18 Cylinders Isotta Fraschini (straight six-cylinder x3 )

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Soooooo.......

When it first popped did you run around yelling "It's Alive - It's alive!", or did you just get a silly grin that absolutely refused to leave your face?

Congratulations, this has been quite the adventure so far. I'm looking forward to when you can say it's complete and you're happy with it.

Don
 
It's a long story, I tried first with the 6 cylinders on the left, then the 6 central ones, then the last 6 on the right.
During these attempts I encountered many problems which I have partially solved, but I still can't get it to work properly, it only works at idle speed, when I open the carburettors the engine stops.
 
Some of the numerous problems detected during start-up attempts

pistone cilindro.jpg



I made this recess on the piston to facilitate ignition of the petrol but the oil accumulates here and the spark plug doesn't work
Solution: reduce the oil level in the oil sump

I reduced the oil level too much and the result was this:


pistone.jpg



 
One of the problems with building scale engines, you can not scale down the oil or fuel or air density to suite. Other problem that you found is the sizing of parts for the load.
Great work and perseverance on building and getting it to run in the first place.
Cheers
Andrew
 
You need the 3. oil ring to preventing the oil is pumped up to combustion camber and make holes in the piston ring groove to lead oil back to crankcase. The oil ring is slightly thicker than the compression rings to have a groove in the center of the piston ring with many small holes to guide oil back to the crankcase. The japanese model engineer nickname "PAZ" had problem with oil into the combustion camber in his 4 cylinder Cirrus then he created the 3. oil ring fitted to piston, then the engine ran well without smoky exhaust due burn oil.
 
What a great build.
Maybe you can mix some 2 stroke oil to the fuel while you reduce the oillevel in the motor. Moder 2 stroke oils doesn t smoke much.
 
NICE WORK !!! !!! !!!

you said "here in Modena in the valley of engines (Ferrari , Lamborghini , Ducati )", I can see how you are inspired !!!

to break in my V-12 I used a temporary "once through" oil system so that no particles could re-circulate, I had a fresh oil reservoir feeding the oil pump, and a drain in the oil pan, I put the once used oil in containers and let the fine stuff settle to the bottom (for a couple weeks) then when it looked clear I thought it was safe to decant and re-use (but I didn't instead I used it as cutting fluid ! ). After a few quarts of oil it started coming out clean, so I reverted to the as-originally-designed re-circulating oil system and haven't had any problems.

one problem with V-12 and W-18 is that the sheer number of sparks per revolution overwhelms the electronic ignition, so I use a separate electronic ignition circuit and distributor for each bank (only fire one plug per cylinder, even though I have two per so it looks authentic for an aircraft engine).

I'll go out on a limb here had guess your intake manifolds don't have enough cross section or volume. The R.R.Merlin intake manifold diameter is 75% of the cylinder bore, and there are no exhaust manifolds just short stacks.

FYI, if you take off the exhaust manifolds you can feel the exhaust separately from each cylinder, some will be hot (good), some will be cold (not so good), and then the question is why, typically either not enough intake flow, or not enough compression. for example I have an inline-4 without any path-length-equalization in the intake manifold and the cylinders that are farthest from the carb definitely run cooler, I'd be surprised if you don't notice the same thing even with your attempt at equalization, given that the cross section is so small.

lastly, I made my own extra small spark plugs with #8-40 threads, and instead of recessing the pistons for them I recessed the head (and not by much, no where near what you did, just a slight angled trough that blends to the existing surface).

HTH, let us know if any of this was helpful

Pete.
 
