Doug Ireland Posted August 16, 2009 Share Posted August 16, 2009 After looking at the new CDI units and "glowplug" sized spark plugs on the Just Engines site I was wondering if anyone has done this conversion? I'm particularly interested to know what happens to the needle valve and spray-bar in the carby? Fitting the magnets in the prop driver looks pretty straight forward though. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 16, 2009 Share Posted August 16, 2009 hello doug-a few year's ago i bought a merco 61-that had a petrol conversion on it-it used the normal 2st carb ok--it was a clever bit of kit...... ken anderson...... Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted August 16, 2009 Author Share Posted August 16, 2009 Thanks for the reply Ken. What oil mixture did you use and how many turns open for the needle? On my MVVS 45 I use a 40:1 mixture and to date I've not had to adjust the Walbro (not the same I know) carb on it. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 16, 2009 Share Posted August 16, 2009 hello doug - it was that long ago(you were prob running around in short pant's) can't remember...someone reading your post will jump in with a reply reguarding the merco........there's still some knocking around........... ken anderson..........Edited By ken anderson. on 16/08/2009 23:10:03 Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted August 17, 2009 Share Posted August 17, 2009 Merco !!! I was weaned on the --------- things ! Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted August 17, 2009 Share Posted August 17, 2009 PS Mine were diesels -by the way - you're off topic Quote Link to comment Share on other sites More sharing options...
kiwi g Posted August 17, 2009 Share Posted August 17, 2009 Doug any chance of a link to the conversion you suggested. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted August 17, 2009 Author Share Posted August 17, 2009 Not so much as a link kiwi but just an advert in "Just Engines" for the parts. They supply the CDI unit and a spark plug with the same thread as a glow plug. There are a couple of pictures with the conversion done but it doesn't say what to do with the original carburetor. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted August 18, 2009 Share Posted August 18, 2009 Details are here but I have to agree with Doug...it all looks a bit half baked (& I'm a great fan of JE!!!) If they are selling this as a glow conversion I would have expected chapter & verse on how & what to do......my immediate questions would be oil ratio & carb settings.... Most petrol engines have needle roller bearings & these are happy on a very low oil (2-3%) but most glow motors have plain big & little ends & these need a lot more oil (15-20%). All that JE say is that they ran it with 15-1 (approx 7%) oil & it worked so now they are going to try 25-1 (4%) & see how that goes...... H'mmm a bit basic.....I'd want to see a lot more long term testing to ascertain the right oil ratio....yeah I'm sure it will run on such a low percentage but for how long?? No good saving on fuel if you have to replace the motor!!!!!! Also petrol has a much higher calorific value than methanol so we need less of it to get the same sized bang...(around 14-1 air/fuel for petrol as against 4-1 for methanol I think it is) hence we need to run a "leaner" mixture.....is the standard carb able to supply this or will the needle valve be practically fully closed & horribly sensitive with it? Another thought is compression ratio....methanol will stand being squeezed a lot more than petrol so do we need to add a few head shims?? Still interesting though.......methinks I'll watch & wait however.......maybe the WOO will get his hands on a unit & test it for us!!! Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted August 18, 2009 Author Share Posted August 18, 2009 Hi Steve, The addition of shims was mentioned but again it appears to be a bit suck-it-and-see. There is a video of a conversion done to an MDS engine (on the JE site) but I can't get it to work. Quote Link to comment Share on other sites More sharing options...
Ultymate Posted August 18, 2009 Share Posted August 18, 2009 Doug as far as the needle setting goes you will have to screw it in considerably to run petrol. If you convert the other way ie modify a petrol type carb to run methanol for racing purposes then the jets in the carb have to be drilled out to three times their original size approx Edited By Ultymate on 18/08/2009 12:26:26 Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted August 18, 2009 Author Share Posted August 18, 2009 I think I may just give up on this idea. Knowing my luck I'd get it all wrong and blow up a perfectly good glow engine and burn down my house in the process. It was a good thought though while it lasted! Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 25, 2009 Share Posted August 25, 2009 I have fitted one of these cdi units to a brand new TT91 fourstroke and my findings so far are as follows; The unit is a superb piece of kit but i did have to dismantle the engine to drill the front bearing housing to tap to hold the hall sensor,there is a fair amount of carb spit at idle which i feel could be a fire hazard if a backfire were to occure in a wooden cowl.The idle speed on spark is incredible and reliable as is the transition to full throttle.Using petrol and a 25 to 1 oil ratio i feel is far to low a oil content on a bushed conrod and i stopped running when i felt there was a possibility of damage to this when the engine was hot.What am i going to do now?Well i am going to run with the spark unit using glow fuel.This has been done a few times over the years when converting glow engines and one guy on utube is doing this with all his 4stroke motors calls himself eulboyington,there is a short vid of him running a 120 surpass sp.I shall be buying another spark unit from just engines but running on glowfuel.(all those old engines from the past,pre the invention of the glow plug,ran spark,did they run petrol or methanol fuels?Did they have needle bearings or were they just plain bushed?There is a lack of feedback on this spark convertion.) Quote Link to comment Share on other sites More sharing options...
