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Author Topic: Hi Everyone!  (Read 701 times)

or83

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Hi Everyone!
« on: August 12, 2017, 02:57:39 AM »

     Hi everyone,
My name is Oral. i am 34 and from Turkey. Mechanical Engineer (Msc. Machine Dynamics) . I have worked in automotive industry as a production engineer and newby at diagnosing and repair motorbike engine.
    I bought a 08 EFI gt250 comet(my first bike) 2,5 years ago and it always had problems. It was burning oil and working on only rear cylinder. i had given it a mechanic to rebuild the engine but i guess he couldnt adjust cam timing and both cam shafts of the front cylinder were broken and valves were bent). I left it in the garage for about 1,5 years and now i quit the job and have enough time so i decided to build it again.

 I bought a used 2012 gtr250r cylinder head with valves and 2 cam shafts(one of them was for rear cylinder, i changed its sprocket now its ok). Assembled them as how it is supposed to be and adjusted cam timing. Now the problem is;

 After I adjusted ,2 and 3 marks on the sprockets and notch marks on the cam shafts are same as shown in the service manual. Rotated the crank with a socket 360 degree to the lF mark again and controlled everything still ok but after a few full rotates, sprockets are upside down(180 degree). i removed the chain tensioner and re-adjusted everything and same happened again. I think lF mark somehow shows different TDC's (comp. and exhaust). As i adjusted cams due to the lF mark and as it may show the wrong TDC(%50 chance), i cant realize if it is in the copmpression or exhasut stroke by looking at cam positions.

So i need advice to how to determine which one is the compression stroke TDC without looking cams and pressure in the cylinder? (maybe from ignition time or backtracking from rear cylinder which is used to work properly)

Nice to be here, and looks like i will have lot of questions for you ;D 8)

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umop-ǝpisdn

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Re: Hi Everyone!
« Reply #1 on: August 12, 2017, 06:18:53 AM »

Welcome or83.

Do you have the service manual?
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Cloud

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Re: Hi Everyone!
« Reply #2 on: August 12, 2017, 07:19:44 AM »


Yeah, that's normal.

You get two TDCs (four strokes) per camshaft cycle, so sometimes the crank will be TDC but the cams will be half cycle.


It's been a couple of years since I built up a Hyosung engine, but someone else will be able to correct me if I am wrong here. I think one does the front cylinder first, then go a full turn on the crankshaft, and keep going a little bit more until you get to the rear cylinder's second TDC, then place the cam timing mark there..?
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or83

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Re: Hi Everyone!
« Reply #3 on: August 13, 2017, 09:55:18 PM »

thanks for replies.


i didnt understand exactly what you mean but lF mark on the crank doesnt show both TDC's , it just shows the compression stroke TDC. Service manual says when you see lF mark you can set your cams so its the TDC of compression stroke. And also it doesnt swap the sprocekt's position each full rotates. For example after second adjustment i rotated crank 6-7 times and cams were still ok on lF mark, then suddenly it did it again and my cams were upside down.

Yeah, that's normal.

You get two TDCs (four strokes) per camshaft cycle, so sometimes the crank will be TDC but the cams will be half cycle.


It's been a couple of years since I built up a Hyosung engine, but someone else will be able to correct me if I am wrong here. I think one does the front cylinder first, then go a full turn on the crankshaft, and keep going a little bit more until you get to the rear cylinder's second TDC, then place the cam timing mark there..?

« Last Edit: August 13, 2017, 10:43:57 PM by or83 »
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or83

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Re: Hi Everyone!
« Reply #4 on: August 13, 2017, 09:56:08 PM »

Welcome or83.

Do you have the service manual?

thanks. yes i have.
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Cloud

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Re: Hi Everyone!
« Reply #5 on: August 13, 2017, 10:49:14 PM »


1 camshaft rotation = 2 crankshaft rotations
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or83

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Re: Hi Everyone!
« Reply #6 on: August 13, 2017, 11:09:22 PM »

ok i got it. :)
i know "1 camshaft rotation = 2 crankshaft rotations" but i thought it has a mechanism(for ex. 1:2 ratio gear mate) and it shows lF mark once a couple rotations so it always shows TDC of compression ratio(because service manual doesnt say be aware of you are in comp. stroke etc). now i see it is wrong. it is midnight here i will adjust it tomorrow referring to rear cylinder as it was working nice. thank you for your answers.

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Cloud

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Re: Hi Everyone!
« Reply #7 on: August 14, 2017, 01:13:39 AM »


The crankshaft doesn't know or care whether it's TDC about to intake, or TDC about to ignition, and neither does the TCI. I think the EFI still has wasted spark.
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or83

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Re: Hi Everyone!
« Reply #8 on: August 17, 2017, 12:08:49 PM »

    i adjusted the cams and give a try without assembling the air filter and the fuel tank to their place. It seemed ok except small amount of oil leakage. i assembled them and cranked it again and now the rear cylinder!! looks doesnt work. This bike really annoying me.
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mrcrum

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Re: Hi Everyone!
« Reply #9 on: August 17, 2017, 11:20:10 PM »

The key is to set the front cam timing and then turn the flywheel 285 deg counter clockwise to the R mark and then set the rear cams.
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