RE: compression ratio
There are two ways to work out compression ratios, one is called geometric which uses the full swept volume from BDC (the actual size of the engine) and the other is trapped which uses the swept volume from the point the exhaust closes. Neither method is accurate so it's a matter of choosing one and staying with it. As a general guide, trapped compression will be ~2/3 of geometric, depending on exhaust port timing. Most standard engines will have a compression of around 9:1 measured geometrically so about 6:1 measured as trapped. Squish clearance is the closest the piston gets to the cylinder head and a minimum figure is around .005" although I prefer a little more than that at .008"-.010" to be on the safe side. Solder isn't a good way to measure this clearance because most engines have a tapered squish band so it's near impossible to get an accurate reading by squashing the solder. You need a digital caliper, which can be used as a depth guage, to measure deck height and cylinder head projection into the liner. The difference between the two is the squish clearance.
Posted on: 5/15/2013 7:59 AM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11512200

RE: Merco 49?
Derek Yours appears to be a Black Streak, AKA a heavy case, where the backplate screw lugs are extended all the way to the front and a heavy rib runs from under the exhaust port down to the RH mount. The photo shows my light case Mk1 with single plug, the Mk2 had twin plugs. After the Mk 2 came the Mk3 heavy case (twin plugs) but a similar crankcase to yours. Attached for your reading pleasure are the instructions for my 49 Black Streak. Earlier engines had a natural finish cylinder head.
Posted on: 9/17/2012 7:36 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11231827

RE: Gas engines and glow plug nitro engines, differences and can a new engine be born?
[quote]ORIGINAL: 1QwkSport2.5r I kinda feel like Darzeelon's spirit is roaming the forums... [:@] [/quote] MWAHAHAAA...thanks for that...coffee all over my keyboard :D As for the coil used in glow plugs for FAI engines, they're the same as used in glow engines that have nitro added to the base fuel but will normally be a hotter heat range than is generally used for a fuel with nitro added. FAI (no nitro fuel) engines are still used today but it only applies to 3 classes of international competitions, control line speed, RC pylon and free flight power. These 3 classes rely on ultimate engine power for performance so what's called FAI fuel (80% methanol and 20% castor) is used to exclude any exotic (and dangerous) fuels.
Posted on: 9/7/2012 7:55 PM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11221352

RE: Effect of a Scratch
[quote]ORIGINAL: 1QwkSport2.5r I can't find the picture of it, but I have a Fox airplane engine that ate a wristpin G-clip.. [/quote] There was an early run of the 40th Anniversary Fox 35 where the circlip groove wasn't machined quite deep enough causing them to pop out. The check for these is to push the wristpin quite hard and if the circlip came loose, get another piston from Fox :).
Posted on: 9/5/2012 9:22 AM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11218311

RE: Venturi for OS Max H 40
That venturi has an OD of 10mm but the H-40 needs a venturi of 13mm to fit the crankcase. The bore size of 7mm is OK although I wouldn't go any larger than that. The needle valve is also designed for a smaller venturi so wouldn't fit either.
Posted on: 9/2/2012 8:52 PM by Author "downunder" in the forum "Control Lines"
http://www.rcuniverse.com/forum/fb.asp?m=11215180

RE: Taplin Twin
[quote]ORIGINAL: fiery Taplin Twin Mk III. [/quote] Hey Derek, a couple of those photos would go really well in my collection of engine tests. Oh wait, it seems they're already [link=http://sceptreflight.net/Model%20Engine%20Tests/Taplin%20Twin%20Mk%20III.html]there.[/link] :D.
Posted on: 8/27/2012 9:54 AM by Author "downunder" in the forum "Everything Diesel"
http://www.rcuniverse.com/forum/fb.asp?m=11207723

RE: Engine test reports
Thanks guys, there's still a few hiccups I have to sort out, for instance my daughter informed me that there's a program for joining seperate .pdf files together, but I'll get there. I've started the next phase which is adding photos of actual engines, whenever I can find them, below each test.
Posted on: 8/25/2012 9:36 PM by Author "downunder" in the forum "Control Lines"
http://www.rcuniverse.com/forum/fb.asp?m=11206127

