Have I bent con rods?? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 17 (permalink) Old 05-25-2014, 06:53 AM Thread Starter
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Have I bent con rods??

Hi, can anyone advise on how to check for bent con rods without stripping engine :-( . Bike was sat, fuel on, tried starting and it turned twice but locked up. Took sparks out, turned engine and fuel spat out holes. Bike runs on idle but compression really low. Can I measure at TDC from spark hole? Really gutted!!
Thanx for any help

Vn750A9
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post #2 of 17 (permalink) Old 05-25-2014, 09:30 AM
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Wolfie was able to check timing without dropping the engine. He'll be able to guide ya!

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post #3 of 17 (permalink) Old 05-25-2014, 10:53 AM
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I'm not much on internals and troubleshooting, but I'll try to throw things out and see what others say...

Keep in mind, none of this is from experience, just from thinking in theory....

1: bent Conn rods don't provide the compression needed (your idea)

2: damaged valve(s), bent or chipped, resulting in a small amount of gaseous escape during compression stroke, resulting in lower compression

3: piston rings..... Without knowing the history of the bike I have to make assumptions and I don't know how probable this is, but maybe the Rings froze in place, and moving the piston through the cylinder damaged a ring, or rings, causing blowby and losing compression.

4: cracked/warped head, damaged head gasket, or cylinder. I suspect this option would likely show other symptoms, but what do I know? I'm just a noob that doesn't know sheit.... Hehe
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post #4 of 17 (permalink) Old 05-25-2014, 11:07 AM
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What are the compression numbers? 100 is enough to make it run.

How much fuel out of the plug holes? Fuel wash can knock compression down, oil the cylinders.

Using the free download repair manual, align the timing marks to TDC for each cylinder, insert tool into plug hole, check to see if piston is actually at TDC or still traveling. If not at TDC while on the mark, rods could be bent.

I don't think the starter alone could bend rods, I think it would have to be running or at least firing.

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post #5 of 17 (permalink) Old 05-25-2014, 11:13 AM
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Quote:
Originally Posted by Spockster View Post
I don't think the starter alone could bend rods, I think it would have to be running or at least firing.
I feel like some inordinate circumstance would be needed to bend the rods, and j think there would have to be some other issue to cause it. I just don't see a properly running engine bending rods. You say it idles fine, so timing should be fine... I've heard one tooth off will be shytty...

I'm going to cast my vote for valve problems. I'll follow to see where this goes
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post #6 of 17 (permalink) Old 05-25-2014, 11:20 AM
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Ok, I had to re-read the first post....

Idling now but comp. down, ... could have been a rusty cylinder and stuck ring, now a busted ring.

Yes, the starter isn't all that stout, I don't see it bending rods. But if rust gets piled up at the top of the cylinder, it can definitely break rings and ring lands on the piston.

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post #7 of 17 (permalink) Old 05-25-2014, 11:28 AM
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Boy, who woulda thunk that Crowley noob had a legitimate suggestion!

To eliminate the Conn rods theory, have someone make a measurement of TDC through spark hole, make the same measurement yourself, and compare.
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post #8 of 17 (permalink) Old 05-25-2014, 11:44 AM
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IMO, Spock has this. The starter should not be able to bend the rods. 60# of compression will fire after the engine is running.

Why not do a leak down?
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post #9 of 17 (permalink) Old 05-25-2014, 12:39 PM Thread Starter
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Quote:
Originally Posted by wmsonta View Post
IMO, Spock has this. The starter should not be able to bend the rods. 60# of compression will fire after the engine is running.

Why not do a leak down?
Thanx for all the suggestions, after picking my chin up off the floor I'll try the tdc and timing marks before going any further. Gutted if [email protected]@ered the lump. Had a great few rides converting myself from my bandit 12. Tickover sounds fine, few pops that's all. If I hadn't done a compression test the week before with 30psi better each pot wouldn't have rang alarm bells with hydrolok. Does anyone know the measurement tdc to plug face? Timing marks will maybe do as well as suggested . Thanx again for supporting newbie!
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post #10 of 17 (permalink) Old 05-25-2014, 12:50 PM
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Quote:
compression test the week before with 30psi better
That could be from fuel wash, if it was a lot of fuel.

Since the chance of bending both rods would be pretty remote, you can measure both cylinders to compare. I would use the shallow spark plug holes. No need for the marks really, just feel TDC and measure to the top of the plug hole threads.

Leakdown would show if the comp. loss was terminal.

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