Help determining if I have a seized motor or lower unit issue

[ThomW]

I have a 1987 Black Max 200hp. I thought I had a starter issue, but upon further investigation found out that the flywheel won't spin freely. It will spin about 7/8 of a rotation in either direction, but then stops. My question is this: do I have a seized motor (thrown rod of piston issues) or could it be something locked up in the lower unit? The prop spins freely in neutral. It will turn in forward and reverse while moving flywheel, but again wont allow flywheel to fully rotate. The prop spins the flywheel until it hits that spot and stops, then I can's turn prop anymore. Does this mean the issue is in the engine block, or could it still be a lower unit issue?

 

[racerone]

What happened to the motor ?-------Remove lower unit and test again.----Or remove cylinder heads for inspection.

 

[GA_Boater]

If the motor locks in neutral, a good chance it's the powerhead.

Easiest way to find out to by removing the lower unit and see if the motor turns.

 

[fhhuber]

There are an assortment of ways the engine might only be able to be turned slightly back and forth... and some are in the engine, some in the lower unit.

Drop the lower as if changing water pump.

I would lean toward a top end issue.

 

[ThomW]

Thanks everyone. I was thinking it was top end, but was hoping for an easy out. the flywheel spins almost all the way around, but stops just short. I will try dropping the lower unit off tonight and see if the flywheel spins then. If it is top end, do I pull off the exhaust covers under the carbs to see what is going on in there?

 

[hemi rt]

Before pulling parts off the engine, remove the plugs, check their condition and try and turn it over by hand.

 

[ThomW]

I did that. Plugs seemed fine, not wet or fouled at all. Even with plugs out, the flywheel only turns about 7/8th of a full rotation in either direction.

 

[racerone]

??------Did this fault happen at full throttle ?-------Did it stop while idling ?------Has the motor sat for years ?-------Checked the gear oil ?-----Any water in the lower unit ?

 

[ThomW]

No, it did not happen at full throttle. We were out on the lake and hit a rock, dinged up the prop pretty good. Switched prop for the same exact prop (pitch and diameter) but boat would not idle or go above 3000 rpm's under load. Prop shaft is NOT bent. The flywheel does not have a pin that could have sheered to mess up timing. Anyway, being the dummy I am, I adjusted the idle a bit so it would stay running at an idle and allow me to get back to the dock. Well, on the way into the dock the motor would not come out of forward gear, and then all of a sudden it clunked into neutral and stopped the motor dead. I was only going at about 1500-2000 rpm's at the time. Then it would not start again. As part of my investigation of this, I discovered the flywheel would not spin all the way around. Upon further looking I see that all 6 pistons are moving when I turn the flywheel, but after about 7/8th of a turn is seems to hit something that prevents it from spinning any further. Same thing when I spin prop. In neutral the prop spins freely, but flywheel still stops. In forward and reverse the prop spins the flywheel up until it hits that same stopping point. Haven't drained gear lube yet to look for water in it. I plan to remove the lower unit and see if flywheel spins with lower unit off. If not, what could it be in the upper part, if all pistons are moving with flywheel? How do I go about inspecting the rods, crank, or pistons to see if the issue is there?

 

[Silvertip]

The engine crankshaft rotates roughly 2 times to make the prop turn once. With that bit of mechanical information, turn the engine either direction until it stops at the point where it binds up. With the shifter in forward, turn the prop so the engine turns in the other direction until it again reaches the point where it binds up. If the prop was turned less than 1/2 turn before stopping, the problem is in the engine because 1/2 turn would make the crankshaft turn one full turn. My guess, based on what you said points to an engine issue. But pulling the lower unit would provide proof either way as was pointed out.

 

[ThomW]

Thanks Silvertip. I will try that tonight or tomorrow evening after work. If teh prop spins more than 1/2 a rotation, what would that mean? Lower unit issue?

 

[Dukedog]

same motor ya askin' questions 'bout timin'?... drop tha case and end all tha mystery!.. if thats tha cause your already ahead, if not ya have lots bigger problems............

