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Post by Walms on Jan 25, 2016 7:54:36 GMT -5
It dawned on me yesterday that measuring the port timing on an unknown modified cylinder really is useless without taking into consideration the deck height. My cylinders have been decked to produce a .5mm deck height and are 1.05mm less in height compared to a set of virgin H1 jugs that I have. I've been told that the jugs do vary in height from the factory. It seems to me that all timing numbers are normally specified using the top deck as a datum but yet it's a secondary datum and useless unless the overall height of the cylinder and the cases height is not taken into account. As an example, 1.05mm difference in deck height comparing my 2 sets of cylinders would change the measured port timing duration by 2 degrees, which is a big jump! If the jugs from the factory vary in height, I suppose it's fair to say the cases vary in height from crank centreline to deck as well? If I add up the theoretical number for a H1 to have zero deck height
stroke - 58.8/2 = 29.4mm + con rod length =110mm + distance from pin to dome = 32.5mm + base gasket = .5mm
Total = 172.4mm
The height of the stock head is 95.4mm and the height of my modified cylinders is 94.35mm. I can round things up a bit and say that 94mm is the zero deck height number for the H1 assuming the crankcase height is fixed at 77mm
All this because I think I'll need to measure the overall height of Neal and Niall's cylinders to get a real port timing number. I think it's significant enough to change things a bit.
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Post by mraxl on Jan 25, 2016 10:33:23 GMT -5
It dawned on me yesterday that measuring the port timing on an unknown modified cylinder really is useless without taking into consideration the deck height. My cylinders have been decked to produce a .5mm deck height and are 1.05mm less in height compared to a set of virgin H1 jugs that I have. I've been told that the jugs do vary in height from the factory. It seems to me that all timing numbers are normally specified using the top deck as a datum but yet it's a secondary datum and useless unless the overall height of the cylinder and the cases height is not taken into account. As an example, 1.05mm difference in deck height comparing my 2 sets of cylinders would change the measured port timing duration by 2 degrees, which is a big jump! If the jugs from the factory vary in height, I suppose it's fair to say the cases vary in height from crank centreline to deck as well? If I add up the theoretical number for a H1 to have zero deck height stroke - 58.8/2 = 29.4mm + con rod length =110mm + distance from pin to dome = 32.5mm Total = 171.9mm (It's probably 172 and a measurement error on pin to dome distance) The height of the stock head is 95.4mm and the height of my modified cylinders is 94.35mm. I can round things up a bit and say that 94mm is the zero deck height number for the H1 assuming the crankcase height is fixed at 78mm All this because I think I'll need to measure the overall height of Neal and Niall's cylinders to get a real port timing number. I think it's significant enough to change things a bit. I'm not an expert in this area at all, but isn't port timing technically derived via crank angle? It actually doesn't make any difference about gasket thickness, deck height, etc. The measurement is only conveniently measured from deck... what is important is crank angle. See: www.3cyl.com/mraxl/manuals/hseries/sec3.pdf page 15 Somewhere along the line I calculated stock deck height from piston TDC to cyl. It differs by model. Found it: kawtriple.com/mraxl/pistonposition.xlsx
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Post by Walms on Jan 25, 2016 10:52:23 GMT -5
I guess that's what I'm saying, measuring from the top surface is easy but not necessarily an accurate method if not taking into account the variable deck height. I'm fairly sure that John mocks the cylinders on a bottom end in his shop to confirm what needs to be removed from the deck before he marks up the port timing.
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Post by pipe welder on Jan 25, 2016 12:38:11 GMT -5
Obviously the TDC and BDC is a direct reference to crank angle but the TDC location on the cylinder can be changed with spacers and machine work etc. Not much point in using port measurement numbers for comparison if the location of TDC on the cylinders is not the same as the other.
I assumed that measurements would be x" from TDC or BDC
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Post by Walms on Jan 25, 2016 13:08:10 GMT -5
I missed your 2nd link... It looks like you used 1.52 as a deck height which matches the Vannik software. For the life of me, I haven't inputted any dimension for pin height or cylinder height so I don't understand how the software knows the deck height??? I'm missing something obvious, but can't seem to sort it out.
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Raimo
2nd Gear
Posts: 289
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Post by Raimo on Jan 25, 2016 13:29:11 GMT -5
Interesting stuff for sure. The deck height is required for sure to caculate port timing. Here is some reading that I found on port mapping. I'm sure there is more of this but this was a start for me. www.macdizzy.com/cyl_primer.htm
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Post by Walms on Jan 25, 2016 13:32:10 GMT -5
Obviously the TDC and BDC is a direct reference to crank angle but the TDC location on the cylinder can be changed with spacers and machine work etc. Not much point in using port measurement numbers for comparison if the location of TDC on the cylinders is not the same as the other. I assumed that measurements would be x" from TDC or BDC From Dale's first link Kawi uses 1.52 deck height if you compare measured height to the port spec. (Taking numbers from exh. on H1)
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Post by JA-Moo on Jan 25, 2016 13:41:22 GMT -5
The most accurate way to measure is to pull the heads and measure the actual deck height of your motor. But most guys already have the cylinders off, so I use a mock up motor. I'm sure there would be a few 1000's off, but that's not a big variance on a non total "all out racing motor". The big thing, is getting all the port heights equalized.
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paulh
3rd Gear
Adrenaline is brown
Posts: 528
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Post by paulh on Jan 25, 2016 14:21:15 GMT -5
From my notes: Centreline of crankshaft to deck height H1 3.045 (vernier) But me thinks your looking for something different... Edit:I see.. not what your looling for... that note is from block deck ht in inches
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Post by Walms on Jan 25, 2016 14:22:09 GMT -5
Good link Raimo, thanks. John, I'm guessing you could just mill the cylinders to a specific height if crankcase height is a constant. I forgot to add base gasket fto my first post, I'll go back and correct that stack up.
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Post by JA-Moo on Jan 25, 2016 14:35:22 GMT -5
Actually I have a decked cylinder that I set up on the lathe, that I zero out on.
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Post by Walms on Jan 25, 2016 15:09:01 GMT -5
From my notes: Centreline of crankshaft to deck height H1 3.045 (vernier) But me thinks your looking for something different... Edit:I see.. not what your looling for... that note is from block deck ht in inches That's close to what I came up with playing with what was supplied by Kawi.
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Post by papagriff on Jan 25, 2016 15:22:49 GMT -5
I thought on some two strokes there was a modification that by adding a spacer on the cyl bottom and milling the top of the cylinder you could gain some power. perhaps a model that has no material for raising the exhaust port?
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Post by triplecraze on Jan 25, 2016 15:48:08 GMT -5
I thought on some two strokes there was a modification that by adding a spacer on the cyl bottom and milling the top of the cylinder you could gain some power. perhaps a model that has no material for raising the exhaust port? Yes I've read that you machine cylinder tops to reduce negative deck height then shim base of cylinder to bring back original compression with cylinder head installed. You must also machine intake side of piston skirt to compensate for intake opening duration. Did I say this correct?
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Post by Walms on Jan 25, 2016 15:54:36 GMT -5
IMO a spacer will definitely change the port timing but it actually slightly reduces blowdown from stock which is the opposite you want to do. Stock blowdown is 29 deg. Where you want to be at least 31-34 It's only a small amount but due to where the port is in relation to crank angle, the transfers end up getting more duration than the exhaust by just putting a spacer in. For example a 2.4mm spacer raises the exhaust duration by 10 deg but the transfers 12 degrees. The intake can be adjusted with a piston cut but if it were me putting a spacer under the barrel, I'd still open the exhaust further to bump the blowdown back to stock or ideally further.
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