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Convert GMS 120 glow to Gas

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Old 10-20-2007, 09:30 PM
  #26
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Default RE: Convert GMS 120 glow to Gas

I tried the pressed sleeve on the crankpin on one of my 2300 and it eventually worked lose after a few runs so I had to replace the pin with a hard ground dowl pressed into the crank and have no problems sense .
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Old 10-20-2007, 09:31 PM
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Default RE: Convert GMS 120 glow to Gas

by the way I am in clearwater Fl. now for a few months if you want to see one of my engines.
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Old 10-21-2007, 04:45 AM
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Default RE: Convert GMS 120 glow to Gas

Florida??? Does this mean you've officially retired of being a Texan
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Old 10-21-2007, 06:33 AM
  #29
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Default RE: Convert GMS 120 glow to Gas

we will be here for 3-6 months , we still have a texas residence and adress . Did you get that engine converted yet?
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Old 10-21-2007, 09:06 AM
  #30
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Default RE: Convert GMS 120 glow to Gas

I'm on the east coast Palm beach area. So clearwater is far for me otherwise definitely I would have met you.

Now I wonder why the press fit sleeve would come out? Do you know the reason?
I had to apply a lot of force to fit it in..

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Old 10-21-2007, 11:39 AM
  #31
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Default RE: Convert GMS 120 glow to Gas

I got this far then moved on to another project, I'll get back to it one of these days.
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Old 10-21-2007, 05:59 PM
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Default RE: Convert GMS 120 glow to Gas

I think it is because the piston and rod kinda starts beating on it ans eventually gets lose and starts turning, my opinion but it did it on 2 engines and both were press fit.
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Old 10-25-2007, 01:25 PM
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Default RE: Convert GMS 120 glow to Gas

I pressed on a commercial inner race on a pair of ST-3000's and never had a problem.... you need a TIGHT press though....
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Old 10-29-2007, 10:02 PM
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Default RE: Convert GMS 120 glow to Gas

flipflop: Are you still running the Mack MB260 engine yet. Mine is taking a heck of a beating in my leaf blower this fall. She screams!!!! Capt,n
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Old 12-03-2007, 02:37 PM
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Default RE: Convert GMS 120 glow to Gas

Ok guy,
I'm planning to test the engine sometime this week. My question is, usually in this kind of conversion what should be the initial ignition timing? 10 , 20, 25, or 30 degree before TDC and why?

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Old 12-03-2007, 03:52 PM
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Default RE: Convert GMS 120 glow to Gas


Quote:
ORIGINAL: borna

Ok guy,
I'm planning to test the engine sometime this week. My question is, usually in this kind of conversion what should be the initial ignition timing? 10 , 20, 25, or 30 degree before TDC and why?

Thanks
Borna
Pe suggested I try 20 on mine and move up in small increments until I found the right amount. I started there and worked my way up to 32 where the idle was pretty rough. The top rpm's didn't gain any more after 28 so I moved it back there. The idle is OK there as well so I locked it down and flew it for the first time this weekend. It runs much better than I expected. Since I am stuck running 16:1 gas to oil your timing might be a little different with less oil. I am thinking the oil might slow the flame down initially which is why I might be needing the 28 degs. I have to say though that is where my Zenoah G26 runs it's best too. I just would have thought the smaller cyl. and combustion chamber wouldn't need as much timing lead. Mine runs 30 mins in the air on just about 5 oz. of fuel. Good luck and let us know how it runs.
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Old 12-03-2007, 04:46 PM
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Default RE: Convert GMS 120 glow to Gas

Generaly speaking there is little or no gain after 20 degrees of advance for smaller engines
and they start easier at 20 than 28 degrees.
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Old 12-03-2007, 05:18 PM
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Default RE: Convert GMS 120 glow to Gas

Thanks guys.
So what are the disadvantages of less than 20 degree. Let say 10 degree BTDC?
Also since this will be my first gas engine, what should be the starting procedure as far as how much gas I need in the carb before starting it?

The carb I'm using has a pump but no chuck or primer bulb, so I have to prime it with my finger on the hole. When priming it do I need the throttle opened or should be closed?

Thanks
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Old 12-04-2007, 11:50 AM
  #39
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Default RE: Convert GMS 120 glow to Gas


Quote:
ORIGINAL: Ralphbf

Generaly speaking there is little or no gain after 20 degrees of advance for smaller engines
and they start easier at 20 than 28 degrees.
Ralph, I respectfully disagree as I just did this on my SuperTigre 51 this past week. It lost almost 1700 rpm's going from 28 back to 20. My Zenoah G26 exhibited the same behavior when I first converted it to EI. I can't tell you why your results are different but other respected engine guys, one of which no longer frequents this forum, have said 28 is the place for the small gasers like the G26. Pe Reivers suggested that I might try 20 and work up from there as he didn't think it would need 28. I assure you it gained close to 1000 going from 20 to 24 and almost another 700 going from 24 to 28. It gained nothing advancing it beyond that, just idled worse. It is very hard to imagine it starting any easier. Yesterday I started and ran it for the guys I work with. Some of them are into RC and were interested in seeing a converted ST51 running on gasoline with spark ignition. After a few prime flips with the ignition off, I turned the ignition on, flipped it once, it fired then died. One more flip and it was running and stayed running until I shut it off. The temp outside at the time was approximately 50 deg. No electric starter needed. Again, I am not sure why you are seeing different results but that is how mine is behaving. Fly's great in the SuperSportster too. I am very impressed with this little motor other than it is just a little sensitive on the main needle. Nothing I can't live with though. Have a great one all.
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Old 12-04-2007, 08:34 PM
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Default RE: Convert GMS 120 glow to Gas