Last edited:
NICE WORK !!! !!! !!!

you said "here in Modena in the valley of engines (Ferrari , Lamborghini , Ducati )", I can see how you are inspired !!!

to break in my V-12 I used a temporary "once through" oil system so that no particles could re-circulate, I had a fresh oil reservoir feeding the oil pump, and a drain in the oil pan, I put the once used oil in containers and let the fine stuff settle to the bottom (for a couple weeks) then when it looked clear I thought it was safe to decant and re-use (but I didn't instead I used it as cutting fluid ! ). After a few quarts of oil it started coming out clean, so I reverted to the as-originally-designed re-circulating oil system and haven't had any problems.

one problem with V-12 and W-18 is that the sheer number of sparks per revolution overwhelms the electronic ignition, so I use a separate electronic ignition circuit and distributor for each bank (only fire one plug per cylinder, even though I have two per so it looks authentic for an aircraft engine).

I'll go out on a limb here had guess your intake manifolds don't have enough cross section or volume. The R.R.Merlin intake manifold diameter is 75% of the cylinder bore, and there are no exhaust manifolds just short stacks.

FYI, if you take off the exhaust manifolds you can feel the exhaust separately from each cylinder, some will be hot (good), some will be cold (not so good), and then the question is why, typically either not enough intake flow, or not enough compression. for example I have an inline-4 without any path-length-equalization in the intake manifold and the cylinders that are farthest from the carb definitely run cooler, I'd be surprised if you don't notice the same thing even with your attempt at equalization, given that the cross section is so small.

lastly, I made my own extra small spark plugs with #8-40 threads, and instead of recessing the pistons for them I recessed the head (and not by much, no where near what you did, just a slight angled trough that blends to the existing surface).

HTH, let us know if any of this was helpful

Pete.
Hi Pete
your suggestions are useful and interesting, I'm designing important modifications for my 18 cylinder , in the next post I will make a list of what I think to do
 
Important modifications to get a better functioning of my 18 cylinder , I hope :rolleyes: :

I would like to put the spark plugs on the heads and no longer on the cylinders, I solve the problem of oil dirtying the spark plugs and I improve fuel ignition. I'm looking for space and the correct position. I therefore have to redo all the cylinders and all the pistons, so I will be able to have a compression ratio of 1:8
As Pete suggests I could recessed the heads, but having a single head for 6 cylinders it is difficult to obtain 6 planes perfectly level with each other and I would have to completely redo the 3 heads

I remove all the transmission gears from the crankshaft to the camshafts and distributor and will be replaced with backlash-free timing belts (T5) , Using the T5 belts I can put 3 distributors, one for every 6 cylinders, consequently 3 electronic ignitions, possibly without Hall sensor, I fried at least 6 of them during the tests. A single distributor for 18 cylinders must be of generous dimensions, I don't have the necessary space , the sparks jump and fry the Hall sensor.

the piston has a bore of 24mm, the valve head is 10mm, the intake and exhaust manifolds are 7.5 - 8mm , I think they are sized correctly
When the engine runs, on two manifolds (6+6 cylindrers ) I can feel a strong depression with my finger, on the third a little less, I have to improve here.
The temperatures on 6+ 6 cylinders reach 95 degrees C on the exhaust manifolds, after 2-3 minutes of operation, on the remaining 6 cylinders around 70 degrees and not the same on each cylinder.

I think this is the problem that doesn't allow the engine to accelerate and reach at least 3000 rpm, now it only works at idle, in addition to this also the single distributor for 18 cylinders.

I also redid the intake manifolds to have a more direct flow
old type with welded brass tubes
new type with 2 brass plates hollowed out and screwed together with sealant

collettore.jpgcollettore immissione 2 pezzi new.jpg
 
Important modifications to get a better functioning of my 18 cylinder , I hope :rolleyes: :

I think in the long run you are going to be happy with the modifications, I have two whole shoe boxes full of throw-away parts from designing and building my V-12, including a complete set of no-good con-rods, a complete set of no-good cylinder liners, three versions of the "wheelcase" until I got one that satisfied all the requirements, lots of experimental parts, and also lots of machining mistakes. its just normal when you're on your own not following someone else's plans.