RE: Engine test reports
There are a couple of kinks I need to work out and I'm searching for photos of as many engines as possible to add to each page but that's going to take some time to complete (if ever :)) so I'll probably just add them as I find them.
Posted on: 8/24/2012 9:11 AM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11204498

Engine test reports
I've mentioned this in the CL and glow forums but I've been asked (thanks Derek :)) to also mention it here. For the last month or so I've been collecting glow engine test reports that were posted on another forum and putting them all together on a web site to save hunting through hundreds of pages trying to find a particular test which may not even be there. Yesterday I finally finished all the diesel tests and got it up and running. You can find the diesel tests [link=http://sceptreflight.net/Model%20Engine%20Tests/Index%20Diesels.html]here.[/link] Hopefully more scans will appear later in which case they'll get added too.
Posted on: 8/23/2012 9:48 PM by Author "downunder" in the forum "Everything Diesel"
http://www.rcuniverse.com/forum/fb.asp?m=11204142

Engine test reports
For those who enjoy reading engine tests in magazines, I've collected about 500 tests (glow and diesel), which were spread throughout a couple of topics in another forum, because it was near impossible to go searching through hundreds of pages for a particular engine on the chance it might be there. The tests can be found at [link=http://sceptreflight.net/Model%20Engine%20Tests/Index.html]this[/link] web site.
Posted on: 8/23/2012 7:43 AM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11203295

Engine test reports
In another forum there were topics started on vintage glow and diesel engines and many test reports got scattered through them, although they both morphed into just about any engine right up to some modern ones. I've gone through both topics and collected all the tests and have now got them all in one place on [link=http://sceptreflight.net/Model%20Engine%20Tests/Index.html]this[/link] web site. It's a work in progress because sooner or later more tests will get added but for now it's all up to date. Have fun browsing :).
Posted on: 8/23/2012 7:23 AM by Author "downunder" in the forum "Control Lines"
http://www.rcuniverse.com/forum/fb.asp?m=11203269

RE: Piston Ring Question
Here's a tip that came in the instruction leaflet for my new Enya 61 ringed engine. First insert the piston into the bottom of the liner so the ring has just barely been compressed. This allows for a lot of sideways movement (wobble) of the piston and rod. Then fit the liner down into the crankcase until the rod can slip onto the crankpin then slide the liner the rest of the way down over the piston. Enya obviously understand that guys will always strip an engine and they even give instructions on a tightening sequence for the head.
Posted on: 8/14/2012 10:01 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11193992

RE: Twin Cylinder nitro engines?
About the only twin I can think of in that size is the Taplin Twin diesel in both .42 and .49 sizes. The originals were made in England but others were later made by Aurora in India. Be prepared to pay though when one occasionally comes up on Ebay.
Posted on: 8/14/2012 8:30 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11193891

RE: rc diesel engines?
A true model diesel engine (as used in full size cars and trucks) is almost impossible, mainly because of the need for a very precise fuel injection system. Diesels always run with a wide open intake system to have the maximum possible volume of air to compress for maximum heat. Power is controlled solely by the volume of fuel injected at the correct time. I remember someone once wondering if an ink jet nozzle and electronics could be adapted as an injection system. Not bad thinking actually :). A glow engine also uses compression to some extent because compression helps the catalytic reaction at the plug coil to begin, essentially because the compression packs more methanol molecules tighter against the platinum. They're sometimes called a semi-diesel. Model diesels are a pure compression ignition engine because, like a glow, all the fuel is mixed with air just waiting for the air to get heated enough to ignite a part of the mixture [b]somewhere[/b] inside the combustion chamber. Any type of burneable fuel could be used but only if the compression was high enough to reach the auto ignition point of that fuel. To keep compression to practical limits ether is added to the fuel because it has a very low auto ignition temperature and will ignite even when the throttle is closed for idling and volume of air inducted is very low. The ether essentially takes the place of a glow plug and ignites the actual fuel which is the kerosene. Because the ether is spread fairly evenly amongst all the kero, most of the mixture will start burning all at once (no real flame front) giving a very rapid rise of pressure in the combustion chamber and most of the fuel will be burnt immediately. This is where a model diesel gets its very high torque from but it's hard on the mechanical parts.
Posted on: 7/31/2012 7:25 PM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11176644

