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PAW .29 locks up?

Old 06-30-2009, 10:38 AM
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J_L_G
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Default PAW .29 locks up?

I am quite new to diesel operaton. I have a .29 plain bearing PAW with venturi. Yesterday I had it bolted down to my test stand. I reduced compression because the ambient temperature was 94 degrees F. I ran 4 ounces of fuel through it using a clunk tank. The fuel was Davis Diesel fuel. The tank was mounted a little low and as it emptied, the engine sounded like it was getting lean. I opened the needle valve and propped the tank up and that got the engine running a little richer. Then, when it started to lean out again, I pinched off the fuel line stopping the engine. I attempted to turn the propeller and it was stuck. Frozen. I couldn't believe it was locked up when the engine had been running nicely just a minute earlier. I forced the propeller to turn just a little and it felt like metal was scraping on sand in the engine. Rough and scratchy. So I filled the venturi with diesel fuel and carefully rocked the propeller. Very soon, the engine was turning over smoothly and when flipped, the propeller rocked back and forth freely bumping off of the compression.

Anybody know what's going on here? I'm interested in pursuing more diesel projects but I don't want to invest in another diesel engine if this is what happens with them. I've never had this problem of freezing up with a glow engine. I'd appreciate any advice. I'll check back for more info later. John G.
Old 06-30-2009, 11:33 AM
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Jim Thomerson
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Default RE: PAW .29 locks up?

Take the engine apart and see what is going on. I had a similar happening with a Taipan 2.5. Turned out that the rod was hitting the crankcase and knocking off flecks of aluminum. I didn't follow my own advice and destroyed the engine; big score lines on the piston and cylinder. Ended up giving it to someone in Australia as a parts engine.
Old 06-30-2009, 12:34 PM
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Default RE: PAW .29 locks up?

MY original answer was incorrect it was not the fuel it was an overlean situation and the engine using the little remaining in the crankcase ran out of lube a iron piston steel liner will be gone in a very short time seconds with no oil martin Mr davis pointed this out in his post
Old 06-30-2009, 05:06 PM
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J_L_G
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Default RE: PAW .29 locks up?

Thank you, Jim and AMB. I sure hope I have not chewed up the inside of my engine. John G.
Old 06-30-2009, 05:44 PM
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Default RE: PAW .29 locks up?

Now to use the site as it was ment to be, to be helped. The reason your engine got leaner is that got hotter from being over compressed when you pinched it off to stop it that was like the kiss of death as you diprived the engine of all lube as it shut down thus seizing. Sorry
Old 06-30-2009, 08:00 PM
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J_L_G
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Default RE: PAW .29 locks up?

Again, thank you all for responding. I also received a separate email from Eric Clutton. Everyone is very close in assessment of what happened. The engine likely seized up from lack of adequate oil. The reasons for this include (a) not enough oil in the diesel fuel I was using or the fuel needs shaken up to redistribute the castor in it, (b) I pinched off the fuel line thus starving the engine of oil just as it stopped, (c) the engine was running lean anyway, was likely overcompressed and overheating in the hot weather and (d) a combination of two or more of a, b, and c. In addition, Mr. Clutton recommended that I not run a diesel on a test stand for long periods. He suggested I run it about 2 minutes and then let it cool.

This exchange has been very helpful. One of the reasons I took the engine out to run on a hot day is that I noticed that the compression setting I used with the engine last spring when it was about 50 or 60 degrees F ambient temp were certainly wrong in the hot summer weather we have here in Oklahoma.

Thanks again to each of you. John G.
Old 07-01-2009, 08:46 AM
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Default RE: PAW .29 locks up?

John,

In addition to the information you got from Eric Clutton, here is a club site that has excellent information about the care and feeding of PAWs:

http://www3.bc.sympatico.ca/dieselcombat/index.htm

Also, Eric Clutton wrote and sells a very informative diesel reference, "Dr. Diesel's Diary". I have it and highly recommend it.

George

Edit: Additional thought. If you get into a habit of lowering compression until RPM drops off then increasing to peak, you can avoid over-compression. As you go from the lowered setting up to peak, you will usually then encounter a "flat" spot as you increase compression, then RPM drops off again as it becomes more over compressed. The lower end of this flat spot is where you want to be. From there, as compression is increased, so is running temperature.

