the Wasp

My Feedback: (1)

I believe I said that to Pete in a reply

Jim

SrTelemaster150

As usual, after missing a days worth of posts, I failed to read all of them before replying.

the Wasp

My Feedback: (1)

LOL I do that too much

Jim

SrTelemaster150

Try 30% nitro O'Donnell Speed Blend with 8% oil in an FA-180HC running CDI

Holy moly will it howl! Hit nearly 9000 RPM with an 18 x 8 Dynathrust prop.

Boy oh boy was it ever thirsty though.

SrTelemaster150

But it snarls like a tiger when you open the throttle.

the Wasp

My Feedback: (1)

to add, even tho the rockers have an adjustment, the angle of the longer rod will change, as he suggested in my video, the result will be more lift


is there any info on Saito's Rocker Ratios ??

Jim

the Wasp

My Feedback: (1)

LOL Pete will like that

Jim

SrTelemaster150

Just measure the distance from the center of the rocker pivot to each end and divide the distance from center of the pivot to the center of the valve stem pad (A) by the distance from center of the pivot to the pushrod socket. (B)

The geometric change will be insignificant since the pivot point toes not change. To compute the change use the square of the B - the square of the deck reduction (C) to get (D squared) A/D will give you the new rocker ratio.

Glowgeek

New data just in. Measured three more times and no need to average as the difference was unmeasureable (visually). There are two differences in how the measurements were taken than previous; I was much more careful about dripping drops everywhere and I adjusted where I was aligning the syringe plunger to the graduation marks.

Previously taken measurements:
Combustion Chamber: 1.80 cc
Glow Plug (Type F): .030 cc
Mechanical Swept Vol: 13.97 cc
Mechanical Compression: 8.63:1

Latest measurements:
Combustion Chamber: 1.75 cc
Glow Plug (Type F): .030 cc
Mechanical Swept Vol: 14.05 cc
Mechanical Compression: 8.89:1

Conversion shows that my 82 is an 85.7 LOL!

Here's the thing, I have no way to calibrate a graduated 3cc syringe so take the volume numbers with a grain of salt. The CR however is probably very close to real because it's a ratio between swept and combustion chamber volumes.

Clearances:
Cylinder skirt to case relief: .017" . I have removed .015" from the bottom of the cylinder skirt in preparation for milling as much as .020" off the case deck if needed.

Valve to Piston:
Mechanical valve to piston interference occurs if the case deck is milled down .036". For now I will be limiting milling to .020" so no problems there.

Cylinder fin to Cam Gear Housing:
A small notch was cut in one cylinder fin to allow clearance for lowering the cylinder.

Compression Ratio:
The starting CR is approx 8.89:1. I will be shaving .013" off the case deck initially yielding right at 10:1 CR. From there I'll increase CR until I'm happy or something breaks.

Goal:
Currently both of my FA82's spin an APC 14x6 at 9200 rpm using 15%/17%. I'm looking for 9800 rpm without increasing nitro content.

Lonnie

SrTelemaster150

What algebraic formula are you using to compute CR?

Are you adding the chamber volume to the swept area before dividing the sum by the chamber volume?

Glowgeek

(Swept Vol + Comb Chamber Vol + Glow Plug Vol) ÷ (Comb Chamber Vol + Glow Plug Vol)

SrTelemaster150

What did you use on the piston crown to do a real world valve to piston crown clearance check?

Glowgeek

No clay or anything, removing the piston is not necessary for that measurement and I didn't want to unseat the ring. Instead I first measured the full opening distance for each valve. Next I removed the pushrods and rear cover then measured the the distance from the big end of rod to the case rear cover opening at TDC. Next I wedged the rockers to bring both valves to there full measured travel and slid the piston up until it stopped against an open valve. Lastly I remeasured the big end of rod to case measurement and took the difference.

As it turns out I later noticed the cylinder skirt - case relief issue and had to remove the piston anyway just to sand the bottom of the cylinder.

the Wasp

My Feedback: (1)

SrTelemaster150

yes I understand that part, but because I will have to eye it I wont get an accurate measurement, and I rather not be wrong in doing so, and I have been wrong enough over the years


what ?? LOL

Jim
Saito engines, if you are good to one, and you let it go free, it will come back to you

Glowgeek

Made perfect sense to me Jim, you better hurry and catch up...lol
I hate when Algebra gets in the way of my Geometry!

the Wasp

My Feedback: (1)

why can't you just bring up the piston to TDC and allow the valve to drop in the cylinder and see how far it goes ? you should be able to measure it.

Jim

Glowgeek

Could have but didn't want to try to get the retainers/keepers back on without removing the piston.

Also that method doesn't tell how far the piston can move up before striking the valves. This is because the valves are at an angle to piston travel.

the Wasp

My Feedback: (1)

LOL you know, my dad was a borderline math genius, really!! but when I rebuilt my 327 I showed him the stock cam and the performance cam I was going to use, he asked me why is it "that the stock cam's lobe is "higher" than the racing cam's lobe" I told him that it's simple, the racing cam has a smaller base circle, he smiled and called me a little s***

Jim

the Wasp

My Feedback: (1)

you will just have to use clay or play doh

Jim

the Wasp

My Feedback: (1)

battery discharging question,


guys, I am cycling two 3000 milli amp 6 cell 7.2V NiMH packs that I use on my engine starter, I have a great charger, a Reedy 1216C2 charger,

at this point this one pack has been discharging for 88 minutes, the pack voltage going in is 7, 77 volts,
well, I have the charger set to pull 2.4 amps yet the pack has only been pushing 1.4 amps out,

even tho the volts are 7.77 couldn't I still have a bad cell ?

Jim

acdii

If you want to find a bad cell with NiMh, charge the pack full then hook up the starter and load it. If you have a bad cell the voltage on the pack will drop quickly and not recover. That shock of drawing high amps will drain a bad cell in a matter of moments. Don't stall the starter, just slow it with your hand or something that will spike the amps.

SrTelemaster150

Hard to do while rotating the engine through TDC

^^^What he said.^^^


Clay or Play Doh doesn't work on such small surfaces. Been there, dine that.

I use .015" dimensional "pattern maker's wax". It comes in sheets and has an adhesive back that sticks well to the small piston crowns.

In such small engines .015" is plenty of piston/valve clearance.

Hobbsy

My Feedback: (102)

The swept volume is constant, it should not change unless you change the bore or the stroke.

Glowgeek

Using wax, clay etc and rotating over a fully assembled engine allows for a dynamic valve interference measurement. The way I measured it is a static measurement and doesn't account for the fact that the valves are only partially open at TDC during the exhaust stroke and not at all during the compression stroke. Still, it allowed me to see if there was room to drop the cylinder without removing the piston.

Captcrunch44