RE: OS 1/4-28 Prop nut
I have to agree with jeffie on the hardware store nuts. They may be the softest of all but if you strip the threads on them then you're WAY overtightening them. On occasion I've made T nuts from aluminium bar stock and have never come close to stripping them.
Posted on: 7/19/2012 10:26 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11162069

RE: What glow engine would you choose
It's a bit difficult for me to narrow down a favourite engine but I'd have to say my Dooling 29 (which isn't even fully run in yet) is one I'd never part with. Of useable engines I'd give the nod to my Irvine 40RLS which is magnificent followed very closely by my latest which is an Enya 61 CXLRS. These are CL engines but the best of my RC engines is the Enya 60X-III.
Posted on: 7/19/2012 10:20 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11162062

RE: Little compression but runs like a champ???
[quote]ORIGINAL: The_Shark ...looking at the crankshaft to piston arm bushing and i can see slop in the parts, [/quote] That's the fit of the conrod to the crankpin. A new clearance is generally about .002" but anything up around .006" is usually considered acceptable. Most rods use a brass bush as the bearing surface but some rods are unbushed so use the rod material. And be aware that the conrod only fits one way onto the crankpin. One side of the rod (or bush) has a tiny chamfer and that end has to be fitted back on the crankpin first so it goes up against the crankweb. The reason for this is that there's a very small radius ground on the crankpin where it comes from the crankweb and the chamfer gives some clearance to that radius.
Posted on: 7/16/2012 9:24 AM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11157303

RE: Stunt tanks and muffler pressure.
Plastic clunk tanks set up as Uniflow are the way to go. I set mine up with a solid (copper tube is best) Uniflow line bent so it goes from the stopper to the outside wall of the tank then runs along the centre of the wall almost to the clunk feed line. That just makes sure the clunk line doesn't get obstructed by the Uniflow line. Usually the tubing used for the Uniflow line will have a slight bend in it (from being coiled up) so use that bend to help point the clunk at the centre of the outside wall when you hold the tank on its side (simulates what happens in flight). Fit the tank to the model so the back end of the tank is further outboard than the front to use the last drop of fuel (that accounts for the natural yaw of the model in flight). Set up like this you can experiment with using muffler pressure or not or by blanking the Uniflow line and venting the other (with or without muffler pressure) you can find the set up that works best for you. Chances are the best will be Uniflow with muffler pressure although right now my latest model is Uniflow with no pressure, mainly because the engine/muffler combination I'm using didn't have any provision for muffler pressure so I gave it a try as is and have been perfectly happy with it. It works in Adelaide, not sure about Perth though :D.
Posted on: 7/12/2012 12:54 AM by Author "downunder" in the forum "Control Lines"
http://www.rcuniverse.com/forum/fb.asp?m=11152229

RE: Induction Timing
[quote]ORIGINAL: nitroexpress Does this really seem reasonable? [/quote] Regardless of the info I've given long ago I totally agree with you. Any manufacturer worth his salt (like Rossi for instance) knows far more than any of us as to what's needed for high performance and has the equipment to make it. Other manufacturer's of lesser quality engines would also likely know the tricks used by Rossi etc. but most would be too time consuming or expensive for mass production. For those who like to fiddle then it's necessary to know some of the finer details about what they want to try and what affect it could have. I've read some fantastic claims in this forum for mods that are totally dreadful and will absolutely ruin an engine so it's wise for anyone thinking about doing mods to have a good understanding first as to how they work.
Posted on: 7/10/2012 11:56 PM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11150982

RE: Engine test scans
[quote]ORIGINAL: spaceworm Are you still collecting data? If so, there are several more Saito engine test reports and scans in the Saito History folder here on RCU. [/quote] Thanks for the heads up on the Saito history pages. I've just finished adding another 16 Saito tests from there.
Posted on: 7/9/2012 10:58 AM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11148863

