.25 VFDF issues
05-06-2010, 05:55 PM
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.25 VFDF issues
I'm having issues with my 25 VFDF engine on my 25 demon, I'm going thru too many plugs[>:], even after a short bench run ,rich, the coil looks distorted already. I've added a .002" head shim and I lengthened the header 1/2 an inch, and tried some different props...just trying things.
Any thoughts?
Thanks
Any thoughts?
Thanks
05-06-2010, 06:18 PM
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RE: .25 VFDF issues
The engine is not very old, just broken in, running a trimmed 6.5x6.5 apc pylon prop down to 6x6.5 spins about 24000 on the ground, from glow plug to fat portion of pipe is 9 -1/4" long.
05-06-2010, 09:05 PM
#4
RE: .25 VFDF issues
Get the problem nipped in the bud before you damage the engine.
bubbless tank OK
20% oil fuel with some castor
bearings with no axial play, good fitting rod, wrist pin, crank pin, no slop anywhere
head button with tight fit in liner
pipe too small?
raise liner
stack in more head shims
coldest plug
too much prop diameter, blade area, blade thickness
too much nitro for combustion chamber type and chosen head clearance
fuel delivery system isn't keeping up with demand because of pressure leaks, crappy carb
[run a venturi and fuel line pinch]
stiffest of the stiff engine mount
balanced prop
It's possible to get an engine to run in this range without getting hot, but the plugs can get buzzed out of shape if you combine certain factors or just find the single culprit.
Too much compression is a biggie, same with too small/short of an exhaust system.
Setting the needle so that the engine doesn't completely clean up until the tank is almost empty, then slowly get more aggressive in subsequent flights is a good way to go.
Expect to consume plug elements [turned to chalk] every few flights when you're running this hard.
bubbless tank OK
20% oil fuel with some castor
bearings with no axial play, good fitting rod, wrist pin, crank pin, no slop anywhere
head button with tight fit in liner
pipe too small?
raise liner
stack in more head shims
coldest plug
too much prop diameter, blade area, blade thickness
too much nitro for combustion chamber type and chosen head clearance
fuel delivery system isn't keeping up with demand because of pressure leaks, crappy carb
[run a venturi and fuel line pinch]
stiffest of the stiff engine mount
balanced prop
It's possible to get an engine to run in this range without getting hot, but the plugs can get buzzed out of shape if you combine certain factors or just find the single culprit.
Too much compression is a biggie, same with too small/short of an exhaust system.
Setting the needle so that the engine doesn't completely clean up until the tank is almost empty, then slowly get more aggressive in subsequent flights is a good way to go.
Expect to consume plug elements [turned to chalk] every few flights when you're running this hard.
05-06-2010, 11:07 PM
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RE: .25 VFDF issues
You are either running too lean or the pipe is too short. What % nitro are you running? Start with an apc 7x6 and around 15% fuel to get things running right before going for max.
Also picture appears like maybe you are not pressurizing the tank? If not the thing wont run worth a damn.
Also picture appears like maybe you are not pressurizing the tank? If not the thing wont run worth a damn.
05-07-2010, 04:04 PM
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RE: .25 VFDF issues
Sorry thats a old picture, I'm definately running a pressure line from the fat part of the pipe, that pic is all I had on hand to show a pic of the pipe set-up, the pressure fitting is turned away from the photo and the fuel line is missing the extension to the pipe fitting...comon guys[sm=bananahead.gif] I know that you need a pressure fitting to the tank, I'm not that slow.
CP thats a pretty overwhelming list of issues it could be[:-], that almost makes me want to pack this all in for good and go electric
I do plan on trying a bladder tank though, and the engine is almost new barely broken in..so i don't think anything should be loosened up yet. Also I'm using K&B 1L plugs, should I try a different plug?
CP thats a pretty overwhelming list of issues it could be[:-], that almost makes me want to pack this all in for good and go electric
I do plan on trying a bladder tank though, and the engine is almost new barely broken in..so i don't think anything should be loosened up yet. Also I'm using K&B 1L plugs, should I try a different plug?
