V8 nitro engine

[petertha]

Google your model number carb & should get some hits. The fundamentals should be available on-line through OS parts schematic breakdowns (in terms of identifying which screw does what).

There are general procedures along these lines
http://www.osengines.com/faq/product-faq.html#q16

You will probably find both good info & maybe what I'd loosely call mis-information where people are having issues or solving problems that are aircraft orientated & maybe not quite applicable to your specific application.

I think a new/unknown engine with its own teething pains is an additional consideration to the carb itself, even assuming its set up 100% correct. But I'd say try & get a mid-range rpm running to begin with, then worry about idling & top end as a secondary goal. Generally if the AF mix is out of whack in the mid/high range, it only makes solving low/idle running even more challenging. Double check for air leaks like on the carb throat o-ring/gasket & fuel line leaks like on inlet nipple.

I also have a feeling 'starting' is a ritual itself with these glow/methanol jobbies. I've ran so many RC engines that were set up perfect. But that was with the classic electric starter. Now if I decided to hand flip the exact same beast, it seems to require more effort & tries to get it going. Then its so tempting to diddling needle valve & adjusting things trying to find a sweet spot. I'm not saying go to starter right away but keep in mind if required. Even something moderate like a low rpm cordless drill will help, especially if its being difficult. Just beware any hint of hydro-locking when using starter. Remove plugs, drain every bit of methanol, resume operations.

Sorry, cant speak to your 4-plug (reduced cylinder) trial with any experience. You're miles ahead of me!

 

[Parksy]

Thank you again Petertha. I do value your input (and others) very much so.

I had another play around with the engine today and found the intake wasn't sealed properly and leaked. I don't know why, but I was pleased that I found this. I'm still having issues with leaking glow plugs also, and I'm too worried to torque them down too far in fear of stripping the thread. Does anyone have any torque figures or rules with torquing glow plugs into aluminium?

I haven't found any plugs or leads that will plug into glow plugs so I'm going to try and make my own out of brass. My main concern is how to retain it onto the plug itself. If anyone has any pointers on this, I'm all ears.

Cheers

 

[10K Pete]

I know it's a bit late but would Heli-Coils or similar inserts work in the glow
plug threads to help with the torque issue? I mean, would they fit? They would
allow about double the torque.

Pete

 

[wirralcnc]

Are you using annealed copper washers under each glow plug. Shouldn't have to over tighten to get them to seal. As for glow plug leads try just engines.

http://www.justengines.co.uk/acatalog/Just_Engines_Online_Starting_Gear_115.html

 

[petertha]

The plug clips I've used are really pretty simple. I prefer the flat meal ones that have a slit so they kind of pinch the plug terminal. probably what you are envisioning with brass. Copper might be a better choice resistance wise. You just want good contact & vibration proof. The heat shrink or some sort of shroud protects from oil adversely affecting electrical conductivity.

https://www.google.ca/search?q=onboard+glow&biw=1680&bih=999&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiDpPfNp8PLAhUO12MKHf9dBwwQ_AUIBigB#tbm=isch&q=onboard+glow+clip&imgrc=12QTyNjZJe44mM%3A

https://www.google.ca/search?q=onbo...sch&q=onboard+glow+clip&imgrc=CXZNLff4nKQuBM:

For sure you need to use the copper squish washer with plugs. Avoid plugs directly threaded in head threads, they wont seal proper. Torque is gentle hand tighten like with a socket nut driver. Avoid doing this when engine is hot because it can equate to over tightening & thread damage. I don't know an exact in-oz torque but most guys even in HP applications don't bother with those click-off torque handles & just do it by hand & feel.

Also check your grounding & wiring: a new (non oily) plug should light nice & red & stay that way. if its dull or glows sporadically, it could be your electrical wiring, drive battery etc.

 

[petertha]

As for glow plug leads try just engines.

http://www.justengines.co.uk/acatalog/Just_Engines_Online_Starting_Gear_115.html

Sorry, missed your link. Half way down the web page - that's a nice looking connector, either to buy or replicate.

 

[10K Pete]

Sorry, missed your link. Half way down the web page - that's a nice looking connector, either to buy or replicate.

I remember those!! Used that type of clip 55 years ago on my control line planes. Really good. But maybe not for permanent installation.

Pete

 

[t.l.a.r. eng]

Quite by accident I found using some small stiff spring stock will connect to the glow plugs quite nicely.
I was trying to run my Kinner for the first time and was rummaging for a quick dirty way to make it work. By clipping short lengths of spring and soldering it to the glow wire, it fits the glow plug nicely and won't vibrate off.

When the plugs were first hooked to my homemade glow driver the springs smoked a little bit but still lit up the glow plugs quite nicely. The engine has many runs on it using these springs as clips.

 

[Parksy]

Thanks all for your suggestions. I've taken it all onboard and will work something out. At the moment I'm using a temporary method with alligator clips. Trying to start the engine is a frustrating process especially when using batteries that don't last long. I get a few minutes of glow time then need to recharge.
Anyway, I tried rotating the engine by hand and I can feel it fire and want to kick the crank in the opposite direction. I'm in the process of experimenting with cam timing and will wire the glow plugs up to a car battery so I can have more time to experiment. Just waiting for some Buck converters to arrive in the post.
I think I'm getting there.

 

[Brian Rupnow]

I'm curious. What is a "Buck converter"?--Brian

 

[canadianhorsepower]

I'm curious. What is a "Buck converter"?--Brian

The buck converter is a very simple type of DC-DC converter that produces an output voltage that is less than its input. The buck converter is so named because the inductor always “bucks” or acts against the input voltage.