Hugh Coleman Posted August 25, 2009 Share Posted August 25, 2009 http://www.dlenginesaustralia.com/dlshop/index.php?_a=viewProd&productId=125 I found this. I have a few questions. Is a 52 Surpass 4 stroke too small an engine to try this on? How is the power output altered? Will running on Petroil give more or less power? BTW, there was an article concerning just this area in the latest "Airborn" magazine here in Australia. It was stated that petrol has inherant lubricating qualities whereas methanol has none. So there is a lot less oil required in the mix when running petrol. Also, compression will need to be reduced somehow as at higher compression petrol will preignite and probably destroy the engine Cheers, Hugh Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 25, 2009 Share Posted August 25, 2009 helo alan-i'm not being cheeky-but if your going to run on glo why bother with the fiddle/expense of the spark unit's........ ken anderson. Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 25, 2009 Share Posted August 25, 2009 Hi Ken,what you state is a very valid point,at the start of this i did wish to run on petroil mix for the reduced fuel costs and the ease of being able to run the same fuel as my Zen 260's.I just felt that the petroil was causing alot of wear to the conrod bushes very quickly but wished to retain the spark unit for its other good running characteristics.Maybe all that is required is a different oil ratio,maybe my choice of engine to convert was the wrong one.This is just what i have found out myself to date,like i said there is a big lack of information about these conversions so we have to just experiment at our own expense?It is nice to be able to just swing the prop and have it start and tick over so slowly without the need for hanging a glowlead on or carting the model back to the flight box. Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 25, 2009 Share Posted August 25, 2009 Sorry guys am trying to add the utube link to this guy running his os 120 on spark and glow fuel but these computory things dont seem to work right with me on the end.perhaps someone else could add the link to eulboyington .If not i shall have my son do it later Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 25, 2009 Share Posted August 25, 2009 alan-latest RCME-has an article/review of the saito petrol engine(which in it's normal form is a 4st)..few tip's on the big end /oil reqd ect........... ken anderson..........(old ashby has his pic in again and again in the Mag).... and timbo is in there again............... Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted August 25, 2009 Share Posted August 25, 2009 Posted by Alan Blackett on 25/08/2009 11:05:35:Sorry guys am trying to add the utube link to this guy running his os 120 on spark and glow fuel but these computory things dont seem to work right with me on the end.perhaps someone else could add the link to eulboyington .If not i shall have my son do it later I presume this is what you mean Alan? Inserting U Tube videos is easy, if people just bother to read and follow the tutorials we have done.Edited By Timbo - Moderator on 25/08/2009 17:49:08 Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 26, 2009 Share Posted August 26, 2009 Reading peoples responses makes me think that maybe the running on petroil requires some more experimentation.Ken the Saito engine also comes with a walbro type carb does it not,this would help with the spit experienced at idle being a more sophisticated carb.I shall read the Saito review with intererest.Perhaps RCME could do a review of the CDI unit from Just engines .AlanEdited By Alan Blackett on 26/08/2009 01:23:22 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted August 26, 2009 Share Posted August 26, 2009 Alan I agree...I think a review in the mag would be most useful (David are you listening!!!!!!???????) It would make a nice change to see an IC biased review rather than lots of electric stuff (tongue firmly in cheek!!!)!!! I've just read the review of the Saito SG 20 petrol. That motor has an aluminium conrod with no bearing & no phosphor bronze bush even & Brian ran it on 20-1 which is 5% oil....not a lot!!! The carb seems to be a "standard" glow type carb but with the addition of a pump to bring the fuel up to the carb. Alan, I wonder about the fire hazard too!! Is petrol more likely to set on fire than methanol....?? I don't know but methanol is pretty flammable...thats why we use it. Maybe a good idea to coat the engine bay with that BVM "Heat Shield" paint the Jet boys use. To reduce the spitting, it might be worth trying a short (1" or so) length of tube over the mouth of the carb....a sort of "velocity stack".....what you need to do is keep the blow back around the carb mouth so it can be sucked back in on the next