Cranks w/ no plugs - No crank w/ plugs

douglee25

douglee25

m3booooy
Location
South Jersey
I am trying to help a buddy troubleshoot a 750sx over the phone. I personally have not looked at it yet, but I am exhausted for ideas at the moment.

Background - Bought ski 2 weeks ago, ran fine in water, 30 seconds into running he saw no water coming out pisser, shut it off and found incoming water line hose came off, reconnected line, now the ski won't crank.

Engine - 750sx small pin motor, RAD lightened flywheel (blue in color?), some sort of taper bore carb, stock everything else.

Problem - We have narrowed it down to an engine that does not want to crank over. The motor is out of the ski and ebox is not connected. Hooking jumper cables up to ski batteries or car batteries, the motor cranks like mabye 1rpm with the plugs in the engine. If you take the plugs out, the engine turns over fine.

Things we've tried:

1. Brand new starter
2. Different working bendix
3. Inspected flywheel off the engine - flywheel and key look OK
4. Apparently friend suspected washer on end of bendix was slightly bigger than ones he's seen in the past, so we thought maybe the flywheel cover was interfering with the bendix after it was tightened down. We loosened the cover bolts so there was an 1/8" gap between the block and cover - No change. Washer is on bendix end towards flywheel cover.
5. Pulled off crank case drain - No water in crank case
6. We eliminated the ebox, cables, etc by jumping the battery directly to the starter - Still slow crank with plugs in, cranks fine with plugs out.


I am at a loss right now. Any ideas? Has anyone seen this before? Thanks for the help. :Banane01:

Doug
 
Crab

Crab

thanks darin...noswad!
Location
Seattle
See if it will turn over by hand with the plugs out, it should without trouble. We had trouble cranking Petes X2 at Daytonal last year, tuned out to be a bent rod.
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
most likely if you have tried a new starter and that did not cure it. Either 1 of 2 things.

1. The cables are bad, they will flow enough current to turn the motor over without the plugs because there is zero compression. But does not flow enough current to turn over with full compression.

2. Battery is bad and or jumper cables you used were bad. You really need a new battery or a known good battery. Trouble shooting with jumper cables is hit or miss at best.
 
douglee25

douglee25

m3booooy
Location
South Jersey
crab said:
I would guess, bad starter then or bendix issue of some kind. Starters are really powerfull normally, but I have heard of new ones that are bad.
Click to expand...

The starter was brand new 2 months ago that he used in his 650sx. The starter works fine in that ski. He tested it prior to taking apart.

Big Kahuna said:
most likely if you have tried a new starter and that did not cure it. Either 1 of 2 things.

1. The cables are bad, they will flow enough current to turn the motor over without the plugs because there is zero compression. But does not flow enough current to turn over with full compression.

2. Battery is bad and or jumper cables you used were bad. You really need a new battery or a known good battery. Trouble shooting with jumper cables is hit or miss at best.
Click to expand...

1. The ebox is disconnected. No cables or ebox in place.

2. I think he's tried at least 3 different ski batteries plus a car battery. The ski batteries were used with OEM cables and ebox in place. The car battery and ski battery have both been tested using jumper cables. Same result.

Doug
 
douglee25

douglee25

m3booooy
Location
South Jersey
Big Kahuna said:
how did he get power to the starter then?
Click to expand...

When he used the OEM batteries, the engine was still in the ski. The ebox and OEM starter cables, etc were still used. The engine barely cranked with plugs in it. Plugs out - cranked fine.

With the engine out of the ski now, ebox and cables removed, the ski batteries and car batteries were used with jumper cables. Same result - plugs in, barely cranks. Plugs out, cranks.

Doug
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
This could be a case of bad cables, and then using jumper cables could be giving the same results. Jumper cables are not the best way to test. I would go buy some cables from an autoparts store, bolt up to the starter, hook the positive lead to the battery, and then ground the negative to the battery. This way you are getting positive connection at both the ground of the battery and the positive terminal of the starter. If this still does not work, then you have ruled out cables and batterys. From that point it would have to be starter, bendix or bent crank rod.
 
Crab

Crab

thanks darin...noswad!
Location
Seattle
Sorry to say but it sounds like you may have gone right past the problem like BK was saying, been there done thay myself.
 
douglee25

douglee25

m3booooy
Location
South Jersey
crab said:
Sorry to say but it sounds like you may have gone right past the problem like BK was saying, been there done thay myself.
Click to expand...

It's quite possible it could be the cables. This was my original guess when he first brought up the problem. It sounded as though the cables were shot and not able to carry the heavy current. Again, I haven't seen the ski myself. I'm only trying to help him troubleshoot over the phone. I've asked him to inspect the cables, etc and according to him, they look fine. Looks can be deceiving though.

Doug
 
douglee25

douglee25

m3booooy
Location
South Jersey
Today during lunch I went down and saw the motor for the first time. I spun it by hand with no plugs in it. The motor turns but does feel slightly tight. I'd have to compare for sure on another motor. It feels as though a plug is in it, the piston compresses air slightly, TDC is reached, and then you get that slight snap when it starts to descend on the down stroke. Again, I'd have to compare to see how 'normal' this is.

I hooked a pair of HUGE jumper cables up to the starter... directly, no wires... right to the starter stud. These jumper cables are HUGE and are industrial... no crappy deal here. With no plugs in it, the motor turns over fine. As soon as I put the plugs in it, the motor maybe turns one revolution, and then you hear a squeal?? coming from the starter (bear with me). Again, the starter is brand new and works fine in the 650sx that he has. I removed one plug and tried again, same thing. I swapped the one plug to the other hole, same thing. I verified the plug is the correct length (BR8ES - actually he had B8ES's in it).

I'm leaning towards something internal.

Doug
__________________
 
SJBrit

SJBrit

Extraordinary Alien
Location
Bradenton, FL
That does not sound good. If you're feeling resistance with the plugs out, and the resistance changes as you go over TDC, then I'm definitely going for the bent rod theory. Sounds like you had a partial seizure due to over-heating when the water line came off.
 
douglee25

douglee25

m3booooy
Location
South Jersey
SJBrit said:
Also, pop the head off - a bent rod is very obvious by seeing how far up the cylinder the piston comes at TDC. Compare front and back.
Click to expand...

I tried measuring that already but I didn't have a dial indicator on me. I tried using a socket extension and marking it, but I couldn't get an accurate measurement.

Doug
 
douglee25

douglee25

m3booooy
Location
South Jersey
Good news and bad news....

We tore the entire engine down today... no bent rods, no scoring, no loose bearings, nothing. The engine spun freely once I took off the flywheel cover and the flywheel magnets were no longer part of the equation.

More good news is that we're glad we tore it down because the cooling track from the exhaust manifold to the cylinder was about 80% blocked with salt/sand buildup.

The bad news is that we still don't know exactly what the cause is. I don't know if there were problems or not with RAD flywheels on 750's, but we're going to go back to a stocker to eliminate it from the equation. We will also try another bendix and starter if the current ones still don't work.

Doug
 
#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
Have the battery checked by an automotive parts store that has an electrical battery conductance tester, this will give you the exact CCA and voltage.

Did you every check the voltage at the starter while cranking or perform a voltage drop or ohm test on the cables?

Also double the check the resistance of your starter solenoid while it's energized, you might not be getting the sufficient amperage to your starter.
 
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