buzzard bait

I think the bronze bushed crank gives a very different feel when turned over. My 20 is old style and felt sluggish when I'd try to flip it when it was new. I needed an electric starter for the first couple of starts. Then as I broke it in it began to feel freer-turning, and the compression also increased (very poor compression when new). Even at the end of a dozen runs, it felt slightly sluggish.

My 28 has not been run yet. It feels completely different..no sluggishness when I turn it over; it has a metal on metal feel with little resistance, though certainly not as smooth as even a plain-bearing OS. I suspect it has the bronze bushing.

I really liked the 20 on the test stand and I'm looking forward to breaking in the 28. Throttling was excellent, noise was quite low with the stock muffler, and you could use practically any prop size you wanted.

Jim

1QwkSport2.5r

I'd seen a post about a guy using a 12x6 on a .20 with good throttling from 1400rpm to 5800rpm and no overheating. Now that is a lugger! Crazy. My .28 has a tight pinch and a metal on metal feel but the bronze bushing has a superb fit. The .20 was in such bad shape internally I didn't turn it over much. Looking forward to running both though.

spaceworm

I never did it myself, but it is said that you can put a flexible extension on the end of the stock muffler and gain performance. I assume there is a length limit, but the original idea was to route the exhaust down and away from the airframe. Must be some kind of tuning effect.

buzzard bait

There was an old Model Builder article years ago that the info about the 12x6 prop came from. Stu Richmond had powered a Simplex old timer, 60 inch span, I think, with that combination.

I worked my way up to a 12x4, which the engine ran just fine. I don't know why you couldn't do the same or better with the 28, but I don't know anyone who's tried it.

Jim

1QwkSport2.5r

I'll put a 12x6 on one of these little buggers and see what happens. Haha.

Heres a few photos of my basketcase .20. It has a spot about 1/4 down from TDC that feels "notchy" as if the piston is catching on a port. But it isn't. If I put the exhaust on the opposite side of "normal" it doesn't catch at all. It feels good other than that one notchy spot - compression is good and piston seal is actually pretty good considering how badly corroded everything was. I'll try to run this engine back in after I get my new Jett broke in and ready to go.

1QwkSport2.5r

I ran my basketcase .20 Sportster today. I treated it to an abbreviated Sportster break-in of about 35-40min and half a quart of fuel. It ran well and idles nicely at 3,400rpm. I'm sure with a bigger prop it will idle lower. I used 5% nitro 25% castor fuel and 8x6 APC prop. After running nearly half a quart of fuel through it I peaked it out on the 8x6 and got 14,600rpm. Richened back to 12,500 and let it run the remaining fuel out. It hand started okay - with more time and getting broke in better I'm sure it will hand start better. So far it seems the previous owner didn't totally destroy it.

buzzard bait

That's too much. Find out what he did to it so the rest of us can do the same thing!

Mine did 7350 rpm on a Zinger 12x4, among other things. Never tried an 8x6.

Jim

earlwb

Well some people will take apart something just to see what it is like on the inside. Then they either can't or don't want to put it back together again. So maybe nothing was wrong the engine. With the K&B Sportster engines, sometimes the flyers at the field will bully the owner and he switches to some other engine instead. I wound up getting a number of engines from people who fell into that trap before. Where people would tell them the engine is no good, blah blah blah, and they go and buy something else that the others say is better. Of course with the Sportster engines, there are other arguably better engines, but who cares if the engine can do the job OK.

1QwkSport2.5r

The pictures below are a glimpse of what it looked like inside when I got it. I thought I'd taken more pictures, but I didnt. I posted these pictures in the GlowHead thread too. Corrosion on the head, cylinder, lower crankcase, and the crank and wristpin had a little rust and crud on it. The wristpin was seized in the piston. Took me a half hour to get the wristpin out. Steel parts got soaked in Evaporust and the aluminum got scrubbed with scotchbrite and Bar Keepers Friend kitchen cleanser. The carb was soaked in methanol and wife wheeled to remove the corrosion from the barrel and carb body. It turned over when I got it but it felt like bearings feel when they skid, but we know these don't have bearings. The inside of the engine was absolutely none dry as if it never had any oil in it ever.

earlwb

Humm, maybe the previous person was using RC car fuel. You know the stuff with 8% synthetic oil in it. It is OK for RC cars but not good for airplane engines.

1QwkSport2.5r

That could be the case, but even low oil fuel would have left some residue behind. It was bone dry, and even appeared to have saw dust in the crankcase.

buzzard bait

It does look pretty nasty in there. Funny it doesn't seem to matter.

Whatever happened, those numbers for an 8x6 are extremely good. You're getting about 1000 rpm better than RC Report got on an 8x6 Zinger with 10% nitro and I think a synth/castor mix.

When I was breaking mine in I found it was extremely stiff at first and very gradually got looser, yet even after many runs it still felt a little bit stiff. So maybe they keep getting a little better over a long period of running, and yours has just had plenty of time to completely break in.

It's amazing this thing will run well on 8 inch to 12 inch props. I don't think a lot of engines can do that.

1QwkSport2.5r

Based on what the piston and exhaust port looked like, I doubt this engine had more than a couple short runs on it. There's no pinch but the piston seal is quite good. After I ran it, there is no leak down at all. There was slight leak down before I ran it though. My .28 that I got with the .20 is new and unrun and has a noticeable pinch. That engine will take a long time to break in. Go figure too - my rpm figure is with the muffler installed with the baffle in place.

The pair of .65 Sportsters I have came from the Army RCMAT target planes and neither of those had any pinch at all when new either and the piston seal and compression is stellar in those.