 

[jimmbo]

Was the prop AL or SS?

 

[ThomW]

DukeDog--Same motor I was asking timing questions about. When it was only going up to 3000 rpm's and wouldn't idle, I thought maybe I knocked the timing off when I hit the prop. However, then the shift into neutral killed it and seized something up, so any timing issues are going to have to wait until i get this figured out!

Jimmbo--it was an aluminum prop. However, the seizing happened after I turned up the idle slightly to keep it running in neutral. It didn't wanna come out of forward gear and then "clunk" it did and the motor stopped dead. Now flywheel only spins 7/8th of a full rotation.

 

[racerone]

So remove the lower unit and do some turning on it and the motor !!!!!

 

[ThomW]

Will do. I will post back this weekend when I get a chance to pull the lower unit. Fingers crossed!

 

[ThomW]

Sorry about the delay everyone, been pretty busy. So here's what I have discovered:
1. I dropped lower unit and to my surprise the pre-loaded pin on the top of drive shaft was gone. ( It is a MC-1 Lower unit). So that's not good.
2. With lower unit off, initially flywheel was still only spinning 7/8th of a rotation, but a went back and forth a few times and it started fully spinning.
3. Motor will now start, but is not idling in neutral. Didn't sound like it was running smooth.
4. With plugs out, it initially seems like I might not have compression in cylinder one. I didn't have compression tester on hand, but even putting finger over holes while spinning flywheel, I felt pressure on the 5 other cylinders, and not #1. All six pistons are moving up and down.

So, I know the pre-loaded pin is not replaceable, right? Do I try and replace drive shaft or just start looking for new lower unit?
Any thoughts on the upper part of motor? Open to ideas on where to go from here. Thanks for the input everyone.

 

[Dukedog]

Sorry about the delay everyone, been pretty busy. So here's what I have discovered:
1. I dropped lower unit and to my surprise the pre-loaded pin on the top of drive shaft was gone. ( It is a MC-1 Lower unit). So that's not good.
2. With lower unit off, initially flywheel was still only spinning 7/8th of a rotation, but a went back and forth a few times and it started fully spinning.
3. Motor will now start, but is not idling in neutral. Didn't sound like it was running smooth.
4. With plugs out, it initially seems like I might not have compression in cylinder one. I didn't have compression tester on hand, but even putting finger over holes while spinning flywheel, I felt pressure on the 5 other cylinders, and not #1. All six pistons are moving up and down.

So, I know the pre-loaded pin is not replaceable, right? Do I try and replace drive shaft or just start looking for new lower unit?
Any thoughts on the upper part of motor? Open to ideas on where to go from here. Thanks for the input everyone.

1. a pre-load "with out tha pin" will self destruct ina mater of minutes.. jus an "empty hole doesn't make it a pre-load... lotsa those around... what is an MC-1?
2. power head is broke.. at least one hole and/or crank may be done...
3. makin' it worse...
4. pull tha heads and have a look... ya got nothin' ta lose....

 

[ThomW]

1. MC-1 is what the old drives for Mercury were called before the Alpha drives. Might have seen them called a R-MR, or "pre-alpha drives. I know it was a pre-loaded pin because I have had the lower off before to replace water pump. I know just having a hole doesn't make it a pre-load, but having the pin there before does.
2. That's what I thought.
3. I only ran it for a second, was actually just seeing if it would turn over as it was seized up before.
4. What kind of price am i looking at for repairing the upper? Is it worth it for a 1987, or do I start looking for another motor and or power head?

 

[Dukedog]

first i've head 'em called that and i been doin' V6 merc motors and parts in tha dfw area since 1976.. alpha, pre-load, ratcheting and non-ratcheting is all i've ever heard of.... guess i learned something from a different part of tha country!... guess ya know not ta run like that then... if ya don't wanna take a chance on used tha sei is cheap for new.... any year 2.0, 2.4, 2.5 will work.. gear ratio will vary though....