Hobbsy

My Feedback: (102)

The aforementioned OS LA 25 on the LT 25, it's angled to the right because I originally flew it with an Enya .25 Diesel and the muffler wouldn't clear the fuse side with the engine straight up. LT 25's build fast and accurate and I use only Super Phatic glue, no epoxy or CA.

N1EDM

My Feedback: (2)

Hi guys,

I need help with another engine question. I purchased a OS FS-91 Surpass (not Surpass II, etc., it's an early one). It needed bearings but that seemed about all. I fired the engine up on 10% fuel (just cracked the jug last week) and it smoked like a banshee. She got 9400 RPM with a 14x6 prop (pretty respectable for a vintage 4-stroke, eh wot??) but still smoked badly. I was able to get a nice idle out of it, too. Plug is an OS Type F.

I realize that the LSN also tunes the midrange but this seemed to have little to no effect. The HSN is on the verge of being lean. The carb is clean, the valves are set to about 0.4mm, and the piston is clean, as are the valves.

I had originally suspected a stuck ring but the ring is clean, unstuck, and has plenty of expansion left in it.

Any thought? The engine seems almost perfect except for the great gobs of smoke (no exaggeration) coming from it. I haven't checked the timing, but would I get those good an RPM number if the engine was mis-timed?

Thanks,

Bob

Broken Wings

My Feedback: (20)

Sure, why wouldn't you want to modify an OS Engine.......the Fox stuff worked out so well......(Smiles) If only (you know who) was here to show you the way.......

Broken Wings

My Feedback: (20)

Have you found any advantage in running an engine on diesel prior to using it with glow fuel?

Hobbsy

My Feedback: (102)

John, not many engines will run on Diesel fuel without changing the head, a few will though. I have an OS LA .46 that I bolted a Davis Diesel head on to without breaking it in first on glow. Mr. Davis recommended breaking converted engines in on glow first. My Saito .80, (15.5 to 1 compression ratio) will fire up and run on Davis fuel with the coil removed from the plug. It will turn a Bolly 13.5x8 at 8,760 rpm and idle below 1.400 rpm.

Bob, it sounds like the .91 is in good shape and timed correctly. My guess is that the LS needle is too rich. I'd personally would screw it in until the engine hesitates when opening the throttle then back it out 1/8th to 1/4 turn, you should find the sweet spot close to that setting. Let us know how it goes, Thanks, Dave

1QwkSport2.5r

I've done a Picco and Novarossi engine too. They run damn hard compared to stock. Buggy/truck engines often gain double their horsepower output and 30-60% more torque by making modifications to the internals. Boring the crank and changing the inlet timing alone can have a dramatic effect on power - often increasing fuel efficiency enough to gain 20-30% more runtime per tank of fuel as well.

I don't care what brand of engine it is - if there is a purpose to change the powerband or change the overall behavior of the engine, then I will make changes to get the result I want. So far I haven't had an engine fail except one and that was due in large part to a defective engine from the get-go.

sarpet

Imade boost port cva engine and it rews 1000rpm more with apc 8x4 prop.
icopy it from cvr engine.

1QwkSport2.5r

The CVA didn't have a Boost port either? I thought the LA was the only series like that.

Broken Wings

My Feedback: (20)

I understand that, I was just wondering about a relatively cold break in. What is the reasoning for breaking in the engine on glow fuel first? Because it's a conversion?

Hobbsy

My Feedback: (102)

Mr. Davis says that the reason is to get the carb settings right and of course to limber up the moving parts although the Davis Diesel fuel being more "luby" I don't see how a break in on the Diesel fuel would hurt. I didn't break in my SuperTigrre .51 or my LA .46, they ran fine.

1QwkSport2.5r

Generally, diesels run cooler than glow engines do, so for the engines that take a long time to break in, it takes a lot longer to break the in as a diesel. In general, diesel fuel is about twice the cost of glow fuel, so I can see why Bob Davis recommends breaking in conversion engines on glow fuel first. I would surmise that ringless tapered bore engines wouldn't be a big deal to break in as a diesel conversion, but a ferrous engine would undoubtedly benefit from a glow fuel break-in due to the need for heat cycling the ferrous parts for the right fit.

