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Post by magoconnor on Jan 28, 2018 15:46:37 GMT -5
Hello.
I have Port matched a 139qmb head and opened it up a little ( not to much).
Since i decided to grind/ lap the valves, I thought I might as well revisit the in/out ports.
I've been hearing good things about, going over the intake port with 40 grit sandpaper.
Has anyone tried it? Is there any other performance tricks out there?
The exhaust valve is clearly not sealing, the intake is a little better.
I've bought some rough and fine grinding agent.
Both inner valves springs appears to be broken.
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Post by 90GTVert on Jan 28, 2018 17:53:43 GMT -5
Sounds like a good candidate to experiment with. Sometimes there are some pretty rough areas in Chinese ports. Just be careful cleaning them up. You don't want to scratch or nick the valve seats. I did that after spending a bunch of time on a 139QMB head and my ride ended with flames shooting from the exhaust before it died as the exhaust valve burned. Don't take out a bunch of material, just try to clean it up. Some of these heads don't leave much margin for error because there's not much meat around some areas of the ports. You don't want casting flaw kinda rough, but you don't want a mirror finish either anywhere where fuel is present (polish the exhaust port all you want, but not any post-carb inlet parts). David Vizard has 5 "golden rules" that may be helpful if you don't want to read a whole book : www.cartechbooks.com/techtips/the-five-golden-rules-of-porting-cylinder-heads-part-7/ |
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Post by jeff84 on Jan 28, 2018 18:47:31 GMT -5
try and straighten out the bends but be careful not to take out too much material especially on the exhaust side. feel free to hog out the intake a bit though. but as mentioned above be certain there is material to remove before you go at it with a dremmel. this is a good product if you ever need to add back material. www.youtube.com/watch?v=RCrixbXz4rc |
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Post by magoconnor on Jan 28, 2018 23:45:09 GMT -5
Ok cool.
I'm going to change the head gasket (the cylinder head, will be the only thing I will be removing)
Do I need to change the base gasket?
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Post by 90GTVert on Jan 29, 2018 7:38:13 GMT -5
Try not to disturb the cylinder and you can probably get away with not changing the base gasket.
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Post by lilpinny on Jan 30, 2018 8:57:52 GMT -5
Try not to disturb the cylinder and you can probably get away with not changing the base gasket. Be real careful. Have a buddy hold pull the cylinder to hold it on it's case. When you remove the head it's going to want to tug on that base gasket. If it's a paper gasket it'll tear easy. And that'll suck 'cause you'll have alot of work to do to get at it to put new one in. |
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Post by jeff84 on Jan 30, 2018 18:19:18 GMT -5
Try not to disturb the cylinder and you can probably get away with not changing the base gasket. Be real careful. Have a buddy hold pull the cylinder to hold it on it's case. When you remove the head it's going to want to tug on that base gasket. If it's a paper gasket it'll tear easy. And that'll suck 'cause you'll have alot of work to do to get at it to put new one in. on a ruckus, maybe. on most air cooled scooter engines its not much more work at all. the hardest part is getting all the old gasket material off, and reseating the piston rings. honestly unless its really low mileage engine and I was going to do a base gasket I would replace the rings too. |
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Post by lilpinny on Jan 30, 2018 18:33:54 GMT -5
I’m talking gy6 but yeah. If I gotta remove the cylinder I take the piston wrist pin out and and leave the piston head in the cylinder and do it that way. That’s the work I was talking about you want to avoid... anything having to do with the cylinder 😀
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Post by jackrides on Jan 31, 2018 14:19:08 GMT -5
90GTVert's reference to the '5 golden rules of porting' are the real thing. Ports should have a uniform cross sectional area. If size transitions are not avoidable, use a gradual taper.
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Post by magoconnor on Jan 31, 2018 20:21:35 GMT -5
I bought a new BVH.
The exhaust pipe is not lining up with the exhaust port.
The port is bigger than the pipe, not much but some, whitch will in-turn make the exhaust gasses, flow straight into a wall.
The problem is the exhaust pipe's little "stub"/tip that comes after the mounting-bracket. The "stub" is some what smaller, than the rest of the pipe (bottlneck).
My exhaust is a sito leo-vince
Will it hurt anything if I just cut it off?
Also will it be to rough to finish the intake port with 40 grit sandpaper?
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Post by magoconnor on Feb 1, 2018 17:00:26 GMT -5
Anyone ?
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Post by GrumpyUnk on Feb 2, 2018 9:55:16 GMT -5
I think I read this post a second time... double posted? Any way, looked up 'sito leo-vince' as it's new to me. If you paid what I think they are asking for a system: scooterpartsco.com/leo-vince/leo-vince-4-stroke-exhaust-for-50cc-kymco-scooters?zenid=486fe6b99c2a112acc5e926bc04c4b81 Almost $200, maybe more with shipping.... AND It did not fit. I would be on the phone to the vendor. Especially if the diameters don't match the exhaust port on the BBH, or as noted, the diameters changed as you move along the piping. Fluid flow dynamics indicate the gases must accelerate and slow down as the diameter changes. Not too sure that's a good thing... If you can stand the turbulence that a 'flat wall' will cause, you can use the system 'as is', but the gas will have to maneuver to get out of the cylinder head, and that will affect flow. FWIW, I don't think small 4T's need much exhaust help. You may be able to 'tune' for a little wider power curve, but I dunno if it will be noticeable. I'd go for the lower-priced exhaust pipe, without muffler, and then find a muffler that had the 'tone' that I wanted. I don't need to make noise and draw attention, and doubt the louder systems have much, if any, more hp/torque. A 2T can be tuned more, as it uses piston timing via port position to set up harmonics within the exhaust that can help extract exhaust, but the 'rpm range' is not wide in them either. They go 'on peak', and are not happy in lower or higher rpm ranges. Most 4T's will have a bit wider 'power band', I think. Someone who does this for a living(or it is their life) may have a different opinion. tom |
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Post by 90GTVert on Feb 2, 2018 11:55:10 GMT -5
40 grit is pretty rough by hand. Most are stopping 40-80 with rotary tool bits. Probably OK, but you don't need it real rough, just not polished smooth. If you do some google searches, you can find pics of finished ports to give you an idea of what you're after. So you're saying your exhaust has a pipe that extends up beyond the header flange? That's done in some pipes so they hold a crush ring gasket easily. I have cut it out of 2T pipes before. That's shown in this thread : 49ccscoot.proboards.com/thread/374/remove-restrictions-aftermarket-pipes |
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Post by magoconnor on Feb 2, 2018 15:14:28 GMT -5
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Post by magoconnor on Feb 2, 2018 17:02:54 GMT -5
Do you even need the intake spacer ?
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