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Sep 26, 2014, 07:46 AM
DJS Johnny
johnshannon's Avatar

Interesting


Quote:
Originally Posted by 2gun
Re Gluehands fixed compression diesel assembly issues. Geoff, how do you think it would go if you made a piston and rod assembly with a ball joint instead of a gudgeon (ala Cox) and had an oversized hole in the big end. Insert the piston with the rod deflected to the back to allow it to be swung forward (but with clearance) on to the crank pin. Then insert a loose big end bush (like series 100 Veco .35) to fill up the gap???
Charlie (It is OK to make fun of me) Stone
Geoff, 2gun, all,

Interesting idea. Does the "loose big end bushing" have clearance to both the rod and the crankpin? I once used a lower end bushing that screwed into the rod.

Everyone, you can make fun of me anytime. I probably deserve it!

Johnny
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Sep 26, 2014, 08:26 AM
DJS Johnny
johnshannon's Avatar

Nice Pictures


Quote:
Originally Posted by Gluehand
Johnny,
A few pictures as requested.
#1. Yes, the liner is an interference fit.

Bosse,

Perfect! It does look like the rod body is in the center of the piston (that is great) and has a nice slot in the "backplate-lower crankcase can" in which to run. A relative thin rod that would clear the inside of the baclplate and the shaft counterweight. Maybe just a spacer on the crankpin to take up the space forward of the rod?

I would think you would use my Engineering Design Rule #1 - "Try the easy thing first - It just might work!".

Is the top of the cylinder blind ended forming the combustion chamber? i.e. Is it one piece?

The assembly problem still exists to some extent. Two piece pistons and ball joints (with possibly two piece piston) have been suggested and have possibilities. I have never seen a rod lower end that would go high enough to insert a shaft. But, off to the side might work. You can also rotate the piston-wristpin-rod 90 degrees, place it at TDC, and swing the rod to the rear. This just might allow the rod to get out of the way in that radius volume where the backplate thingy goes. Installing the wristpin through the exhaust is still in play. Many possibilities. Something will work, I am sure. Most of the answers can be had with a little CAD work.

BTW, your pictures were great, exactly what was needed.

Do you have a strong preference of a "runner" vs a "flipper"? A flipper would be very easy.

Johnny
Sep 26, 2014, 08:52 AM
Registered User
If the rod was meant to be thin on the big end ,why make a long crank pin and then space it . This guy was an engine builder ,the rest of the engine is engineered ,he wouldn't scrimp on the rod piston construction . If the big end eye of the rod was the length of the pin then it won't move back far enough on the gugeon pin inside the piston to put it on the crank I'm afraid .
Sep 26, 2014, 09:23 AM
DJS Johnny
johnshannon's Avatar

I Agree


Quote:
Originally Posted by Geoff Potter
If the rod was meant to be thin on the big end ,why make a long crank pin and then space it . This guy was an engine builder ,the rest of the engine is engineered ,he wouldn't scrimp on the rod piston construction . If the big end eye of the rod was the length of the pin then it won't move back far enough on the gugeon pin inside the piston to put it on the crank I'm afraid .
Geoff,

I agree. I was not implying this is the way it was designed. I was only saying it is a possible solution. There is no question that the rod body was thin. The space from the back of the shaft counter balance to the backplate is small. Maybe a steel rod with a bushed lower end was intended. I agree that a rod lower end the length of the crankpin would most likely not move back far enough to get it off. You could make the rod lower end bushing a larger diameter at the front, smaller and threaded at the rear that screws into the rod lower end with the proper direction threads to maintain tightness. Of course, the thread direction would depend on rotation. And piston ported engines can run either direction, sometimes as the results of a "backfire".

