Port height Questions

[catchacuda]

Please be advised im fairly new to the 2 stroke thing.

When I first got this 1e40qmb the piston hit the (correct NGK) plug and closed the gap (while running). It had 1 base gasket.

I've put 3 base gaskets on after noticing how low the ports were with the piston at BDC. Now, do I want the piston level with the bottom of the ports? The piston is still covering them a little.

Is all of this pointless unless I make a port map and calculate durations, compression, and of course squish clearance?

Please excuse the dirt, I am going to clean, tear it down, clean again, re assemble.

BDC


TDC for reference


I also need to purchase a head, PO tried cutting singh grooves... LOL.


Note the plug in the head at the moment is a lawn mower plug, simply so my lil one could tote around, need to pickup a new ngk.

[oldgeek]

Generally speaking it is best if the piston is flush with the floor of the intake ports at bdc, however doing that usually causes too much squish at the top end which will have to be dealt with. Also sometimes when you set it up flush, your durations can get a little crazy, then you really need a pipe to work well with the high durations. So depending how far you want to go there is loads of info here to get you there.

A degree wheel will show your durations, there is a printable one here somewhere and directions on how to use it.

Also the PO had the wrong plug in it if the piston was closing the gap. Must have been a very long plug because the head is pretty deep.

[gsx600racer]

From the looks of the first picture(BDC) you could maybe raise the cylinder a tad to fully open the transfer ports.

Id suggest getting a "degree wheel" and map out your ports openings, closings, and durations to get a better idea whats going on.

49ccscoot.proboards.com/thread/353/port-durations-degree-wheel-methods

The second picture, there looks like there is a little squish, not much tho. You can measure that with some solder and micrometer or digital calipers.

49ccscoot.proboards.com/thread/2355/video-squish-clearance-info

The third pic, looks like the previous owner cut in "singh grooves or torque grooves" into the head. Iv seen this stuff out there but have never seen it done on a scooter engine before.

[catchacuda]

I very much appreciate the input you both have provided. Just want to add, my current base "gaskets" are simply cut from a cereal box so I'm not sure how they compare to a real gasket in terms of thickness.

I suppose I have more research to do. I'll print the degree wheel and make a port map. Practice for the upcoming 70cc kit, pipe, and jetting.

[ThaiGyro]

Greetings 'Cuda! I think the grooves can be a good way to go, once you have the squish band better optimized. I have never personally done this on a two-stroke, but seen it on high rpm four banger race engines. After a bit of reading on Singh's site, I like the potential. Better turbulance gives better cylinder cooling and combustion. They claim cleaner plug color and reduced exhaust spewage...hmmm, possible if tuned in a slightly leaner condition and correct plug range for the fuel being used.  Oh...and lower idle rpm can be achieved, which is also nice.

They did say tons of data from people around the world. Wish I could see more data and photos. On our project here, we are trying to first optimize our 49cc engines in various configurations before going to 70cc's.

[catchacuda]

Thank you I'll check out your project, maybe optimizing my 49 is the better way to go especially considering how new I am to these. Never thought I'd enjoy small engines so much!

As for the grooves... I like the thought, yet must ask myself why no manufacturer with huge amounts of money and testing resources has put grooves in their heads if it offers any benefits.

[ThaiGyro]

Aug 10, 2017 0:08:42 GMT -5 catchacuda said:

Thank you I'll check out your project, maybe optimizing my 49 is the better way to go especially considering how new I am to these. Never thought I'd enjoy small engines so much!

As for the grooves... I like the thought, yet must ask myself why no manufacturer with huge amounts of money and testing resources has put grooves in their heads if it offers any benefits.

I could easily be wrong, but I think the answer to that is manufacturing cost. Not seemingly hard to machine cut some grooves, but they would have one more machine, one more machine operator, plus the cost of handling to and from that machine/operator. Doesn't seem like much, but face it...these are low powered machines that WE enjoy making perform better. They put cash into 4 strokes to make the EPA types happier.

I have a few OEM heads for my Gyro, so I can easily play. I am going to bump compression a tad, so will try with only head changes first. My approach is simple, as I earlier suggested. Better fuel mixing and transfer port efficiency. Slight timing bump there. Ignition is set, which was huge!  OEM box was set to ramp as follows: 18° BTDC @ 2000rpm, 20° @ 4500, 15°@ 8000. We were told that it was rev limited to 8400 rpm.  Funny, but with throttle/fuel overlap, that is about right with the timing retarding. My DIO box is more progressive from 17° @1800 to 21° at ~9200.  Doesn't ramp linear, however. I suspect that it was programmed to "step", or "jump" by the way it reacts. 17°-21° all at once.  I prefer 17-18-19-20, maybe 21 is too much for long runs, maybe not. I did have a few soft seizures, but with the oil pump...nothing since switching to premix.

Those are my baby steps, along with our own pipe build to match the test setup. We are hoping for 7 or 8 hp with our mild/mid pipe, port work and some carb...TBD. We are testing my PBHG 19 and maybe a 17.5 to compare.  We also have a diaphragm carb.  A Tillotson clone, that I am slightly modifying. The part total is not even $150 yet. Pipe cost not included however, because I want better quality welds. Oh, we have many roller weights and such to play with also...just collected them from tear-downs/wrecks and such.  My friends buy every used pile-o-poop they can find...clean them, fix the engines, paint them, polish them and sell them. Fun...work.

[catchacuda]

I apparently don't know what Im doing, trying to check port durations.

I position the piston just above the exhaust port on the down stroke. Put degree wheel at zero. Rotate the crank to bdc, and back to just covering the exhaust port. Time and time again Im seeing 305°

Im sure im doing something silly here...

Transfer duration shows 235°??

Also, using one base gasket.

[190mech]

Take a look here;
49ccscoot.proboards.com/thread/353/port-durations-degree-wheel-methods
Hope this helps...

[oldgeek]

When using the easy method, you have to count the degrees the wheel moves from the zero setting. Do NOT use the numbers printed on the degree wheel. Hope this helps.

[catchacuda]

So exhaust @ 152°

Transfers @ 107°

Does that sound more realistic?

I really feel like a fool here.

[oldgeek]

Don't ever feel like a fool here, that's my job!Lol

Numbers are pretty tame, but that is a stock 50cc. You could do some work like raising the exhaust port roof a tad and get the transfers flush with the top of the piston at BDC, but there is still the issue of too much squish that will require milling of the cylinder deck or a step cut head that extends into the cylinder a bit.

I also might mention a lot of paper base gasket can compress or settle in over time, it is best to cut some from a metal material or buy some pre made shims.

[catchacuda]

Thank you, what kind of durations would be recommended to wake it up some? Yes, the squish will need some work. I'm not bad with getting things flat on glass with paper, but there is also a machine shop literally 5 minutes from me. I figure I'll get the cylinder done and then see how it behaves and move to the cvt.

[90GTVert]

Here's a little info on porting. A post above it shows adjusting with base gaskets/spacers.
49ccscoot.proboards.com/post/30229/thread


This may help to show you some potential pitfalls of porting and why you need to be careful.





Those numbers are really low, so I would advise double or triple checking everything. If you decide to port, do the same. Make multiple checks before you start slinging metal.

[catchacuda]

Great, thanks for the link and video. I'll check again to be sure of the durations. I've come to realize I have no idea where to find a pipe for this thing. Plenty of scooter pipes I could maybe modify to fit.