|
Post by 90GTVert on Oct 1, 2009 19:54:19 GMT -5
I've been expecting my cylinder head any minute now, and I just got an email that USPS has been notified to expect shipment of an item from monstergy6.com. I ordered on Monday, they contacted me on Tuesday and after confusing me for a few about what the head really is, said they'd ship it. 2 days later they've notified USPS to expect a package for shipment. I really thought I'd have my head or cylinder in the machine shop by tomorrow. Not so much.
|
|
|
Post by 90GTVert on Oct 5, 2009 23:59:49 GMT -5
I got the new big valve head in today. 50mm combustion chamber with 21mm intake/19mm exhaust valves. 47mm port matched head vs big valve head. I had planned to drop the head or cylinder off to the machine shop tomorrow to get a little milling done, but I wanted to do some checking first. Using the stock 49cc head, I came up with about 0.170" of clearance, so I thought I'd be milling off at least 0.030". This time around I got .055" of clearance on the intake valve and 0.080" on the exhaust valve. That's with no head or base gaskets, so I can assume an additional 0.010"-0.020" of clearance when using gaskets/RTV. I'm not sure why lol, but I made a quick diagram to show why the big change. The piston is flat on the edges and dishes in in the center of the piston. There are also valve reliefs in the dished area. The new valves miss the reliefs and hit in areas that are less recessed. The red marks are basicaly where the valve edges are in relation to the pistion. I'm used to .080"/.100" of clearance being proper spec for larger engines, now I'm dealing with roughly .070"/.095". I'm thinking those numbers will be fine for this engine, but I sure don't wanna mill anything off. I cc'd the combustion chamber just for comparison's sake. This thing is huge compared to the stock and 72cc heads. This head is roughly 7cc while the others were 4.5cc and 5cc. I hope this extra flow really works for me, because it sure won't be a high compression engine.
|
|
|
Post by 2strokd on Oct 6, 2009 8:37:10 GMT -5
Me to, hope it works out that is....
|
|
|
Post by Enviromoto on Oct 6, 2009 17:03:56 GMT -5
That head looks really good what did it cost? Name brand?
|
|
|
Post by 90GTVert on Oct 6, 2009 18:58:18 GMT -5
NCY $116 monstergy6.com/product_heads.htmThey changed their description. It did say 47mm or 50mm and you chose which you wanted. Then when they looked at the order they were confused and eventually figured out that they only had 50mm. I was going to contact you, but I'm not a patient person when it comes to getting parts and you didn't seem to carry it and they had it in stock. No one but them listed it in 47mm, and then I found out why.
|
|
|
Post by 90GTVert on Oct 7, 2009 21:21:20 GMT -5
I did some port matching and clean up work and put the engine back together with the big vavle head, 150cc intake, and 150cc carb. I didn't really do a lot of work because I have been reading and thinking and I don't think this setup is going to be too great anyway. I think that the valve sizes (21mm In/19mm Ex) are pretty well suited for a strong running little GY6, but the intake track is a bit large. Here's part of why I think this... A. Graham Bell, very famous for his 2T tuning book, wrote a 4T tuning book. In this book he states that intake port area should be 81 to 83% of the intake valve area. I have a 21mm intake valve... Valve Area = Pi x radius² Intake VA = 3.1416 x 10.5² Intake VA = 346.36mm² Intake port area should be 81-83% of intake valve area so... Intake Port Area = 346.36 x 0.82 Intake Port Area = 284.04mm² Now I need to see what size port is needed to achieve that area. 284.04 / 3.1416 = 90.4 √90.4 = 9.51 9.51 x 2 = 19.02mm So an ideal intake port size would be around 19mm if this is all correct. Exhaust port area is much more simple, according to Bell. He says that exhaust port area should be 95-100% of the exhaust valve area. I don't need math to figure out that 100% of 19mm (ex. vavle diameter) is 19mm. lol I have seen more modern porting articles that noted that the exhaust port could be slightly larger than the valve. Bell also notes that he does not agree with port matching the exhaust port to the header. He feels that the step is necessary to reduce exhaust gas backflow into the cylinder and believes that port matching here will certainly reduce power, specifically in the midrange. OK, so go port the intake to 19mm and open the exhaust up to 19mm right? Not that easy. The stock intake port on this head is 21mm, 2mm larger than Bell believes is ideal. The exhaust port is just shy of 19mm, so that could be handled easy enough. From what I have read and seen, the carburetor should be basically the same size as the intake port. That makes the stock 19mm carburetor nearly ideal (perhaps a slide carb with no butterfly to restrict flow may be a little better?). This also makes a ported and port matched stock intake ideal. Since the intake port was already 2mm larger than the stock intake, I decided to just port match and use the 150cc stuff and see what happens. This thing might end up being a dog. We'll see. Knowing all of this, I'd like to see a stock 49cc head setup for a 21mm intake valve, 18-19mm exhaust valve, 19mm ports, 19mm intake, and a good 19mm carburetor. Of course some real port shaping would be cool with that setup too. I may be way off on all of this, but it makes sense to me anyway.
