combatpigg

My Feedback: (3)

I wear hearing aides, unless I'm flying speed planes.
With the launcher, it's not too bad...fire up and step back. It is loud even with ear muffs while holding the plane during break in. The header slipped off right before the first take off, so the runs were totally open. The header pipe's supposed to have a slight tuning effect, I'm not sure how it works. I think it helps scavenge the cylinder each cycle...in theory.
The plane sure handles nice with the light engine.

MJD

My Feedback: (1)

I weighed one of the K&B 7.5's, with carb, coupler and OPS open pipe, and it is 60 grams less than an SJ50 with muffler. Very compact engine, no extra metal that's for sure. Looking forward to running them.

MJD

combatpigg

My Feedback: (3)

It got stupid loud, never got stupid fast, but then it got stupid quiet. 10 seconds into today's first flight the engine died, I landed it in a huge mole hill, broke the prop, then discovered why it got so quiet.

The crank broke.......the pressed in pin un-pressed from the cracked crank web. Now I know why the web has a steel ring around the perimeter, it's a scattershield to keep the whole works from blowing a hole in the case.

I'm not sure if the rod I made was the culprit, it could have bent and then teaked the crank pin. Funny thing is none of the wear / friction surfaces are damaged anywhere except the backplate has a little gouge now. It seems that I've heard of this problem before, home made rod or not.

So this ends up being a short lived thread. So much for antique / nostalgia hotrodding for awhile.

summerwind

yep, that was just like the one in my brothers FF ship.......going up for a 10 second run, but the engine popped at around 7 sec.........when it landed we saw the hole.

sorry this happened to you.

call Randy at Mecoa............he may have what you need.

Broken Wings

My Feedback: (20)

Man, That sucks.....You had some time invested in that connecting rod.

Look up a material called AERMET 100, 310,340 the next time you need to make a crank pin...... If you need a chunk I've got some 100

combatpigg

My Feedback: (3)

I wonder if pressed pins are done any more?
Too bad, because the engine for the most part looks like it's well engineered to scream.
If there is a better crank that fits, I'm game to try it.

proptop

My Feedback: (8)

Wow...that stinks...[]

AFAIK all the 6.5's have pressed in pins...when I talked to a couple guys who raced these things in the 80's they were more concerned w/ the pressed in pin vs. the rod. (well, a bit of both actually ) That's why they warned me about 22K maybe 23K tops. (I think Highplains said maybe a little more, but he's got a pic of that alum. crank stuffer ring poking out the side of the case )

I know it doesn't help you any now CP, but the 7.5 RIRE Marine has a 1 pc. crank.
I have had an inboard version w/ disc rotor apart and seen the 1 pc. crank. I believe the last version of the 7.5 DF (w/ drum intake and machined F. housing ) does too, but I've never had one of those apart to actually see.

combatpigg

My Feedback: (3)

Thanks PropTop, that isn't good news for the 6.5 lovers, but the late model 7.5s sound like they might be up to the task.
When you stop to think about it, choosing a pressed in pin that gets hit 400 times a second is insane.

IIRC, there was a guy when I first got in the hobby who made 1 piece cranks for K&Bs........Brasher or Athens?

proptop

My Feedback: (8)

I don't know about the guys making 1 pc. cranks...maybe someone in the Pylon forum would know? (or C/L speed guys? )
Might just find somebody who has one sittin' around collecting dust?

The FIRE 7.5 DF series 9100 has a pressed in pin too....crank looks like the 6.5's just a wee bit more stroke.
The RIRE 7.5's would be the ones to get.

I have a couple of Picco car engines with pressed in pins...they turn 40K+ but then again, they're only .21's..
They went back and forth with pressed in pins and then 1 pc. cranks after a few pins worked loose. Last I heard though they still had some versions w/ pressed in pins? (some of the 1 pc. cranks had premature wear on the crankpins )


I think the reason they used a seperate pressed in pin is a hardening issue? The pressed in pin can be hardened, then ground to size, then pressed in.
From what I gather, with a 1 pc. crank, there can be a problem hardening just the pin area vs. hardening the whole crank (and possably making the crank brittle ) It's a delicate operation, and maybe K&B wasn't set-up to do that back then? The .61 has a pressed in pin too...until some of the most recent mecoa versions.

Some of the early Evolution engines had over-hardened cranks. Two of us in our club had the crankpin shear off right at the face...Evo .52's...and I heard of it happening to a couple others.
We were only turning them to around 15K.
Makes me wonder how durable the new .60 is going to be...especially w/ a pipe on it?

combatpigg

My Feedback: (3)

Tempering and plating sound like black arts. I spoke with a guy at a automotive crank shop about fixing a gouged crank and he explained what a crap shoot it was. I always took that stuff for granted.
The energy it takes to do the heating and normalizing drive the cost of doing business up. I have no idea how they can selectively harden just the pin without effecting the web, unless they quickly attack the pin with several flames, or run a current through electrodes that short circuit just the pin.

