Holy crap! half of my transfer ports were blocked.!

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crmachineman

crmachineman

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May 24, 2012
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Man, I've just started figuring out these 2 stroke engines, and with all my poking around, I was shocked to find that almost half of my transfer ports were blocked by the piston when it was at the bottom! I was a new GT-5 motor, runs real smooth, especially after crank rework. I'm sure some of you guys have seen this, but jeez, I noticed the engine seemed anemic when I was testing it, although it had really good low end torque. I machined some channels on the top of the piston for each transfer port and a little for the exhaust port because that was a little blocked by the piston as well. I picked up 3-5 MPH just from that little tweaking. I wonder if there are other porting modifications that can be done to improve high end power? How about it?
-Fred
 
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young grease monkey

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You can stuff the crankcase for more primary compression, that will help high rpm power a lot. Also a better carb like the one from dax will help. You might want a custom head so it fits perfectly with those cutouts on the piston and for higher compression. I could help you with that, you will need to take a head and use JB weld to fill in parts of it to make a squish band. Install the head with JB weld smeared inside it and some wd40 on the piston so it doesn't stick. Then slowly crank it over without a spark plug. Let the JB weld cure and ship it to me. I will refine the shape of the JB weld into a squish band, then make a casting. If you are interested, pm me. I think I am the only member here with a foundry, many guys have lathes and mills and I wish I had those but a foundry is really cheap to make a crude one. I have less than $20 of materials in my furnace and it can melt aluminum alloys using charcoal or oil.
 
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crmachineman

crmachineman

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Wow, you'll make your own castings? That's very cool! I wonder how much you would charge for a head? Your right, I could use higher compression now. I also think additional cooling is needed too. Do you think you can do something about that?
-Fred
 
crmachineman

crmachineman

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May 24, 2012
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young grease monkey said:
You can stuff the crankcase for more primary compression, that will help high rpm power a lot. Also a better carb like the one from dax will help. You might want a custom head so it fits perfectly with those cutouts on the piston and for higher compression. I could help you with that, you will need to take a head and use JB weld to fill in parts of it to make a squish band. Install the head with JB weld smeared inside it and some wd40 on the piston so it doesn't stick. Then slowly crank it over without a spark plug. Let the JB weld cure and ship it to me. I will refine the shape of the JB weld into a squish band, then make a casting. If you are interested, pm me. I think I am the only member here with a foundry, many guys have lathes and mills and I wish I had those but a foundry is really cheap to make a crude one. I have less than $20 of materials in my furnace and it can melt aluminum alloys using charcoal or oil.
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Hey, Young grease monkey, I've been thinking about cylinder head designs for these engines. I am becoming increasingly informed about the nuances of these kind of engines mainly from this writing http://www.2strokeengine.net/gordonjennings/twostroketunershandbook.php
Are you familiar with this writing? It's really good. This guy really knows his stuff, and I have already learned quite a bit, and I havn't even read half of it. There are some interesting things he mentions about squish bands; that you can have a "semi squish" band that squishes the exhaust side of the piston only. That seems like a good approach, what do you think?
-Fred
 
RicksRides

RicksRides

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Feb 22, 2012
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CR b4 I would stuff the crankcase on any 2 smoker I would elimanate the head gasket and replace it with copper o ring after milling a small graove in both jug and head this will increase your compression on the up stroke only and stuffing the crankcase will only increase compression on down stoke , you may still want to stuff the crankcase but only after eleminating the head gasket when I was younger i raced karts this is how we got that extra out of them and it will bring it to LIFE, just my 2 cents worth. rick
 
crmachineman

crmachineman

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May 24, 2012
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Hey Rick! Thanks for that tip. I've been reading a 2 stroke tuners handbook, and it recommends that style of head gasket. I'll try to find an appropriate copper o-ring. The kind of o-ring that is hollow and open to the compression gases will actually maintain a seal better than a flat gasket cut from a sheet. I can do the machining here at the shop. There has been a lot of talk about stuffing crankshafts, and I'm not sure what to think: In this 2 stroke tuners handbook I've been reading, which is largely based on Yamaha's relentless work they did in the past, said that there were negligable preformance gains by increasing the crankcase compression ratio. I'll do more research, but when it comes to the topic of wheter to stuff or not?...-I'm confused, so I'm going to leave that alone for the time being.
Thanks again,
-Fred
 
killercanuck

killercanuck

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ygm said:
I think I am the only member here with a foundry
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There are some others making castings. Norm has a great thread you should check out.

Yea those half covered ports seem like a waste, eh? Guys have experimented with putting a milled block under the jug and milling the top of the jug. So they open all the way, but then your port timing would need a lot of tweaking.

I've never heard of stuffing the crank. Only dimpling, like a golf ball for better airflow. Know what I mean?
 
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young grease monkey

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i would send you a couple rough castings for free if you let me keep the original! you will need to drill and tap the spark plug hole and stud holes, as well as lap the gasket surface. you could make the fins bigger by using some plywood and jb welding it to the fins, but they must all be parallel so that when I make a mold using it as a pattern, i can pull it out of the sand without any edges catching. Also, it needs to have at least 1 degree of draft, that is a taper so that it pulls out of the sand cleanly. not hard to do, just smear some jb weld on there and sand it down. as for head design, i would just go the normal squish band because there is already a feeble attempt of a squish band in the head design, and leaving it that way would cause areas that don't get ignited with the rest of the fuel/air mix because they would be blocked off at tdc. you would have to remove material to make a good head with a half squish band. look at jaguar's site and what he says about crank stuffing; http://dragonfly75.com/motorbike/
the reason that stuffing a yamaha didn't give much power increase is that they probably already had very good case compression, and the same with go cart engines. these are terrible, and that's a big part of why they can't rev very high.
 
