K&B 6.5 FIRE / SCREAMIN' DEMON
 

Here we go with engine #4 for this plane. The plane is starting to look used. The linkages are getting a little bit loose again, time to replace the servo arms.

The K&B engine was bought NIB. I made a high strength rod and a remote needle using a ST NVA.
Test runs on the engine indicate it's ready to be flown.
I used to run 7.2x8.6 on my first K&B 6.5. I suppose 8x8 props will do OK on it.

I'm expecting 170 mph from it, we'll see.......

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

I think you will have more than 170 CP [8D]

Yeaa beby..... go for it !!!!!!!

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

SB, I hope it really screams. It's got a double hemisphere [double bubble] head and really good looking machine work everywhere else. I heard this model engine was made in the 1970s.

..........are you still ripping up the sky with your Patriot?

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Good Grief that thing is going to be stupid loud!:D

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Cool!
So did you make the rod for this engine because you didn't think the original was going to be strong enough?

What sort of r.p.m. are you seeing? I have a FIRE 6.5 in a mod. Sonic 500 (like a Scat Cat ) that turns an APC 8x8 at around 19K but it's a bit tired. (I got it used thru ebay )

I was told to prop the FIRE 6.5 Q500 to around 19,500 static (give or take a few ) and that the stock rod was supposed to be good to about 22K. 15% nitro was suggested, and K&B HP plugs, and .015-.018 head clearance.

Yours is the early version...don't know exactly how long that one was made, (into the 80's I'm sure ) but the 2nd version was made into the early 90's at least...from what I'm told anyway.
The differences are the 2nd version has a stronger case with more meat around the base of the jug (in front, at the joint where the front housing bolts on, there's a fillet ) and there's more material around the head bolt holes. (and longer head bolts )
The 2nd version also has a thicker sleeve and a longer/beefier RPM style rod AKA the DF rod and the pin height in the piston is higher to compensate for the longer rod.
The F. housing has a draw bar venturi/carb retention bolt set-up.
There is also a 2pc. 6.5 head assy. similar to the 7.5 DF engines.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

And SILLY FAST

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Vic, I just won't fly it near the hospital.....;)

PropTop, I was told the cast rod would fail predictably before all else. I've only been running this with a 8x5 for break in on 25% nitro. I won't have any tach numbers until I prop it "for real".

C4F, these really ROAR when you put them in a dive....:D Just to be funny, I should apply to a new local club for membership and use this thing for the "check out the new member" flight.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

I just scored a pair of K&B 7.5 DF RIRE engines (as you know CP) and I am really looking forward to putting one in a Demon. Very slim engine profile, perfect for ducted fans and speedy prop jobs.

So I am quite interested in this for engine and aircraft reasons. And btw with an open pipe these 7.5's come in at 465-475 grams versus typical 520-525 for the .50 side exhaust engines with 1/4-wave muffler. I have been madly drawing a compact little sport speed around the engine. I like them, they look and feel well made FWIW. Haven't run 'em yet, gotta get some props yet - doesn't everyone around here seem to have that problem lately?

MJD

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

MJD, if you breeze through the trials with the OPS .65, the K&B 7.5 will be a nice project to follow up with.
I'd set 1 of them up for a tuned pipe.
If the OPS turns out as good as hoped, you'll probably forget you own the 7.5s.........;)

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Yeah I know, but it is a more realistic powerplant for kit customers, and I wanted a RIRE engine in that size to check out on the kit mods anyway and two came up for a good price and... So it would be more of a R&D project related to the Demon MkII than something designed to top something else - more of a "how-to-do-this?" project I guess you'd say. There's a bunch of .40 block DF engines out there in auctions and marketplaces.