RE: Will mixing fuel brands damage glow plugs ?
[quote]ORIGINAL: Bobhend Evidently the platinum probably contains 2 - 8 % tungsten but the exact formula is a trade secret. [/quote] The platinum is usually alloyed with either iridium or rhodium which are from the platinum family of metals. Pure platinum is rather soft so these other metals mainly give strength to the coil but they also make it capable of handling much higher temperatures. The plug manufacturers just buy coils of the wire from distributors but different manufacturers of the wire will have their own particular alloys. I heard a story about Gordon Burford (he made the Taipan etc engines) who wondered why all his plug wire was disappearing. Eventually he found out that one of the guys in his factory was using it to bind pieces of wire together for soldering. He kept it locked up in a safe after that :).
Posted on: 7/8/2012 9:17 AM by Author "downunder" in the forum "RC Fuels"
http://www.rcuniverse.com/forum/fb.asp?m=11147486

Engine test scans
There's a thread running in another forum with many scans of engine tests in amongst its 300+ pages (so far) which I've collected, sorted into alphabetical order and uploaded to a web site to keep them all in one place. At the moment they're all (bar one or two) glow engines, mainly because that was the topic (which began for vintage glows) but, as is the nature of these things, it quickly morphed into any glow. If I've counted correctly there's 333 individual tests which can be found [link=http://sceptreflight.net/Model%20Engine%20Tests/Index.html]here.[/link] I have to thank all those who contributed scans and their willingness for me to compile them in one place.
Posted on: 7/7/2012 7:50 AM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11146394

RE: OS Max III .15
These engines came with either a venturi or carb and that was the only difference between them. You'd probably only find a second hand carb by now although a later carb may fit. [link=http://sceptreflight.net/Model%20Engine%20Tests/OS%20Max-III%2015%20%282%29.html]Here's[/link] an engine test report on the R/C version and you'll see that the same engine was tested earlier but with a venturi fitted.
Posted on: 7/4/2012 8:31 AM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11142591

RE: Air Leaks...do you really need to seal your engine ?
[quote]ORIGINAL: Foxy I leave it in the hands of the members... How many pages of entertainment do the F2A speed flyers need!? lol [/quote] Well F2A speed is very [b]very[/b] serious stuff so they need some lightening up :D. They really know their stuff though and modified car engines are treated as beginner engines :).
Posted on: 7/4/2012 8:20 AM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11142579

RE: Mobil Jet Oil II mixing with Methanol
I suspect it's just the brown dye Mobil uses, maybe reacting with sunlight? I didn't have any problem like that with my fuel which was a similar blend to yours. If the engine still runs the same then the fuel itself will be OK.
Posted on: 7/3/2012 10:25 AM by Author "downunder" in the forum "RC Fuels"
http://www.rcuniverse.com/forum/fb.asp?m=11141400

RE: Air Leaks...do you really need to seal your engine ?
[quote]ORIGINAL: supertib You are wrong son ! Something you need to understand is some of these modified race engines make extremely high HP and [b]extremely high crankcase vacuum[/b]............ [/quote] That is [b]so[/b] wrong. There's a small reduction in pressure in the crankcase during the induction period but only small because air is rushing in to try to balance crankcase pressure with ambient. When the inlet closes the downwards movement of the piston compresses the air in the crankcase giving a higher than atmospheric pressure until the transfer ports open. So pressure is cycling between slightly below atmospheric to somewhat above. So what's the [b]average[/b] pressure? Around 1.5psi which is often used in some applications where much more than muffler pressure (about .2psi) is required to get fuel to the engine. This is called untimed pressure. With some engines (not car engines) there's a tapping off the crankcase which is only open after the crankshaft port has closed so only feeds the compressed crankcase pressure to the tank. This is called timed pressure and is on the order of 6psi which is the pressure that tries to force oil along the crankshaft towards the front bearing. The actual seal against oil and crankcase pressure loss is the fit between the crankshaft and the crankcase housing which generally runs at around .001" clearance and this is sealed by the oil film. The critical point along the crankshaft is between 1/3 to 1/2 from the crankweb and obviously behind the crank port. It's critical because, under high loads, the crankshaft actually bends very slightly around this area so tends to keep the .001" clearance better than the rest of the crankshaft. Particles of dirt greater than this clearance will scour the crank and bush decreasing the seal from loss of oil film. Glad to help son! BTW, the blue sealed bearing you showed (P/No 607-2RS) is a fully sealed, grease packed bearing which will very effectively stop any fuel or air leakage. They do have a much more limited max rev capability though if you leave the grease in there. Your crankshaft shows evidence of the crank spinning in the bearing's inner race.
Posted on: 7/1/2012 7:07 PM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11139230