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nightcruiser

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I'm all for tweaking and improving these little 2-strokes, but putting JB Weld inside the head??? I don't know for sure, but to me it certainly sounds like a problem waiting to happen?
I don't know what it is about that stuff, I guess it's the new duct tape, it seems to be the new go to fix whenever things aren't working out. In my world zip ties are the new duct tape! LOL

PS WHEW, I just noticed the part where you said CASTING... Shaping a head with JB weld and then making a new cast should work out wonderfully.... I guess I just jumped to conclusions because I read so often here people using JB Weld for everything and anything...
 
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ivan H

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Oct 8, 2011
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regarding reshaping a head so u can cast a new 1, first decide whether ur looking 4 low/mid power, (wider squish band, higher C.C. ceiling & higher compression ratio around 9.5 or 10 to1), or top end power, (less squish area, low, broader C.C ceiling & lower compression ratio of around 8 or 8.5 to 1). Wot was said about stuffing the cases was right, these benefit due 2 a low ratio. Dimpling lessens the boundary layer effect, improving flow thru the crankcase. Cheers
 
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crmachineman

crmachineman

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May 24, 2012
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ivan H said:
regarding reshaping a head so u can cast a new 1, first decide whether ur looking 4 low/mid power, (wider squish band, higher C.C. ceiling & higher compression ratio around 9.5 or 10 to1), or top end power, (less squish area, low, broader C.C ceiling & lower compression ratio of around 8 or 8.5 to 1). Wot was said about stuffing the cases was right, these benefit due 2 a low ratio. Dimpling lessens the boundary layer effect, improving flow thru the crankcase. Cheers
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Alright Ivan. Now hold up, let me try to understand what you are saying... If I wanted more high end power, I would keep the compression ratio a little lower? How come? My intuition tells me that a higher compression ratio would help at all speeds. Please enlighten me.
Thank you!
-Fred
 
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young grease monkey

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I wouldn't go over 8.5 anyway, otherwise you will start blowing gaskets and bearings. Upgrade the small end bearing with one from bearingsdirect.com , they have a 10x14x15 for $7. Do the bottom end as well if ya got the time to split the cases.
 
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nightcruiser

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crmachineman said:
Alright Ivan. Now hold up, let me try to understand what you are saying... If I wanted more high end power, I would keep the compression ratio a little lower? How come? My intuition tells me that a higher compression ratio would help at all speeds. Please enlighten me.
Thank you!
-Fred
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Sounds to me like a situation that begs some experimentation! I hope you end up casting a few different heads and report back some info on the results...
 
crmachineman

crmachineman

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May 24, 2012
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Right! Well, it's funny cause I was just looking over my scrap pile of odds and ends, looking for some aluminum to make a head. I found a nice piece of solid round aluminum which would do the trick. Someone on this forum even mentioned two spark plugs, and I'm thinking about possibly trying that. I've even thought about a water cooled head, because it would be pretty easy to machine. but I don't think this engine deserves such a radical treatment. I've got to do some more research on combustion chamber shapes and squish bands before I start. I'll definitely keep everybody posted when I start farting around with that.
-Fred
 
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ivan H

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Oct 8, 2011
622
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Hi, the (general) figures I gave on head design come from years of testing by many people. Do a bit of reading on Macdizzy's technology exchane, or from publications by Jennings, Bell, or Eric Gorr's baasic 2 stroke tuning (where figures came from) for an in depth answer on why. If trying 4 more power out of these, upgraded bearings is a must, especially the small end. U'll fit aa 10x14x16.5 in there. Cheers
 
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ivan H

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I also run an RSE head that has a good bit higher static compression ratio than 8.5: 1 (have upgraded bearings) & have advanced the initiaal firing, with no adverse effects. Cheers
 
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LaLongueCarabine

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Aug 15, 2011
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nightcruiser said:
I'm all for tweaking and improving these little 2-strokes, but putting JB Weld inside the head??? I don't know for sure, but to me it certainly sounds like a problem waiting to happen?
I don't know what it is about that stuff, I guess it's the new duct tape, it seems to be the new go to fix whenever things aren't working out. In my world zip ties are the new duct tape! LOL

PS WHEW, I just noticed the part where you said CASTING... Shaping a head with JB weld and then making a new cast should work out wonderfully.... I guess I just jumped to conclusions because I read so often here people using JB Weld for everything and anything...
Click to expand...
I had some friends and brother get stuck 4 wheeling in the woods. They broke an axel. They had a tube of JB and pulled the axel cleaned it with gas, JB welded the break and cured it over a slow fire. They drove slowly but got out.
 
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nightcruiser

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Mar 25, 2011
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LaLongueCarabine said:
I had some friends and brother get stuck 4 wheeling in the woods. They broke an axel. They had a tube of JB and pulled the axel cleaned it with gas, JB welded the break and cured it over a slow fire. They drove slowly but got out.
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JB Weld is good stuff, I have used it on occasion to repair things and it has worked well. But when someone says "I sealed my carb on my intake with JB weld" or something similar, I start to wonder. People people seem to advocate using JB weld in ways that just don't make sense to me. It's great stuff, but not a silver bullet for every problem....
 
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Drewd

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nightcruiser said:
JB Weld is good stuff, I have used it on occasion to repair things and it has worked well. But when someone says "I sealed my carb on my intake with JB weld" or something similar, I start to wonder. People people seem to advocate using JB weld in ways that just don't make sense to me. It's great stuff, but not a silver bullet for every problem....
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Blasphemer! You can build an engine block out of that stuff!

Seriously, JB weld is used in many unorthodox ways. It is even used in 1.3L wankel (Mazda) engines to seal off certain internal engine bay areas when porting is done.
 
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