Some engine facts & pics

[rallyfinnen]

Disassembled my engine today and took some pics for my own reference, and thought I would put them here as well together with some facts and observations.



This gasket needed some trimming, was covering the ports abt 1mm





exhaust



intake



Trimmed a bit on the sides of the piston skirt. Was pretty good from the beginning, so I doubt it makes a difference



Top of the piston was not machined at all and the surface very rough. I used some sand paper to smooth it out a bit.
Did not want to remove too much material so there are still some pits left (yeah, and I'm lazy too :-) )



Underside of piston:



The intake and the 'middle piece' between the carb and cylinder needed quite some matching, there was a 1mm step between these. All the material visible inside the gasket on the intake pic needed to be removed too



I also did some measurements
Bore: 34mm
Stroke: 28mm
Con rod length: abt 52mm
.. and yes that makes 25,4cc on an engine marked 30cc..

Squish is more than 1mm. Tried it with a 1mm solder, and it was not even close to pinch it, so i would guess almost 1,5mm.
This could be brought down by removing the bottom gasket, but it was stuck and i have no replacement, so left it there.
Removing the gasket also alters port timing and compression, but my 'guesstimate' is that those changes would improve mid range power, possibly with a cost of some top end power.

EDIT: Forgot to mention that the shaft seals on the crank seem a bit suspicious.. turning the crank with no cylinder made squeeling noise from the seals, and a lot of friction, even if i tried to lubricate them from both sides with 2-stroke oil and some teflon spray..i suspect these won't last long..

[fsmt4wd]

excellent post!! these engines have potential thats for sure

[speedyd]

wow, great work! i think with some good parts inside one of these engines could be awsome! ive got one that we are going to see how crazy it can get.

[hoppy]

throw a zen g270rc rebuild kit on it... when my zen motor starts to fade, i'll be getting the zen 4 bolt rebuild kit on my fs crankcase- apparently an easy rebuild, and potentially a faster motor than the original zen g270rc, coz ironically, i've heard the porting is better in the fs crakcase... go figure...

[speedyd]

i am collecting some bits and peices to throw a modded fs engine together. so i can see just what can be had. i may even see if i can get some dyno numbers from innovative on it.

[speedyd]

so far i have a zen gasket set, fast eddy crank beareings,and new seals.an ada intake manifold,813 walbro, and a jp pipe will all find theire way into it.

[rallyfinnen]

Adding the FS engine port timing for those interested in calculating a pipe:

Exhaust 167 deg
Transfer 128 deg

These numbers are with the standard cylinder foot gasket. If the gasket is removed for higher compression, the timing angles will decrease a little bit.
Note: these are not absolute numbers, my guess is that they are of an accuracy of 2-3 degrees.
I only used a scanned degree wheel that I rescaled, printed on thick photo paper and taped to the flywheel. I used a piece of paper in through the exhaust port to know when the ports were closing.

You also need an exhaust port area, and a very approximated value for this would be 230mm^2

[rallyfinnen]

Checked the ignition advance with a strobe light today, and it's approx 33deg BTDC. (More than I expected actually)
I also tried filing the holes of the ignition coil to try more advance, but the screw heads hit the coil, so the extra advance possible is abt 2-3 degrees. Did not notice a big diffrence from standard after changing it either.
Maybe a slight increase of mid-range torque, and a little bit less top revs.
I would like more of both!

[rallyfinnen]

I measured the throw (or what is it called?) of the crank the other day.
The total movement on the flywheel end was 0,1mm, and on the clutch side 0,06mm.
Not so good, but it seems the reason is that the distance between the main shaft and the big end shaft is not the same on the two halves of the crank. So, no chance of correcting it.

[rallyfinnen]

I measured the crank on the old engine yesterday, and that was only 0.01mm! I was impressed!
Replaced the bearings and seals on that one, so now it's ready to use as a spare.

[theydontwantmusic]

i measured the stroke of my engine through the spark plug hole, and the bore through the exhaust port.

its probably not overly accurate, but I got 27.5mm stroke, 33.7mm bore...

i wasn't overly accurate, but yes, its only 25cc...