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Old Graupner boat with OS .21 SE-M engine. Questions...

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Old Graupner boat with OS .21 SE-M engine. Questions...

Old 02-16-2016, 04:54 PM
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1QwkSport2.5r
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Default Old Graupner boat with OS .21 SE-M engine. Questions...

I got this boat from a friend, and I'm gonna try to get it running. The engine is locked up solid from old dried castor oil. I have yet to remove the engine and clean it up yet. My main questions are; is this engine (circa 1985) worth a damn? Any idea what a good length for a tuned pipe would be? It was also suggested to replace the drive unit/rudder assembly with a standalone rudder and run the prop directly off the drive cable. One of the yokes on the prop shaft is broken, so I need to obtain parts anyway.. Might as well do it right the first time. The hull is in decent shape - some small cracks above the waterline that's easy to repair. The inside of the hull/engine compartment is pretty castored up, but the wood is in good shape. I'm gonna try to refurb it some and get it running if it's worth doing so. Pics attached. Any help or ideas welcomed.
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Old 02-18-2016, 08:09 PM
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I pulled the engine out of the boat and tore it down for an overnight soak in the antifreeze crockpot. It is so slimed up its not even funny. It seems the piston/liner fit is still reasonable, so I'll order a set of bearings while I'm at it.
Old 02-21-2016, 06:21 AM
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I should have taken a picture of the "before" of this horribly abused engine, but this is what it looks like now. Everything is clean and smooth. I'm gonna test run it with an airplane prop and an old fuel tank siphoning water through the head. I've not found much info on the engine of what fuel they are setup to use, so I'll test run it on some 20/20 fuel I have here.
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Old 02-26-2016, 08:49 AM
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I was able to test run the engine from this old Graupner boat I have. I used some 15/22 aircraft fuel in it with a 7x4 Scimitar aircraft prop and a gravity fed cooling water tank. I went with a heavier load prop as its what I had on-hand. The engine runs rather good and thankfully the nickel plating isn't peeling in the cylinder yet. http://youtu.be/bKsKRhR59VA
Old 05-20-2016, 04:29 PM
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I'm getting ready to tackle getting this boat running and repaired. I found some new u-joints for the prop shaft and in looking closer at the boat, I found the stuffing tube is loose in the channel. And unfortunately the inside of the boat is horribly oily and nasty. So my question is... If I can get all of the oil slime removed so adhesive will stick, what is the best way to affix the stuffing tube back to the hull so it's rigid and won't move/leak? It looks like this boat came as a kit and it appear the stuffing tube was originally epoxied in. I don't know how well this would work since there are no brackets or anything that holds the stuffing tube in one spot other than the glue/epoxy. Is this normal? The boat can easily be made ready to run in a matter of a couple hours minus glue curing.
Old 05-21-2016, 04:08 AM
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I started pulling stuff out to clean the slimy oil mess up inside the hull, cleaned the fuel tanks out and installed new tubing, and examined the whole prop shaft/stuffing tube scenario a little closer. It appears the framework of the boat was coated in epoxy, but the stuffing tube and exhaust tube was glued in with what appears to be Shoe Goo or something similar. I cleaned the globs of "goo" off and ran a rag soaked with acetone and through the whole channel where the tube sits, then followed with a rag soaked in methanol to [hopefully] remove the oily slime coating. I have my doubts whether the glue will actually stick, but I'll cross my fingers. I figured one of the "Goo" glues would be fitting for the transom where the tube comes through the transom, but would I be best off to use the same for adhering the tube to the bulkheads too?
Old 05-21-2016, 05:12 AM
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Some more pictures.
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Old 05-22-2016, 03:05 PM
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Nothing huh.... Interesting. I'll have to ask elsewhere..
Old 05-30-2016, 06:33 PM
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I just found this thread and I'll throw a couple of things at you:
1) That engine is an aircraft engine with a water cooled head. You will probably not get more than 15-20K RPM from it. This is not a bad thing, just won't be a speed demon
2) The stuffing tube was probably held in with silicone caulking compound. This is used to seal the exit points and absorb vibration to prevent damage to the hull. This is a common practice with boat builders
3) Epoxy coating the wood is, again, common. Wood acts like a sponge when it comes to oil and, since an engine crank and exhaust are not tightly sealed to prevent leaks, you're actually lucky it's there.
4) That original engine mount is garbage. If the engine rails are spaced at 5", I'd look for for an actual engine mount set to fit your engine and install the engine properly
Old 05-30-2016, 07:20 PM
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Originally Posted by Hydro Junkie View Post
I just found this thread and I'll throw a couple of things at you:
1) That engine is an aircraft engine with a water cooled head. You will probably not get more than 15-20K RPM from it. This is not a bad thing, just won't be a speed demon
2) The stuffing tube was probably held in with silicone caulking compound. This is used to seal the exit points and absorb vibration to prevent damage to the hull. This is a common practice with boat builders
3) Epoxy coating the wood is, again, common. Wood acts like a sponge when it comes to oil and, since an engine crank and exhaust are not tightly sealed to prevent leaks, you're actually lucky it's there.
4) That original engine mount is garbage. If the engine rails are spaced at 5", I'd look for for an actual engine mount set to fit your engine and install the engine properly
1. I know the engine is a slouch - I indexed the timing and found it is timed for a tuned pipe, but not being ABC its not any sort of performance engine. I was going to port it out and put a pipe on it and see what it'll do. I didn't pay a dime for the boat, and I don't intend to sink a lot into it.

