Hi the engine sounds very good, I fitted it to 70" edge 540 today, I think this plane is to small for it but I used a 90 ic, 120 ic ,26cc petrol (wich was very heavy and slugish) and it can cope with the weight, today I just mounted the engine and fitted the wing just to check how violent the engine will be to the frame, (petrol engines shakes a bit more than ic) started it and it was very smooth, it was vibrating less than with the crrc pro 26cc, holded the plane up and it was pulling a lot, the frame is an old cmpro on the heavy side, im using it just as a test bed.
One thing about this conversions is the fact of petrol engines uses a neddle bearing on the conrod I think is not just for the difference on lubrication, just based on my previous attempts (I burned a couple of engines trying), at one point I was trying with a TTpro 120R with the ignition on ,walbro carb and the timming right it was idling ok and pulling a lot but the strokes were vilolent and despite having removed 3 mm from the compresison chamber, I know these TT 120r they are tunned to the limit they go well over 10k while ST are around 8K, less revs more torque, thath's wy Im trying with this one now.
Anyway, when I was trying the TT120 and the strokes where very sharp like a machine gun, I switched to glow fuel, swaping the carb for the stock one but I left the ignition on, aaaand it was doing the same,running nice but with violent strokes, so put the glow plug back and it was very smooth!, so I think because the glow fuel ignites more progresive, ex, the glow plug is glowing and as the piston goes up compressing the mixture it starting burning earlier and progresive, using the spark ignition piston goes up and spark fires the mixture all at once, that's wy (I think ,is only my theory
) they shakes more, I think they must have a difference on the porting timming, and I think that's wy the normal brass bearing will not survive much on petrol, Im used up to 20% oil on the TT120R and it was ok on the bench like te ST but in the air didn't last 5 minutes. I know if you are flying a scale model purring around the skyes it will be ok, but abusing them on 3d machines or acrobatic planes don't know I want to hear more about this of people flying them for long periods of time without problems or burned conrods!.
Just browsing in to a bearings website I found a needle bearing which mesures 8mm in 12mm out and 10mm long, almost the same size of the ST 3250 conrod big end, Im going to order a couple and a new conrod to modify and see if will be ok.
Wy all this hassle?? well, one some of us enjoy getting our hands greasy, Im a mechanic and had enough of doing cars during the week! and doing a model engine overhaul is much easy!, but the thing is Im flying a 70" goldwings 3D sukhoi su26 im love this plane to bits, at the moment Im using a CRRCpro 26i 26cc, and the power and weight is more than adecuated, but Im not happy with the engine quality it cost me under 130 euros new with ignition exhaust etc, is very good looking comes with a walbro carb and cdi autoadvance unit , but after 4 hs running it started nocking a bit, so took it apart and for start, 2 of the 4 cranckase bolts were lose,allowing the mixture to get lean when pulling, because the threads were stripped from factory, becasue they used big washers which where dragged down the bolt location betwen the cranck ribs, putting more pressure on the threads.
Also found on the cranck shaft under the prop hub, by the spares manual should have a oil seal a cricle clip and then a bearing, and other bearing on the back, this one has instead the oil seal an other sealed bearing then the clip and then other sealed bearing (both sides sealed), they confused one oil seal with the bearing (same diameter), but being these bearings in no contact with fresh oil and being spaced for the circle clip on the outer rim when tighening the prop hub, the ball bearings where extra loaded on they tracks, so having just few hours running they where allready rough, so order a new cranck shaft assy,bearings and oil seal, spares where cheap, re-tapped the threads and got rid of the washers, used just locktite on the threads, it runs very nice and smooth again, but saddly I discovered on these engines crrc pro use very cheap neddle bearings in fact they are roller bearings, they are very spaced betwen them only 9 rollers where could fit 15, so the pressure of the piston going down is just on this 9 rollers and the pressure is not eaven on the journal, so I think this engine will not last much! if goes again will replace the cranckshaft again its only 10 euros. and sell the engine. it put mi mind on an evolution 26gt, they are light and they comes with proper neddle bearing on the rod yes they are twice the price of crrc pro, but it will last few years!!.
Please keep me informed on any progress with conversions.
have a look to the just engines website [link]http://www.justengines.unseen.org/acatalog/Customer_Feedback__and_Our_Experience.html[/link]
there are few people doing conversion here
Regards!
Luis