1/4 scale V8, first project.

[Lakc]

Smoke is a good thing, it means it is running.
Sticking an oil ring in is more then just tricky, you have to have a place for all the scraped oil to go. Smoke may get better with some runtime, or it may not. I personally would not worry about re-engineering the pistons at this point, I would concentrate on baffles and crank scrapers, and save the oil rings for the next design. However, thats me, you have to do what makes you happy.

 

[keith5700]

hi Jeff, the engine's got to come apart anyway to get rid of the ptfe head seals so I'll assess the ring job then.
I did consider a crank baffle so I'll look at that at the same time.
MY next engine, which is being slowly drawn up at the moment, will have a dry sump. I decided this a while ago, purely because it will look better, but it may now be a better choice for oil control too.

Next engine is 1/3rd scale V10 if anyone's wondering. Can't remember if I've mentioned this before. The V8 is just turning out to be a test bed for the REAL engine.

 

[propclock]

O.K.!! Smoke is a good thing. Small engine combustion is not trivial.
I have been following the post since the beginning. I Still can't
believe the realism. And you have smoke.
You have a distributor and ignition system you are happy with?
Looks like an O.S. carb for now?
Spark and fuel / air is the hardest part of this hobby in my opinion.
These are the lessons that are the hardest to learn and the most valuable to
others.
When you are desperate to hear a pop most do not take notes.
The failures are just as important as the successes.
An absolutely gorgeous engine please tell us what you finally found out that
worked and just as importantly, didn't work.
I have read the entire post over time and truly appreciate all your posts.
The final solution still has me wondering ? How did you make it run?
Again please document now, before you forget. The lessons learned.
Just my 20 cents.

 

[dsage]

Yes. I agree. We'd like to know what happened.
Unless I missed something, last I noted you were still trying to decide which carb to use and how to make it work and what to do about spark. You had rigged up a GM HEI but it quit and you were going to go to a conventional points ignition. Inquiring minds want to know

As far as your oil issue. A few items you might want to check:

How did you make your rings? I don't think I caught that part of the build (unless it was way back). Rings are a stumbling block for a lot of modelers. Oil rings are not a necessity. If the compression rings are working properly you should have minimal smoking. I have no oil rings in any of the engines I've built and they run (sometimes disturbingly) smoke free. A little smoke is a good sign though. It shows the upper parts like rings are getting oil.
I recommend the Trimble method of making rings. Seems to work well for me.

How much pressure do you have on the mains. Could you have free flowing oil (due to excessive clearances somewhere) that is being excessively thrown about in the crankcase and being thrown up into the cylinders?

Is the engine running well? Do you have a nice push from each exhaust pipe. i.e no suction. (oops I guess you can't tell with the collectors and mufflers).
You might consider some straight pipes for a while. It might just be one cylinder in each bank giving you issues. (i.e bad rings).

Improper intake valve timing (excessively early closing) can cause a vacuum in the cylinder which will pull air up past the rings from the crankcase - and oil vapour with it.

I'm still amazed at the engine. It's a piece of art.

Thanks for sharing it with us


Sage

 

[keith5700]

Maybe it is time for a recap. The ultimate plan is, or was at he start, to build a fuel injected V8. Although I have started designing my next one, I still intend finishing this, even if only to sell it on.

This is the injection bit, but no injector yet.

So, on the carb side I'm not too interested now, my little RC aero carb was just intended to get the engine to run. It won't rev through the range with this carb, the mixture screw has to be set for low, mid or high rpm manually.
It turns out it is a good carb from an atomising point of view, probably because of it's small bore. This is all that's required at the initial fire-up stage, to reduce the number of unknowns. I would use this carb again next time.

My particular issue with getting the engine to start was almost entirely down to a not strong enough spark. The simple pressure chamber tester showed this up very clearly, that just because the plug will fire in free air doesn't mean it will fire in the cylinder at, say 90psi?

For what it's worth I would probably test run my next engine with points initially, as again it reduces the number of unknowns. You can't really go far wrong with points, condenser and coil.
Now I know the engine runs I need to re-visit my first electronic ignition system and find out why that didn't work. I suspect he coils are crap.

The way I would look at it from now on it if it won't fire with a little rc carb and points, then there's something else wrong.

One other must on initial fire up would be to pre-heat the engine, to 60c at least. This helps to get fuel vapour into the cylinder, rather than just droplets.

I'm going to follow straight on with piston rings, but will post this before I lose it.

 

[keith5700]

On the smoking issue, the engine will run with just a bit of smoke when there is no oil in the sump. As soon as I filled the sump the engine smoked, badly. I did put enough oil in initially so the crank would pick some up and fling it up the cylinders, but this was stupid. The opposite is what is required, so the next time the sump is off I will try and fit a baffle, or wiper plate. Or windage tray, whatever it's called.