2. The adhesive they used initially felt more like goop - shoe goo type adhesive. It wasn't a typical silicone type caulking material.

3. I know. I've build many airboats with glow and Diesel engines on them. Without epoxy, it's only a matter of time before the oil and water cause the whole thing delaminates.

4. I'm not gonna put a ton of money into this thing. If it runs, it runs. If not, I'm out $2 for the engine bearings and $3 for the prop shaft out drives. I don't think the hull/frame would stay together long enough to enjoy a higher quality/purpose built Italian marine engine.
Old 10-03-2016, 09:28 AM
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So I ran the boat more recently and ran into a few things that needs some attention.


My boat runs okay and turns pretty well, but not having turn fins causes it to spin out easily if I head into a turn too fast or two slow. It seems like the butter zone speed for turning (and the engine running consistently) is a bit of voodoo - too fast and it's super boggy throttling back up (regardless of needle setting)... Too slow and it bogs a little but not bad. I think the carb is too big (2D) and fuel draw isn't that good in the low rpm. It seemed to throttle better with more nitro though. This OS 21SE-M seems to be a bit of a turd, but a few guys already told me not to expect much... I want to try a tuned pipe and see if she wakes up some. Need to find a good replacement u-joint for the prop shaft.
Old 10-03-2016, 09:29 AM
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I'll just add - the fuels I used was 10% nitro 20% oil, 15% nitro 21% oil, and 25% nitro 20% oil. The engine was much more boggy on the 10% & 15% fuel - it ran much better on 25% nitro albeit still a bit boggy at times.


Before I installed the engine back into the boat after installing new bearings and going through the carburetor, I ran the engine on my test bench with an air prop on it. It ran perfect and throttled awesome on the 15% nitro fuel. In the following video towards the end you can hear it bog a little when throttling back up. The top end is still a little rich and if the low end is adjusted richer it stumbles a bit more and spits a bit of fuel from the carb until it cleans out. Much leaner and it cuts out. After installing in the boat, I ended up leaning the idle mixture down a little bit and fattened the high end a little more and got good performance from it on top with good idling and throttling except when going to WOT. It sounded lean, so I fattened the high end up even more and it would barely wind up and clean out. Going back to where it ran the best still have a WOT big at first. Only until I changed to the higher nitro did it behave much better. The WOT bogging is not consistent - sometimes it does it and sometimes it doesn't. I have a strong feeling it has more to do with poor fuel draw. The boat uses two tanks, so I may go down to using just one tank and see if that problem goes away. The tanks are plumbed so the muffler pressure goes into the second tank and the feed line from the carb goes to the first tank. During operation, the first tank stays full and the second tank drains first. Exactly how it should work (and the tanks are plumbed how they were when I got the boat which had significant use prior to me owning it).


https://youtu.be/bKsKRhR59VA

FWIW, this engine has a 9mm carb choke and an 8.5mm crankshaft gas passage. Seems a bit bass ackwards since no other engine I've had in my hands has been setup with a larger carb than the crankshaft gas passage.