RE: Old Soviet Union 10cc engine
Way back on page 1 I mentioned the Russian Stas's 42 and almost 2 years later I've finally found the info on them after following a couple of leads. I guess everyone is aware of the Marz 2.5 (both diesel and glow) which were made in Russia. When they ceased production in about 1990, Ilya Leydman (who had a business in Sydney called Macheast selling Russian engines) went to Russia in 1992 and, with some Russian friends, bought up most of the Marz machinery with the intention of making his own engine. As a trial run to learn how to make engines they decided on a simple 42 size with design cues based around both Webra and Profi. The Russian manager's son was called Stas so the engine was named Stas's. One of the things they played with was external finish so some had as cast finishes while others had machined fins. In all, they made 200 of the side exhaust and 50 of the rear exhaust. Ilya brought all of them back to Australia where some were then sold to Carlson Imports in America with the remainder being sold through Macheast. At the top of page 2 Hobbsy mentioned that my Stas's looked similar to his Zeus 61 which just happens to be the engine that Ilya wanted to make :). Ilya told me that he made both the Zeus 42 and 61 as well as a couple of rear exhaust 61's. For those interested, [link=http://www.holdfastmac.com.au/Stass%27s%2042RE.html]here's[/link] a review I did on my RE version with a photo of my SE which shows the differences in finish.
Posted on: 6/27/2012 11:14 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11134763

RE: Varying Intake Disc Rotor Housing
Kind of the way BW was thinking but if you modify the backplate so it can be rotated a little with the screws loosened you could then adjust the intake timing. Someone gave me a beaten up example of one of these Webras and the intake is at the bottom left corner instead of the more normal upper right. None of the backplate screws go into a transfer port so they're not needed for sealing anything off.
Posted on: 6/26/2012 9:52 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11133362

RE: Air Leaks...do you really need to seal your engine ?
[quote]ORIGINAL: HWM77 My [b]Profi F2a[/b] has the burps coming onto the pipe,it may have leak some where,but it only runs on straight fuel,will this nitro spray find the problem area,many thanks in advance. [/quote] You've got a what?? Holy cow, a car guy would give his left you-know-what for an engine that powerful :D. Kidding aside, there's very few areas an engine can leak from. With no carb that's eliminated but it could leak from around the plug seat ot plug post although you're probably using a Nelson plug so it's unlikely. Head button seal to the liner is another area and the backplate (I think yours has an O ring seal). What I use to check for any tiny leak is Gas and Air Leak Detector that you can get at any plumbing supply shop. A drop or two on a suspect area will quickly show any leak by foaming when you turn the engine over and hold against compression. It might pay to check all the pipe connections too. That said, I'd guess your "burps" are just from the mixture when it transitions from normal running to the pipe because this type of engine is extremely critical. However I've never flown speed so you'd probably know more about this than I do.
Posted on: 6/26/2012 9:33 PM by Author "downunder" in the forum "Car Nitro & Gas Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11133341

RE: Norvel 25, 40 long term reviews
I believe the bolded portion only applies to the small Norvels (049, 061) which apparently are set up very tight. For the .15-.40 I've treated them the same as any ABx type as far as running them in because they're not exceptionally tight. Other than running them in I haven't used mine so far so can't say anything about how they hold up or whatever. I do think though that the "ceramic" technology is a big step forward. Norvel calls it AAO which is aluminium piston and aluminium oxide coating. In hardness, aluminium oxide is somewhere between chrome and diamond so should be very wear resistant and is also porous enough to trap oil. At the moment it seems only the Russians know how to do it commercially. I must admit I only bought my Norvels because of the technology :).
Posted on: 6/14/2012 9:46 PM by Author "downunder" in the forum "Glow Engines"
http://www.rcuniverse.com/forum/fb.asp?m=11118768