induction stroke.... With regards to oil content of the fuel then if you think about it despite the 15-18% oil we normally run in our fuel how much oil actually gets to the big end? Just a spitful that squeezes past the piston..... so would running more oil means more gets to the conrod or indeed does running less oil means that less oil gets to the rod....who knows!! I think the fact that petrol has some lubricity is a bit of a red herring as far as the crank, rod & camshft goes......I for one don't want any petrol sloshing around here thank you very much....petrol needs to stay in the combustion chamber ABOVE the piston!!!! (Also remember we will be using much less petrol than we would methanol....) In a two stroke however the fresh petroil mix comes in via the crankcase so the crankshaft, & conrod are positively bathed in petrol!!! Certainly our glow motors seem to run happily so maybe we are worrying unnecessarily!!! I would still rather see full test data from the retailer of these units however!!! Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 26, 2009 Share Posted August 26, 2009 Well i have today run the TT91fs on glowfuel with the spark unit and with a glow plug.Interestingly i found that combustion seemed to be more complete with a glowplug than with the spark unit,alot more smoke(unburned fuel)was produced with the spark unit.Starting was also easier with a glowplug than with the spark unit.This is hand starting only and NOT changing any needle settings on the carb while swapping ignition systems.Both ways the engine felt that it was running more strongly with glow fuel as opposed to running petroil previously.There was also approx 200rpm increase in top speed with the spark unit as opposed to the glow plug.Thinks maybe the extra rpm and the carb spit while running on the petroil could be caused by the variable timing of the cdi unit?While running on spark or glow plug the engine i think ran better than on the petroil mix.The engine also feels alot nicer to turn over and compression is up to what it was before.From the limited feedback on the just engines site it would appear that all the modified engines have been previously run in or run on glowfuel.Should i have run this new engine in on conventional glow before trying to convert?Experiments to continue but i shall have to decide soon as this engine is destined for the model on the building board now. Quote Link to comment Share on other sites More sharing options...
Solly Posted August 26, 2009 Share Posted August 26, 2009 Hi Doug. Regarding the Merco on petrol. I still run one of these engines in a vintage Chester Lanzo Record Breaker using 2 per cent oil mix. It has had many hours of running and is still in A1 condition with excellent compression. The only drawback is the sensitivity of the needle valve setting to the plane's attitude. - ie. climbing will lean the mixture and nose down will richen it. To overcome this I mounted the fuel tank at the side of the engine instead of behind, this has solved the problem. Cheers. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted August 26, 2009 Share Posted August 26, 2009 Interesting stuff Alan, thank you. It would be interesting to see how the rpm figures vary as this is the best indicator of the power produced.....a comparison of:- Glow with methanol fuel Spark with methanol fuel Spark with petroil would be great.....certainly no surprise to see that the spark unit gives more RPM than the glow....a glow plug is a pretty hit 'n' miss affair compared to a spark after all & the engine will definitely miss a few beats when run on a glowplug. No idea why it should smoke more on spark ignition though. Certainly the carb spit is NOT caused by the CDI unit...this is a fuction of the valve timing....this has to cope with rpm figures betwen approx 2000 & 11000 rpm hence its always a bit of a compromise....did it not spit with glowfuel? Did you try a length of tube on the carb intake as suggested earlier...? How did you find the needle valve setting? did you have to screw it right in? Was it very sensitive? If you read WOOs test on the SG20 he makes some interesting points about the relationship between cylinder head temp & needlevalve settings.....Edited By Steve Hargreaves on 26/08/2009 17:19:47 Quote Link to comment Share on other sites More sharing options...
Alan Blackett Posted August 26, 2009 Share Posted August 26, 2009 Hi Steve i think as you more or less state i need to do my experimenting a little more scientifically i shall see what i can come up with later this week.On my Zen 260pum power boats we remove the intake stack which helps to get the rpms up a bit,but i do need to try this on the TT91.Regards Alan Quote Link to comment Share on other sites More sharing options...
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