This line of engines really needs to be handled like a 4-cycle. Put a tree limb on one and go at it and the engine won't bat an eye (if it had one).

dennis

My Feedback: (90)

That's an early sportster 20. It has the silicon rubber gasket. K&B eliminated them fairly fast and like the 28 it is a precision machined head and case fit like many of the older Enya engines.
As your probably aware by now they do take an inordinate time to really run in and that was a real problem to the instant gratification expected with most of the R/C crowd. Higher then normal oil expectations also didn't sit well in the era of 14 % oil. They really do better with larger props and you should treat them like a 4 stroke engine. They are moderate rpm engines that really do best in the 8/9 range just like a c/L stunt engine from years ago. Treated correctly they are almost indestructible.

wnewbury

I like Sportsters. I only have eleven of them. A guy gave me a 20 Sportster. He was disappointed with its power. The engine is so large for a 20, that he thought it was a 40. Says his trainer flys better now with a 40.

1QwkSport2.5r

I figured it was an early one due to the head sealing setup and it's crankshaft is not bronze bushed. It's been dormant for a long time. It will be cared for much better now. 25% oil worked well. I run my .65s around 9.5-10k on 12x6-13x6 props. I'll probably use a 9x4 or so on the .20/.28.

rcmichael

My Feedback: (21)

I have a NIB sportster .28 You can pm me if interested. Thanks Mike

dennis

My Feedback: (90)

I figured it was an early one due to the head sealing setup and it's crankshaft is not bronze bushed. It's been dormant for a long time. It will be cared for much better now. 25% oil worked well. I run my .65s around 9.5-10k on 12x6-13x6 props. I'll probably use a 9x4 or so on the .20/.28

actually that might be good for a break in prop on the 20 but you will be amazed at how well they do on a 10/5 when broken in. I routinely run my 28 on an 11/4.5. The engines do well when loaded, trying for high rpm is possible but it really doesn't get you more power if you go over the torque limit of the engine.
The thing to remember is that there is really no hard fast rule on props for any model. It is discouraging to watch a person use only one prop on his model and never try to optimize the performance of the model. But in this case the Sportster is not an engine that you will use to hover or do waterfalls. It is more at home pulling stumps.

copelab

I have a .65 sportster which runs very hot. I use Byron 15% nitro +16% synthetic/castor fuel. I usually add 1oz. or so of castor to the gallon jug.I have used a 12/6 and a 11/9 prop with no change.Last week i blew two O.S. #8 plugs. I can have five flights in a row with no problems then it starts going dead stick on me. I must say this engine starts like a charm and idles pretty well. Is less nitro and more oil the secret to lowering the operating temperature. Can I use Klotz Benol if I cannot find Sig castor?
Bob

1QwkSport2.5r

These engines do not like much nitro at all, period. I experienced the same things as you minus the blown plugs using 15% fuel. I noticed a HUGE improvement in throttling and handling when I switched to 5% nitro 20% all castor fuel and a hot glow plug (I used a McCoy MC59). If your fuel is at least 20% oil and a 50/50 blend of castor/synthetic, you should be okay. Really though, you should use more castor than that. As for prop loads - these engines are compressed a bit high and timed really low which means it's a stump puller. Load it down with a heavier prop - 12x8, 12x9, 13x5, 13x6 are good props. They'll turn a 14x5 or 14x6 and be fine too. My .65 turns a 13x6 APC at right around 9,500-10k on 5% nitro 20% castor fuel and mc59 plug I mentioned. Single backflip starts and 1,200rpm idle speeds with instant throttle response. This is of course after you put 2-3 gallons through it breaking it in.

Keep your ground rpm limited to 9,000-10,000rpm (several hundred rpm rich of peak) and it should run good. They do not like to spin fast.

If cowled, baffle the cowl so the engine gets adequate cooling. Klotz benol is okay, but regular castor is better. SIG raised their castor price to nearly $40USD/gal. There are several outlets that sell castor for $25/gal or less. S&W fuels (SPLube.com) is around $25/gal. There's another site that sells castor for about $17/gal, but I cannot vouch for it being virgin first pressing (degummed) castor. Some guys have been using it without issue though. http://www.bulkapothecary.com/raw-in...ls/castor-oil/

Hope this helps you.

copelab

Thanks for your reply.I gathered from reading this thread that low nitro and an at least 20% castor is the key.I can only use a 12" prop due to ground clearance.I may have a problem finding 5% nitro around here but 10% should be no problem.
Bob

spaceworm

Just add methanol to reduce the nitro to 5%. Make sure you add more castor oil to bring the oil up to at least 20% after adding the methanol. My Merco .61; ASP .91 and 1.08; K&B .40, .60 and .65; and OS .80H all like 5%. All would likely run ok on FAI 0% nitro. Good luck.

1QwkSport2.5r

I would be inclined to use a 3-blade 12" diameter prop then. If you can find FAI fuel, mix equal parts 10% nitro fuel and FAI fuel to get 5% nitro. You can try 10% if that's all you can find, but you may need to set the needle a bit fatter.

AmishWarlord

My Feedback: (5)

R.i.p RC Airboat world?

1QwkSport2.5r

Yep. RC Airboat World forums went down for good. The Admin didn't have the time or money to keep her going. Sad, we airboaters lost a LOT of great build info/logs.

Good news is I have a .20 and .28 sportsters in my drawer. The .20 was run horribly lean and was rusted up pretty good. Cleaned up well and runs good though, the .28 is unrun and possibly destined for a Mojo .25.