It is a start...

[trumpy81]

I think so. The picture I meant was this: (posted by yourself). You can see that the holes overlap the lowest ring groove other than emerge fully in it. (sorry for bad english)

Leuc

Leucetius, that picture is from MrBaz, but now I understand what you were saying.

Don't feel bad about your English ... mine's just as bad sometimes ... lol

 

[user 13000]

An update. I've been working on the cylinder. The pictures below are of the assembled set, obviously. The iron sleeve is approximately 1/8" thick. The 'bulk' of the aluminum running the length of the cylinder stays a minimum of 1/8" thick as well. I've been debating on whether the cylinder should be made of 6061 or 7075.

Are 4 bolts enough to hold the head on to the cylinder? I'll be using a copper gasket (0.01" thick). This will be a high compression engine (maybe supercharged).
Is the iron sleeve too thick?

 

[Dinkum]

G'Day Mr Baz,

I like this project. Thm: Would high compression with forced induction cause knocking though? And don't copper gaskets corrode alumiminium kinda quickly? Just a couple of thoughts. Keep up the good work - would love to do this myself.

Regards,
Dinkum

 

[user 13000]

G'Day Mr Baz,

I like this project. Thm: Would high compression with forced induction cause knocking though? And don't copper gaskets corrode alumiminium kinda quickly? Just a couple of thoughts. Keep up the good work - would love to do this myself.

Regards,
Dinkum

I would alter the compression a little if I know for SURE I'm going to supercharge it, but it would still be pretty high. This engine will run off of 99.9% pure methanol (maybe nitromethane added in later) which has an octane rating around 115 if I recall correctly. Plus, methanol has the added benefit of cooling the intake charge.

I picked copper just because I've seen many other RC engines use copper gaskets. Should I not? I honestly don't know. I could annodize the alumnium to prevent any corrosion or reactions between the copper and the fuels.

 

[trumpy81]

As far as copper gaskets on aluminium go, there's no problem with them. Old Triumphs use copper head gaskets to no ill effect, in fact I find the copper gaskets slightly better than the fibre gaskets on my 72 Trophy. The Rocket III is a different horse altogether though ... lol

The trick to using copper gaskets is that they have to be annealed directly before fitting and torquing down the head. Annealing is simple, heat to cherry red and dunk in water. This softens the copper and allows it to 'flow' into the contours of the sealing areas. A quick soft wire brushing helps to clean off the scale left from the heating/quenching process.

Although that is my personal choice, there is no reason you cannot use paper, cardboard, teflon/nylon or just about any other material for a head gasket. Some things will work and some wont, it depends on a lot of factors like how true the mating surfaces are, how much compression, the total area of the sealing surface, placement of retaining bolts etc... etc...

For your cylinder liner, I would recommend a wall thickness closer to 1/16 inch and only slightly larger for the cylinder, around .080 inch should do. You have to take the thermal properties and expansion rates into consideration. Of course it really depends on what sort of usage this engine will see as to how thick the wall needs to be.

Running pure methanol can make it hard to start, adding 5% Nitro will help. You should aim for a compression ratio around 8:1, that way you have a bit of wiggle room if you want to supercharge at a later date and it shouldn't detonate with normal aspiration.

Four head bolts should be sufficient but try to keep the bolt pattern as tight as possible. It's the distance between each bolt that makes the difference between success and failure. More bolts is good, but not always practical or possible depending on the physical constraints of your design.

 

[trumpy81]

MrBaz, just another small note, the mounting flange at the base of your cylinder, it looks great, but can you actually get a screw and a screwdriver in there??

Just food for thought and yet another thing you have to consider when designing an engine

 

[mu38&Bg#]

Methanol with spark ignition easily will run at 15:1 in cylinders larger than this. You can probably run pump gas at 15:1 in a 1" bore without issue. If you're thinking glow plug ignition ~8:1 would be normal, but up to 15:1 has been used in production model four strokes. 8:1 with a supercharger will be OK with glow ignition. Mode airplane engines almost universally use 1mm (.040") rings. Head gaskets are usually aluminum, but copper or what looks like brass is sometimes used. Corrosion from methanol will be a much bigger problem than the gasket.

