Big OOPS on 650 - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 32 (permalink) Old 10-02-2018, 11:50 AM Thread Starter
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Exclamation Big OOPS on 650

Ok, long story short, I believe I may have just blown a motor. I was doing about 50mph and downshifted twice from 5th to 3rd as you usually do to pass a car, but as it turns out I was in 4th and downshifted into 2nd. Loud noises, super high rpms and now the motor is running on 1 cylinder. Give it to me straight boys, how bad did I just screw up? To make things worse, it is my wife's bike.

I don't have to have fast, I just have to have fun!
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post #2 of 32 (permalink) Old 10-02-2018, 12:07 PM
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if you threw a rod it would be clacking like it was full of steel ball bearings the size of golf balls.

When you red line an engine by down shifting, the valves might not be able to close fast enough and the piston can hit them - but since the spring is floating it open and not the cam, nothing would get crushed.

Maybe you threw a timing chain and the cam stopped with the valves closed? (lucked out and nothing crunched).

if there are no banging or knocking sounds, take the cam side (timing) covers off and turn the engine by hand with a wrench on the crankshaft (quarter sized access cover on the left side). only turn it clockwise.

If it feels ok, and both cams are turning, then take the plugs out and do a compression test. Go from there.

when you take the plugs out, make sure one is not crushed.

Last edited by KCW; 10-02-2018 at 12:13 PM.
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post #3 of 32 (permalink) Old 10-02-2018, 12:39 PM Thread Starter
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Plugs are ok, a little blacker than I would like, but not crushed. I am not sure about the cams turning, what "ok" feels like. I have never done that before. I also have no way of doing a compression test and have never done one of those either. It didn't sound like metal in the motor when it happened just a lower pitch from the exhaust and the engine itself was louder. It also still sounds fine at idle, for whatever that is worth.

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post #4 of 32 (permalink) Old 10-02-2018, 01:30 PM Thread Starter
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Clockwise rotation of the crankshaft is not smooth. It tightens to a point then releases. The engine is still to hot to take the timing covers off. It will end up in the shop, because I admittedly have no idea what I am doing from this point.

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post #5 of 32 (permalink) Old 10-02-2018, 01:39 PM
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Although it's not the greatest thing to suddenly change revs that drastically when under load in theory you can reach ~66 mph in 2nd gear at ~9K rpm... the rev limiter should have kicked in by then. So there's that.
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post #6 of 32 (permalink) Old 10-02-2018, 01:44 PM Thread Starter
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Quote:
Originally Posted by Diogenes415 View Post
Although it's not the greatest thing to suddenly change revs that drastically when under load in theory you can reach ~66 mph in 2nd gear at ~9K rpm... the rev limiter should have kicked in by then. So there's that.
It definitely didn't like it. I'm guessing I have messed up the timing or bent a valve. The massive loss in power is what has me most concerned. I rode it home (another 10 +/- miles) after it happened. I wouldn't have, but I had no choice. I was in an area with absolutely no service, and wasn't about to walk that far.

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post #7 of 32 (permalink) Old 10-02-2018, 02:14 PM
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when you put a wrench on the crankshaft and turn it clockwise, you are cranking both pistons thru the compression and exhaust cycles.

When a piston starts to compress it will require more torque to keep turning. Once it gets past top dead center it will be very easy to turn, because the compressed air is pushing the piston back down.

it should then do the same thing on the next full 360 on the crank shaft, on the other piston, but about 80 off from the other one. If you feel the compression stroke on both pistons (once on each 360 turn of the crankshaft) then your valves and rings are doing what they should. So that is a simple compression test in itself.

If you only feel one piston doing the compression stroke on two full turns of the crankshaft (720) them something is wrong with one of the combustion chambers.

If you do this with both plugs out it will just spin freely, but you could stick a finger in each spark plug hole and feel if its building compression. If only one piston is building compression, that would be a way to tell which one is bad, take the plugs out one by one, or use your finger in the plug hole.

The reason for only going clockwise BTW, that is the direction the engine runs, opposite from the front wheel. If you turn it backwards the timing chain goes slack and bad things.... dont turn it backwards. One exception: while you are turning the crankshaft over, if you feel it clunk, like metal is hitting metal, you can back the wrench handle off about an inch, then go clockwise again. If you keep feeling a clunk on the wrench in the same spot, that could be a failed connecting rod bearing.
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Last edited by KCW; 10-02-2018 at 02:20 PM.
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post #8 of 32 (permalink) Old 10-02-2018, 03:47 PM Thread Starter
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What you describe as far as how it should feel while building compression, is exactly how it felt. Like I said, I do not know what I am doing, but I am glad to learn. I was watching the top dead center line while rotating clockwise, to stay aware of full rotations. I believe I did 3 full rotations. I heard NO clunk during the process. So what is next? I will be glad to continue as far as my limited ability allows. I had never changed wheel hub bearings on a vehicle either, but now I have on 2. I have mechanical ability, tools and knowledge are what I am short on.
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post #9 of 32 (permalink) Old 10-02-2018, 04:32 PM
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According to the Yamaha speed calculator, the redline ,7200rpm, is 53 mph in second gear. So maybe you didn't screw it up as bad as you think. Fingers crossed!!!! As if that helps.
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post #10 of 32 (permalink) Old 10-02-2018, 05:32 PM
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You might want to check that again and make sure its compressing on each rotation. You said it sounds like its only running on one cylinder, so maybe one is creating compression, and the other is not.

If you got compression in both cylinders and nothing is clunking or slamming or tapping, I cant think of what else red lining the engine would damage. I cant imagine the carbs being damaged.

I guess check to make sure you have spark on both plugs?

Last edited by KCW; 10-02-2018 at 06:15 PM.
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