1/4 scale V8, first project.

[Lakc]

As the GM pole piece is nothing more than a coil of wire around an armature with a poled magnet running inside, why not just use four magnets in the flywheel and a small coil of wire for the pickup?
This could make it a simple crank trigger system, and the pickup coil could be slotted for timing adjustments. The GM ignition module has an advance curve built into it but that is a whole new subject.

The modules with advance curve have additional pins attached to them, and you usually wont find them in distributors with a vacuum advance.
With two distributors, and only one coil to feed them, you may be able to use a Y coil wire. One distributor should lag the other by 45 degrees and the spark should travel to the side with the least resistance. It may work as a demo but I wouldnt design something like that on purpose.

 

[stevehuckss396]

If 2 distributors is a problem why not convert one of them to 8 cylinder and plate off the other?

 

[keith5700]

I want to keep the 2 x distributors, at least on the final engine. For now though anything goes.
The twin dizzys aren't a problem for the Powerspark, as it will fire each one in turn, so hopefully it will turn out to be the coils which are the problem and not the Powerspark.
If the Powerspark is the problem then I can just fit 2 x ignition systems.
For now tho the task is to get it to fire up with minimum expenditure.

It may be that the spark will follow the path to the correct plug, as that will have the rotor arm in line, but the other dizzy's rotor arm will only be 45 degrees off, and the spark may find it easier to jump the rotor arm gap and fire a plug at atmospheric pressure, than trying to fire the correct plug at 60-70psi.

The other option would be, as Steve said, make an 8 way dizzy, although just a temporary thing, just to get it started.
I can't get on it for a few days so I'll report back when I have done something.
Cheers.

 

[dsage]

Keith:

Sorry I haven't gathered what it is you are using to trigger your ignition module. I built a V8 - pictured below. I used a rotating brass disk with 8, 3mm magnets inside the distributor (well below the high voltage stuff) to trigger a hall sensor and then used the CDI ignition module available here.
http://www.cncengines.com/ic.html
Pictured in the middle of the webpage and labelled as the "single spark CDI". The unit is about 1-1/2" square. No coil required - it's on the board. It runs on 3.6 to 4.8 volts. It runs my V8 fine. If you do the same for both distributors you'd have no problems.

Ditch all that other stuff and use the CDI unit. You won't be disappointed.

Just be careful you don't operate with an open circuit on the HV side. Although the newer modules I believe have a built in spark gap to protect the coil it is never a good idea on any ignition system to operate with a gap much larger than a spark plug.


PS> The engine is about 7-1/2" long. It's my V8 version of Jerry Howell's V4. The ignition module is hidden between the rails behind the rad along with a NiMH cell phone battery for power. I hate to see huge coils and stuff external to the engine and not in the proper scale of the rest of the engine.

I'm amazed at your workmanship. Keep up the good work !!

Sage

 

[keith5700]

Sage, thanks for that. Don't think I've seen your V8 anywhere before, looks nice.

I did think about those cdi ignitions early on, but couldn't figure out where the coil went, so discounted them. Seems like the coil is built into the unit then.
I will have a look and see how much these are in the UK.

At the moment I have rigged up a full sized crank sensor to trigger the Chevy HEI ignition system.
I only have 2 magnets fitted to the flywheel, so I wired the engine up to run just as a 4 cyl for now, just to see if it would start.
I used one dizzy to fire plugs 1,4,6 & 7.
I tried both carbs, propane gun and Easy start, but still not a murmer.

Some testing shows that the spark is going into the dizzy but not coming out.
It does not seem to be arcing inside, but obviously the voltage is draining away somewhere.

I am going to make a single dizzy for 8 plugs, and try that.
Firstly though I have decided to finish off the oil system so I don't wear the crank out even before it's fired up properly.

 

[JLeatherman]

I just wanted to say that I love this picture. Really drives home the scale of the engine.

 

[Lakc]

Some testing shows that the spark is going into the dizzy but not coming out.
It does not seem to be arcing inside, but obviously the voltage is draining away somewhere.

The HEI system is notorious for having enough spark energy to shoot through its own full sized rotor right to the distributor shaft. You may want to switch to a plastic shaft in your distributor, and or increase the distance inside. Also, make sure its vented as well as possible, first couple of sparks can ionize enough of that atmosphere in a tiny cap to make it inevitable the spark will go to the shaft or base.
Unfortunately, you cant scale electrons.

