Hi all,
Yesterday I was running two of my engines, the AH special .1cc and the VA bamby .15cc before running and after they both had the great compression that they always had then this morning I went to give them another quick run for youtube both engines had nearly zero compression and wont run. I honestly have no idea what could have happened. I have/had lots of engines and this has NEVER happened to me before.I filtered the fuel as I always do so I doubt that was the cause.
I have not owned these engines from new and both looked and look a bit dirty but had perfect compression.
Any help would begreatly appreciated because on the 2 engine combined I have spent nearly £300.
Any comments appreciated,
Indra

That is a interesting mystery.
I would think that the contra pistons is leaking and wound up not sealing after the last engine runs. But both different brand engines having the same problem is pretty unique though.
You might want to remove the backplate on the engines and look to see if the rods look like they are bent or not. Or worse the big end of the rods is worn out or something. You stated you got these engines used from someone else?

Ok,
I am going out for lunch now and whe i get back i will check.
Yes i got them both used and both from different people.

If you have overprimed the engines you may rinse away the oil from the cylinder walls and loose the seal/compression. Put a drop of pure castor oil on the piston and check if that brings back the seal and compression. On older worn engines a higher oil content (about 25%-30% pure castor) can help with the seal.

If compression was lost overnight before you attempted a restart, there might be a more severe problem. One thing that can happen is that the diesel exhaust residue is highly aggressive and you can get corrosion over night on lapped iron/steel constructions. You should preferably run the engine dry and lubricate the piston directly with after run oil. If you have a muffler you might have to undo it in order to access the piston (it is not enough with a few drops down the carb). Then leave the engine with the piston at BDC to help with the venting of the crank case.

To me this issue is larger on engine that have been run on smallish props with a little higher compression setting, i.e. a darker exhaust residue.

So, check the piston and cylinder for signs of corrosion.

<div style="text-align: justify">Mr. Cox hs a very good point - corrosion is a not unlikely issue.It's amazing how rapidly it can set in, too. That's why I always rinse my engines after running in Varsol (inside and out) followed by some time in the ultrasonic cleaner in methyl hydrate (eliminates the "diesel aroma"!). Then the after-run oil (I generally use air tool oil).

The thing to remember always is that the smaller the bore, the greater the effect on compression of any wear in the piston/cylinder set-up (whether through running wear or corrosion makes no difference). This is because the circumference of the piston or contra-piston(the leakage "pathway") varies with the square of the bore, while the volume of gas above the piston varies more or less with the cube of the bore (assuming near-square bore/stroke dimensions). So the volume of gas that's there to be leaked is reduced far more rapidly with decreasing displacement than the pathway through which leakage can take place. The result is that a given linear leakage rate along the piston or contra-piston circumference drains the compression off far more rapidly as you go smaller. Hence fits become more and more critical, and the slightest slackening of the fit can lose you all of your compression.

So with the smaller engines, it's more critical than ever to do everything possible to avoid either corrosion or running wear. I've always found that the tiny engines don't last as long as their larger brethren, and I'm sure that this has a lot to do with it. If you must run them, use plenty of good-quality lubricant and keep the engine clean and free from fuel residues at all times!

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I always run it dry and then use a drop or two of "Xena Lube".
The fuel was 28% all castor oil.
I always make sure they are clean before storing.
I tried the castor thing and still no cigar.
As long as I have had the Bamby it was run a little under compressed because I dont think this one likes being pushed.
I followed instructions for the real Bambi and cut down a Suoer 5-2 until I was getting 10000 rpm.
As for the AH it has been run on a grey cox 3-1.25 and near enough at peak NV and comp.
I have done everything I kow about to preserve these engines.

Are you doubly certain that the oil was Castor and not any form of synthetic?

The use of a man made high detergent oil will surely strip any seal forming varnish gained from the castor in just one run!

Last ditch try no kero, original drone fuel was 75% ether 25% castor oil martin
you could go 70/30 might give enough seal with the castor and not a lot of compression needed for high ether
also an oven bake on the piston if cast iron might swell it too

Indra,

this possibility was suggested earlier on in the discussion.