|
|
|
Post by 2strokd on Oct 8, 2009 6:49:34 GMT -5
Makes sense to me, thanks for the input on the 4strokes. I would have never thought about needing a "step" in the exhaust for more lows and mids. Bell knows his motors so i want argue with him. I have wondered about these lil cv carbs. Seems like it takes too much energy to make energy, allot for a small motor to handle, even worse if its an emission motor. You should try a different carb, ide be curious to here if that helps. Of course after you try this setup out. Hopefully it a power house and Bell,s theory will just make it badasser lol.
|
|
|
Post by 90GTVert on Oct 8, 2009 7:04:48 GMT -5
If this setup works alright, the goal is to leave it alone for a bit. I do enjoy trying new setups but, even on such a small engine, money goes quick swapping things over and over. I wasn't even thinking of the effort exerted to control the slide in the CV carb. My main thought was that you have an 18.8mm carb, so if you looked at that as surface area it would be 277.59mm². The butterfly shaft takes up 18.8mm by roughly 3mm, or 56.4mm². 277.59 - 56.4 = 221.19mm². 221.19mm² is equal to the surface area of a port that is only 16.78mm in diamter. I forgot to mention, I took care of that pesky stock tail light socket last night too... and it only cost about $3. www.49ccscoot.com/lightfix.html
|
|
|
Post by 2strokd on Oct 8, 2009 7:11:45 GMT -5
Good job on the TL! A $3 repair is on the good fix list.
|
|
|
Post by 90GTVert on Oct 8, 2009 15:54:56 GMT -5
The engine is back in and running. I haven't done any tuning. It's still got a miss at idle, so I set the pickup back to stock. It still misses. I was suprised that it can be moved and isn't absolutely horrible just bolting on a 150cc carb/intake. I expected it to bog terribly, then really pick up once it starts to rev. Instead, it has good power at 1/4 throttle and under, and does nothing really once it revs up. It's gonna need carb and trans tuning from what I can see so far. The good news is that it's acting like it won't be a complete dog.
|
|
|
Post by 90GTVert on Oct 8, 2009 20:12:24 GMT -5
The stock main jet in this carb is 105. I tried going up to 115 and down to a 95 (seems like a lot of 70-80cc users like 92-95). I can't really tell a lot of difference either way. I replaced my stock plug boot with an NGK resistor boot hoping it would help make a tach work. Nope. I put a Kitaco super coil on that I used to use on a midbike. Nothing. Maybe I've got a bad ear, but it sounds like pretty much the same RPM with every jet. It's dark so I can't see the speedometer, and it feels like it's going about 30MPH each time. I'm done for now. Hopefully I can do some tuning tomorrow and actually get somewhere. I will note that using the 95 main there is a spot in the throttle that does throw me back a little from a very low speed for just a moment. Of course I'm not trying to tune for anything buy WOT right now, so it's sorta irrelevant. There's a light trying to shine through... will I let it out... prob not. lol
|
|
|
Post by 90GTVert on Oct 9, 2009 7:12:15 GMT -5
I went out this morning and made 2 mods before I did any carburetor tuning. First, I moved the ignition timing towards advanced again. I had moved it back to stock because my father keeps telling me that's why I burnt the valve. I just don't see it. If anything, I would think that retarded timing would be more likely to burn an exhaust valve because the combustion would be happening closer to the time the exhaust valve opened so it would heat the valve. I still think it was solely because I screwed up and knicked that valve seat. I've advanced the timing on midbikes to the point that they would barely run and then backed it off just enough to get good performance and ran them that way from then on. Never burnt a valve that way. Second, I replaced the 5.8g rollers with 7g rollers. Naraku recommends 5.8g with 72cc and 6.5g with larger kits. I see a lot of people saying 5-6g depending on rider weight. It just seemed like it was hollow up top and I didn't think it was the carburetor tuning causing that, so heavier rollers made sense to me. Now that I can see the speedometer, I went out and