 

[Brian Rupnow]

Thank you Luc. My first wife was a buck converter. She could convert a buck to 35 cents faster than a speeding bullet.----

 

[petertha]

Parksy, there are more than a few HMEM posts on this subject and similarly related to multi-cylinder glow engines. The topic comes up quite often. You might have to do some keyword query searching but would be worth digesting IMO.

The solutions vary from ganged single cell batteries to jerry-rigged step down voltages using larger capacity batteries to dedicated circuit boards that do some solid state switching in order to use smaller or more common batteries.

The bottom line is: each plug requires nominal 1.5 volts & current draw between 3-5 amps depending on a bunch of parameters, but probably a minimal guideline for starting mode. So 8 cylinders all lit could draw 24-40 amps. There aren't too many 1.5 volt / 40 amp capable batteries lying around, hence the varied solutions making use of what you have or want to buy. Also, you cant exceed the 1.5v by much or the element will burn out. And you cant be under the 1.5v by much or it wont glow properly.

An important parameter related to cells (of any chemistry or shape form type) is its C rating. This relates its ability to deliver current as a function of its capacity. So for example a single cell NiMH 1.5v battery of 2000maH capacity and C=5 means it deliver 1.5 volts at 10 amps discharge (5C * 2A) for 1 hour. So it could power 2 plugs at 5A simultaneously for one hour before dying/requiring recharging. Or light 1 plug for 2 hours. C is dictated mostly by cell chemistry, internal resistance...another topic. But just be aware of 'max amps' spec & you get the same answer.

C-rating also relates real world voltage decay. For example a AA penlight battery may well deliver its 1.5volts at 20 mA load to light an LED. But push 4-5A though it & the voltage will decay so maybe 0.7 volts. Which is hard on the battery & wont properly light the glow plug element.

These days you can buy high-C, high-capacity, lithium polymer packs dirt cheap. This one will deliver 200amps! (40C * 5A). But... lithium comes in 3.7-4.0 nominal voltages, not 1.2-1.5 volts like NiCD NiMH. So Lithium cells have the power no problem, but voltage exceeds glow plug 1.5v requirement, so we are back to some sort of step-down requirement.
http://www.hobbyking.com/hobbyking/store/__18562__Turnigy_5000mAh_1S_40C_Lipoly_Single_Cell_.html

The big car battery solution works no different. It has a huge capacity so the 40A current load just tickles it. However its 12-14v nominal, so you need something in the circuit to step down to 1.5v. Hope this helps!

 

[t.l.a.r. eng]

The solutions vary from ganged single cell batteries to jerry-rigged step down voltages using larger capacity batteries to dedicated circuit boards that do some solid state switching in order to use smaller or more common batteries.

The bottom line is: each plug requires nominal 1.5 volts & current draw between 3-5 amps depending on a bunch of parameters, but probably a minimal guideline for starting mode. So 8 cylinders all lit could draw 24-40 amps.

I used two chips as a basis for my Kinner glow driver from http://www.jamesengine.com/index.htm
Using 12 volts and pulsing the on time at the plug to get the 1-1/2 volts.

The amperage stays around 4 amps for a 5 cylinder, so a v-8 may only need 6 amps or so to operate.

 

[petertha]

TLAR - thanks for link reminder. That's the one I was looking into for my 5-cyl when I get that far. I was trying to say for basic batteries, the current draw per plug is more than people typically expect & the 1.5v is a rather narrow voltage window. The pulse timed / circuit board solutions are the way to go IMO.

Question for you - that circuit design that presumes input 12v source, how much leeway can the voltage be? For example my gel cell utility battery is probably closer to 13-14v resting. Do you just mean 12v 'nominal' like how we loosely describe car auto batteries, or it has to be quite close to 12v like of a DC power supply? Another reason I ask is a 3S lipo pack at 3.7-4.0v / cell is real close to that (11.4-12.3v) & would be a perfect & inexpensive matchup.

 

[t.l.a.r. eng]

I realized you were talking straight dc voltage, but wanted to share what the pulsed amperage would be.

At the time I built my circuit Jerry was offering just the chips and i built my circuit around two of them from him. I don't know if he offers parts only or if completed circuits only now? He has an e-mail on his site.

The 5 cylinder driver I built used two chips and used non adj resisters to come up with the output. The circuit works well except for the heat given off the output transistors will cause the voltage to run away if not cooled and heat sinked properly. So heat sinks on the outputs and a computor cooling fan to blow across them works great. The glow driver is on anytime the engine is running to prevent any cylinders from droping out.

The driver I made will run [that I know] on 10 volts to 16 volts with no effect on the glow plugs. I suspect the 5 volt voltage regulator to operate the chips would be the reason for that, and the wide range of the output transistors.

I have noticed that the new drivers listed on his websites are a redesigned version using mosfets eliminating the need for heatsinks.

 

[Parksy]

I have been able to drive all eight glow plugs using a couple of Buck converters and a car battery. Unfortunately I haven't had much luck starting the engine. While turning it over with the drill, all eight cylinders get nice and hot, unfortunately no firing under its own steam.
Might have to give it a break for a little while before I get too frustrated with it.

 

[dsage]

What rpm are you turning it over at?
Faster might be better until it break in a bit.
Might be just a change to a different drill required (if that's what your using)

Sage

 

[Parksy]

Cheers sage.

I've tried it with a couple of different drills for this reason thinking that I wasn't spinning it fast enough. Even at 3000 rpm. Still no luck unfortunately.

 

[canadianhorsepower]

Cheers sage.

I've tried it with a couple of different drills for this reason thinking that I wasn't spinning it fast enough. Even at 3000 rpm. Still no luck unfortunately.

What fuel are you using
It should puff and huff a little