 

[LongRat]

Keith, if you want to get one of those CDI systems, check out either Just Engines or the Hobbyking UK warehouse. Both sources sell them, and they are not expensive. I am planning to go that route with my engines.
Dsage, it is great to hear that this system works on your V8. I haven't seen a simpler system and to my mind, simpler is better when it comes to ignition.

 

[dsage]

Longrat:

Yes, the CDI unit from the site I quoted seems to work fine but I rarely rev the engine higher than about 5,000rpm. Probably a good thing.

My carb is too small for the engine so that also contributes to not being able to rev it - Also a good thing.

I wasn't aware that the CDI ignitions were available from Hobby King. I know the guy from the website I quoted in the US. As I understood it he had them made to his specs in China (possibly Hobby King) but I'm not sure if they would be the same.

Keith:
Yes the coil is very tiny and is on the board. It can be so because the primary voltage is boosted to 350v or so from the battery 4.8v.

I would be careful using the GM HEI ignition. With a typical coil it can produce as much as 50kv at the plug. More IS NOT better. That kind of voltage will fly all over the place inside your cap and between leads. The HEI distributor cap is large for that reason.
You will likely not need much more than about 7kv to do the job.

If you go with 1 dizzy remember it will probably need to be bigger in diameter to increase the space between spark towers.

You say that the spark goes ito the dizzy but does not come out??

If you temporarily add an extra gap in the path to the spark plug about the same as the sparkplug gap you should see the spark jump that gap at the same time as it jumps the plug inside the engine. Perhaps by leaving a sparkplug boot loose with a small gap to the plug cap or make a stable jig with two fixed points.
(Remember - no large gaps or you could damage your coil)

I'm sure you probably did this but confirm once again.
Piston TDC on compression stroke
Valves closed properly with compression.
Spark is triggered at TDC (as a starting point) and is nice and hot.
The contacts in the distributor are pointing at the correct tower and plug and there is no large gap anywhere in the path from the coil secondary to the plug. (minimal spacing inside the cap).

If you have all that then it's probably a fuel issue.

Re carbs:

A lot of folks use the Walborough (sp?)carburetors commomly found on weed-wackers. They are about the right size (CFM capacity). Be aware though that many of them are designed with an integral fuel pump that requires the crankcase pressure pulses present on two stroke engines to operate properly. There are 4-stoke versions that are just the carb and require either an external fuel pump or gravity fed fuel. Have look on line for the Walborough (sp?) website or visit your local small engine repair shop. They should have them in stock. They are VERY common although quite expensive. Another alternative is one of the carbs from one of the newer 4-stroke model airplane engines from your local hobby shop - also expensive (perhaps borrow from a modeller)

If the carb is too big you will likely not have enough vacuum capability to make it atomize fuel properly.
If the carb is too small you will have no problems other than not being able to reach high RPMS.
So.. better too small than too large.

You should be able to feel a distinct vacuum if you put you palm over the intake manifold while cranking. If not you may have valve issues (timing or leakage)

Good Luck

Sage

 

[e.picler]

Hi Keith.
In order to know if it is carb problem, I would do a quick test spraying gas on carb intake and crank the engine. If the ignition is OK the engine will show just a quick response and dies.
Don`t get mad nor disapointed it for sure will wake up soon.
Congratulation for the quality of your finishing work, it is amasing.

Hey Sage!
One of this days I was waving on the internet and found that someone was doing a V8 version of Jerry Howell's V4, so now I know that you are the man. How is the engine running? It must be something to watch it making noise. Do you have a video of this little beast running?
Did you make drawings of your V8 version?
Congratulations your work look very good.

Edi

 

[alihureiby]

th_wwp.........

 

[dsage]

I don't want to Hi-jack this thread.
My V8 is on my website (along with other things I've built) at www.davesage.ca there is a video of it running but it's a very early video and was not running very well. It's not a screamer by any means.

It is also on Jerry Howell's website under the Howell V4 topic.

Thanks for the interest.

NOW - PLEASE back to the really impressive V8 we're all supposed to be talking about.

Back to you Keith......

