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Old 01-04-2019, 11:03 PM
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Happy New year!!!

Hi all.

I have been very busy the month of December and I have not been able to do much work on the assembly after my initial failure. I have learned a couple of things:

Loctite excelerant is not needed as it makes the set too fast at elevated temperatures.

The initial method used placed the front bearing in place and the intermediate bearing on the shaft. In this method, the inner race of the front bearing can be supported when the crank shaft is pressed in. This did not work well at all because I took too much time.

The other issue with the initial process is that the case expands .012" linearly when heated and a pressure must be held on the components through cooling after the crank is pressed in. This procedure does not give one an accurate placement of the shaft in the upper case.

What I will try next is placing the bearings in the bores expanding the case with heat, then shrinking the shaft with dry ice or nitrogen and pressing in.

My concern has always been pressing in the shaft without supporting the force on the inner race of the bearings. Pressing without support can damage the bearings.

I was in the shop two days ago and started working on a test stand. I will place the stand on a linear slide and hook up a load cell to do static curves on a few props I have for this project.

I welded a 3/8" plate to a 14" long x 8" channel. All I have to do is drill and tap any surface to attach the engine and electronics. I picked up the metal from the scrap bin.

I love the previous picture where the throttle servo is on the engine. Thank you Mr. Heiman, it is a neat idea. I wonder how long it will last with the direct vibration.

I was going to go to a shop to make a test stand like the the one in this video I found on Youtube, but it would cost too much. The one I put together is free, and you can't beat that.
DA 170 Test Stand (1 min 24 sec)
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Old 01-23-2019, 05:56 PM
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Update

I am on the way to completing the test frame. I have been on hold finishing it since I need to get a kill switch and I wanted to do static load testing of some props I have for these engines. I have been looking for a 50 lb load cell which can handle the vibration but have not been able to find one less than $300. This cost plus the readout and computer hookup and we are north of $600. I am not sure that prop thrust gives me that much of a tingle up my leg to make this investment. So far I have 8 hours and around $30 to build this frame. I may put a 1" block in back of the engine since the heads are very close to the firewall.

I have purchased a DA150 carcas to do assembly trials. I am unhappy with my work so far as it is not perfect and I have not been able to reproduce the original dimensions.

This was an engine without pistons, heads or other accessories. It is totally unfinished. It is one of the newer drone engines that is basically an aluminum block. This will be a throwaway piece as the only good thing about it is the case.
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Old 01-25-2019, 04:59 PM
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Outstanding effort you've gone through trying to find workable solutions. Amazingly I was told by a well respected DA employee that all their techs use for disassembly and reassembly were some basic hand tools and a hot plate to heat the components. After watching your endeavors I find that comment very hard to comprehend. It makes me wonder if they hold looser tolerances and rely heavily on the Loctite material.
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Old 01-25-2019, 05:40 PM
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Thanks Kevin for the kind words.

I am trying to put out accurate information to the community and not just slapping this thing together.

I am building some jigs and fixtures to help in the assembly. One of the problems is I have not done this before as I would normally not work on the engines given how good the repair jobs are at DA. If I were doing many of these per week, this would be a lot simpler.

I have a time issue as I can not dither during assembly. I have to be quick and smooth or have a better way of assembly.
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Old 01-25-2019, 09:04 PM
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I concur the biggest obstacle for most of us hobbyists is lack of experience. We'll never get up to same familiarization as a tech doing this 40 hours a week. Even if I did a dozen engines I'd likely forget most everything during the down time.

What we need for assembly is a Loctite decelerator rather than accelerant. I have not researched, but I'd be surprised if a slower setting substance does not exist for the very reasons you're experiencing.
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Old 01-29-2019, 09:50 PM
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Engine 3

Ok ... I started to work and try to reverse engineer the assembly of engine 1&2 from this recently acquired third block. First I am looking at the intermediate baring and shaft radius. From my measurements, the shaft has a 2 to 2.25 mm radius. It was a little hard to tell, and the bearing looked like it has a 3mm radius on the fillet. Now other manufacturers do not seem to have a radius on the shaft. I believe this is an excellent design as it reduces stress in the highest loaded part of the crank shaft. If the shaft had no radius, a crack or shaft failure could occur.

I started to inspect the new 150 block, a video follows. The block shows the same basic affects of a crash, namely bent prop shaft and out of round hub. This block also has a tight turning shaft due to compressed bearings. I removed the bolts and could fit a .004 gauge in between the two halves of the case. This shows that my initial conclusion that the bearings are tight due to compression of the case is correct. I will have to verify any shaft damage.

