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Author Topic: Backfire, timing after rebuild need help!  (Read 187 times)

Me Too

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Backfire, timing after rebuild need help!
« on: March 28, 2018, 04:16:56 AM »

Hello again everyone!

Last summer was wasted. Every sunny day, every meet-up every cross town tour and every night ride was 100% shut down and destroyed due to a compounding series of issues I experienced with my bike trying to fix , waiting for parts and having ti go wrong.... now that the summer is ending I NEEEEEEEED to get this #@#$@-ing thing back on the road or I'm going to lose my mind.

Problem:

I eneded up re-building the rear cylinder. Did all kinds of damage in the process ( because of what started as a simple problem that I blew up into a major... super frigging major one.. ( NOOB) ) which included replacing; all valves, valve seals, piston rings, piston head. I've put it all back together to find I'm getting a backfire. Bummed I've waited until it was arm enough to start working again and just finished taking it apart to have a  look/ adjust the timing chain and BANG, again, no start/idol ( been sitting and need new starter :(  ) . I have pics to show where the Cam shaft/Chain is currently and the service manual that shows it should be 16 pins apart... where did i go wrong... im so lost guys.

I moved the magnito to the "R" position and lined up the indicators as it said in the manual...what is happening!?!? I couldnt get the cam shaft's indicators "level " with the cylinder head because of pressure from the valves so I slanted both cam shafts a little left to provide slack but lined up the chain as it should be...

Like if you could draw- along the face both cam shafts- a pointed arrow towards the ceiling and that pointed arrow  would make both cam's "upwards" or "90 degrees" then I rotated both shafts left so they would both be about 85 Degrees but I account for the rotation and was able to get the chain in the right spots 16 lengths apart....

Anyway, any help would be greatly appreciated.

Thank you in advance.... SO much!
« Last Edit: March 28, 2018, 04:18:28 AM by Me Too »
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Cloud

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Re: Backfire, timing after rebuild need help!
« Reply #1 on: March 28, 2018, 10:28:57 AM »


Is this for the GV650?

Front cylinder is F on the magneto rotor. Start by doing the front. IIRC she runs a wasted spark so any TDC is fine TDC. Once your F is lined up, then rotate the engine over less-than-one-rotation to get to the R on the magneto rotor, then do the cam uplining.

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Me Too

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Re: Backfire, timing after rebuild need help!
« Reply #2 on: April 02, 2018, 05:48:57 AM »

Maaaaaaaaaaan, you have to be my favorite person throughout he entire planet I have never met. You've given me direction, thank you, but I've given it another shot and would love to ask you if I should be able to line up the cams with the plane of the cylinder without issue or is it common to fight with the valve springs?

Yes it is the gv650, and the exhaust cam is unable to line up with the plane of the cylinder head without intense pressure from valve springs. Intake, no problem but the one just doesn't want to be upright.... thoughts?
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Cloud

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Re: Backfire, timing after rebuild need help!
« Reply #3 on: April 02, 2018, 03:47:56 PM »

If you're on-cam at |F or at |R on the rotor, per cylinder you've done it wrong.

The rear will be on-cam at |F and the front will probably be on-cam at |R

In theory, if we start with front cylinder, the |F TDC you're timing to should be -exhaust just closed- and -intake about to open- on the front cylinder. Then line up the timing marks, 16 links on the chains, and so on. Once that's done, you can more or less forget the front and everything it is doing.

Rotate the crank 285 degrees (or whatever) to get it to |R TDC. It'll be the same again -exhaust just closed- and -intake about to open- and the timing marks should be there the same, 16 links on chain, etc
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Hylife

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Re: Backfire, timing after rebuild need help!
« Reply #4 on: April 06, 2018, 02:26:09 PM »

Cloud is right.
Must first line up front cam marks when magneto is on the F mark.
Then using a socket, rotate anticlockwise "almost a full turn until the R mark on the magneto hits its mark and then get the rear cam marks and chain set.
Need to remove or back off the rear cam chain tensioner whilst you set the cam marks and then fit/release the tensioner afterwards.
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