The universal magic timing number for 95% of our engines is 28-30 D BTDC.
The oddballs are the YS engines and some of the older big tigers on gas. The YS likes 25-26 and the ST's 26-28
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Old 12-04-2007, 09:06 PM
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Default RE: Convert GMS 120 glow to Gas

When the piston is at TDC there is a few degree of free play on connecting rod and crankshaft before piston starts to move down. Are you consider that free play as part of TDC or not.
For example, when piston is all the way up, it will take for example 2 or 3 degree of conterclock wise before piston starts to move down.

so TDC consider + the extra 3 degree of the free play or - the extra 3 degree?

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Old 12-04-2007, 09:52 PM
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Default RE: Convert GMS 120 glow to Gas

There is only ONE good method for finding top dead center, and all degree measurments when working with engines are measured from that. It is called the "positive stop method", and it deals with the dwell period at TDC that you speak of, and it is used in everything from race engines worth many thousands of dollars, all the way down to our little engines.

You insert something into the spark plug hole that will not move in the slightest, but will stop the piston just before it reaches top dead center. You then install a degree wheel, and "eyeball" top dead center on the wheel/pointer. Then turn the engine over gently until it stops, and note the degree setting. Then turn the engine over gently in the other direction until it stops and note the degree setting. What you are looking for is a degree wheel position that affords the exact same number when the engine stops in either direction. Adjust the degee wheel until you have this condition. When you achieve this, the degree wheel will be indicating an actual top dead center when the degree wheel reads 0 degrees, TDC, (once you take your "positive stop" out). All measurements, whether they are for port timing, cam timing, ignition timing, whatever, are referenced from this point.

Here's a pic of the "postiive stop" that I made for my engines. It uses a hollow tube in the center so that you don't have to fight compression when turning the engine over.

AV8TOR
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Old 12-04-2007, 10:02 PM
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Default RE: Convert GMS 120 glow to Gas

Yeah I know Terry, you just "fake it" and it's probably close enough that one couldn't measure the difference, but then you have been doing this for a while....

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Old 12-05-2007, 12:38 AM
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Default RE: Convert GMS 120 glow to Gas

We have done this a little different.

Turn the crank one way until the piston just stops moving up the cylinder and mark the crank.

Turn the crank the other way until the piston just stops moving up the cylinder and mark the crank.

Measure the distance between the two lines, divide by two and mark the crank.

You now have top dead center.

You can put most anything in the spark plug hole and watch it rise so you can mark the crank.

This works very well and takes no special tools .
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Old 12-05-2007, 03:05 AM
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Default RE: Convert GMS 120 glow to Gas

That'll work too. Same idea, slightly different method. I made the tool with an old spark plug and a piece of aluminum tubing JB Welded into it. It's handy and works faster for me, especially if I happen to be working on an assembled V/8!!

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Old 12-05-2007, 12:51 PM
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Default RE: Convert GMS 120 glow to Gas

A dial indicator is real precise....and not that costly. Handy for many engine projects. Capt,n
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Old 12-05-2007, 03:19 PM
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Default RE: Convert GMS 120 glow to Gas

A dial indicator will not find TDC unless used along with the manner posted by Ralphbf. By itself, a dial indicator will not allow for the dwell time of several degrees of crank rotation at TDC.

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Old 12-05-2007, 03:50 PM
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Default RE: Convert GMS 120 glow to Gas

It will work...just depends. On some engines with a flywheel you can have degrees marked on the flywheel. But you can use a dial indicator to make sure "O" Top dead center is marked right. The point I was making ...instead of using a spark plug "stopper" you can use a dial indicator in it place. Of coarse you would use the other gizmo's if you like.! Ha! If you want to try something interesting, use a timing light while engine is running. Some of the stock mag systems do have advance built in...like on my MB290. You can freeze the prop and read the size on it!!! Capt,n
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Old 12-05-2007, 05:13 PM
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Default RE: Convert GMS 120 glow to Gas

After I put the degree wheel on and find TDC I mark that and 28 degs. on the drive washer so I can set it with a timing light later and not have to use the degree wheel again. It is just sooo much easier to clip the timing light on and check the marks.
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Old 12-05-2007, 09:06 PM
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Default RE: Convert GMS 120 glow to Gas

Sorry to disagree Captain, but I don't want others to be mislead. A dial indicator will not show true top dead center. It will show when the piston reaches it's highest point, but that is not true top dead center by a number of degrees. How much depends on rod/stroke ratio, etc. but the point is, it is not true top dead center.

After the piston reaches it's highest point, the crankshaft will rotate several degrees before the piston starts back down. That's called it's dwell time, and that's why you can't simply use a dial indicator to find TDC.

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