The piston will work fine as is. Placing the wrist pin that low only makes the cylinder taller. The length of the skirt is really dependent on the bore. Extremely short piston skirts like the Wiseco pictured are only for racing applications. Anything with a long expected service life will have a much longer skirt. Your piston has plenty of skirt area. I wouldn't bother with dish, but if you take head geometry into account to get a decent squish area it will be fine. Dishing at this scale has a large impact on compression ratio. What is the volume of the dish and cylinder displacement?

Engine design is all about compromise.

Greg

 

[Leucetius]

Full-scale engine construction rules ask for a compression height (distance from center wrist pin to top of piston) of 36% to 45% of bore diameter. For skirt length (center wrist pin to bottom of piston) 40% to 50% of bore diameter are asked. Shorter skirt length are for racing engines, as stated by dieselpilot.

Source: Verbrennungsmotoren - Motormechanik, Berechnung und Auslegung des Hubkolbenmotors (ISBN-10: 3-528-43108-3)

 

[user 13000]

As far as copper gaskets on aluminium go, there's no problem with them. Old Triumphs use copper head gaskets to no ill effect, in fact I find the copper gaskets slightly better than the fibre gaskets on my 72 Trophy. The Rocket III is a different horse altogether though ... lol

The trick to using copper gaskets is that they have to be annealed directly before fitting and torquing down the head. Annealing is simple, heat to cherry red and dunk in water. This softens the copper and allows it to 'flow' into the contours of the sealing areas. A quick soft wire brushing helps to clean off the scale left from the heating/quenching process.

Although that is my personal choice, there is no reason you cannot use paper, cardboard, teflon/nylon or just about any other material for a head gasket. Some things will work and some wont, it depends on a lot of factors like how true the mating surfaces are, how much compression, the total area of the sealing surface, placement of retaining bolts etc... etc...

For your cylinder liner, I would recommend a wall thickness closer to 1/16 inch and only slightly larger for the cylinder, around .080 inch should do. You have to take the thermal properties and expansion rates into consideration. Of course it really depends on what sort of usage this engine will see as to how thick the wall needs to be.

Running pure methanol can make it hard to start, adding 5% Nitro will help. You should aim for a compression ratio around 8:1, that way you have a bit of wiggle room if you want to supercharge at a later date and it shouldn't detonate with normal aspiration.

Four head bolts should be sufficient but try to keep the bolt pattern as tight as possible. It's the distance between each bolt that makes the difference between success and failure. More bolts is good, but not always practical or possible depending on the physical constraints of your design.

Annealing copper is no problem. I've worked with copper before. Work-hardening metals are a pain to work with. I was actually thinking about annealing the copper just the other day. You've confirmed it. Thm:

I'll shrink the sizes of the sleeve and cylinder a bit.

I'm still wanting to retain high compression since this will be specifically only run with methanol/nitro. Even gas engines start at 8.5:1. Oh, and this will be 4-cycle.

Head bolts are 0.15" from edge of bore.

If this thing actually works, I'm planning on putting it on an RC plane where it could see 15 minute run times.

MrBaz, just another small note, the mounting flange at the base of your cylinder, it looks great, but can you actually get a screw and a screwdriver in there??

Just food for thought and yet another thing you have to consider when designing an engine

I haven't edited the inventor part for it yet, but I will mill the fins over the holes so that it is easily accessible.

Methanol with spark ignition easily will run at 15:1 in cylinders larger than this. You can probably run pump gas at 15:1 in a 1" bore without issue. If you're thinking glow plug ignition ~8:1 would be normal, but up to 15:1 has been used in production model four strokes. 8:1 with a supercharger will be OK with glow ignition. Mode airplane engines almost universally use 1mm (.040") rings. Head gaskets are usually aluminum, but copper or what looks like brass is sometimes used. Corrosion from methanol will be a much bigger problem than the gasket.