Sage

 

[keith5700]

Well finally I got it running. I had to cobble the insides of the HEI dizzy to the font of the engine to get some decent sparks.
I bought a simple small rc type carb to try. It has a 5mm venturi.
After another week of trying with this setup I started to get some signs of life, and eventually today I got it to run constantly.
The setup is extremely sensitive to throttle position and only runs at one position.

There are 2 adjusting screws on the carb but neither of them seem to do anything. The carb was only £14 and is very basic. So, next question is does anyone know anything about this carb? It came with no instructions.
And, does anyone know of a reasonably priced carb which would be any better than this. I know there are plenty of more expensive small carbs, but I'd like to know if they are actually any better.

Engine makes an awsome sound by the way. Got a video but couldn't put it up anywhere as the engine is such a mess at the moment as you'll see.
Cheers.

 

[Lakc]

Just a guess but it looks severely under carbed. If thats the throttle position it takes to stay running it probably lacks enough signal to the fuel to draw it into the motor. Those carbs are extremely sensitive to fuel tank height and level, as they dont have much venturi effect. Try raising the fuel tank until its just shy of running over into the carb. Too long a fuel line is drag on the fuel flow as well.

 

[vcutajar]

Yes, that is great news Keith. At least now you can put your mind at rest that the engine actually runs.

Vince

 

[trumpy81]

Keith, that is great news that you got it running. The carb is pretty simple and the only adjustment you have on it is the needle jet (black knurled barrel with clicker spring/retainer. Think of it as an adjustable main jet). Adjusting it can be an art form in itself but as you have confirmed it's good enough to get the engine running which was the goal right?

The trick to using this carb is to 'tune' it with the throttle at around 1/2 to 3/4 throttle. Once you have the engine running well at that throttle opening you should not need to adjust the needle much at all. Usually only a click or two in or out depending on the atmospheric conditions, engine temperature and the fuel quality. You'll need to confirm the settings at full throttle, but don't expect a good idle from it.

Keep in mind that the carb you are using was intended to run methanol so the needle taper is probably not ideal for petrol if that is what you are running?

Anyhow, now that you have confirmed it is running you can fine tune/rebuild the ignition system and get that side of the equation sorted, then you can start work on the fuel injection. At the very least you now have a datum to work from.

I'm also going to assume that you don't have any ignition advance system so it may be worth experimenting with different advance settings. Again, you wont get perfect results, it will either run well at full throttle and poorly at less than half throttle or vice-versa.

P.S. If you would like, I can post the video on YouTube or host it on my website for you?

 

[Henry]

Awesome sound? I am eating all my nails waiting for that "noise" Great news... also I am sure that you are able now to pinpoint each different area, ignition, timing, and carb and finish this marvel.

 

[dsage]

First off !! Great effort Keith" I'm glad you got it running.

I generally hate the ads on this site but did anyone notice that in the last post (at least when I looked) there was an ad for "how to find Techumseh carbs". Amazing how the bot's can figure out what ads to post.

Anyway. I too think this carb might be too small. If you are looking for larger ones, I suggested a while back that a lot of guys are using Walborough (SP?) "weed whacker" carbs. (Also on chain saws and the like).
They are very common. Your local small engine repair will have them in stock (or perhaps your local home improvement store). As mentioned before, they are usually for 2-strokes and include a pressure pulse requiring fuel pump in them which will not work. But there are version without the pump which will work so be careful choosing. Alot of them should be about the right size for your application.

Good luck !!

Sage

 

[doubletop]

Time for one of the lurkers to front up. We'll done Keith, greta job. I can imagine getting it going has been bugging you for a while now with so many variables to deal with and no luck. No doubt a few of the things you are about to try now will be a step backwards and you'll wonder what it was that allowed you to get it to go in the first place. So time to baseline so you can get back to working engine if you need to.

....................... If you would like, I can post the video on YouTube or host it on my website for you?

Trumpy; I think the point was he didn't want to post it on YouTube because it was a mess and a video at this point would not do it justice.

Pete

 

[trumpy81]

Trumpy; I think the point was he didn't want to post it on YouTube because it was a mess and a video at this point would not do it justice.

Pete

Pete, I was thinking of an anonymous posting in an obscure place like my YouTube channel which has 0 files on it and my website which has a similar number of visits ... lol

I should have made that a bit more clear I guess. Of course the video would be deleted the moment Keith gave the nod.

Most of us just want to hear it so there is no reason we couldn't post the audio only