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Question about 049 Davis Diesel head

Old 12-14-2004, 11:37 PM
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skid2964
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Default Question about 049 Davis Diesel head

I acquired an old used Davis Diesel head for a Cox .049, My first question is: will this also fit a Norvel .049 and .061?

Second: the contrapiston seems to be stuck in the head, but I suspect this is normal? It is supposed to have a VERY tight fit to the point that you would have to tap it with a hammer to move it?

I assume these 049 heads do not need much adjustment travel? It appears it will only move up or down a 1/10 of an inch or so.

Does this head require "disks" ? I saw another one for sale on **** that had some sort of disks with it, mine of course does not have any of those.

Anyone have some instructions for this thing I can get a copy of?

I am very un-familiar with these diesel conversions, thanks ahead of time for the info.
Old 12-15-2004, 12:16 AM
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Default RE: Question about 049 Davis Diesel head

ORIGINAL: skid2964

Second: the contrapiston seems to be stuck in the head, but I suspect this is normal? It is supposed to have a VERY tight fit to the point that you would have to tap it with a hammer to move it?

I assume these 049 heads do not need much adjustment travel? It appears it will only move up or down a 1/10 of an inch or so.
It is normal contrapiston are very tight in cylinder head and it can have a o-ring fittet in groove at contrapiston.

The engine are small and do not need much to adjust contrapiston travel..

Jens Eirik
Old 12-15-2004, 07:34 AM
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Default RE: Question about 049 Davis Diesel head

I have 2 of then fitted on norvels 061 you do need the discs call davis diesel for them this is the only davis head cox-norvel 049-61
plus cox 020 engines that use them martin
Old 12-15-2004, 09:08 AM
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Default RE: Question about 049 Davis Diesel head

Skid,

The purpose of the disk is to prevent you from frying your engine if you run it over compressed. When it overheats to a certain point, the disk melts and loses compression which, of course, stops the engine.
Make sure you fully break-in your engine as a glow before the conversion. That was part of Davis's printed installation instructions when I made a conversion years ago, I assume it is still valid.
Old 12-16-2004, 12:37 PM
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Tim Wiltse-RCU
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Default RE: Question about 049 Davis Diesel head

Skid,


The DDD head is the worse one to use. The little disks are a pain in the butt to say the least. Get your hands on a RJL head. It's a whole lot better.

Later,
Tim
Old 12-16-2004, 03:15 PM
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Default RE: Question about 049 Davis Diesel head

Get the RJL head. The davis ones are a P.I.A. with the discs. They fry frequently and I ended up just cutting a circle out of thin sheet metal which actually worked well. The cranks on the Cox engines are very weak and break very easily if even slightly overcompressed. I know from experience. I broke three. One while the engine was running at full RPM. It flew right at me though it didn't hurt much as it hit me in the chest. Still quite dangerous if it hit an eye or exposed skin, though. Just a caution!

Max
Old 12-16-2004, 10:44 PM
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Default RE: Question about 049 Davis Diesel head

Davis does have a replacement crank for the cox the will not break I think the norvel 061 is a better deal it has an rc carb and
muffler and have had no disc problems. they are very very tight when new and need a screaming break in on glow before conversion
one was so tight it broke the rod, norvel replaced the engine turn around was one week great service yes they leak around the muffler to manifold with the "spring thing" but I do not have an issue with it with the rotating exhaust outlet a small piece of tubing deflects it
under the plane ( I mount mine in a horizonal position)ie on its side
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Old 12-17-2004, 11:11 AM
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skid2964
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Default RE: Question about 049 Davis Diesel head

Thats what I was going to use it on .... the Norvel 049
Old 12-17-2004, 07:51 PM
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Default RE: Question about 049 Davis Diesel head

Order of assembly on the norvel 061 insert one copper gasket followed by aluminum disk followed by teflon disk then screw on the head davis recomends this for the 061 if running hard worth a try this way on the 049 will not fry the teflon disc
Old 12-18-2004, 10:30 AM
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Default RE: Question about 049 Davis Diesel head

Or better yet get the RJL head and never have to worry about messing with crazy teflon/metal disks that blow out leaving you up the creek at the field!

Later,
Tim
Old 12-19-2004, 09:40 AM
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Default RE: Question about 049 Davis Diesel head

Skid,

Working on the Veco .19 diesel head. So far, looks good, testing needs to wait till we thaw out from 35 below. Will report on the other thread.