The piston will work fine as is. Placing the wrist pin that low only makes the cylinder taller. The length of the skirt is really dependent on the bore. Extremely short piston skirts like the Wiseco pictured are only for racing applications. Anything with a long expected service life will have a much longer skirt. Your piston has plenty of skirt area. I wouldn't bother with dish, but if you take head geometry into account to get a decent squish area it will be fine. Dishing at this scale has a large impact on compression ratio. What is the volume of the dish and cylinder displacement?

Engine design is all about compromise.

Greg

I've been looking at everything corrosion/methanol related. It seems that the methanol isn't really the problem, but the water content it can carry. Many people have no problem with corrosion. Maybe I'll idle some nitro with oil in it when I'm done with it to coat everything with a little oil. Like I mentioned earlier, I could also annodize everything to add some corrosion resistance.
The oil system will be separate from the fuel, so that will help as well.

Dish volume is .524cc.

Full-scale engine construction rules ask for a compression height (distance from center wrist pin to top of piston) of 36% to 45% of bore diameter. For skirt length (center wrist pin to bottom of piston) 40% to 50% of bore diameter are asked. Shorter skirt length are for racing engines, as stated by dieselpilot.

Source: Verbrennungsmotoren - Motormechanik, Berechnung und Auslegung des Hubkolbenmotors (ISBN-10: 3-528-43108-3)

Interesting. Time to crunch some numbers.

 

[user 13000]

Here is some info: (All measurements are in inches)

Enter Cylinder Bore Size: 1
Enter Piston Stroke Length: 1
Enter Head Gasket Bore Diameter: 1.004
Enter Compressed Head Gasket Thickness: .01
Enter Combustion Chamber Volume In CCs: 0
Enter Piston Dome Volume In CCs Negative For Dished Pistons: -.524
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-'): .06

Calculated Engine Compression Ratio: 10.03:1
Total Displacement Volume: 1.425957499409645 cc

For simplicity sake, I was planning on going with a flat head. Any reason not to?

 

[Dinkum]

Wow, it always amazes me how much knowledge and experience is found on this site.
I've heard that copper gaskests are known to cause galvanic corrosion on "real" engines with aluminium heads but it seems that that doesn't apply to model engines. I think that must be because they don't use coolant and therefore there isn't an electrolyte. So I guess I better just sit back and learn. :hDe:

 

[mu38&Bg#]

I didn't see if you'll be using spark or glow ignition. Glow ignition and straight methanol can have problems with detonation at relatively low compression ratios. I was running an FS-40S this year on methanol (no nitromethane in the fuel) and was very surprised when it threw a prop due to detonation. I had not read about it before, but I was trying for the most power and that meant as lean as possible. The FS-40S is only 8:1 or so. The big bore engine was much more forgiving in that regard even though compression ratio should have been a touch greater. I think the slightly larger squish area made a difference.

If you make a flat combustion chamber, that will give you a workable compression ratio. If you haven't designed the head yet, you might check that everything fits in the head the way you want before deciding on the flush combustion chamber. .060" for squish clearance is tremendous in an engine this size and would seem to be non-functional, but is common of many model airplane four strokes. Two stroke glow competition engines can have squish clereance on the order of .005-.010" but .020 is very common for OEM. Unless valves are sized to clear the inside bowl area, you won't see valve clearance issues until the head is designed and the cam added to the model. Mostly, the intake valve can interfere as it opens BTDC as the piston is still traveling upward. While your' designing consider how this will be made. I see a rectangular relief with small corner radii in the bottom of the piston. Unless you intend to, or can, machine with a extra long and tiny endmill (100+USD+) this will be impractical. Assume you'll be using a standard endmill, maybe a 1/4" or an 3/16" XL.

I agree that methanol isn't a big issue for corrosion. Methanol fuel should also be used with a compatible oil in the crankcase, but I think the old Kavans with an oil sump used regular motor oil with glow fuel. Blowby is a reality and you will have fuel, water, and byproducts in the crankcase.

