Blackout

Would the heat sink on this engine be enough for cooling, if the engine was in the open air; no cowl? If so, it would be an option for the larger nitro boats. Just need to find a flywheel. Any thoughts?



Thanks.

Hydro Junkie

I doubt it as the ducted fan engines are designed for high RPM and low torque when compared to a marine engines. You can try it if you wish, but at the same time, you might want to start looking for an aircraft for it to go into.

Ron Olson

My Feedback: (1)

I've heard of ducted fan engines being converted over for marine use but the next trick is finding the parts to make the conversion. First, you are going to need a water-cooled head. The flywheel may be the easier part.
Now a ducted fan boat would be way cool as not too many people have done that!

kgibson4

My Feedback: (4)

Back in the 90's the VR engines were offered in both ducted fan and marine versions.  There was a .46, .65, .77 (I think), and the .91.  I believe the main difference was the direction the case was turned to direct the exhaust either to the front or the back.  I think with the size of that engine you would need water cooling if you didn't have the ducted fan forcing cooling air over the head.  The water cooled head is probably out there somewhere if you can find it.  Same with the flywheel.

Blackout

Thanks for the input guys. You guys are probably right on needing water cooling. O.S. made a .81 vr-marine, but I don't think they made a .91 marine version. Since the .91 has a slightly larger bore than the .81, the .81 water cooled head probably won't work without modifications. I do have access to a milling machine, so I could machine a new one, but my skills are marginal.

advanced builder

Craig, Propcirlcles has 2 OPS .67ns he wanted to sell down in Elmira.

kgibson4

My Feedback: (4)

Oops, sorry. Dang those senior moments!

Still, someone should be able to make you a cooling head. And those VR engines are powerful.


Ken (off to check the supply of ginko biloba)

Blackout

Neil, thanks for the heads up on Bob's OPS 67's, but I think I want something .81 or more for an F-mono.

I'm going to call Octura on Monday and see if they have a flywheel for the .91 vr-df. If not, I will look for a .81 vr-m flywheel and try that. I think I will go ahead and try to machine my own cooling head. Should be a fun winter project, and rewarding if it works out.

Blackout

Just ordered a OS .91 vr-df from Towers for $309.99, sorry LHS, felt cheap, I couldn't resist the no tax, free shipping, and $35 off coupon. I ordered an Octura flywheel for $12 that should work. If I can machine the cooling head o.k., this will work out to be an inexpensive .91 engine.

Blackout

Question, anyone see a problem in using 6061 aluminum for the head?

Thanks.

kgibson4

My Feedback: (4)

Please keep us informed on how this works out for you. I'm betting that with the usual tweeking, this engine will keep up with (or outrun) the best of them.

What boat are you going to put it in?

Blackout

I'm trying to decide between an AC Lazer 40 or a 42" Seaducer. Any other suggestions for F-mono? The hull does not need to be 100% competitive. I like how the Lazer looks and it is suppose to be a great handling hull too. Any feedback on the Aeromarine monos?

Blackout

Here is the cooling head I machined for the engine. To make the head button, I just machined the fins off the stock air cooled head. Looks a bit crude, but should do the job just fine. Remember, I'm a novice machinist. I get nervous machining when the material gets thin, so I leave it a little thick where I can.

Gorgok

Was that with a manual machine? And if so you did that channel in the cooling block too? Nothing crude about that piece to me... The button only looks like it suffered from inconsistent feed. A nice piece of glass plate and some fine sand paper can make it pretty if you care. Though as long as you make a good seal (goop, gasket, or just enough torque) then the internal ridges should not matter (or actually make it work better).

Blackout

Yes, I used a manual milling machine. I used a rotary table to machine the pockets in the cooling block.

I was a little surprised by the tooling marks too on the top of the head button. Like you say, I'll sand them smooth on a flat surface. I had sanded them a little, but surely need to do more. Also, I think they look worse in the picture than they really are.

Forgot to mention, the flywheel is a 60 flywheel from Octura. It mounted up fine with some slight modifications to the collet. I had to chamfer the back of the collet so that it would butt up against the stock aluminum air prop bushing. (Not sure what that part is called...) I would have prefered a flywheel that butts up directly to the inner front bearing race. An .81VR-M flywheel would be perfect, but I haven't found one yet.

The next thing I need to do is pull the crank out and clearance it so that I can spin the case 180 degrees to convert the engine to a front exhaust. Sounds like allot of work, but we have long winters in NY...

advanced builder

Looking Good Craig. Yes to a long winter. Did you happen to see some of the reworked head buttons that Amax has been tinkering with. He's got some good imfo on them. And I know he posted a shot of the rework. Like always he shares his expertise.

Blackout

Yes, I have seen his work. He seems to get good speed from his reworked engines!

For now, engine is remaining stock. Sometimes it runs better that way. Start increasing carb size, timing, the engines can get finicky. I haven't raced yet and need to get the engine started in 1 min, 30 sec, so I'm keeping this project simple. Wanted a F-mono (Open Mono) and didn't want to spend $525 plus on a CMB. Overcourse, a week after I buy the OS 91, Stu Barr advertises a Christmas sale on some CMB's. But the OS91 is a great deal if you are willing to make the changes. It even comes with a 9B remote needle assembly for 3rd channel mixture control; kind of needed in a ducted fan application where the enigine is hard to get at.


Edit: It was Stu Barr with the sale, not Jerry Crowther...

Hydro Junkie

On your reworked head button, before you sand it, put it in a lathe with a good sharp cutter and take between .003 and .005 off the top to even it out. Either that or put it in a milling vice and do the same with a flycutter with a sharp cutting tool. It looks to me like you did all your cutting with an endmill, which resulted in the uneven face. Not being critiacal here, just trying to save you some time

kgibson4

My Feedback: (4)

On the contrary, it looks quite complex and well executed. Good work.

On the .46 VR-M they cut a little fingernail shape out of the piston skirt to clear the crank counterwieght but they also have that little nub on the bottom of the exhaust port to close off the gap when the piston is at TDC. I don't know if all the VR-M engines are like that.

Trimming a little off on the counterweight seems like a viable option.

Blackout

I don't have a lathe or a flycutter. The face is even, it just has the tool marks that I will remove with sand paper. But thanks for the advise, I'll keep it in mind, always wanted a flycutter...

Blackout

I'll look into that when the engine is apart. Thanks.

Blackout

Here is the clearanced crankshaft. I used a dremel and bench grinder, and then a small file and sandpaper. I didn't have to remove a whole lot. The crankshaft now balances out at 32% of the piston/rod/pin weight. I forgot to measure the balance before the modification. Unless I am convinced otherwise, I will try running the engine to check for smoothness before adding a tungsten slug to the counter balance.

f16man

Actualy the OS 77 ducted fan engines and the marine versions use the same piston and sleeve, I know this as I have run a 77 marine in my byron f 16all I did was swap the head out.The engines do have the torque and medium rpm range my 77s would spin a 6inch 5 blade fan at 19,800 producing 12lbs thrust.... not bad for a .77 engine...

rmabe

you would not have the same power as a boat 90, because they run 60 to 70% nitro in their engine, that why they are water cool. If you try to run say as mush as 40% you would problly burn up the engine in one heat race

advanced builder

I can't wait to see he run. Your 30 % nitro should be fine. I f you do want to play with high nitro. You may need some additives. http://www3.towerhobbies.com/cgi-bin...?&I=LXS627&P=0
I ordered some for my .67 .It's in my Gas fuel tank for my Zenoah . Great job on that head. your doing good. I'm watching