce or brass contrapiston.. nice work.

Jens Eirik
Old 05-03-2005, 04:46 PM
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David Owen
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Default RE: DUD Conversions

The engine at the front is a 2.5cc Taipan Goldhead from the '70s, the one behind looks like a Soviet era combat engine, possibly a Typhoon.
Dave
Old 05-03-2005, 04:49 PM
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David Owen
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Default RE: DUD Conversions

Yes, that is a bronze contra running in an alloy head. The 2.5s are fitted with o-ringed alloy contras.
Dave
Old 05-03-2005, 06:17 PM
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Jack Hiner
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Default RE: DUD Conversions

David,

Nice job on the DUD conversions. Are you part of the DUD team?



Jack
Old 05-03-2005, 06:20 PM
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Hobbsy
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Default RE: DUD Conversions

I can just see me calling one of my Diesel Buds and telling I just bought a DUD. Very nice though.
Old 05-03-2005, 07:32 PM
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Default RE: DUD Conversions

Dave,

In this world wide environment sometimes there are things that mean different things in different places. In the USA, a dud is something that should work but doesn't, or at least not very well. When I read it, I knew what it meant because you defined it...still, it brought a smile.

Nice work, by the way.

George
Old 05-03-2005, 08:58 PM
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David Owen
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Default RE: DUD Conversions

To Jack, George and the others,

The DUD acronym has been going around in my mind for the last few days.
I can't resist a bit of levity in an otherwise deadly serious world.
I think Hobbsy's comment explains why no one asked where they could buy a DUD head!

To be serious for a moment, I have read the comments regarding squish bands and contra- pistons not finishing flush at running settings.

Firstly, I do think a squish-band angle of around 6ΒΊ does promote smoother running and definitely less rattle at mid-range and idle settings. I don't know whether such a set-up has any bearing on cylinder temperatures.
Ideally the contra-piston will be full bore diameter, but this is not practical on most glow conversions. A reduced diameter contra-piston is never going to be run flush with the squish- band under all conditions. Any position other than flush must be a compromise which affects performance to some degree.

The only solution in this case is to shim the head as necessary to arrive at a flush surface when the engine is running at full power on a given prop/fuel combination.
Even this degree of fine-tuning will be less than optimal with any variation in factors such as ambient temperature, but it is preferable to a contra that runs greatly recessed or extended from the squish surface.
It is usually possible to adjust the head position so that the variation in contra position at running settings is no greater than 0.2mm recessed. The contra should not be extended from the surface at running settings, although this may be necessary at starting compression settings.

regards to all

Dave
Old 05-03-2005, 09:11 PM
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fiery
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Default RE: DUD Conversions

David

Is the contra-piston actuation similar to the Cairns Engineering diesel head conversions for ASP .32's and .46's in the early '90's?

The tommy bar for those was not threaded into the head, but rather threaded into the contra piston so you could pull it up and not just rely on compression to do it. Also, the Tommy bar would not wind up and down when making adjustments ... I can't really tell from the photo's you have posted.

The Cairns heads also had a spring under the tommy bar to maintain tension and settings without the need for a locking lever or an Irvine-type grub screw friction set-up.

I thought the front engine was a Taipan, just needed your re-assurance! What a great little motor.

Cheers

fiery
Old 05-03-2005, 11:28 PM
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David Owen
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Default RE: DUD Conversions

Fiery,

I'm not familiar with the Cairns heads. The heads on the engines shown here are simple compscrew types with a grubscrew applying pressure to stop the thing from unwinding.
Really not a great idea; neither is the coil spring set-up you mentioned.

I have re-built a number of Irvine diesel heads. These, particularly the .40, have a shallow contra-piston which will not withstand winding up and down like a yo-yo. Some folks just can't resist!

I built push-pull contras on the Irvines. My brass contra-piston had an integral extension shank with a left-hand thread. This was moved by a captive tube nut in the head itself. The nut had a 5/16" A/F hex which fitted a glow-plug spanner. The adoption of a LH thread meant that the compression was increased by winding the compscrew (glowplug spanner) in the usual cw direction. Although the contra could be pulled back, this was usually done by compression.

The extension shank meant that the contra was resistant to cocking. I also limited the total movement to a little over 1 turn to discourage compscrew fiddling.
Squish band clearance was set on the owner's specified prop initially, then I found that certain values were appropriate for a narrow range of loads.

The Taipan 2.5cc Goldhead is a super little engine and runs extremely well as diesel and glow.
It first appeared at the Geelong Nats in 1974 (I think) and wiped the floor in Pylon racing.
Cox purchased samples from Paul Bender and the Cox Conquest .15 appeared about a year later.
Gordon Burford was flattered that Cox had copied his design. It must be remembered that all progressive engine manufacturers purchased the opposition's products for a closer look and few were slow to adopt a sound idea when they recognised one. Gordon was no different.

regards

Dave
Old 05-04-2005, 07:08 AM
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Jack Hiner
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Default RE: DUD Conversions

Dave,

Thanks for all the info. Your remarks lead me to ask some questions. Last year I purchased a couple of Irvine Mills 1.3 cc diesel reproduction. Do you know if these engines have a shallow contra-piston? Back in the late 1950's I purchased a Super Tigre G-30 rear induction 2.5 cc diesel. For starting I would leave the compression fixed at the best running position. Once firing I would quick blip choke the venturi with my finger until the engine warmed up. A rapid pulsing with the finger. Easy to do on rear induction, but I would not try on front induction with the prop so close to the venturi. Is this method of starting a diesel more stressful than the normal starting method? I have also used this method on my Oliver Jaguar reproduction engines. I have yet to use it on the big GB or the Mills.
Old 05-04-2005, 05:22 PM
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David Owen
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Hello Jack,

The Irvine Mills has a properly fitted cast-iron contra-piston. It is correctly proportioned just like the original and will be trouble-free for the life of the engine if operated correctly.

I try to start my engines without touching the comp. In my experience, most diesels will start at the running setting provided they have a good piston/ cylinder seal.
Here's how we start the GBs.
Fill the tank. Open the needle about 1/2 turn from the running position. Choke once. Prime generously against a closed piston. Give one or two sharp flicks and it's running, slightly undercompressed and rich. Allow it to warm up and close the needle down as necessary.
I'm sure your Jaguar and GB will respond to this tecnique.
If the engine is fitted with a muffler and can't be primed, then it will need more choking and the comp will have to be increased to start from cold. Half a turn and no more should do it.

You will note I keep stressing that the comp screw should not be wound up and down like a yo-yo. Most of those engines which have a normal full bore contra-piston will start and run within a range of less than one turn. Those which have a smaller bore contra, such as fitted to the heads we were discussing, may require a greater range of movement, certainly no more than two turns though.

trust this answers your questions

regards
dave
Old 05-06-2005, 02:14 AM
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Default RE: DUD Conversions

DUD!
You've just got to love the name!
Peter
Old 05-06-2005, 06:55 PM
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fiery
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Default RE: DUD Conversions

Never let it be said that Aussies can't laugh at themselves

David, is there a website for these conversions? I would like to know more.

fiery
Old 05-07-2005, 06:47 PM
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David Owen
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Default RE: DUD Conversions

G'day Fiery,

There is no website for any of my work. Sorry!
I do specialist work on engines from time to time and the heads I showed were such a job.
As far as diesel conversions go, I'm sure that Davis and Andrew Coholic have things pretty well covered, considering the small market.

with regards
Dave

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