I'm a little puzzled by your concern about sealing between the cylinders and head, on my DeHavilland Cirrus cylinders I have short tubular stubs sticking up above the top flange and they center each cylinder in the head and this is the perfect place for a little dab of Form-A-Gasket, of course the Cirrus has very, very weird spark plugs, but might be worth looking into (the spark plug is horizontal, up above the flange-and-stub, and the hole for it intersects a vertical hole in the top of the head combustion chamber, weird yes, and mine isn't finished so can't say how well it works, but its a popular engine with lots of working examples).

also I have straight solid rods between my bevel gears, no U-joints, ?

finally, I took a look at the original drawings you are basing this on, and yes the original intake manifold is "weird" and I see why you re-designed something more doable as a model and I might have done something similar, but still worry that your re-re-design still isn't large enough in diameter.

just my $0.02, keep up the great work !

Pete.
 
I've got no clue about what actually would happen with your new manifold design, but my gut feeling is that the 2 outside cylinders would be starved for fuel.

Your carb feeds the center runner, which in turn splits and feeds the last runner between the 2nd and 3rd, and the 4th and 5th cylinders. It looks like the fuel/air mix will want to favor cylinders 2-5 and the outside 2 cylinders would have to really work to get their share, Maybe 3 openings between the center and last runner? One between the 1st and 2nd cylinders, another between the 3rd and 4th cylinders, and the last between the 5th and 6th cylinders. That might give all the cylinders a fighting chance to get their fair share of the fuel/air mixture.

Don
 
Just a suggestion to think about because I am unfamiliar with the carburetors you are using. When an engine transitions from idle to a faster speed the air flow increases and the vacuum signal to the fuel supply decreases leaning out the engine. If there is no compensating feature in the carb to keep the fuel/air mix the same, the engine will die. A possible way to tell if this is the problem, get the engine running at idle and warmed up a bit. Set the carburetors to a rich setting. Then very slowly open the throttles while slowly opening the fuel needle valves. This will have to be done in small increments. If you can get the engine to increase speed and stay running then you likely have a fuel compensation problem. Multi jet RC car carburetors I think have this compensating capability and may help.
Jeff
 
Just a suggestion to think about because I am unfamiliar with the carburetors you are using. When an engine transitions from idle to a faster speed the air flow increases and the vacuum signal to the fuel supply decreases leaning out the engine. If there is no compensating feature in the carb to keep the fuel/air mix the same, the engine will die. A possible way to tell if this is the problem, get the engine running at idle and warmed up a bit. Set the carburetors to a rich setting. Then very slowly open the throttles while slowly opening the fuel needle valves. This will have to be done in small increments. If you can get the engine to increase speed and stay running then you likely have a fuel compensation problem. Multi jet RC car carburetors I think have this compensating capability and may help.
Jeff
I will certainly follow your advice when I have finished all the modifications on the engine, consider that I have 3 RC car carburetors to adjust at the same time and it won't be so simple, but I will try
Now I took the seats for the spark plugs from the cylinders to the heads, so I had to redo 18 cylinders, 18 pistons and drill and thread 18 holes for the spark plugs.
In addition to this I am redoing the entire transmission system from the crankshaft to the 3 camshafts, no longer using gears but with timing belts.
I hope these changes help the engine run smoothly
 
I will certainly follow your advice when I have finished all the modifications on the engine, consider that I have 3 RC car carburetors to adjust at the same time and it won't be so simple, but I will try
Now I took the seats for the spark plugs from the cylinders to the heads, so I had to redo 18 cylinders, 18 pistons and drill and thread 18 holes for the spark plugs.
In addition to this I am redoing the entire transmission system from the crankshaft to the 3 camshafts, no longer using gears but with timing belts.
I hope these changes help the engine run smoothly
That's going to be quite some interesting changes.
You had shown your modeling planning in the past - - - hope you will also show that with these changes.

Thanking you for a fascinating journey!!!
 
Back
Top