Engine 3 (7 min 19 sec)


The height of the bearing in the engine 3 case is .014. The one I installed is .015" . From this measurement, I conclude that DA heats the case ( Upper and Lower), applies the locktite and slides and holds the bearings in place at all locations to the bottom of the
fits. I think that the shaft is installed in a warmed case with potentially cold shaft. As I have indicated in a previous post, I will try dry ice to press the shaft in to reduce the force on the unsupported center bearing.

If this works well, I will amend the procedures.
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Old 01-30-2019, 01:26 PM
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Why I like DA

I wanted to share with you from my experience why I like DA so much. The company though small, places an emphasis on engineering and quality.

In the previous post, I measured the radius on the intermediate bearing shaft journal. This is done for stress relief.

DA placed into their design a feature used in machines that carry 500 tons of load. It is the attention to detail that I like about them.

Below is an example of a machine placed in service 50 years ago that structurally failed. Over time, the point stress cracked the ledge almost causing catastrophic loss. In another picture, its replacement shows the same design but with an internal radius. This radius spreads the load preventing similar failures in the future.

The radius on the shaft should prevent this type of shaft failure. I repair large machines for a living and am happy to see the same principles utilized in a small engine.
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Old 01-31-2019, 08:53 PM
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Engine 3 update

I have disassembled and reassembled engine 3 with the same binding issue. I will take apart the engine tomorrow at lunch and measure all components.

I need to make a fixture to hold and heat the engine( Hot Plate). I used a torch and don't like the results. I also need a fixture to orient the piston rods so they don't get in the way during the pressing process. Also, I had some dirt on the seat of the intermediate bearing surface and the bearing did not sit square. It was out by .001 while the top bearing had 0 variation. This may be why I had some binding. All bearing holes must be perpendicular to the shaft.

I am getting faster at taking the engine apart. If only I was that good at putting it together. It is good putting stuff together without the loctite. Were I working with the loctite, the components would have been solid before I completed the work. I will post an assembly video tomorrow. It is not pretty.
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Old 02-01-2019, 10:57 AM
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Engine 3 Assembly Rev-2

Hi all,

Here is the assembly . I tried a different way which I kind of object. Two problems:
1)unsupported bearings when pressing the shaft in
2)flexing of the wrist pins and counter-weights( This can be solved, see pictures below). Gauge blocks were used.

The shaft had a .0017 TIR. Higher than what I like but still probably usable. This is the same as engine 2. I would not use it myself. I believe DA has a .0015 max tolerance but I can't be shure.

The binding improved by on the re-assembled block but not that much.

Please give any feedback to this process




Engine 3 Assembly (4 min 48 sec)
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Old 02-05-2019, 06:46 PM
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Assembly Procedure -Rev3

Quote:
Originally Posted by ChemE View Post

This is REV-3 (Superseded by rev 4 you will find rev 4 in later posts)

1) Clean all of the components meticulously. Make sure that there is no residual loctite on the shaft and case. Clean your area where you will be doing the assembly of dirt and dust. Remove all gasket material from between the crank case. Chase all of the threads with a tap to ensure old loctite does not go back into the crank case. I would use gasoline or alcohol with a cotton swab or a plastic brush. Do not use steel as you do not want to scratch the surfaces. Make sure all of the old green 620 is removed from the intermediate shaft radius. Compressed air can blow small particles off of the crank wrist pins and needle bearings.
The reed assembly on both of these engines are still filthy so I have to clean them again.
Have handy some Redline oil to lubricate the components( bearings, wrist pins, cylinder heads. The oil will reduce the probability of scoring.