Meanwhile, I agree with Tim. I have both the RJL and the Davis head. RJL uses O-rings and they work well. Davis uses discs of teflon and metal. Inevitably, the teflon melts and you never can tell when they'll fry,,, usually in the air. Send me a PM with your address and I'll make a contra-piston to suit your Davis head. BTW, if your Davis head's contra piston is tight in the head, it's frozen up with gelled oil. Soak in kero or wd-40 to free it up.

On the left is the RJL head, on the right is the Davis head. Both work but as you can see, the teflon disc and even the copper disc gets distorted in use and the teflon eventually blows.

As well, later runs of Norvels have the piston NOT coming up to the top deck of the cylinder. As such, you need to drive the contra-piston down into the combustion chamber to get the compression ratio you need to light off your fuel. The RJL head had this problem and I had to make a new contra-piston that was a sixteenth longer. Stock it was no problem with a Cox engine but you may have problems with either head on a Norvel.

Also, as you can see, the RJL head allows you to use a common Cox glow head wrench. The Davis head is less user friendly in that regard.
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Old 12-19-2004, 09:52 AM
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Default RE: Question about 049 Davis Diesel head

I am VERY interested to see how the Veco project turns out! I would be interested in a head or two for my Veco 19s, maybe all 7 of them!

I have already sold the Davis head on **** and I will be purchasing an RJL head. I will inspect my Norvel engines for the above mentioned problem also.

Thanks
Old 12-19-2004, 10:12 AM
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Default RE: Question about 049 Davis Diesel head

Skid,

All 7 Vecos eh? Whatta you, some kinda diesel nut? [X(] Well, hey, I know the feeling. Glow man all my life,,, now glow feels kinda wimpy and whinie,,, compared to diesel. What's your experience with diesel? Newbie? Geezer?

When you get your RJL head, you can solve the Norvel problem by flipping the contra-piston around so that the O-ring is at the top. This prevents O-ring creep when or if you need to screw it way down to meet the piston. If you need to do this, you may find you run out of threads on the adjustment bar. To solve that, install a one sixteenth disc of ally or brass on to the top of the contra-piston.
This'll give you more meat and range on the screw.

Also while stock Cox cranks can break, I've run dieselized Norvels extensively, even on 8 X 4 props and so far, at least on the bench, no breaks. Got to be careful about bending rods though. Stock, the Norvel rods are a little anorexic. I've bent a few but only when I got careless. The only other crank that broke on me was with an AP Wasp .06.
Old 12-19-2004, 10:38 AM
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Default RE: Question about 049 Davis Diesel head

I am a complete newbie(to diesels) ... but it all makes total sense to me ... more torque, less noise, better fuel economy, no glow plug starter, less mess. Who wouldnt want to run a diesel! I used to love everything about my Veco's now I hate that they cannot be converted to diesel easily.
Old 12-19-2004, 12:51 PM
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Default RE: Question about 049 Davis Diesel head

Skid,

I might be able to help. Keep the faith, I'll report back.
Old 12-19-2004, 04:03 PM
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Tom @ Buzzard Bluff
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Default RE: Question about 049 Davis Diesel head

ORIGINAL: dieseldan

Davis does have a replacement crank for the cox the will not break
Hi Dan,
I beg to differ about the Davis crank for the Cox reedies. Being something of a hardhead I broke a handful of reedie cranks with the Davis head. The story was always the same---just as I finalized the needle valve/compression adjustment to achieve that good, well-adjusted diesel song the crankpin would snap off the crank. Providing of course that the Teflon disc didn't suffer a meltdown first. So I bit the bullet and bought one of the Davis 'chrome-moly' cranks. It did EXACTLY the same thing. And that is when I gave up on dieselizing a Cox reed valve engine.
Until just recently I discovered that Cox made a couple of product engines with heavy-duty cranks for model car applications. Not only is the crank considerably bigger in diameter but the crank cheek at the wrist pin is easily twice, perhaps 3 times, as thick as the normal model airplane engine crankshaft.
I've sent a Davis head and one of the HD cranks to Japanman and Andy W. is also putting one together so we'll soon know if the legendary Cox reed valve crank brittleness is a factor with the bigger cranks. I COULD claim I was just being crafty and am allowing them to be the risk takers but the simple truth is that I'm just a professional level procrastinator.
On one of the threads someone (Zagnut?) once said that the problem with the Cox cranks lay in the heat treating process. That it made them brittle. Whether the dragster cranks were similarly treated I have no idea. If you (or anyone) knows how to reverse that embrittling treatment I would be the first to ask for advice. Respectfully, Tom @ BB
Old 12-19-2004, 04:52 PM
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Default RE: Question about 049 Davis Diesel head

Quote: Tom@BluzzardBluff

[Until just recently I discovered that Cox made a couple of product engines with heavy-duty cranks for model car applications. Not only is the crank considerably bigger in diameter but the crank cheek at the wrist pin is easily twice, perhaps 3 times, as thick as the normal model airplane engine crankshaft.]

