I havent been active in this thread for a long time, mainly because of my frustration with this engine, as well as the fact that I live in a place that is so hot half of the year, that the radials simply dont like running in high temp/high humidity environments..
So lots of discussion here regarding cracked cylinders, piston landing scuffing and out-of-alignment cranks and con-rods......all very interesting discussions and different points of view. Especially the timing discussion, and since I have recently experienced the STUPIDITY of the Saito pin/collet/crank design in the FG40, which mimics this engine; I am inclined to follow with some of my own experience... The FG40 was new, out the box, and farted and backfired at the start of the break in process and was REALLY difficult to start...after much moaning and attempts to sell it, I tried on the suggestion of a forum, to check the timing. With a timing wheel, I determined the firing point was at 10Deg AFTER TDC...! Yeah, thats not gonna work. Pulled the hub to find the pin had sheered off, and the hub was misaligned..put it back, with new parts and she runs well now, althoug could still be a bit off at 30Deg BTDC. Will mess around with that....Anyone had this problem here?
With regards to the cracked cyl, I STILL think (and many will disagree) that the Keleo lateral pressure on the cylinders, is my PRIME culprit for that.....I cannot prove it, and some failures hav happened on the stock pipes too....but Ibelieve it is putting strain on an already fragile system....just my view.
What I really wanted to know from you guys with engines that run well,and there are many of you here, is regarding how you tune the top end. We have installed the engine in a BH Sea Fury, and due mainly to ground clearance issues, will need a 3 or 4 bladed prop. THe most recent attempt was with a 20x10 3-blader which puts it in the performance enevelope of a 22x10 2-blader. It flies OK, but never really 'revs out' like I have seen in videos of others flying similar setups. When tuning on the ground for the high end, we go lean until it starts sagging, then go richer until it starts sagging again, and then get to about mid-way between those points. The manual states that to help the engine 'live longer' that it should be on the rich side on the high end needle. Where are you guys settling? When at the point that I mentioned, between rich and lean position, the high needle is open about 1 1/4, so I am thinking to open t 1 1/2 or maybe slightly richer.
In the test flights we have done, the engine starts sagging after about 5 mins of flight, which leads me to think it is leaning out...temps go up to around 170Deg max, but usually sit around 160. This is in an open cowl arrangement. Is it getting to lean?
Something else to consider, I went with a Morris Mini Motors Walbro conversion, and in doing so, destroyed the phenolic tube/insulator between backplate and carb, I had to get a friend to machine one from bakelite to replace the original, as Saito only sell them with the carb kit..... not paying US$70 for a new tube.... it seems fine, but I am wondering if it is getting hot, and the expanding aluminium case is letting air pass.... the machinist admits that he is not as good as a pro turner, so it may be out a little on the dimensions...Would this affect things?
Lastly, have you seen the backplate mod that Morris Mini has done? It involves using negative pessure in the crankcase, and circulating air through the block..... could be a good idea ultimately...
Regards, Andy