2) Place the top crank case in an oven at 250F or heat with a torch. This should allow a slip fit of the to bearings. You can heat more but will have to cool the case after bearing insertion.
3) Attach bearing to bearing insertion shaft. ( See Picture- I made modifications to the drawing to make it stiffer and to eliminate washer and screw). This will allow for accurate fit of the bearing. Use some Vaseline to hold bearing on the shaft.
4)Take the case out of the oven and place 620 loctite on the leading edge of the case bearing bore or bearing. Do not use a lot as it will spread.
5) Hold the rod and bearing and place into the top bearing slot sitting the bearing fully on the seat( ie all the way in). You may need a press but if you do very little force will be needed. You must work quickly since the components will shrink within a few seconds as the temperature of the components equalize. Keep pressure on bearing while cooling.
(I will put the case in an oven an determine the time and temperature after I do some measurements).
6) Remove the rod from the bearing and swab any excess Loctite with a Q-tip internally and externally. Place top half of case back in the oven.
7) Removed
8)Repeat process for intermediate and lower bearing. The intermediate bearing radius should be facing towards the interior of crank case.
9)Removed
10) Removed
11)Removed
12) Removed
13) Removed
14) Removed
15)Insert shaft into the top case intermediate bearing and press the shaft through the intermediate bearing.
16)Apply Loctite 620 to the inside diameter of the front bearing and on the intermediate crank shaft journal.
17) Press shaft to refusal.
18) Put 620 loctite on leading edge of the rear shaft journal and gasket compound in between case halves at the rabbit fit.
19) Press bottom jornal into the bottom case . Use a .010 gauge shim to prevent full closure of the cases. ( This may change after trial)
20)NA
21)Gaskets are not used on this model.
22)NA
23) Get ready the mounting plate and 4 long screws.
24)NA
25)Torque bolts to desired number after the silicone has dried. The bolt torques to be determined.
26)Place prop hub into an oven at 300F or torque cold to 20 to 40 ft lbs? ( to be determined)
27)Manufacture a spacer of the appropriate thickness to go in between the hub and case. The spacer will do two things. 1)
it will limit the depth you will be able to go, and 2 it will ensure perpendicularity to the shaft.

28) Press pro hub onto shaft. Remember the Woodruff Key. Torque prop shaft to into place.
29) Do qc run-out checks on all rotating components.

This is what I got so far. I may correct or change this in the next few days.
Below is a picture of my small shop. It is all the room I have. My wife is giving me grief for what I have. God help me if I want to put together a 40%. I would have to put a table in the garage.
I need to move. Can't wait to retire.

The bearing insertion tool is also re-posted so that new readers don't have to hunt back to previous posts
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Old 02-13-2019, 11:05 AM
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New vs old design differences

Just wanted to point out some of the differences in the old vs new intake design. ( Please do not look at the new design engine as it is an unfinished block from a drone. This is only to show the difference in the intake area of the engines)

The new design is really nice. DA has taken away some heavier components while making the crank case better without reducing strength in my opinion.

The reid is the same intake size but itself a little lighter.
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Old 02-22-2019, 04:31 PM
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Dry Ice

Hi all!

I am attempting to see if shaft shrinkage would work in reducing the forces to assemble the the engine. In my mind the less force is used in sliding the shaft into the bearings, the less probability exists of damaging the bearings.

As you know, I made a bearing insertion tool. The tool was machined with a .667 od nub which allowed the bearing to slip fit on. (see pictures)

After inserting the shaft in dry ice for 30 minutes, little shrinkage occurred. Not enough to bring it to .667. The bearing could not be pushed on by hand.

I repeated the process by heating the bearing to 200 F, and the bearing slipped right on by hand.

On Monday, i will get another 5 lbs of dry ice ($13 and would last 12 to 24 hrs in a small styrofoam cooler) to do more work in this area.

Observation: The crank rods do not want to turn on the wrist pins.

Use gloves to prevent hand burn!!!!!!!

After 26 hours there is still one lb of dry Ice left.
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Old 02-25-2019, 09:46 PM
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Engine assembly REV-4

Hi all,

Assembled the engine today by heating the bearings and crank case to 250 and cooled the shaft in a freezer. The shaft went in by hand without force. It seems that dry ice is not necessary. I used a new gasket. I will cut one out of copper shim stock for practice as these can tear.

Things learned today:

I took apart engine 1 and found loctite to have gone on the bearing seat. During that assembly, I placed loctite on the case bore. It is advised to always place the loctite on the bearing so insertion will wipe the loctite out and not push into the case. The bearing can sit crocked if the seating surfaces are not clean.

I am still having issues with binding on the bearings. There may be space issues as the shaft is mounted too far back so when pressure is placed on the case bolts it compresses the shaft. No torque settings yet!!!!

Assembly video tomorrow !!!

All in all, I feel I am getting closer to a working process which will not damage the bearings. The big issue that I have as an engineer, is an actual temperature. You can not have a process by working with a torch. If we are to rely on the heating method of assembly, the process must be reproducible. The temp stick may be good enough but I do not have substantial experience working with it.

When I started the project i thought the assembly was going to be easy. It may be easy, but having gone this far, this reminds me of a wonderful line: " The best laid plans of mice and men often go astray"
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Old 02-26-2019, 06:59 PM
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Engine assembly Rev 4 - looks like we got a process

OK all, I think we got a process. I will update our procedure to indicate all of the changes. I placed the crank in the freezer, and we used 250F as a temperature.
Still need a bit more speed, as the heating and cooling units should be closer by for the work which they are not. During the 30 seconds I was away to get the bottom piece out of the oven, the shaft wormed up and did not slip into the bottom bearing. I almost gave up, but used the screws to bring the two halves together.

