bad compression?

[makoman515]

im not an expert at outboards, but i think that my 1998 mariner 2 cyl 25hp might have the cylender o rings shot or something. when i got the engine it was seized up and i dupmed wd 40 and penetrating oil into the cylenders and got it unseized. i got all the oil out wiht a hyperdermic syringe and the spark plugs work ( i tested) and i have the engine on a bench running stand. ive gotten it to rev a few times when ive been starting it, but even if i leave the throttle at max fast idle it still dies after a few seconds. when i crank it over and on the starter i can see the exhaust coming out (sleightly blue) and i can hear ignition but it just doesnt catch. ive sprayed the carb in cleaner and checked the fuel lines. could it be bad compression thats doing this? if so how would i fix it? or could it also be a miswired key switch, in that the run wire isnt on when it should be and the engine dies?<br />thanks so much<br />alex

 

[KCLOST]

Re: bad compression?

Have you checked the compression?<br />A seized motor usually is a damaged motor... Either the bearings, pistons, or cylinder walls...

 

[ehenry]

Re: bad compression?

I'd say your carburetor needs a good cleaning. You got a shop manual on your engine? Have you checked the compression?

 

[JB]

Re: bad compression?

Have you gone through the "Outboard wont start" post in FAQ?

 

[KCLOST]

Re: bad compression?

It sounds more like a possible fuel starvation issue...

 

[makoman515]

Re: bad compression?

the carb ive cleaned out by shooting carb cleaner through it. it could be the small fuel hoses from the carb to the cylenders. is it worth taking them off and cleaning? ar any other bits of the carb that shoudl be cleaned? taken apart?

 

[CFronzek]

Re: bad compression?

If it was a bad sieze you may not have enough compression to start it. When you put oil inside the rings were sealed temporarily so it started. Once it fired the oil was blown away and the seal was lost. <br />You should do a cylinder pressure check first. It will give you a rough idea of how much damage the siezure caused. If it won't start without adding oil it's probably putting out 60lbs. pressure or less. That means new bores, pistons and rings. <br />Charlie

 

[makoman515]

Re: bad compression?

ok i just took the engine halfway to peices, to get the carb off for a rebuild, i had to take the valve ports off for the cylenders to get the fuel delivery hoses off and no i rotated the flywheel and on the number 2 cylender there was a little oil on the cylender head right at the vent and as the cylender went up it bubbled a little, it was also easier to push the flywheel aroudn when the number 2 cylender was going up rather than number 1. could this mean that the compression is bad, certianly looks that way to me. if it doesn need new rings how do i buy them and replace them?<br />thanks so much<br />alex

 

[BF]

Re: bad compression?

you really need to buy a compression tester (gauge). it will screw into the sparkplug hole, you crank motor, it gives you a number in PSI. It's less than $20 at any auto parts store, and the only way you'll really know what the compression is. As already said more that once above, you need to test compression!! It's the absolute first thing you should've done after getting it unsiezed. Don't bother with the carb or anything else unless you know compression is good. Cause if not, you'll need new rings, probably rebore block & new piston etc etc (basically rebuild motor) Not impossible, but more $$$, maybe more than you wanna pay. As was also said above, it's highly likely that a siezed motor has piston/ring damage (low compression). That's probably why the previous owner got rid of the motor in the condition it was in.<br /><br />If you test compression and it checks out, then you got lucky (and probably a great deal). That's when to start thinking about carbs or other stuff.

 

[makoman515]

Re: bad compression?

thanks for the decisive reply. im going out in search of a compression tester. i was talking to a friend and he first assumed that when i said when i got the motor it was seized, he thought it was from over heating. this is not the case to my knoledge, i think it was just left out in the elents too long wihtout proper winterizing. does any advice change, and how hard is it to change cylender rings?<br />thanks for all the help so far and does anyone know where i can download (preferably for free a parts diagram set?)<br />alex

 

[Selles]

Re: bad compression?

www.mercruiserparts.com<br />www.dougrusell.com