When I broke in my .25FSR with a new piston and liner, I followed the process outlined by Adriansmodelengines.com to heat cycle over 8-10 runs. The engine ran beautifully as I'd expect it to (remember that gold standard? ), but even after an hour of heat cycling, it still wouldn't hold a needle setting without sagging. A few more runs should have it ready for diesel duty. I got a NIP Davis head for the .25 for $5 from my LHS. Quite the bargain considering the engine was a freebie and the piston/liner was "only" $40.

Linkan2

Hello
I have bought an OS 200fs.
There is much written about this engine here in Sweden.
About how to get the engine going a lot better.
It is so that the valve springs have different hardness.
Then replace the soft valve spring with exhaust gas.
For harder harder valve spring number 45560210
so now I'm waiting for my valve spring
Lars

Hobbsy

My Feedback: (102)

OSMG924745560220 Exhaust 18mm length

OSMG924645560210 Intake 20 mm length

Hobbsy

My Feedback: (102)

Two years or so ago I bought a new OS 56 Alpha, moved the vent to the back plate because it would nearly stall every couple of minutes during a flight. Now looky here.



FEATURES
Blow-by oil exits through the breather nipple on back plate for more
stable operation
Black rocker covers
40NA carburetor
Power Box designed muffler for quiet operation is fully positionable
for tight fitting applications
Two-year limited warranty through Hobby Services beginning at date of
purchase

It wasn't my imagination.

extra300crazy

Hobbsy,
Perhaps so, but i've been running the 72a, 81a, and the 110a for several years without such a problem. I can't believe it was just my luck. I believe that O.S. simply wanted to skip the machining process involved with the rebreathing design to save money and keep their price point and profit. They raised the price as well. I have 9 of the Alphas that have been trouble free.
Karl

Hobbsy

My Feedback: (102)

I'm genuinely glad your's work well, mine didn't, I'm thankful that the .95v and the .62v I just bought have front vents. But our "speriences" are different for most of us. Variety is good. Thanks

extra300crazy

Hobbsy,
My club has a few of the 95v's running and they seem like fantastic engines. I have to wonder why O.S. didn't see fit to incorporate that design in the rest of their 4 strokes, because their cost is more in line to normal pricing that people would be willing to pay. I just can't see the cost justification in their new line of series ll alphas.
Karl

Hobbsy

My Feedback: (102)

The V series are mfd. in China, that might explain the better price. Here's a shot of the .95v interior I took when it arrived. It is a smoothy. This was taken after a 50 minute run on Wildcat 10% full synthetic. The only fuel I use now.

Hobbsy

My Feedback: (102)

I Have been ciphering on and examining this OS 1.20 Surpass for a couple of months. I have effectively disabled the stock regulator by removing it's spring, so I haven't ruined it. By choking it I got fuel to carb easily through the IronBay regulator. I'll run it tomorrow, the prop is a Graupner SuperNylon 15x8. When the prop is moved either direction the fuel moves back and forth in the return line indicating that the gear pumps works well.. The recirc line is disconnected because it breathes so freely it negates the intake stroke, no kiddin, it needs to be restricted some way.

extra300crazy

Let us know how it runs. Did you attach the header to the exhaust port with teflon tape?
Karl

RACE 66

..
sarpet: Enlighten me about the boost port on the cvr with the transition to the cva. I have a couple of articles on modifying liners/cases for boost port additions. I to have a cva I would like to 'rev up' the little cva up some. Thanks

RACE66

Hobbsy

My Feedback: (102)

Yes sir, that is standard practice for me on four strokes, I've never had one come loose since doing that, no matter the brand. I pulled the head and the engine appears to never have been run. I'll go easy on it because of that and the fact that I am not sure how well the fuel system will pass fuel in it's new configuration.

extra300crazy

Hobbsy,
I'll give the teflon tip a try, thanks.
Karl

Hobbsy

My Feedback: (102)

I don't have any Teflon tape on the adapter because I never removed it.

blw

My Feedback: (3)

I've never had to use Teflon tape, but I know it works well. I always have a roll in my tool box when I fly.