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Engine gets really hot

Old 05-01-2005, 12:49 PM
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Default RE: Engine gets really hot

AJC..
Same here i had never problem with my own made cylinderheads with flat contrapiston and some of them has squishband when the engines ran well without to be hotter.. As i wrote before in early post, there are possible not enough cooling fins in his (Micropuller) cylinderhead since it is a car engine. And if he has used too much MEKP in fuel, it will run hotter.

Jens Eirik
Old 05-01-2005, 05:23 PM
  #52  
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Default RE: Engine gets really hot

Well I must say this is turning into a very interesting discussion!

@gcb;
I'm not abusing my engines to that extent. Experience learns that most engines we use hold up for at least three seasons before they need a new sleeve / piston.

As for why Davis doesn't make a head for my engine, obviously I can't say for sure. But I can imagine that it has to do with the fact that this is an unknown / little used engine. This also leads me to think that Davis never tested these engines (I bought my engines from someone who bought them on a trip to Eastern-Europe and I saw one for sale once on this website, but that's it)

We do allow our engines to warm up before we do a pull, so I don't think that would be a problem?

@Jim Thomerson;
The contra-piston in my head cannot protrude from it's bore, because the set-screw isn't long enough (unless it should fall out)
I also think that there is a direct relationship between making more power (i.e. burning more fuel and / or using a higher cr) and the engine running hot. The trick is to find out how far you can take this safely.

For more info on our hobby, here's a few websites:
http://www.micropulling.nl
http://www.rc-tractorpulling.com
http://www.micropopeye.nl
http://www.micropulling.com
http://home.wanadoo.nl/harry.vink
http://people.zeelandnet.nl/virtua
Most of the are in Dutch or German, but it should give you an idea of what we're doing.

@Motorboy;
I intend to make a new head with more / bigger cooling fins. Hopefully I'll have it ready before next weekend (we have a pull on Saturday), so I get a chance to test it.

Old 05-01-2005, 11:21 PM
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Default RE: Engine gets really hot


ORIGINAL: Micropuller

http://www.micropulling.nl
I saw photo of your car "Citroƫn 2CV" in this webside, there are bonnet over the engine and lack of cooling in speed..[sm=confused.gif]
As AJC wrote, set a fan inside to keep cooling + extra coolingfins..

Jens Eirik
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Old 05-02-2005, 12:20 AM
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Default RE: Engine gets really hot

AJ,

If memory serves, when the squish band first came out it was to enhance the burn pattern on high performance glow engines using FAI (no nitro) fuel. Now, it seems that many sport engines use a squish band with nitro fuels. Not sure of the necessity.
Perhaps studying heads from performance engines that have both high nitro and FAI heads available might help.

Interestingly, it was the Fox Eagle .61 that had the flat squish band.

I have NO IDEA how the burn patten of diesel fuel is affected by a squish band. I have never heard(seen) a complaint about the heads you produce. I would suggest, whatever you are doing...keep it up.

George

Edit: AJ, I just reread your post. Do some of the contras extend below the squish band? It would seem that if burning fuel was "trapped" in the squish band, it would not be scavenged out and may cause a heat buildup.
Old 05-02-2005, 06:27 AM
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Default RE: Engine gets really hot

George,
I dont see how a contra COULD extend down into the cyinder, past the squish band.... without falling out and damaging the engine!

AJC
Old 05-02-2005, 01:08 PM
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Default RE: Engine gets really hot

AJC, Come on! The contrapistons you make stick down into the cylinder without falling out. Either a tight lap fit or the O-ring holds any contrapiston up in place and keeps it from falling into the cylinder. I have been told that the contrapiston in the Cipolla 1.5cc Junior diesel will sometimes fall into the cylinder, but mine havn't (yet).