This may vary a bit depending on how much the engine unloads in the air due to prop size. It may take several flights to get it where you want it.

One very important point I forgot to ask is whether the engine is new or has been properly broken-in? Iron/steel diesels are not plug and play, they need proper break-in to be all that they can be. The site above explains that also.

Good luck.

George
Old 07-01-2009, 12:17 PM
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J_L_G
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Default RE: PAW .29 locks up?

GCB:
to answer a couple of your points. 1. I have the Diesel Diary. I reviewed it last night. If I had been more attentive to the need for good flow of oil instead of only sweating the ether % I'd have been better off. 2. I did back off the compression until the engine was running in bursts but not continuously. It was clearly missing. Tightening up the compression stopped that. So I think I started in the right place compression-wise. 3. I did not know how to use the "flat spot" to judge where to set the compression but I'll use that now. That is a great tip. 4. The engine probably has less than 1 hour run time on it. Eric Clutton also suggested that perhaps the engine was not yet broken in.

I will check into the suggested web site. And thank you again. John G.
Old 07-12-2009, 09:40 AM
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J_L_G
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Default RE: PAW .29 locks up?

Thanks to all who responded and were helpful.

I re-ran my PAW .29 on the test stand making sure I'd shaken up the fuel so as to distribute oil throughout the mix. I did not stop the engine by pinching off the fuel line. I kept the compression down toward the low end of the "flat spot" and reduced it as the engine warmed up. I ran a total of 14 heat cycles of 2 to 5 minutes each (shorter ones to begin with) followed by a full 10 minute cool-down in between runs. The engine is working well so I must have not ruined it when it seized up. I've learned to keep my prime squirt to a minimum the engine needs only a very small 2 drop prime to start it. John G.
Old 07-12-2009, 10:19 AM
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Default RE: PAW .29 locks up?

You have nailed it , the classics are a different beast than the modern aluminum piston, plated liner hot and lean are the death of any engine glow or diesel you see lots of incidents of this one the glow site too. maybe in the future you can pick up a modern schnerle ported glow engine and get a davis head you will not be disappointed great transitions with a modern carb an OS 40LA is reasonable tough, and great preformance and very easy to set up now that you know the basics martin
Old 07-12-2009, 11:24 AM
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gcb
 
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Default RE: PAW .29 locks up?


ORIGINAL: J_L_G
...I did not stop the engine by pinching off the fuel line. I kept the compression down toward the low end of the ''flat spot'' and reduced it as the engine warmed up. I ran a total of 14 heat cycles of 2 to 5 minutes each (shorter ones to begin with) followed by a full 10 minute cool-down in between runs...

John G.
John,

Congratulations, sounds like you are ready to get some good flight tome on your diesel.

For your next engine, you may want to read the "Breaking-in" section of that site I mentioned. After the initial rich run to get any junk out of the engine, you run it at peak for the heat cycles. The reason for pinching or pulling off the fuel line is so it will remain at the "hot" temp for the heat cycle. If you kill the engine by flooding, it apparently decreases the effectiveness of the heat cycle. They explain it. Completely different from glow.

Of course, there is seldom only one way of doing things. I have tried their way and have had success with it. Other ways work also.

George
Old 07-12-2009, 11:39 AM
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AMB
 
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Default RE: PAW .29 locks up?

J L G no more glow plugs prop selection great just by changing compression (timing) bigger prop less compression no changing fuel or head shims ala glow now that you have the "feel" really less hassels than glow, great fuel economy too almost twice that of glow, and no flame outs
martin

stopping can be done by cutting the fuel by pinching or pulling the line I prefer just closing the barrel all the way on the carb no air no run instant engine stop
Old 07-13-2009, 08:50 AM
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Hobbsy
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Default RE: PAW .29 locks up?

One thing that has not been mentioned is that when the engine was shut down (heat soak) warmed up parts that were being cooled by fuel flow, airflow etc.

Mr. Davis has a publication called Diesel 101 that is very informative.

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