Johnny
Sep 26, 2014, 09:33 AM
DJS Johnny
johnshannon's Avatar

However


Quote:
Originally Posted by Geoff Potter
If the rod was meant to be thin on the big end ,why make a long crank pin and then space it . This guy was an engine builder ,the rest of the engine is engineered ,he wouldn't scrimp on the rod piston construction . If the big end eye of the rod was the length of the pin then it won't move back far enough on the gugeon pin inside the piston to put it on the crank I'm afraid .
However, a simple spacer does solve the problem of rod loading. Draw the free body diagram of a rod with the main body under the center of the piston as this appears to be (and is good design). Using a spacer results in symmetrical loading. An asymmetric lower end introduces a moment making the rod tending to ride against the shaft or the backplate. If the rod upper end has the same asymmetric geometry the rod tends to stay put, however a moment is introduced into the piston tending to make it cock on way or the other in the cylinder. I have always liked symmetric pistons and rods.

Johnny
Sep 26, 2014, 05:34 PM
Registered User
So there ya go ,another fascinating piece of model engine building that our erstwhile collector person Gluehand can trot out in another 3 or 4 years and get all the same suggestions from a different set of people . Maybe the guy just hadn't got around to cutting the head off and putting the thread in for the glo plug and making the real liner that slid in from the top therefore eliminating all these last entries ,and the nice buttress thread on the head and in the case to hold it all down . Who knows ,it's still a nice piece of work ,thanks for sharing .
Sep 27, 2014, 01:57 PM
1234567
flyinglog's Avatar
Testrun :

Parra WASP 1,5ccm Diesel (0 min 18 sec)


the head leaks a lot, but otherwise it is running good.

Regards !
Sep 27, 2014, 07:02 PM
Registered User
I think I would either tighten the head or if that has been tried ,I would send it back to Alberto . None of mine leak and shouldn't !
Sep 27, 2014, 07:34 PM
Registered User
Thread OP
On mine with the Nelson glow plug, it also leaks around the plug threads. I didn't want to over tighten the plug. The Nelson plug (maybe cold) takes about 30 seconds (on 15% nitro) to warm up before I disconnect the battery. otherwise it just quits. I'll have to get a glow head that accepts regular plugs (not available from Parra) and accept a few less rpm's. My Webra 1.8 cc "Speedy" will give it a good run for the money, but I won't really know until they fly the same plane.
Sep 28, 2014, 11:40 AM
DJS Johnny
johnshannon's Avatar

Possibilities


Quote:
Originally Posted by Gluehand
Johnny,
A few pictures as requested.
#1. Yes, the liner is an interference fit.
I violated the #1 rule in engineering, sort of, "Do not scale the print!". In this case I digitized the pictures and used the data to guess at a possible solution. It is presented in the picture. This assumes that the proper TDC piston clearance can be approximated and that the wrist pin can be installed through the exhaust port.

To address the possibility that the rod/wrist pin must be installed from below and the TDC clearance cannot be approximated I would use a solution I developed for another engine (having some of the same constraints). I made a "carrier block" for the wrist pin that was bolted into the piston from below with 4 screws. In this case the wrist pin hole could be asymmetric to the mounting surface to provide two distinct positions. Additionally, shims could be placed between the carrier and the piston to provide more adjustment.

BTW, how do you caption pictures with the "new and improved" upload
Johnny
Sep 28, 2014, 03:06 PM
Registered User
Gluehand's Avatar
Johnny,

What your scetch shows, resembles an idea that came up when I brought the engine to a club meet some time ago,
A relatively thick walled, threaded big end bush was also suggested.
The larger "hole" in the big end would - hopefully - leave enough "sloppiness" to fiddle the bits in place, before the bush is finally screwed in...