Tom is a great inspiration for trying new ideas. Some time ago, I had made a unique rotary valve exhaust throttle for any and all of the Cox .049 series. Naturally I had to see how well it worked on a Tecaco engine and amazingly, with a large prop, (7 X 3.5 Cox) idle was so low and the engine so quiet, you could hear the reed vibrating.

Since joining the diesel brotherhood, it was my intention to dieselize a Texaco but the crank issue always held me back. Tom reminded me of the Car engine's larger crank and sho 'nuff I had one. The picture shows the two and there's substantially more meat, all over on the car shaft. I'da been twice as happy if the crankpin was thicker but it all looks real good from this point.

Also illustrated is a cosmetically altered car c/case. The original had some ugly steps cut into it to carry the clutch/flywheel. I want to anodize the whole thing black ('cept the tank) to give it all a distinctive look and right now, I'm waiting for some professional dye. Ink comes out dark blue.

So, once it's together, and the weather warms up, we'll give it a go. An 8 X 4? Fun.
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Old 12-19-2004, 08:23 PM
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Default RE: Question about 049 Davis Diesel head

Tom,

Well knock on wood I have not(yet) broken a reedie crank either on glow or diesel. This past summer I was running a MAS 8x4 on my diesel Cox reedie. Granted due to the Davis head being a PITA I didn't run it a whole lot. I do have a RJL head and I just got some Davis fuel and ran it a couple of weeks ago with a 6x3 and it was screaming. As for the brittleness of the Cox reedie cranks I have heard that baking them in an oven helps them last better. I don't remember any more to the idea and I can't remember where I read about it!

Andy,

Do you do your own anodizing?

LAter,
Tim
Old 12-19-2004, 08:53 PM
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Default RE: Question about 049 Davis Diesel head

[quote]ORIGINAL: Tim Wiltse-RCU
Well knock on wood I have not(yet) broken a reedie crank either on glow or diesel. This past summer I was running a MAS 8x4 on my diesel Cox reedie. Granted due to the Davis head being a PITA I didn't run it a whole lot. I do have a RJL head and I just got some Davis fuel and ran it a couple of weeks ago with a 6x3 and it was screaming.>

I must just be a klutz.;O) I'm not a 'lean it out for the last RPM'. kind of guy so I don't know what I did wrong. But I must have done something.

<As for the brittleness of the Cox reedie cranks I have heard that baking them in an oven helps them last better. I don't remember any more to the idea and I can't remember where I read about it!>

Hmmmm, wonder what temp? Anyone else have any feedback on the subject?

Thanks Tim! Tom
Old 12-20-2004, 12:08 AM
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Default RE: Question about 049 Davis Diesel head

Tim,

If you run the reedie with your RJL head, you might find the crank getting a little stressed with an 8 X 4. This is not a normal size but might illustrate what's happening. The inertia of big lumber being overcome by the punch of diesel combustion just might take the crank over the top. After all, Davis makes tougher cranks.

Yes, anodizing at home. Most times I pull it off. Was using my field box battery for the last few years but for some strange reason, I can't get the current I need, even on small parts unless I go to 24 volts. So, I went and made up a homemade power supply using a toroidal transformer, surplus, from an amplifier. Taps give me 24 volts and 50 volts at 10 and 5 Amps. Now the parts really boil and bubble.

Don Garry got me started and results were spotty till he sent me some PH balanced dyes. Most times I use food colour, right now I'm trying the ink the bingo markers contain. Got one in the jar right now, a great looking blue. Hope it works out. Commercial dyes are expensive and you have to buy too much. I got lucky and one outfit was willing to send me a sample of their black. Most colours I manage but black is the problem. No black in food colour or bingo markers. Tried ink and one brand gave me a dark blue and the other brand gave me a dark gold colour. ????? Not bad but not what I wanted.
Old 12-20-2004, 12:43 AM
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Default RE: Question about 049 Davis Diesel head

As for the brittleness of the Cox reedie cranks I have heard that baking them in an oven helps them last better.
Yes, it will reduce brittleness and less hard surface. Make steel more tough.

Best to annealing between 250-300 degree celsius or you see steel get dark yellow to very light brown steel color when the steel are annealed but still hard surface and now it has tough in steel.

Jens Eirik
Old 05-31-2005, 02:36 PM
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Default RE: Question about 049 Davis Diesel head

All you have to do is call us for free information at 203-877-1670 we advertize in Model Aviation and R/C Modeler

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