OS 21XM Outboard

[engineman351]

Recently switched from K&B power to an OS 21XM Outboard for 20 Sport Tunnel. I purchased an engine off of this forum and bolted on a new, prepped, VS-1. The engine certainly wasn't new, but it has a very noticable 'pinch' (maybe too much pinch). It starts, idles, and in general seems to be in good shape. It is just S-L-O-W!! I did feel the pinch was a bit too much (it squeaks pushing the piston over the top by hand)so I took the engine apart to see what was up. There doesn't seem to be any cylinder or piston damage, but the engine definitely has had some flow work done on the sleeve (outside of the sleeve opened up/tapered on the transfers and boost ports) and the exhaust port has been raised. The head shim has been removed. I have put about a quart and a half of fuel through it so far (45%, and it still squeaks through the pinch. The plug looks good...dull and coils are not distorted.

My questions are:

How much exhaust timing can the OS stand without a tuned pipe?

I have never messed with an ABN combo. Should I try polishing away some of the 'pinch'?

FYI..I have tried the following props (all S&B)in several engine height positions (from prop CL even with the bottom of the sponsons to about 1/4 in above): Grim 40X53;Grim 40X52/3;X440;X437/3;X438. While the smaller ones cavitate a little until the hull is planing, they all run about the same on the top end. I'd guess no more than 30mph. The X437 seems to be the fastest. I have yet to try the stock nylon prop 42X48 to see if than might unload it a bit.

Any comments welcome! RC

 

[Brian Schymik]

So this hull has great directions. I know it sounds simple, but setup the depth, angle of motor and CG just like the directions say for the OS.

Then pick one of grims props... the smaller one first. Don't expect the needle setting to be what the K&B used... get it running then lean it down until it is fast.

If it doesn't do that, u might have some loss of power from the work done on the motor. Raising the exhaust timing cuts torque, but u should still b able to run the smaller prop.

Do not polish the sleeve. A quart and a half is not outrageous for a break in. The motor will still b tight and that is fine.

lean her down until u blow a plug... then back off the next run and u might b there.

Brian

Recently switched from K&B power to an OS 21XM Outboard for 20 Sport Tunnel. I purchased an engine off of this forum and bolted on a new, prepped, VS-1. The engine certainly wasn't new, but it has a very noticable 'pinch' (maybe too much pinch). It starts, idles, and in general seems to be in good shape. It is just S-L-O-W!! I did feel the pinch was a bit too much (it squeaks pushing the piston over the top by hand)so I took the engine apart to see what was up. There doesn't seem to be any cylinder or piston damage, but the engine definitely has had some flow work done on the sleeve (outside of the sleeve opened up/tapered on the transfers and boost ports) and the exhaust port has been raised. The head shim has been removed. I have put about a quart and a half of fuel through it so far (45%, and it still squeaks through the pinch. The plug looks good...dull and coils are not distorted.

My questions are:

How much exhaust timing can the OS stand without a tuned pipe?

I have never messed with an ABN combo. Should I try polishing away some of the 'pinch'?

FYI..I have tried the following props (all S&B)in several engine height positions (from prop CL even with the bottom of the sponsons to about 1/4 in above): Grim 40X53;Grim 40X52/3;X440;X437/3;X438. While the smaller ones cavitate a little until the hull is planing, they all run about the same on the top end. I'd guess no more than 30mph. The X437 seems to be the fastest. I have yet to try the stock nylon prop 42X48 to see if than might unload it a bit.

Any comments welcome! RC

 

[topfuel443]

The OS works great up to 180 on the exhaust with no pipe, the rest of the stuff sounds good. Who did the engine work?

By what you are saying, you are too deep. start with the bottom of the bullet casing (top of the skeg) 3/6 of an inch above the sponsons. You can go up to a 1/4". This is much higher than where you measured with the prop shaft centerline.

Dont touch the nickel in the liner. as long as the pinch seems to have a good seal all the way around the cylinder, its good.

~James

 

[Propwash]

For the time I ran a tunnel with an os outboard , the best prop I found was a prather 215 stainless , this was in stock form , and when I put a pipe on it , it realy sang. Never had a chance to try a mod 440 , but a stock 440 was okay , but always went back to the 215. just my 2 cents.

 

[engineman351]

Thanks to everyone for the replies so far. I do not know who did the mod's, but the flow work looks pretty good. After I make sure I'm back to the VS-1 set-up spec's for eng height, trim, and CG, I'll keep putting some fuel thru it and will try leaning it out more. If the rpm's do not pick up, I'll degree the exhaust so I know what it is for sure. I'll add progress posts. Thanks again , RC

 

[Wally Marsh]

I agree with what has been said, just be a bit conservative on leaning the needle too much. The OS 21-XM is NOT your conventional chrome plated sleeve but is nickel plated, less durable, and too much lean trying to make it "sing" is headed for disaster. The motor in stock form can do very well, you just need to concentrate on the obvious, good fuel (60-70%, 15-18% oil) hot plugs (like K&B 1L), set-up, and props. Also, outboards tend to run too cool and generally need to work on some water restriction to get the motors to run hot enough. Try to hook up with a club and other racers with outboards and learn from them. Also, as with all boat classes, test, test, test!

Wallster

 

[RickGlover]

Just got a new vs 1 and an OS. Set it up to grims specs. The 40\52 three blade prop. The odo88 glow plug, the od 9 didn't do much but it lit up with the odo88. Fastest i've ever been with a stock boat. Sounds to me like the motor is to low. Should be bottom of the bullet even with the set up board.2.5 degree neg trim, 8 5\8 cg location. 5deg posin the motor mount.

Thanks Grim great tunnel hull, easy to put together, and great IW specs.