These tiny engines have really close tolerances and weren't really meant to be more than interesting collectables.

They will run of course but not for long, compared to say a Mills or a PAW.

I'd guess that they were now clapped.

Sad, but probably true!

Then again I'm a "glass half empty" type of dude

Ray

If fit was not not castor I WILL sue the company I got it from.
The fuel was a factory mixed "model technics D1000".
Martin,
Heating the piston has been at the back of my mind ever since I had this problem and did work in a tired Cox 010.
However I dont want to **** it up more than i need to :0

It's disappointing to hear that these engines don't have compression. Did you check the rods? Do the pistons leak, can you see bubbles at the exhaust port when you turn it over? What is Xena Lube? On the site it says it "gets rid of castor gunk". Maybe that washed away the varnish, if there was any to begin with?

I bought my little AE 0.1 as a curiosity. I'm happy it does run OK, but wonder how long it will last. You don't see many of these little engine running much except for a few that were certainly made with that intention. The reproductions I'm never quite certain about. How many tiny Valetine engines are out there, and how many of them run and for how long? I don't think I'd truly expect anything below .25cc to last very long, unless I knew the manufacturing processes and materials used.

Greg

Greg is absolutely right - you can't expect anything really small to run for long. The smallest engine of my own experience that has at least some legs is the K Hawk Mk. II FRV diesel of 0.192 cc. . Even that one only goes about 1.5 hours before needing a rebore. I've rebored my own "runner" example twice!! Mind you, 1.5 hours is a lot of flights in the small free-flight models for which those engines were intended. The original D-C Bambi will hold peak for perhaps an hour if well treated. Again, rebores are a regular requirement if you want to keep running one.

This is why I ony ever started my Valentine Nano-Bee 0.006 cc diesel once and let it run for about 10 seconds. I just wanted to prove that it ran, that was all, and have resisted all calls to run it again for the video! That's about all that you can expect from the real sub-miniatures - start 'em up briefly once to prove that they run, and then enjoy them for what they are -fascinating collectibles!

The only way these daysto ensure that you're using a fuel that is all castor is to mix it yourself. Too many pre-mixed fuels have enough synthetic in them that stripping of the varnish is bound to occur.
I've never had a Valentine engine that didn't run, but I have no intention of finding out how long they'll run for!

The smallest engine I would ever entertain in buying would be a PB 0.33, and the work that goes into ensuring long life is incredible!

http://www.peterburford.com.au/index.php

I'd have no problem with the Schlosser 0.25cc. The one I've seen starts and runs like a much larger engine. They are expensive, but I really should get one before they disappear.

Good luck, Greg. Dave Owen got Benno to make one last batch for him earlier this year, and I bought the last one of those. There was a NIB one on ebay a week or two ago, so there are obviously still a few out there. Well worth having if you can find one.

The analysis above regarding area/volume ratio seems sound, but it is pretty bad news if these engine can only take a 10sec burst of a prime and not actually be used for anything. The cox .010 could/can at least be used on glow. And the .020 peewee does well as a diesel too, in fact it runs better than on glow fuel where I could never get it to run well for a full tank.

Still haven't seen or heard about where they are leaking. A leaking piston is usually quite easy to spot, giving bubbles around the exhaust, while a leaking contrapiston would be harder to spot. A drop of castor usually seals a slightly worn engine enough to start it, at least on larger engines. Do you have any pictures of the piston? Would be useful to see if it is regular wear or corrosion that caused the loss of compression. Surely simply wear would have shown up while running and not the day after, I'm still thinking that it is corrosion that is involved here. It is the only thing I can think of that could set in over night.

Thats what I am thinking too because "wear" in y experiences does not just happen over night.<div>I will try and get some picture soon.</div><div>Yes the pee wee is great as a diesel and a lot better than it is on glow.</div><div>A tee dee .010 yeah I am stilling trying to get that to go on diesel hopefully I can get some cranks made but no one is responding to the emails [:@]</div>