I've attached a drawing of the O.S. Engines FS-48/52 piston. Virtually all of their four stroke pistons look like this except in larger sizes the skirt is relieved. Some of the newer engines use shorter pistons. Anyway, the inside of the piston is forged so my drawing is simplified here. The 20.8mm counter bore in the bottom of the piston facilitates machining of the external features. The piston is put on a mandrel fixture with a pin through the wrist pin holes. The fixture pulls the piston back and holds it.

I think the design belongs to the designer. So the above is just some rambling about things stored in my head. I don't think any of it is a show stopper.

View attachment 45803200.PDF

 

[user 13000]

I'll be using spark ignition. After studying quench and squish, I'm going to redesign the piston and I have an idea for the combustion chamber shape for the head. Something like a wedge design. Either that or create a greater dish in the piston and minimize the deck height (quench distance of the 'rim' around the dish) to something nearer 0.03".

 

[petertha]

... eventually want to work on making a supercharged V12... plan is to run pure methanol with a manual mix of pure nitromethane (not the mixed 'nitro' from hobby shops). Oil control is separate, and pressurized/forced/whatever-have-you. This should allow me to run high compression with slight supercharging...

I used to run YS 4-strokes when I flew RC pattern, then got into pylon (2-stroke HP engines). So I have a bit of hands on experience. Since the 140 4S generation, they have increased in complexity & power. Now direct injection (vs pseudo induction boost) & electronic ignition (vs glow). I would google & study engines like these for sizing & materials etc, because if anything they are probably conservative to what you are embarking on.

http://www.ysengines.net/dz170-cdi/
http://www.gbrcaa.org/smf/index.php?topic=1440.0

On one hand, ignition system is more sophisticated vs glow, but I think net better decision. Varying nitro content in methanol inherantly affects glow plug ignition timing, and sometimes in a not-good way. We typically play with plug selection (varying heat settings) & alter head shims (compression alteration) not just for power, but prevent destructive detonation. And these tweaks are required when the fuel (%nitro) is fully known beforehand. I can tell you that a setup suitable for stock 15% nitro is completely different than 45%, probably the max I ever ran. But at these compression levels, a couple thou thickness in shims is actually pretty noticeable. Some of the HP boaters would run higher nitro, but they had water cooling & even then melted a few along the way. Altering nitro on the fly introduces more variables, least of which will be ignition timing. So I suspect you will likely require a way advance/retard that on the fly as well?

Heat starts to become a lot more problematic at these levels, so that will tax the lube system. The alloys used in pistons, heads, chromed liners etc is pretty sophisticated stuff. Not taking anything away from your exciting project, but I would try & sponge as much information from existing engines as you can.

 

[user 13000]

I used to run YS 4-strokes when I flew RC pattern, then got into pylon (2-stroke HP engines). So I have a bit of hands on experience. Since the 140 4S generation, they have increased in complexity & power. Now direct injection (vs pseudo induction boost) & electronic ignition (vs glow). I would google & study engines like these for sizing & materials etc, because if anything they are probably conservative to what you are embarking on.

http://www.ysengines.net/dz170-cdi/
http://www.gbrcaa.org/smf/index.php?topic=1440.0

On one hand, ignition system is more sophisticated vs glow, but I think net better decision. Varying nitro content in methanol inherantly affects glow plug ignition timing, and sometimes in a not-good way. We typically play with plug selection (varying heat settings) & alter head shims (compression alteration) not just for power, but prevent destructive detonation. And these tweaks are required when the fuel (%nitro) is fully known beforehand. I can tell you that a setup suitable for stock 15% nitro is completely different than 45%, probably the max I ever ran. But at these compression levels, a couple thou thickness in shims is actually pretty noticeable. Some of the HP boaters would run higher nitro, but they had water cooling & even then melted a few along the way. Altering nitro on the fly introduces more variables, least of which will be ignition timing. So I suspect you will likely require a way advance/retard that on the fly as well?

Heat starts to become a lot more problematic at these levels, so that will tax the lube system. The alloys used in pistons, heads, chromed liners etc is pretty sophisticated stuff. Not taking anything away from your exciting project, but I would try & sponge as much information from existing engines as you can.

Thanks for the links.

I found a place that I can source copper sheet from below 0.01" to 0.05" and more if I need to alter the compression ration.

