Mercruiser - Fuel/Spark/Compression no go...

[Crabbing4Fun]

I bought a Mercruiser 3.0 181 with a knock for a good price. It had a knock which turned out to be a spun bearing which was an easy fix. This motor ran before I rebuilt it.

I did not pull the crank or the cam during the rebuild.

I have spark on all 4, tested by grounding and visibly seeing spark.
I have fuel, can see it in the carb when throttle applied, also can smell it in the cylinder.
I have compression, 140-150 in all 4.
I did have the head machined. The guy said that one of the valves was tuliped. I brought it in because I had poor compression on #4 before the rebuild.

The shift interrupt switch is in the correct position (in the middle), and I do get spark.

I checked the kill switch, I even cut the kill switch wires and checked with an OHM meter to make sure it works.

I thought I might have had the distributor 180, so I flipped it around, and it "tries" to start, but also tries to jump out of the boat I am assuming that it was wrong. I put it back to where I think its firing on the compression stroke and it will not fire. It sounds good when its trying to start, it just doesn't fire. I have verified top dead center and that the rotor is over #1 too many times.

The firing order is correct, I had someone else look at it thinking I messed something up.

I am going a little crazy here. By all accounts this engine should fire right up. I have read quite a few great posts by people walking through steps to get spark or fuel, but I have those.

I did something stupid I am sure, I just can't see what because I have been looking at it too long and I am "nose blind". Just need some pointers. Like a sensor that won't let it start for whatever reason?!? I am at a loss.

Thank you much for your time!

 

[alldodge]

I bought a Mercruiser 3.0 181 with a knock for a good price. It had a knock which turned out to be a spun bearing which was an easy fix. This motor ran before I rebuilt it.

I did not pull the crank or the cam during the rebuild.

Your dead before you start

 

[Crabbing4Fun]

Awesome?

AllDodge - Why is that?

 

[alldodge]

If you have a spun bearing (means bearing rotated in journal) it would have scored journal. Only way to fix a spun bearing journal is have the crankshaft turned. Only way to turn a crankshaft is to remove and setup on a lathe

 

[Crabbing4Fun]

Agreed. When I pulled the pistons and looked at the journal it didn't look that bad. Installed the new bearings and torqued with plasti-gauges and it was within spec. I think the guy I bought it from tried to do a rebuild and didn't torque anything.

It should still run though right? Even with a scored journal and a spun bearing it should try and fire right?

I give you credit, I am quit new at this. I did quite a bit of reading and kept the manual open to where I was in the process. I agree that I should have everything machined, but I don't have a bunch of money to spend, and got it for $1500.

Any thoughts on it not wanting it to fire?

 

[alldodge]

plasti-gauges and it was within spec

Not seeing it being in spec, if a groove can be seen then its out of spec. One spec of dirt is enough to destroy a bearing

It should run, but it won't run for long. The bearing is going to spin again or worst.

For a motor to run it has to have air, fuel and spark. Sounds like you have all 3 but maybe to much of one, or timing is way out. In any case, its only going to damage it self more once it starts up

 

[Crabbing4Fun]

Thank you for the honest reply.

Do you recommend that I pull it again, have the crank ground, new bearing, and try again?

If so, what can I do this time to make sure it starts? I would hate to put more money into it and not have it actually run. I guess that would be my big fear there? I don't mind the time spent, it was fun and pretty easy to work on, just the money in this day and age.

I don't know how to have the conversation with my wife by putting more into it, to not have it run. I already have the conversations on why I bought it in the first place

 

[alldodge]

Do you recommend that I pull it again, have the crank ground, new bearing, and try again?

Yes

The block, cam, crank ad everything needs to be gone thru

If so, what can I do this time to make sure it starts?

Its fairly easy to get a motor running, but I'm feeling you skill level in motors needs help. With a 3.0 the cam and crank gears have timing marks and must be aligned prior to distributor being installed. Might be worth the money/trouble to ask or pay someone to put it together for you

Need to find out of you getting a good spark as in Blue or white color and it needs to jump 1/4 or so. A spark gap tester is whats needed to verify

I don't know how to have the conversation with my wife by putting more into it, to not have it run. I already have the conversations on why I bought it in the first place

Understand but as a guy with his own issues in this area, I would not be the guy to ask

 

[alldodge]

Which ignition system is on the motor?

 

[Rick Stephens]

Not to leave all this to AllDodge, I would second that a spun bearing isn't an in the block repair. And you want to see the wife unhappy, fire it up and have it eat itself in short order. Then it gets expensive cause you're doing it twice.

As far as doing the ignition, easiest way I have found to be sure and for certain you are at #1 TDC compression stroke is pull the valve cover and look at the valves. If both are up and timing mark is at zero, you are there. Set up your distributor and make for sure and for certain you got the order right.

Also, it doesn't take much in the way of crappy fuel to make an engine not start. People who don't put motors together with a torque wrench also leave gas in the tank for years at a time. Old gas may not ever fire.