started making 1/8 mile (almost) passes from my driveway to turn off and then back around and recording the MPH. I think the rollers really did the trick, because now I can actually tell a difference. I think the main reason you will see a difference in 1/8 mile speed there (MPH 1) and back (MPH 2) is that there's a slight wind. Main Jet----------MPH 1------------MPH 2 ---95---------------32---------------30.5-- --100---------------33---------------32.5-- --105---------------34----------------33---- --110--------------34.5---------------33--- --115---------------33----------------32--- I'm going to retry both the 105 and 110 main jets and make sure I'm braking at the same point with each since the numbers are so close. I'll try running it out a little farther too. The 110 looks right so far from these numbers, but there's a lot of rumbling and poping when I let off from WOT with the 110 and 115. From plug checks last night, 115 is where I get the golden rim of the spark plug with a deep tan porcelain. That would be good for a 2T, but not so great for this apparently. Just for reference, even though this thing is doing much better, it's no Triton. Doing an identical run with the Triton usually gets me to about 46-48MPH. I will give the 4T credit though, it will get to 15 or maybe 20MPH as fast as my Triton... after that there's no real comparison.
|
|
|
Post by 2strokd on Oct 9, 2009 7:44:56 GMT -5
Well its running ;D! I keep picturing a huge cork thats hiding in it somewere lol. Glad you havent let this little four beat ya. You and your dad gonna ride some more? Bet he dosnt mind it being too slow? Maybe some miles on it will loosen it up a bit and free up some power. That would give you time to examine it running and think about the next cheap idea??? You have a extra carb (non cv) you could try dont you? Or maybe a 19mm setup like Bell says... Either way i would ride with pop if you can before doing anything else, ya know, get sum of your moneys worth out of it.
|
|
|
Post by 90GTVert on Oct 9, 2009 8:31:40 GMT -5
Yeah, at this point the plan is to get it tuned and ride. I've done enough experimenting with the engine stuff. It's pretty much doomed to be slow short of spending some cash on a more correct head setup with larger valves, but a smaller combustion chamber and smaller ports or going up to a possibly bearing killing 80+cc that would also create higher compression with the same head. From what I've seen so far, the stock stuff worked over with the larger cam did as well as the bigger stuff with port matching and the larger cam. In fact, I think the other setup may have been a little better, most likely because of the compression. I moved from 4.5cc to 7cc in the combustion chamber. People claim gains just moving from the 70cc head to the 50cc head for more compression, and that's only a .5cc difference in combustion chamber volume. It's just a shame the valves don;t line up with the reliefs so I coulda had some milling done. Even then, if you took the stock head and milled it down it would be just that much better still.
I've got a 19mm Arreche here as well as the stock carb and then I have a 26mm Mikuni lying around. I don;t think any of those would be good with this setup.
My father said he'd like to cruise at 40. I might be able to make that happen.
Here's what I got from a little more testing...
MPH 1 = 1/8 mile to \ MPH 2 = 1/8 mile from \ MPH 3 = Straight 3/4 mile \ MPH 4 = Curvy 3/4 Mile
Main Jet-----MPH 1-----MPH 2-----MPH 3-----MPH 4 --105---------34.5--------32--------38.5--------39 --110---------34.5-------32.5--------37.5-------39
Kind of odd results. The wind was blowing and switching around so it messed up the results slightly. I think the 2 jets are about equal in performance. I'll have to see if I have a jet drill that will do 107-108 or if I have a 107-108 around. If so, I'll stick that in and call it done. Then I can move on to needle clip and low speed settings.
|
|
|
Post by 2strokd on Oct 9, 2009 9:00:31 GMT -5
Works for me . Just tell your dad to weave around if it wont get up to 40 lol. Weird that you went faster on the weave road. Cool, if he is happy with 40 then you guy outta plan a cruise
|
|