Having had a look at my piston drawing there is no room to fit an oil ring, either above or even below the pin. I really don't want to make new pistons and rings. I'm hoping the lower ol level and windage tray will keep the smoke acceptable.

The pistons have 2 x comp rings.
After talking to my metallurgist mate I decided against the heat treat method of making them. From memory I parted the ring off, split it with a saw, filed the ends square and then slid them into a dummy cylinder bore.
The ring was then clamped up in this position and the cylinder removed.
The cylinder bore was a few mm oversize from the engine bore, to give the tension.

I'm not explaining this very well but it is documented on here somewhere because this is where I got the idea from.

The clamped up rig was then turned to the engine bore size.
This seemed to be a better way of ending up with a circular ring as opposed to heat treating to set the ring tension. I figured when a ring is forced open manually then it must deform into a slight ellipse, as the bending moment will be more in the middle of the ring than the ends. So conversely
if 'set' in an open position then it must be a slight ellipse when squashed into a round bore.

This could be rubbish of course, but I'm happy with it. There were only a couple of rings with any visible light round the edge when I made them.
The gaps were only a couple of tenths, and I didn't use those anyway.

I suspect the initial ring force is only needed to get the engine to start anyway, the gas pressure when running must cause the vast majority of ring load onto the cylinder wall.

I'll go now 'cos I've forgot what my point was going to be, but that's how I did the rings.
Next engine will definitely have oil rings.

Soon be starting the injection...............that's when the real fun starts.
Cheers.

 

[Banjoe]

Like a lot of folks here, I've been watching this incredible build in absolute amazement.

I do have to say that, as remarkable as the build developed, what truly amazed me is the group that adopted this project when it ran into trouble. What an truly impressive group on this web site - I have my hat off in honor of the group for their support of a fellow in need.

 

[dsage]

Keith:

Thanks for the update and for covering the questions.

Your method of making the rings appears sound. And perhaps better than the Trimble method. I'll have to take note of that.
The most important point is to ensure the rings are round and you've done that - best I can tell.
I guess you could tell with a leak down test per cylinder if you need to figure out if there is a weak cylinder.

I think you might be on to something with the excessive oil in the crankcase causing issues..


Keep us posted.

Sage
http://davesage.ca

 

[keith5700]

Crikey, 4 months have just gone. Back on the engine then!

The plan is, modify a standard fuel injector, bodge that in a makeshift manifold, operate it with a manual microswitch, see what happens.
If it works then get the throttle body working, then get some electronics to fire the injector.

I used a Fiat Punto injector. This flowed 150cc/min. The orifice is 18 thou' diameter. The smallest drill I could get hold of is 10 thou' so I stripped the injector and made a new orifice plate. Getting the sealing face flat was a pain but I did it eventually. The new injector flows 75cc/min. at 40psi.

I then had to make new injector internals to halve its overall length.

The injector is mounted upside down to fire up into the plenum. I made a temporary central tube just to see if it worked. The tube has a pin across the bore, against which the injector fires the fuel jet. This seemed to atomise the fuel quite well.

I'll put the pics up first as my computer keeps crashing and I hate losing posts.











Next post following straight on.............

 

[keith5700]

To be honest I never thought this was going to work, so I just lashed it together.
I warmed the engine up with the carb and then swapped over to the injector setup.
The garage filled up with smoke inside 1 minute on the carb, as usual.

I turned the engine over and gave the injector a squirt with the microswitch. It fired up straight away. There is no throttle of any sort, just the open tube. I could balance the revs with the microswitch. It was wierd. Hold the switch down longer and the revs built up, then revert to small taps and it ticked over quite slow.
It was interesting to note how long the engine would run after a squirt from the injector. Probably about a second, which doesn't sound long, but it shows that I'm not going to need a super small injector firing every rev, but this one should be fine firing every 10 or so revs?

Another interesting observation - hardly any smoke. So the smoke is mostly fuel and not oil.

So, next job is to get the throttle body working and see how this works with the manual switch, which I know is crap, but it's all I've got at the moment.
Anyway I'm all fired up again, so we'll see how the next month goes.
Cheers.

 

[stevehuckss396]

Sounds good keith, i'll be watching and waiting.

 

[metalmad]

Hi Keith
Looks like you got your mojo back Mate
Good one!
Pete

 

[t.l.a.r. eng]

I turned the engine over and gave the injector a squirt with the microswitch. It fired up straight away. There is no throttle of any sort, just the open tube.

Another interesting observation - hardly any smoke. So the smoke is mostly fuel and not oil.

With no throttle there is no intake vacuum to pull oil up past the rings into the combustion chamber.

Beautiful engine, can't wait to here and see it run.

 

[moya034]

Holy cow, just saw this thread for the first time. Great work Keith! Looking forward to seeing it finished.