Last edited by 1QwkSport2.5r; 10-03-2016 at 09:32 AM.
Old 10-03-2016, 07:03 PM
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I have had this sort of out drive before too much rudder will bind down the universal joint some and lag the engine.
Turn fins a good thing and can be hand made to save expense will help to reduce line drag in the out drive. Ebay
sells some cheap parts could go with modern aluminum hardware and flex drive. You can get a tuned pipe cheap
too if you choose. All this gear will allow a future boat build too.


http://www.ebay.com/itm/95mm-rudder-...m-L2RuRvqbRS7w

Last edited by Pond Skipper; 10-03-2016 at 07:15 PM.
Old 10-03-2016, 07:20 PM
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Originally Posted by Pond Skipper View Post
I have had this sort of out drive before too much rudder will bind down the universal joint some and lag the engine.
Turn fins a good thing and can be hand made to save expense will help to reduce line drag in the out drive. Ebay
sells some cheap parts could go with modern aluminum hardware and flex drive. You can get a tuned pipe cheap
too if you choose. All this gear will allow a future boat build too.


http://www.ebay.com/itm/95mm-rudder-...m-L2RuRvqbRS7w
The bogging happens in a straight line. My engine video I posted earlier shows it bog a bit towards the end of the video. The needles were set darn near perfect.

Not worried about the turn fins - they're cheap and easy. The tuned pipe (which I have already) is easy too except fitting it into the hull is tricky.
Old 10-05-2016, 11:49 AM
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Okay, I have a question for you. Did you tune the engine the same as it was on the test stand? If so, you're running too lean. That quick throttle response with the airplane prop is totally different than what you should have with a boat prop in the water or on a stand. There should be a bit of lag before it starts to pick up while on the stand due to the bigger load it will get while in the water
Old 10-05-2016, 03:02 PM
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Originally Posted by Hydro Junkie View Post
Okay, I have a question for you. Did you tune the engine the same as it was on the test stand? If so, you're running too lean. That quick throttle response with the airplane prop is totally different than what you should have with a boat prop in the water or on a stand. There should be a bit of lag before it starts to pick up while on the stand due to the bigger load it will get while in the water
No, I opened the main needle up a full turn and idle half turn. Both were way rich in the water - idle was so much it would load up and flame out as soon as it hit the water. The high end bog isn't just a little lag - it's open the throttle, wait long enough to say Mississippi 10-12 times and it might be starting to wind up. Thinking it was lean, I opened the needle even more and the bog got way worse. I leaned it back down in small increments running it on the water each time until it wouldn't run any faster, then I richened it back up about 1/8 turn and left it there until I changed fuels (nitro). It bogged less and less as I used fuel with more nitro - I listed what I used in my last post. It's setup from the factory with a very tight head clearance (.2mm), so I'm not sure how it's gonna run on 30% - probably shouldn't use any more than that. I forgot to mention - it didn't seem to matter how I set the needle - anywhere within 1/3 turn from peak it would rev up and wind out and slowly slow down a little bit - thinking it was lean, I richened it back up which didn't make it slow down (sag) anymore, but the bogging was worse. So it seems that as long as I don't hit a turn too fast or slam the throttle open quick, it will run okay.. But it shouldn't bog like it does. I've seen videos on YouTube of these boats running the same engine without this problem.

The boat is using stock Graupner fuel tanks (100mL each), stock prop, stock muffler (with pressure feed to tank), stock driveline, etc.
Old 10-05-2016, 06:19 PM
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I'd give it a go with more nitro and see what happens
Old 10-06-2016, 02:13 AM
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Originally Posted by Hydro Junkie View Post
I'd give it a go with more nitro and see what happens
That's what I thought I'd do as well as try using just one fuel tank. I really think fuel draw is the issue. I'm going to see if I can single tank of maybe 4-5oz that will fit the boat.
Old 10-06-2016, 07:02 AM
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Is there a prop close to the same size as the stock one (I don't have the number off the prop off hand - I recall it having "30p" embossed on it) that I could mount directly to the prop shaft and omit the universal joint? It would need at least one set screw to lock it to the driveshaft - the u-joint uses only one setscrew.
Old 10-06-2016, 01:57 PM
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Are you using exhaust pressure to push the fuel or just suction from the carb?
Old 10-06-2016, 02:19 PM
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Originally Posted by Hydro Junkie View Post
Are you using exhaust pressure to push the fuel or just suction from the carb?
Muffler pressure using the stock muffler.

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