580 Won't Start - but has spark ?

[kscycler]

I've got a '93 GTX that I did an engine swap on about 2 months ago. I had some earlier problems with fuel supply, but got those sorted out (rebuilt the carbs) I was at the lake last week and the boat was running fine, but suddenly died. Now I can't get it started, although I have plenty of spark.

I've tried priming the motor with gas in the spark plug hole, but it just won't fire. It won't even try, so I'm wondering if the timing went awry somehow (during the engine swap, I remounted my old electrics on the front of the motor). Or is there something in the electronics that's grounding out and keeping it from running? I'm at a loss...

[Bill O'Neal2]

Re: 580 Won't Start - but has spark ?

It is possible that something in the rotary valve has meesed up, like a stripped gear. In that case the RV won't turn and the motor won't start. You say you have spark. Do you have good compression in both clyinders?

The ignition timing is fixed, so I doubt it changed.

[kscycler]

Re: 580 Won't Start - but has spark ?

Thanks for the reply. I guess it's possible that the RV is messed up; however, when I spin the engine with the plugs out, it seems to be pumping. Also, when holding my hand over the intake (again when spinning), it appears to be pumping air as well. So I suspect the RV is spinning properly, although I'll check it.

Compression is 135 lbs, both cylinders.

You say the timing is fixed, although I guess it's possible that the fixing bolts worked loose and the timing went wacky. I just hate to pull the front off the motor...

Any ideas on what else in the electronics might allow it to have spark, but not start? Perhaps the "brain" went wacky?

[Bill O'Neal2]

Re: 580 Won't Start - but has spark ?

There is no "brain" in an old 580 motor. It is a very simple ignition.

Pumping while spinning the motor has nothing to do with wether the rotary valve is even on the motor. The "pumping" you describe is only the pistons going up and down.

If the bolts worked loose, the stator would be hitting the flywheel and probably be damaged and not sparking the sprakplugs., but if you find nothing wrong with the RV, then by all means look at the stator. If the stator plate were fully advanced, it would still run. If too retarded, it may not start.

[kscycler]

Re: 580 Won't Start - but has spark ?

Thanks for the suggestion. I'll pull the RV tonight. Not too excited about that, but I guess it's the next thing in line. Stand by...

[kscycler]

Re: 580 Won't Start - but has spark ?

Aargh! I pulled the RV cover off and apparently the RV shaft has sheared the soft gear at the crankshaft. The shaft is not spinning at all and when I try to engage it by turning it a bit with the engine, it must have smoooshed the gear because it won't engage.

What are the chances that I can pull the RV shaft, change the internal gear, clean out any wayward pieces and continue on? The motor has good compression, ran well, and I ran premix, so I can't imagine the cylinders are bad. Just don't understand why it crapped out. I'd rather take a $14 chance (cost of a gear) and a little sweat than give way and part out the boat (93 is probalby not worth the investment), but won't attempt it if the chances are that the motor's toast. I'd sure appreciate your insight.

[Technical Support]

Re: 580 Won't Start - but has spark ?

I would not just change the gear unless you carefully check the shaft for runout. Even a 0.001" deflection will strip the new gear. I would put a new shaft assembly in.

[Bill O'Neal2]

Re: 580 Won't Start - but has spark ?

Rotary valve drives do not usually just strip gears for no apparent reason.

Did it run dry of oil?
Did some foriegn object go down through the carb and jam the rotary valve ?
Is something inside of the engine broken, like a bearing or piston skirt and that jammed the RV ?
Is the rotary valve bent on the edges like someting was caught in the port?
Are there deep scratches in the RV cover or case?
Did the last "mechanic" replace the brass gear onto a bent RV shaft and sell the boat, or tell his customer all is well?

Chances of just replacing it are slim. When a gear shears off, it bends the RV shaft, so putting a new gear on a bent shaft will result in the same thing happening again. When an RV shaft gear shears, it sometimes forces the gear on the crankshaft to move rearward. In that case, you will need to tear into the motor all the way to the crankshaft to fix it.

[kscycler]

Re: 580 Won't Start - but has spark ?

Bill,

As usual, all great question and suggestions. I'll work on them one by one and see what's what in the motor. Thanks for being there...

[frankey01]

Re: 580 Won't Start - but has spark ?

I have the gear for 29.50 shipped to your door and the gear and shaft for 100 shipped to your door. take paypal and money order.

[cashman]

Re: 580 Won't Start - but has spark ?

It sounds like I have the same problem and I'm not to familiar with these motors so can someone tell me where the rotary valve is located at. Thanks.

[Bill O'Neal2]

Re: 580 Won't Start - but has spark ?

Under the cover that the carb is mounted onto.