Base Spacer

Well, I got to working, and I built myself a degree wheel :cool:. I printed the wheel form an image I found, glued it to a piece of cardboard, and punched a hole in it and put it on a 14mm socket that fits nicely onto the not holding on the magneto. I also used a piece of 22 gauge solid copper wire as a needle. The result are in. (I should also not I measured port area's as well)

Exhaust Port Mean Area: 1.1 square centimeters
Exhaust Port Open For: 140°

Transfer Ports Mean Area: 1.19 square centimeters
Transfer Ports Open For: 110°

Intake Port Mean Area: 0.95 square centimeters
Intake Port Open For: 120°


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Chad the duration is probably a little more if you tighten down at least two studs, I stack a few larger nuts on two and torque down for more accurate measurements.
 
I figured it would not be that accurate, so that’s why I took some tire scraps and cut out a “washer” to put on the nut to prevent any play in the socket. Though as a point of fact, the disk is just loosely on the socket. But once I got the disk aligned correctly with the crank, I used a sharpie to mark a place on the disk and the socket; so Incase I hit the disk accidentally, I will be able to correctly align it again.
 
Greg58 said:
I'm referring to compressing the cylinder base gasket, it could be a few degrees off without it.
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Oh yes, when I was turning the engine over, I noticed that the cylinder kept popping up, making it difficult for me to measure, so I tried compressing it with my left hand, and it seemed to suffice.

Also I seem to of take some of the wrong measurements, I was at first under the impression that mean port area is just half the port uncovered, but it is actually half of the degree that the port is opens, then graphing the area. But instead of me calculating all over again, I just took the total port area that I had recorded earlier, and multiplied it by 0.7 to get the correct mean port area. Also just to be extra sure I took the total port height measurement, then I took the port height measurement when it was half the degree of when the port begins to open (for example: exhaust port opens at 70°, so I would take height measurements at 35°). when I plugged these numbers into a percentage calculator (where full port height is 100%), the port height when the crank is half the degree of when the port begins to open was ~63%-70% of the full port height, which further confirmed my theory. So here are the true result:

Exhaust Port Mean Area: 1.54 square centimeters
Exhaust Port Open For: 140°

Transfer Ports Mean Area: 1.57 square centimeters
Transfer Ports Open For: 110°

Intake Port Mean Area: 1.25 square centimeters
Intake Port Open For: 120°
 
Sorry if that was hard to follow but... Anyways. This is probably not accurate in any appreciable degree, but like you said

Greg58 said:
it is accurate enough for what I’m doing.
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So Imma just roll with it. I'm mostly just doing this to get an idea of where this engine stands, so I can work from there, also to practice the skill so I prevent screw ups in the future. I really won't run over anything with a fine tooth comb until I start doing some precise tuning.
 
Regardless, the my engine lacks (quite horribly in) good port timing. According to Gordon Jennings' my:

Exhaust Port's Specific Time-Area Value Is: 0.000087 sec-cm2/cm3
Hence, it is time-area deficient in the order of: 38%

Transfers Ports' Specific Time-Area Value Is: 0.000069 sec-cm2/cm3
Hence, it is time-area deficient in the order of: 14%

Intake Port's Specific Time-Area Value Is: 0.00006 sec-cm2/cm3
Hence, it is time-area deficient in the order of: 57%

Now al there is to do is wait, I ordered some Dermel bit on eBay and I am patiently waiting for their arrival so I can begin porting right away. Also, one good bit of news, the MZ65 Clone Expansion Chamber finally came in :) The only problem is that the pipe hits the frame now, any suggestions on fixing this? I was just planning on heating up the pipe with a torch so I can bend it, but I didn't really want to burn the paint off, oh well, I guess.
 
I had to heat one of mine, I bent another in a vise. The CDH pipe was used when I got it and had been heated and bent, a painted pipe is easier to clean up than a chrome one.
 
Be careful with porting, if you have a G4 type open tranfer cylinder it will be very hard to keep the roof of the port angle the same. I increased my port timing by ramping the piston at the transfers and exhaust port, you can raise the cylinder with a second base gasket and then remove the thickness of the gasket from the deck of the cylinder to get the compression back to where it was. You don't need to work on the bottom of transfers or exhaust, the piston crown doesn't go that low, go slow or you can make a mistake. Remember what you gain on top end usually is a loss of bottom end power.
 
Greg58 said:
Be careful when porting transfers, they have to match. If you get them wrong it will hurt performance.
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Just asking, how much could this hurt performance? What problem does it cause? I seen an image of one guy's motor and it had all the transfer ports flush with each other, except 1, which was greatly exaggerated in area. Would that engine have running issues?
 
It's complicated, the ports need to be closed long enough for the piston to compress the fuel mixture as the piston travel towards BDC, so it will fill the cylinder completely. You also need the transfers angle pointing towards the intake to sweep or force the previous Burnt charge from the cylinder, if one port opens before the other the charge transfer will be uneven. The idea is the mixture sweeps the sides of the cylinder then forces the burnt charge out of the exhaust.
 
The exhaust port need to be open long enough to reduce the compression in the cylinder before the transfers start to open, think of the cylinder as a air tank, if it under pressure you can't add more air.
 
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