05-07-2010, 05:18 PM
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RE: .25 VFDF issues
ORIGINAL: combatpigg
Get the problem nipped in the bud before you damage the engine.
bubbless tank OK
20% oil fuel with some castor
bearings with no axial play, good fitting rod, wrist pin, crank pin, no slop anywhere
head button with tight fit in liner
pipe too small?
raise liner
stack in more head shims
coldest plug
too much prop diameter, blade area, blade thickness
too much nitro for combustion chamber type and chosen head clearance
fuel delivery system isn't keeping up with demand because of pressure leaks, crappy carb
[run a venturi and fuel line pinch]
stiffest of the stiff engine mount
balanced prop
It's possible to get an engine to run in this range without getting hot, but the plugs can get buzzed out of shape if you combine certain factors or just find the single culprit.
Too much compression is a biggie, same with too small/short of an exhaust system.
Setting the needle so that the engine doesn't completely clean up until the tank is almost empty, then slowly get more aggressive in subsequent flights is a good way to go.
Expect to consume plug elements [turned to chalk] every few flights when you're running this hard.
Get the problem nipped in the bud before you damage the engine.
bubbless tank OK
20% oil fuel with some castor
bearings with no axial play, good fitting rod, wrist pin, crank pin, no slop anywhere
head button with tight fit in liner
pipe too small?
raise liner
stack in more head shims
coldest plug
too much prop diameter, blade area, blade thickness
too much nitro for combustion chamber type and chosen head clearance
fuel delivery system isn't keeping up with demand because of pressure leaks, crappy carb
[run a venturi and fuel line pinch]
stiffest of the stiff engine mount
balanced prop
It's possible to get an engine to run in this range without getting hot, but the plugs can get buzzed out of shape if you combine certain factors or just find the single culprit.
Too much compression is a biggie, same with too small/short of an exhaust system.
Setting the needle so that the engine doesn't completely clean up until the tank is almost empty, then slowly get more aggressive in subsequent flights is a good way to go.
Expect to consume plug elements [turned to chalk] every few flights when you're running this hard.
05-07-2010, 07:34 PM
#9
RE: .25 VFDF issues
Your welcome...[.there's always something forgotten off these lists]. Before getting involved with real high rpm tuning it's good to have an assortment of head and liner shims, plus an assortment of props. Once you get the compression backed off so far that the engine barely runs, then bring it back up gradually to where it makes the engine seem happy, but still making soot. You always want to start out undercompressed, nothing gets harmed this way.
The prop is a fine tuning tool, too. If you aren't willing to scrape, chop, modify, the odds of finding just the perfect prop right off the shelf aren't good. The load on the engine plays a huge roll in plug life, heat build up, detonation, etc. Sometimes you get lucky and find a stock prop that's perfect. Eliminator has an "infinite" selection in some size ranges.
We're talking about high timed, piped engines.....not the lower rpm sport stuff. Sticking a pipe on a low timed sport engine is much less critical....but can still require a fair amount of time to get sorted out.
The prop is a fine tuning tool, too. If you aren't willing to scrape, chop, modify, the odds of finding just the perfect prop right off the shelf aren't good. The load on the engine plays a huge roll in plug life, heat build up, detonation, etc. Sometimes you get lucky and find a stock prop that's perfect. Eliminator has an "infinite" selection in some size ranges.
We're talking about high timed, piped engines.....not the lower rpm sport stuff. Sticking a pipe on a low timed sport engine is much less critical....but can still require a fair amount of time to get sorted out.
05-07-2010, 08:28 PM
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RE: .25 VFDF issues
ORIGINAL: smoknrv4
Also I'm using K&B 1L plugs, should I try a different plug?
Also I'm using K&B 1L plugs, should I try a different plug?
05-07-2010, 08:39 PM
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RE: .25 VFDF issues
ORIGINAL: freakingfast
In my DF engines, that plug wont last a tank, its just too hot. I use K&B HP plugs.