Jim
Old 05-02-2005, 01:38 PM
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Default RE: Engine gets really hot

I have six AJ heads and about a dozen Davis heads, none of these contra-pistons stick down out of the head, most run about midway of their extremes. Left to right are an Irvine .40 stock Diesel head, a Davis Fox .50 head, a Davis SuperTigre .40/.51, Davis MVVS .61, and an AJ Coholic MDS .78 head. All are about midway in their travel except the Irvine .40 which is near the botton of its bore.
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Old 05-02-2005, 03:17 PM
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Default RE: Engine gets really hot

Nothing to worry about contrapiston are falling out of cylinder head...
I had never lost the contrapiston with o-ring fitted out of cylinderhead. The sign before the contrapiston with o-ring fitted are too lose from cylinderhead: The oil are coming out of compression screw.
I replaced the o-ring at my OS 10 FP Marine after 8-10 year use, discovered oil was leaking out of compression screw.

Jens Eirik
Old 05-02-2005, 04:15 PM
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Default RE: Engine gets really hot

JIm,
If you have the contra in my head so it is protruding past the lip you wont have to worry about improper scavenging - you will however have to worry about a damaged contra and/or piston! If its that low there is something wrong, as the combustion chamber volume will be near zero. I know they will hang there due to the twin O rings its just that its not possible in normal operation for the cp to be that low.

AJC
Old 05-03-2005, 09:35 AM
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Default RE: Engine gets really hot

AJ,

If the squish band is not on the contra, my question is valid. I assume by your and other responses, that the answer is no.

I had no intentions of ruffling feathers, just trying to understand a guy's heat problem.

From looking at the picture of some of your heads, it APPEARS that the contra is smaller than the bore (on some?). I would guess that this provides a finer adjustment than a full bore contra.

Nice work, BTW.

George
Old 05-03-2005, 11:33 AM
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Default RE: Engine gets really hot

George, my current heads have the contra slightly angled (about 4 or 5 degrees) convex and the bottom edge - the squish band - flat, thats right. No worry I wasnt ruffled I was merely stating that it is impossible to have the contra out of the bore without damaging the engine, or having the compression WAY too high anyhow (assuming the piston/liner is not worn out).

AJC
Old 05-03-2005, 04:20 PM
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Default RE: Engine gets really hot

Ok, here's the idea I have for my modified diesel head. What do you guys think of it?

Cyril
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Old 05-03-2005, 04:56 PM
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Default RE: Engine gets really hot

Well thats a lot more cooling area! But you may still need some airflow over the fins to help get rid of the heat.. only trial will show if it is needed or not.

Keep us posted...

AJC
Old 05-03-2005, 06:16 PM
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Default RE: Engine gets really hot

AJ, I was checking some of my heads to check out their squish bands, I was amazed at the different approaches to it. Some are perfectly flat, Fox's for example, except the little .15 which is concave from the outside edge all the way to the glow plug, the LA .46 glow head is beveled from the outside edge to a small chamber near the glow plug. I guess the engineers have some rhyme or reason for what they do but it sure isn't obvious.
Old 05-03-2005, 07:48 PM
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Default RE: Engine gets really hot

Yes and then look at all the 4 strokes with various comb. chamber designs and so forth... I bet its a lot of try this and try that as opposed to engineering the perfect head on paper...

AJC
Old 05-03-2005, 11:19 PM
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Default RE: Engine gets really hot

I has 4 stroke engines converted to dieselengine with combustion cell and these engines ran well without too be hotter. The combustioncamber are flat and measured about 1-1,2 mm between piston and cylinderhead.

Jens Eirik
Old 05-05-2005, 03:34 PM
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Default RE: Engine gets really hot

Well, I finished the new head today. Still a couple of things to do to the tractor, but I think I'll be ready for testing on Saturday!
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Old 05-05-2005, 03:49 PM
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Default RE: Engine gets really hot

Nice work! [8D] All materials are thinned so much as possible to prevent save hot in material. Also easier to lead hot out of cylinderhead. Hope it is better than first cylinder head! You can smear a pasta (Pasta for between heatsink and proccesor) between coolingfins and cylinderhead make better lead hot out of cylinderhead.

Jens Eirik
Old 05-09-2005, 07:57 AM
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Default RE: Engine gets really hot

I did some testing last Saturday and the results up 'till now look very promising.