Using spark ignition, I could have a iginition table for straight methanol and build some others based off of tuning done beforehand. Like you said, I would have to know exactly what I'm running BEFORE and load the correct timing table to the ignition accordingly.

This project is a learning experience in so many different ways than I even imagined before I set out on it. I've learned SO much so far in just engine design, let alone honing my skills in Inventor. This forum has been just fantastic so far. I never thought I would get so much excellent feedback from so many knowledgeable people.


After studying quench and squish more, it seems that a wedge head isn't really a good design to help reduce the chances of detonation/preignition. A dish design is supposedly GREAT for high compression engines -- as long as the rest of the design is adequate. I can get great quench distance with a dish if I rely on the piston design to set the combustion chamber. My worry is that a large dish might induce TOO much heat into the piston.

If I go with a flat top piston and match the combustion chamber in the head, I can get better quench/squish. This will allow me to deposit more heat into the head instead of the piston.

 

[mu38&Bg#]

With spark ignition in a 1" bore, detonation will not be an issue. I run kerosene in ~23mm bore engines with spark and they do not detonate. If you were using glow ignition it would be a much greater concern.

Greg

 

[petertha]

Probably jumping ahead a bit, but you might also want to check this old post I started on 4S valve timing re metahnol based model engines. I noticed a lot of variation amongst designs (particularly the YS-4S). Your project will likely be on the bleeding edge.
http://www.homemodelenginemachinist.com/f26/valve-timing-4-stroke-glow-17093/

 

[trumpy81]

Wow, it always amazes me how much knowledge and experience is found on this site.
I've heard that copper gaskests are known to cause galvanic corrosion on "real" engines with aluminium heads but it seems that that doesn't apply to model engines. I think that must be because they don't use coolant and therefore there isn't an electrolyte. So I guess I better just sit back and learn. :hDe:

This is false as far as I can tell Dinkum. I have two old Triumphs, a 1972 Trophy and a 1976 Bonneville and both run copper head gaskets with aluminium heads and no ill effects.

Also, Top Fuel Dragsters run copper head gaskets and most teams use a VHT product made for copper head gaskets. It's a spray on copper coloured glue for want of a better term. I have some somewhere because I have used it on my Triumphs a few times, but in all honesty it is not really needed on them.

When I crewed for Peter Gratz (Top Doorslammer) he also used copper head gaskets on his aluminium KB block and heads. No ill effects were observed at all on this engine either.

Copper is a fairly inert metal and it takes a long time for copper to corrode under normal atmospheric conditions. It has even been used for roofing in Europe in past centuries.

 

[user 13000]

With spark ignition in a 1" bore, detonation will not be an issue. I run kerosene in ~23mm bore engines with spark and they do not detonate. If you were using glow ignition it would be a much greater concern.

Greg

Good to know.

Probably jumping ahead a bit, but you might also want to check this old post I started on 4S valve timing re metahnol based model engines. I noticed a lot of variation amongst designs (particularly the YS-4S). Your project will likely be on the bleeding edge.
http://www.homemodelenginemachinist.com/f26/valve-timing-4-stroke-glow-17093/

Thank You! This is GREAT info. I will definitely be using this later. Thm:

This is false as far as I can tell Dinkum. I have two old Triumphs, a 1972 Trophy and a 1976 Bonneville and both run copper head gaskets with aluminium heads and no ill effects.

Also, Top Fuel Dragsters run copper head gaskets and most teams use a VHT product made for copper head gaskets. It's a spray on copper coloured glue for want of a better term. I have some somewhere because I have used it on my Triumphs a few times, but in all honesty it is not really needed on them.

When I crewed for Peter Gratz (Top Doorslammer) he also used copper head gaskets on his aluminium KB block and heads. No ill effects were observed at all on this engine either.

Copper is a fairly inert metal and it takes a long time for copper to corrode under normal atmospheric conditions. It has even been used for roofing in Europe in past centuries.

Even more excellent information/assurance.

 

[user 13000]

Here is a updated rendering of the cylinder using the new dimensions.