I will update the procedure in the next post.


No Loc-tite was used in this assembly trial









DRONE ENGINE ASSEMBLY REV 4 (10 min 41 sec)


Temperature Stick Demo (1 min 24 sec)
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Old 02-28-2019, 09:47 AM
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Engine Assembly Procedure REV-4

DA150 Engine Assembly Procedure- REV4


1) Clean all of the components meticulously. Make sure that there is no residual loctite on the shaft and case. Clean your area where you will be doing the assembly of dirt and dust. Remove all gasket material from between the crank case. Chase all of the threads with a tap to ensure old loctite does not go back into the crank case. I would use gasoline or alcohol with a cotton swab or a plastic brush. Do not use steel as you do not want to scratch the surfaces. Make sure all of the old green 620 is removed from the intermediate shaft radius. Compressed air can blow small particles off of the crank wrist pins and needle bearings.
The reed assembly on both of these engines are still filthy so I have to clean them again.
Have handy some Redline oil to lubricate the components( bearings, wrist pins, cylinder heads. The oil will reduce the probability of scoring.

2) Place the top crank case in an oven at 250F or heat with a torch. This should allow a slip fit of the bearings. Use a temperature stick to validate temperature. Apply loctite to intermediate shaft journal and place crank in a freezer. You need about 30 minutes for both heating the case components and cooling the cranc.

3) Attach bearing to bearing insertion shaft. ( See Picture- I made modifications to the drawing to make it stiffer and to eliminate washer and screw). This will allow for accurate fit of the bearing. Use some Vaseline to hold bearing on the shaft.

4)Take the case out of the oven and place 620 loctite on the leading edge of bearing only. Do not use a lot as it will spread. Putting loctite on the case bore may push loctite on the bearing seat causing it to not sit flat. If 250 has not been reached, you can use a torch to bring it to 250 F. The case will cool quickly so you need the oven to be close to where you are working.

5) Hold the insertion rod and bearing and place into the top bearing slot sitting the bearing fully on the seat( ie all the way in). You may need a press but if you do very little force will be needed. You must work quickly since the components will shrink within a few seconds as the temperature of the components equalize. Keep pressure on bearing while cooling.

6) Remove the rod from the bearing and swab any excess Loctite with a Q-tip internally and externally. Place top half of case back in the oven or reheat with a torch to go back to 250F (always verify temperature)

7) Removed

8)Repeat process for intermediate and lower bearing. The intermediate bearing radius should be facing towards the interior of crank case.

Make sure that you do not move the bearing while the case is cooling as you can trap the bearing not perpendicular to the case.

9)Removed
10) Removed
11)Removed
12) Removed
13) Removed
14) Removed


15)Apply Loctite 620 to the inside diameter of the intermediate bearing. Re-heat case maintaining the temperature to 250F. Apply heat evenly and let heat be absorbed by the bearings to allow them to expand. The crank will not go in the bearing if you install the bearing and immediately try to insert the shaft.

16)Insert shaft into the top case intermediate bearing and press down with hand. Experiment timing with a removed bearing. Make sure the crank arms are located correctly with its corresponding port. You can assemble this thing backwards.

17) Press shaft to refusal.

18) Put gasket/ compound in between case halves at the rabbit fit.

19) Press cold bottom jornal into hot bottom case(250F) . This must be done quickly.
20)NA
21)Gaskets are not used on this model (Engine 1 and 2).
22)NA
23) Get ready the mounting plate and 4 long screws.
24)NA
25)Torque bolts to desired number after the silicone has dried. The bolt torques to be determined.
26)Place prop hub into an oven at 250F or torque cold to 20 to 40 ft lbs? ( to be determined)
27)Manufacture a spacer of the appropriate thickness to go in between the hub and case. The spacer will do two things. 1)
it will limit the depth you will be able to go, and 2 it will ensure perpendicularity to the shaft.

28) Press pro hub onto shaft. Remember the Woodruff Key. Torque prop shaft to into place.
29) Do qc run-out checks on all rotating components.

This is what I got so far. I may correct or change this in the next few days.[/QUOTE]


AFTER DOING THIS WORK, I HIGHLY ADVISE YOU TO GO TO THE OEM TO REPAIR YOUR ENGINE
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Last edited by ChemE; 03-01-2019 at 09:25 AM. Reason: correction
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