In my DF engines, that plug wont last a tank, its just too hot. I use K&B HP plugs.
Yeah I wondered about that, I've tried OS#8's too they are just as bad. I'll order up some HP's from mecoa.
CP thanks for your imput..always appreciated, I'm thinking about putting it back on the test stand to do some more fussin, w/ shims props and such.
05-07-2010, 10:19 PM
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RE: .25 VFDF issues
How much exhaust timing does it have? I'd start there first and get it to at least 180 with shims. Once there, you might find that the compression is also low enough. It seems like a 6x6.5 would be pretty close to ideal, but you could take a MAS 7x6 and chop it to 6 inches to see what happens. Ideally, Eliminator would have a selection in this size range. You might find that the engine will tolerate a lighter and thinner CF prop and make it possible to turn a 6x7?
The litmus test is making the power without the out of control heat build up....it can be done.
This is why I feel you can ultimately make more power with higher oil content. I have used 20-25% straight castor in the higher revving engines with good results in hot weather, or mixed with Klotz. I haven't heard of any optimum ratio of castor to synthetic....the engines land cool and the planes are a goopy mess.
The litmus test is making the power without the out of control heat build up....it can be done.
This is why I feel you can ultimately make more power with higher oil content. I have used 20-25% straight castor in the higher revving engines with good results in hot weather, or mixed with Klotz. I haven't heard of any optimum ratio of castor to synthetic....the engines land cool and the planes are a goopy mess.
05-08-2010, 05:32 AM
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RE: .25 VFDF issues
I add 5 oz's of klotz oil to Omega 15% nitro fuel which is 18% oil when you buy it, that should be enough oil I would think, and yeah a goopy mess is right[:'(]. I also found an unused MA 7x6 prop in my prop collection last night, so I'll try that.
05-08-2010, 08:36 PM
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RE: .25 VFDF issues
You dont need extra oil in that fuel. I ran an os25df for a couple years only time it blew plugs regularly was when I tried to shorten up the pipe to get more rpm. Used an mc09 plug, you shouldn't need any shims with 15%. Again it just sounds like your pipe is too short. No need to over complicate things.
05-08-2010, 08:44 PM
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RE: .25 VFDF issues
Should have said you dont need any other shims, think there is one shim stock. And if I remember correctly that engine is timed at 180. The 25VF has a bit lower timing.
05-08-2010, 09:32 PM
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RE: .25 VFDF issues
you should be using short reach plugs if my memory serves me right, my testing notes were with K&B 1S plugs, and i am with the others in thinking you maybe too short on the pipe
05-21-2010, 06:53 PM
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RE: .25 VFDF issues
the short reach plugs dont protrude into the bowl of the combustion chamber, when you use a long plug it puts coil very close to the face of the piston which beat the heck out of it plus it really whacks the combustion process, IE weird needle settings and very short plug life.
the plugface should be as close as possible to flush with the top of the bowl or dome
the plugface should be as close as possible to flush with the top of the bowl or dome
05-26-2010, 11:26 AM
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RE: .25 VFDF issues
Hi!
What fuel (How much nitro) and what plug do you use?
I would recommend 5-15% nitro, a cold plug like the Rossi 5-6 (t Rossi 8 are the coldest plug) and of course a Tettra "Bubble lesstank"!
What fuel (How much nitro) and what plug do you use?
I would recommend 5-15% nitro, a cold plug like the Rossi 5-6 (t Rossi 8 are the coldest plug) and of course a Tettra "Bubble lesstank"!
05-27-2010, 09:28 PM
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RE: .25 VFDF issues
as set from OS engines it will tolerate 20-25 percent nitro quite well, this is what we tested this engine with on the kress fan unit with mac's wizard exhaust as well as full pipe setup, shims are easy to obtain as the 25 series os engines head gaskets work just fine
05-28-2010, 10:10 AM
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RE: .25 VFDF issues
Well I'm going to set it up on the bench again and play with a longer pipe length and the 1S glow plugs you recommended Lfinney, also using 10% nitro Omega fuel.