There was just one problem as in that I couldn't test it during a pull. In my haste to get everything ready on time, I forgot to include some sort of means to block the compression screw (on my earlier head I did do this, but for some reason I didn't have to use it, the screw just staid put)

So, using an Allen key to keep the compression set, I ran the engine through a couple of tanks, both at idle and whilst revving it. I adjusted the idle and the high speed needle so that the engine ran as lean as possible and set the compression as low as possible without the engine quitting.

The engine ran much cooler. Just waiting for 20 or 30 seconds after shutting it down was enough to let it cool down to a temperature where I was able to not only touch the head, but to put my hand on it and hold it there comfortably (and that's with the tractor standing still, without any forced cooling whatsoever!)

So, the only ting left to be done is to provide some way of blocking the compression screw and then try again. Our next pull will be in two weeks, so I'll see what happens then!

Finally, I just want to say thank you to everybody who contributed to this thread. You were all a great help!



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Old 05-09-2005, 11:14 AM
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Default RE: Engine gets really hot

Well done, nice to see all works well with coolingfins added at the engine.

Jens Eirik
Old 05-09-2005, 12:09 PM
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Default RE: Engine gets really hot

Did you state that your calculated compression ratio was 20:1? That is what I gleaned from the info. That sounds way to high for a model Diesel engine, but more inline with what full size Diesel engines utilize.

Just curious.

I do agree that regearing would seem appropriate, but if you are overheating at the present gear ratio, mixture or compression ratio would appear to need adjustment.

I am surprised at the low oil content in your fuel. I'm an old plain bearing, airplane, Diesel flyer from decades ago. I'm sure that the new ball bearing engines would use much less oil, still - 16% seems low. I guess it depends upon the type of oil that you are using too.

That sounds like a fun hobby.


Ed Cregger
Old 05-10-2005, 06:54 AM
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Default RE: Engine gets really hot

Cyril,

That's a nice looking rig. Good luck with it.

George
Old 05-13-2005, 09:00 AM
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Default RE: Engine gets really hot

Did you state that your calculated compression ratio was 20:1? That is what I gleaned from the info. That sounds way to high for a model Diesel engine, but more inline with what full size Diesel engines utilize.
I removed the new head after running the engine. According to my calculations, the compression ratio is now about 1:12

There is one thing I still find strange though;
As I understand it, most people state that a converted methanol-engine's carburettor should be set to about 60% open at full throttle to get a correct fuel mixture. Even better would be to exchange it for one with a smaller bore, because the smaller venturi makes it easier for the engine to suck the fuel out of the tank.

But what happens if the original carburettor is still set to open 100% at full throttle? Should the engine die, because it gets flooded with fuel?

I still have the original carb on my engine and I still can get it to run at wide open throttle, but only if I open the main needle up about 3 turns (if I don't do this, it will just stall)

Should I be able to get the same RPM and power with the carb only opened 60% and the main needle closed down?

What seems the most logical thing to me is, that if the engine is getting more fuel/air mixture and still can run at full RPM, it should be making more power. At least, that's what people try to establish when tuning a full-size engine. The problem with trying to burn more mixture would be getting it to burn at all (e.g. increasing compression an thus increasing engine-temperature, which can lead to detonation if taken too far)

Any ideas?

Cyril
Old 05-13-2005, 04:49 PM
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Default RE: Engine gets really hot

"But what happens if the original carburetor is still set to open 100% at full throttle? Should the engine die, because it gets flooded with fuel? "

The good news is you need more load.

You will usually develop more horsepower with the stock carb than with a smaller carb, even if it's not open 100%.
But the transition should be better with the smaller carb.

I know it's not easy for you to check rpm and load.

For most of us we simply change props and check the rpm and the color of the exhaust.

By the way, I have really enjoyed this thread.
Old 05-13-2005, 10:42 PM
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Default RE: Engine gets really hot

My control line flying of Super tigre G20-15's has been with the same venturi as I would run on the glow version. My tower 40 ran diesel/runs glow on the same venturi. If you open the carb, you will get less suction and thus probably will have to open the needle as you said. Two cycle engines are in one sense just air pumps and the more air you pump, the more power you get. Also the more fuel you will burn.

Jim

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