 

[keith5700]

With no throttle there is no intake vacuum to pull oil up past the rings into the combustion chamber.

Darn it! I think a little test for tonite then.
I will fix the carb on top of the tube and use it as the throttle.
I know whereabouts the carb throttle was set, so I can just fix it at that position and adjust the injector to that amount of air.

Hope you're wrong but the more I think about it, the more likely it sounds.
Thanks.

 

[John Rus]

A V10, that would be sweet! Growing up my dad had a triton V10, smooth as butter and great throttle response. I will have to wipe the drool off the keyboard every time if you start that build thread!

John.

 

[Lakc]

Looks good Keith. I think your about to venture into that land of pulsewidth's and square waves. A simple 555 chip driving a transistor would be a start.

 

[gbritnell]

Hi Keith,
I've been following along with some of your problems but to this point haven't offered much as I really had no answers, until now. First lets have a go at the ignition. When I first drew up and built my V-8 I went with a point type distributor. This was mainly because there was no model electronics around at the time, mid 80's. In trying to stay close to scale with the distributor I naturally had to make a tiny set of points. I found that they worked but due to the small size of the cam I couldn't get enough dwell time so although the engine would start and run the higher rpm's were limited. Some time after that I took a whole different approach, still using points but with a totally different design. I won't get into the details but suffice to say that the improvement was marginal. Since I have gone to the Hall type trigger I have had no problems. At first I had some blown Halls but that was due to poor grounding with which I'm meticulous about today. I would recommend you go with whatever system works best for you but I sure wouldn't rule out the electronic route.
Now to the next issue, the smoke. Having followed you build since day 1 and knowing the detail and and precision you have built into your engine I was really baffled by this problem. Would an oil ring help, I can't say for sure but if both compression rings seal good it shouldn't be that big of an issue. I do notice that when I lose a plug on my V-8 that I will get a little fuel smoke when I rev it up. It runs so clean that this is my indicator that there is something else wrong. I have a wet sump with a full pressure oil system. When the engine was originally built it would hold about 30 lbs. of oil pressure. Where it is now after countless hours of running I have no idea. I hasn't frozen up yet and it makes no noises so I suspect that it's still oiling. In a conventional push rod engine the oil goes through the lifters and the pushrods to get to the rocker arms. Not having hydraulic lifters I had to come up with another way of getting oil to the top end. In the lifter valley I tapped holes into both lifter oil galleys and ran an oil line up through the head into my rocker shafts, my rockers are on a shaft. When I first got the engine running well I had more smoke than I wanted and like you thought about the rings but after running the engine for some time and the smoke didn't go away I started looking elsewhere. What I found was that the top end was getting too much oil and without any type of valve seals it was being pulled through the valve guides. I do have oil return passages in the heads and block. I put little restrictor plugs in the feed lines but I could never get the smoking down to where I wanted it. I ended up unhooking the feed lines and now I just put a squirt or two into the shaft via the breathe caps before running.
I know your engine has overhead cams so my pushrod valving system is only to point out that maybe your smoke is coming from your top end. I know from your pictures that you have oil feed lines to the heads to lubricate the cams but maybe you are having a similar problem to what I was having. With a bath of oil slinging around in the upper end it doesn't take much for it to be sucked into the combustion chamber on the intake stroke, even with tight tolerances. Find an old engine with dried out valve seals and they will puff oil all the time.
I can't say for sure that this is your problem but it's just food for thought. With all the work done on this engine I personally would want to correct all the it's deficiencies before jumping into another, otherwise you're going to go through the same frustrations.
gbritnell

 

[smpstech]

Looks good Keith. I think your about to venture into that land of pulsewidth's and square waves. A simple 555 chip driving a transistor would be a start.

555 timer would work excellently. You could affix a small potentiometer to your butterfly's and use that to control the frequency of the injector pulse.

Something like this:

http://www.555-timer-circuits.com/low-frequency-555-oscillator.html

Using a 1uf capacitor with one of the resistors being a potentiometer would give pretty good results. Idle would be firing the injector about once every 2.2 seconds if you use two 100K resistors. You can slow it down by using a larger value capacitor. Depending on how much amperage the injector pulls, you may be able to run it directly off the 555 timer. It can only deliver about 200ma, and at that point it would need to be well heatsinked.

 

[t.l.a.r. eng]

Agree with gbritnell, anything that sees a vacuum from the cylinder can draw oil if there is oil present. If the piston rings are seating and compression is good, I would look at the upper engine first. Intake manifold gaskets are often overlooked as a source of oil consumption as the bottom of the manifold on most v-8 engines are open to oil in the lifter galley. Even too loose exhaust guides can lead to oil smoke.

Your problem may well be from the excessive oiling of the top of the engine. Maybe a metered restrictor in the top end oil feed would help.