HighPlains

My Feedback: (1)

Actually the 6.5 was a pretty durable engine running on open exhaust with 65% nitro. We propped them for 21,000 +/- 500, and on pylon models they unloaded about 5000 above of the ground rpm.

The main weakness was supposed to be the stuffing ring around the crank, but I never had one fail. I did have a rod failure, but it had be highly modified with a knife profile. Didn't seem to help the power, but sure shorten the life.

I had ten of them that I raced with for about four years. The two best were built by Bill Wisniewski for use in his Formula 40's at the Nats in '85 and '86. Wish I had them now, though they looked as stock as could be. But the parts inside fit perfectly, and the case work around the sleeve, bearings, and head made all the difference. While production engines were more or less "line bored", Wisniewski compensated for the distortion of the case due to the heat when running. So when cold, the sleeve was tipped back slightly from vertical. Since the back side of the case does not cool as well as the front, the engine grows slightly with heat and the cylinder tips forward to perfect vertical alignment. Another tip was the importance of getting the head to the proper tightness to avoid distorting the top of the sleeve. He maintained that several hundred rpm could be lost if the tension was not correct.

Clarence Lee also built me 4 engines that ran well. He did a special porting trick called "free porting", where the engine could pull some additional air through a couple holes just under the rear exhaust. But in the end, as my flying got better, I eventually reached a point where the K&B was just not quite on par with the ST X-40, so I sold my remaining stock of engines and parts and bought 10 X-40 engines. Then a few years later, the Nelson F1 engine came to dominate, and the X-40's got shoved into a draw.

HighPlains

My Feedback: (1)

Inductive heating is often used, with a very low frequency (50-100 kHz) RF generator at about 500 to 1000 Watts of energy.

proptop

My Feedback: (8)

One thing just came to me when you mentioned bearing fit HP...
The rear bearing needs to be a nice snug fit in the case...if not they have been known to spin. If the R. bearing is not a tight fit in the case, that will allow the crank to wallow around just a bit, correct!?

That would not be good for the rod and crankpin either...

HP...you guys were hitting 25-26K unloaded then...w/ stock rods, cranks [8D]
But for how many flights though?

combatpigg

My Feedback: (3)

HP, thanks for sharing some of the history behind the 6.5. I can't help think that this early model I've got now was a "work in progress" at the time.

The only other K&B6.5 I owned was the RIRE and it put up with a lot of abuse.
Now we're talking about a pressed pin driving a rotor too....IIRC, that engine had a 1 piece crank?

I've seen the ST X40s [ebay] and didn't know enough about them to hazard a bid. Their .35 combat special used to spit out crank snouts just when they started running real good.

HighPlains

My Feedback: (1)

Hard to say how many flights on any engine. All the engines (except for hard crashed) were rebuilt over and over. While I went through piston/sleeves and bearings, I never replaced any of the cranks or rods.

When the bearings are properly fitted, they just barely slide on the crank (which may not matter anyway, because the inner race of both bearing is more or less clamped to the crank). The outside fit is the tricky part. When the bearings are clamped to the crank, and the rear bearing is taking up the thrust load, the front bearing should be floating with no thrust load. What makes this difficult is the amount of head causes unequal expansion of the crank and the case due to materials. As far as the external fit of the bearing, it should be tight enough not to ever spin in the case, but not so tight to distort the case. Maybe a third to quarter of the bearing is able to be pushed into position without heat.

The front bearing on these engines take a beating when you turn and burn. Most front bearings were replaced after 10 or 15 runs, while the rear bearings usually lasted two or three times as long.

combatpigg

My Feedback: (3)

PropTop, this rear bearing slid out of the case with the crank when I tore the engine down, it did not stay at home. I wasn't sure if that was caused by the trauma or not..........now I wonder

Broken Wings

My Feedback: (20)

When I was a young man I worked as a tool and cutter grinder and we manufactured alot of single point carbide cutting tools. We used an induction welder to melt the silver solder that attached the carbide insert to the tool shank.

There was a copper coil that you would place the part/tool into the center and it would start to glow red hot. The copper coil would remain cool. Took me a little while to wrap my head around that machine and try to figure out "what makes it go"...

The farther you inserted the part into the coil the farther you could heat soak that area.

lfinney

My Feedback: (44)

the first gen 6.5 engines had weak front ends the second gens were improved, some guys used loctite to keep the bearing from walking or fretting, the pins coming out is rare, the silver colored band is aluminum, to cover the crank cutouts, for maximum crankcase stuffing, this design of crank goes back to the side exhaust torpedo .40 which were run on 50 plus nitro at around 19-20k as well...with 10x3 and 10x4 narrow props.. rods and pistons werent very durable, i have two of them they run very well

combatpigg

My Feedback: (3)

Thanks LF......I'll keep one eye peeled for a crank then. It could have been that the [slender] rod I made aggravated a marginal condition / weak tendency that the engine had.
I originally figured that a lighter piston and rod would help keeps things together.