 

[Scott Danforth]

if you spin a main bearing. the crank needs to be removed and ground, and the block needs to be line-hones and the caps re-sized

if you spin a rod bearing, the crank needs to be removed and ground and the rods need to be trued up and the caps re-sized, or new rods used.

from post #1, your dizzy is 180 out and off a few teeth.

you also never mention using a timing light. so how do you know if you are even close to firing at TDC?

did you set the cam and timing gears up properly?

if you missed all this during the rebuild. did you align the motor with an alignment bar upon re-installation?

 

[Scott06]

If you didn’t pull the cam or crank during rebuild, cam ti crank timing should be ok. Just need to time the distributor to tdc on cylinder 1 dump a little gas down the carb and it should fire.

per the other comments if the bearing was spun such that it nocked , no way in hell just dropping in a new bearing and checking clearance with plastigauge will fix it. Bearing spun either because big end of rod is out of round or lack of oil. Either way crank and rods need to be mic’d and resized otherwise it’s just going to spin a bearing again.

wouldnt run it long like this if you get it going. Will only do more damage when it goes

 

[Crabbing4Fun]

Thank you all for the replies!

All - I 100% agree that everything should be machined. This isn't a boat I plan to use more than 10 hrs a year for maybe 4 years? Question, if I spin a bearing again, I am right back to this spot where I need to pull it, drop the pan, pull the crank and have it honed, new bearings, etc. Everything I am saying is a sin to a professional, I understand that, and I am not trying to take away from your experience. I am just trying to justify $500+ now vs $500 later? My goal isn't to make a tank of an engine that I can pass down to my kids if you get my drift.

All Dodge - You are correct, I am not a mechanic in real life, and it is always easier to just pay someone to do it. How you do learn though, and how do you get better . I am getting good spark, gap is set at .035, and spark tester is showing good spark.

Rick Stevens - I will pull the valve cover to make 100% sure I am not 180, good thought. Also you are probably right about the fuel, I will pull the feed line and jam it in a fuel can and see if that helps. Ran fine a month ago on the current fuel, but that doesn't mean its still good though.

Scott Danforth - I haven't used a timing light because I can't get it running. I didn't pull the cam nor the crank and it ran before I tore it down. I assume the alignment is still good.

Scott06 - I think the bearing spun because the guy that did the rebuild before me didn't torque the caps down? When I took them off to look they were all very different in torque.

I do appreciate you guys, you are right. Wish I had the money to do it all the right way, right now.

 

[alldodge]

OK, lets just see if we can get it running.

Remove No 1 plug and put you thumb or a cork over the hole. Bump the motor over until your thumb/cork pops out. This is compression stroke.

Look at the timing mark and it should be real close to TDC

Remove distributor cap and see if the rotor is pointing to No 1 plug wire

 

[Bt Doctur]

Why not start at the beginning. Remove the valve cover , rotate engine untill you see the intake valve open and close , now your on a compression stroke, adjust both valves. move to the next cylinder Go back to the front cylinder again, rotate motor unitll the intake opens and closes, slowly turn motor untill timing notch in damper is lined up with timing tab, this #1 TDC, install dist with rotor pointing to a lug in the cap, firing order is 1,3,4,2 clockwise

 

[Crabbing4Fun]

BT Doctor/Rick Stevens

You guys were right. I pulled the valve cover and set it to TDC with both valves closed, pulled the cap and you were right 180. I set it back and tried to get it as close to 1 as I could. I started it and no go, bumped the cap, a little better, bumped again, and it fired.

This thing is super picky about how close to timed it needs to be before it will fire. I was almost right on the money (1 degree before) before it would fire. Weird. I did those procedures when I installed the distributor, but I must have just been a little off.

Sounds good, I had to shut it down as it was overheating (gauge isn't working) and there is no water. I think I found a pretty good troubleshooting section on that. I don't know if I don't have the muffs on right, or clogged, or pump. I can fix that

Just wanted to say thank you all. Always nice to be able to bounce ideas and have a second set of eyes.

 

[Scott06]

Thank you all for the replies!

All - I 100% agree that everything should be machined. This isn't a boat I plan to use more than 10 hrs a year for maybe 4 years? Question, if I spin a bearing again, I am right back to this spot where I need to pull it, drop the pan, pull the crank and have it honed, new bearings, etc.

Scott06 - I think the bearing spun because the guy that did the rebuild before me didn't torque the caps down? When I took them off to look they were all very different in torque.
.

look not trying to **** in your corn flakes here, but this engine is on half azz rebuilt number two hoping two half azzs make a full azzed rebuild?

It’s your show, but if it truly spun a rod bearing no possible way to just put a new bearing in properly torque it and have it hold up very long. The way you could end up worse than you are now is if it damages the crank to where a resizing of the journal won’t fix it or you throw a rod through the block. Then the $500-1000 you’d pay for parts and machine work looks like the bar tab it is in the boating world.

again not trying to pour salt in the wound just never seen any corners cut on engine assembly work out very well or for very long.

 

[Scott Danforth]

This thing is super picky about how close to timed it needs to be before it will fire.

no crap. get a timing light