I added the bush (+ a minor reinforcement at the back of the rod) to your scetch, below....
Last edited by Gluehand; Sep 28, 2014 at 07:31 PM.
Sep 29, 2014, 03:30 AM
Size doesn't matter!!!
Quote:
Originally Posted by Geoff Potter
I think I would either tighten the head or if that has been tried ,I would send it back to Alberto . None of mine leak and shouldn't !
I have 2 wasps in use and none of them has any sort of leak around the head...
Yesterday I flew both of them on Dementiev combat planes. I have used nearly 1liter of fuel yesterday... I used both engines alternately and with just 2 flicks on the prop they ran. I still have to shorten the 7x4 taipans but right now they are just fast enough for me. I am very pleased with these engines.
Sep 29, 2014, 04:10 AM
Registered User
Why go to all the trouble of another head and plug ,which will not perform as well, when it would be easier and more productive to find the problem and fix it and retain the Nelson type setup ,it is far superior John . I would send Alberto an email if they didn't perform A1 ,he is very good with his products .
Sep 29, 2014, 05:07 PM
Registered User
Thread OP
Thanks for the info Geoff. Yes, the Nelson plug may be superior, but I still have several "cards" of other plugs (life time supply). I don't need 100% power from the Wasp as it will be used for sport flying. I didn't tighten the Nelson down firmly, so it leaks. I seldom run any of my engines to maximum. If I need more power I just use a bigger engine. I have a fun fly model that had a K&B .21 that ate lot of fuel. Swapped it out for a tired old OS .50 that had the same power, but got about three times the mileage running easy on a 12x6 prop. I guess I've been lucky, but I've only had a few engines that broke parts (rings, rods, crank pin, bearings) while running in flight. I even had my Cox Conquest eat all the ball bearings while in flight, slowed down, but kept running till the end. Piston and liner got badly scored, but over half the little balls from the race were missing.
Sep 29, 2014, 07:28 PM
Registered User
edholly's Avatar
The Jaguar 1.5ccm arrived yesterday after a 3 weeks journey across the Tasman Sea. And this is the jet age !

Bought the engine off the same modeler that I got the MOD Oliver Tiger from, and Ken said although he had owned it for a very long time he had never run it. Certainly looked in fine form out of the box it came in and when a prop was put on, it had a wonderful feel to it, plain bearing yes but a lovely pop over comp and bouncy back and forwards off compression.

I can find so very little about this engine on the web, so I thought I'd describe it a bit here. Seems there are 2 versions - a 2.5cc and this 1.5cc, maybe the 2.5 is more common. Provision for radial mount or beam mount with a slightly recessed backplate so it doesn't foul when radially mounted. Has a knurling on the prop driver which no longer grips, but also has a shoulder where the prop driver pushes against the crankshaft, which allows the drive to be transferred without slippage. Is embossed with JAGUAR and 1.5CCM on top of cylinder muff and has nice black anondising as can be seen in the photos. The needle valve appears incorrect as the 2 outlet holes don't line up in the middle of the venturi - biased towards the inlet side, and the needle valve only rotates 4 turns.

Handling - this definitely has a WOW factor to it. 9,700 on the test Turnigy 9 x 4 wood I use as the test is very impressive. It actually out-turns my Owen Mate Mk2 by 200 rpm even though .5cc less - damn ... First flick it wanted to go 2nd flick it whacked me on the back of the finger. A few more flicks and it was obvious it wanted more fuel via the NVA, gave it that and away it went. As the comp went up so did the revs until it was happily singing at well over 9,000, then a tweak of the NVA a tad leaner and a few more revs then a bit more comp and 9,700 and I reckon there's more there, but more than happy with that result.

It is triple slot ported a bit like a Webra I guess, it has 2 transfer ports cast into the sides and 3 ports that breath into the upper cylinder, so it must have some sort of annulus that allows the gases to go from 2 passages to 3 passages, whatever they've done it sure works very well. The backplate came off ok but only after I tried to tighten it then untighten it did it free up. Conrod is hand scribed back and there is no balancing attempted on the crankdisc the rod is quite robust with quite a large crankpin. The piston diameter is around 1.6 cm and the stroke is around 15.4 mm. NOW ... I have triple checked and quadrupled checked these measurements and my calculations and I come up with a cylinder volume of 3.097cc ... not 1.5cc ... I know I am measuring sizes as best I can - but I know my measurements are not out by a factor of twice ! ... So what is going on ... ? Have put in a comparison photo of the Jaguar between a 2.5 Webra and a 1.5 Webra .. and you can see it looks bigger than the 1.5 and taller even than the 2.5 ... so why would it be called a 1.5 ccm ?

Anyways, very very happy to have this engine on the shelf, and it sure packs some power .... Ed
Last edited by edholly; Sep 29, 2014 at 07:51 PM.


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