MJD

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

The DF engines scare most buyers because they aren't sure about adaptability to prop planes and there sure is no way I'd buy one that is used! If you could build fast enough to make it profitable, RTF Demons with engine combos might attract certain types of flyers. I bought a 3D profile from Morris Hobbies a similar way...kit+engine.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Well , has been a lot of time since I flew it last time ( the SKF bearings didn't last too long ) BUT I changed the bearings some days ago, this time I bought the ceramic ones I hope they work as good as its reputation is . I hope the weather allow to fly soon , I already took out the dust of my Patriot and she is ready to come back [8D] , I still need to test a prop that I modified on that beby , lets see what happen . :D

CP , just curious , do you balance the spinner that use those engines at very high RPM ???

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

SB, I've never noticed much vibration at the spinner.
For example, the Nelson has a very out of balance spinner [done on purpose] It needs to be installed a certain way to help balance the internal parts of the engine...it is what you call "external balancing", like the 454 Chevy.
The spinner on this K&B is a little bit beat up, but the retainer screw still registers perfectly with threads on the prop shaft, so it spins true.

A speed plane spinner only has a 3/4" radius, so the effects of imperfection aren't going to be very noticable. Bad engine bearings will make a spinner look bad, plus wear your servos out quickly.
Running heavy props and flying like a wildman [hard turns] wears out bearings faster......;)

I think having a solid engine mount that doesn't allow the engine to "swim around" while it is running is more important.

I thought SKF were good bearings? Look up DXF Bearings in the future, they have a good selection if you ever need to compare price or need to find a hard to get size.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

hey in regards to the K&B 6.5's rod........we ran these in Free Flight with 9.5x4.5 FG props at around 21K.............the rods were always replaced with RPM rods when they made them.
these are still excellent engines with some brute torque if they have been properly fitted...........some were so tight that you had to heat em up just to start em and those were the ones that would pop the stock rod the second you got just a tad rich;)

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

I picked up a OS 46VRDF at a swap meet for 50 bucks NIB:D, should be a good candidate also for an SD.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

50 bucks????......man i'm never in the right place at the right time.
congrats on the score

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

SW, that seems to be this engine's happy zone for rpm. I raised the timing of the only other one I've owned to get it into the 24,000 range with a 7.2x8.6. That engine was also lightened enough to require removing weight from the counter balance. This one isn't squeaky tight......it just feels perfect......like a human being who cared put it together.

You'd really have to be nuts to let go of an airplane powered with one of these?........[X(]!!

SRV, I need to start hanging out with you!....[8D]

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

I forget why I missed that swap meet but now I am truly pissed..

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

MJD too bad too, the guy had two of them NIB, if I'd been thinking at the time I should have bought both and gave you one.[:o]

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Oh yeah I was probably thinking about how much cashola I had left to buy a bunch of balsa, my supply was getting too depleted.

CP I'm liking your engine trial threads, very good info to put away in the library, thanks.;)

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

SRV, my pleasure. This engine might not be mainstream, but they do show up now and then NIB. Knowing what I do now about this early model 6.5, the later model 6.5 or 7.5 would be a better choice....
Your OS46DF is still a better deal.......!!

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Thats good to know, you do see those come up quite a bit for sale.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

I probably have all the balsa you need. How ironic.. and now someone else has the other nice VR-DF.. [&o]

Maybe they'll buy a Demon for it.. [&o]

MJD

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Nothing spectacular to report. The right side release pin of the launcher was late, so the model was wrapping around the lone pin and pulling to the right. I found a 3/16" difference that I corrected. The launches are straight now.......but the servo rails inside the plane popped loose today [X(]!

Luckily, the model was just a little bit wobbly in roll axis, still fine in pitch. Just needs some glue and maybe some more wood wedged in the mount area.

The engine ran OK with a 8x8, but I ran it overly rich today. The engine showed signs of surging into a full scream, but it's still pretty new to be set on "kill" yet. I didn't tach it or clock it. It might be smart to cut a 8x8 down to 7.5 or so for the first hard runs as a safe guard. I think it's easier to smoke a racing engine with too much prop than too much rpm.

RE: K&B 6.5 FIRE / SCREAMIN' DEMON
 

Hows your hearing?[:@]