Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

heckmonkey

Cadet
Joined
Mar 23, 2010
Messages
11
Hey Everyone,

NOT SO QUICK OF A QUESTION and sorry but I figure it would be better to provide as much info as necessary to get an accurate answer.

I am new to the boat world. I have a 1991 Mercury Force 150 on a old 91 cobra bass boat (bairly used, still in good shape other than seats) The motor has very low hours and I am supprised by how decent shape this boat is in for its age.

On to my Outboard. My mechanic said the motor has good compression in all cylinders but one, he said it would not be worth the money to pull the top end and repair. Sorry wish I had the results of the compression test to share. He did do a scope inspection of cylinders as well, and said they all look amazing, they show little to no scaring, wear, or carbon deposits, within any of the cylinders.

Mechanic said these are the needs or repairs of the motor he recomends:

Carb rebuild cost with parts etc., $300

Seals need replacement, $300 includes seals, lower end water pump, and lower end fluid.

Prop (chuncked up by me, but it did not cause any lower end damage per mechanic) Roughly $100 - $200 as seen on IBOATS.

Trim Tilt Relay Motor goes up, but will not lower???? Cost I think roughly 12 - 20 bucks after shipping.

And finally there is an issue with the hydrolic tilt - trim, not sure if there is an air bubble in the line, or if its low on hydrolic fluid, or if there is an actual leak (because I do not see signs of a leak and have not pulled the drain plug yet to inspect the issue), but with the motor trimmed up 3/4 way in reverse at very low speeds to back off trailer or to pull boat away from beaching it, will slam the motor to full lower possition which is why I chunked up my prop last time I had it out? I will push my boat off from beaching before I put it in reverse, but even then it will slam down with no resistence on the boat itself. Cost of repair unknown right now till I pull plug and cycle out old hydro fluid hell if there is any, and add new fluid etc. (Mechanic said if after doing all that, and it appears to be the hydrolics it is definately not worth the the money to repair, just run it as is and be careful, not even sure thats quality advise!)

Anyway - Looking at about $1000 bucks (minus repairs to hydrolic motor).

So question are the repairs worth it.

My mechanic said this and I quote, "these motors are hit or miss, you could spend the money on repairs and wind up with a dead motor in less than a few months, parts are getting to be nearly impossible to find, and costly, OR and a BIG OR (seeing as how the cylinders look good other than the one compression cylinder), you could make repairs and if you have luck on your side these motors "SOME OF THEM" will run like a sewing machine and last for quite a while enough to get your money out of it, and seeing as how the boat was for free" you wind up on top!

He personally said if it was his, he would probably do a carb rebuild, and seals/lower unit water pump? But even that would be questionable? And he would probably run it till it just died swapping out lower end fluid every once in a while! To me that seems a bit exagerated but he also has whatever boat he wants and I ONLY HAVE THIS ONE!

Should I repair or should I not! I fish tournaments as a co-angler, and really want to get out on the lake w/ my own boat, at least just for practice, I fish from shore now, unless I go out w/ friends, and I am tired of it! Would love to fix the boat, but want to know if the repairs seem worth the trouble.

Please any advise would be great! Thank you for your time!

The Heck!
 
Last edited:

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,927
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

First thing fill out the profile,you might be close to someone who can help. Get the manual,factory is best.
Then the second FIRST thing figure out what is causing the low compression.
Pull the head and check for damage to the piston and cylinder walls.
Take some pics and post the results.
You just might need a new head gasket.That's a cheap fix.

Then clean the carbs your self.$2 for a can of carb cleaner.They just might need a little cleaning.

Lower unit won't necessarily need re-sealing.Change the oil and if there isin't any water there probably ain't no problem.Just change the impeller $20

Prop can be rebuilt $50-80

Change the relay or just jump it so it works.Till you figure out why it won't work.Could be dirty contacts.

The T/T make sure it's full.(fill while it's down)
Then test it.Run it all the way up and leave it up.
You can find NEW trim motors for under $500 and that may be what you need.


Just cause some mechanic says something is bad or needs replaced doesn't always mean it true.


Do the head check and post the pics.
Look up Trim/Tilt threads on here.
There's a couple of good T/T repair guys here.J


Post your results. J
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

Your mechanic is telling you some things that are true, and some that are not.

Do yourself a favor and buy a compression checking gauge at the local auto store or Sears. It will be the best 30 bucks you will spend. You won't be at someone else's mercy. Check the compression on all cylinders and get back with the results.

Like jerry said: Clean the carbs--yourself! Unless there is something physically wrong, a rebuild is not necessary. 95% of the times a good cleaning will suffice. HOWEVER---BEFORE you run the engine, read the post on synchronizing carbs and timing in the FAQ at the top of this page. Mis-set carbs are just about the fastest way to ruin a good engine.

Ditto--Like jerry said about the lower unit.

Force engines are about the easiest outboards to repair and if you know where to look, almost all parts you would need are available.

With a manual and the help you can get here, you CAN get your engine in tip-top shape, and for much less dinero than paying a marine mechanic.

And your Force, once set up correctly, and if you keep oil in the gas, keep the impeller in good condition, and keep lubricant in the lower unit, she might just run until you die.

The tilt cylinder was never meant to hold against engine thrust. It has a relief valve and somewhere around 1000-1500 RPM the valve is forced open and yes it is normal, the engine slams down.
 

foodfisher

Captain
Joined
Feb 18, 2009
Messages
3,756
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

Listen to these guys. Find out yourself what's up with the one cylinder.
 

snowman48047

Petty Officer 1st Class
Joined
Jul 24, 2008
Messages
371
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

I've got a '92 Force 150 and these guys are all correct. Start with the compression. Fix that issue. My motor runs like a dream.
 

RRitt

Captain
Joined
Mar 30, 2006
Messages
3,319
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

i don't think '91 had a tilt only option. Get a new relay in there and then see what happens. Your problem description is a little off. A bad trim system will pop up out of water in reverse. Slamming down in reverse would mean that the engine is mounted backwards.
 

heckmonkey

Cadet
Joined
Mar 23, 2010
Messages
11
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

I am pretty sketched out to do the work myself, but I do thank you all for your advise. I am really freaked out about pulling the head, but I am certain that I could do it, used to be a mechanic for ford for 6 years. But still I have ZERO knowledge about boat motors but will take it easy and slowly start working on it. This saves me nearly a grand, and will also teach me about marine motors, which can only help me down the road to understand potential problems on or off the water! This website is amazing, and everyones advise is worth its wait in gold. Especially how to navigate and find certain things on this website. Its amazing and please keep the advise and comments comming. I will shortly here start doing the work, and will post pictures, etc., to get more advise from everyone. I have to believe that if I can take care of some of these isssues, this motor should last longer than me! PLEASE KNOW THIS, I COULDNT THANK YOU ALL ENOUGH, FROM A NOT SO RICH MAN WHO IS TRYING TO JUST ENJOY THE LOVE OF BOATING AND FISHING! THANK YOU ALL! I really hope I can do this!

Happy holidays,

The Heck
 

Cannondale

Petty Officer 1st Class
Joined
May 22, 2010
Messages
278
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

i don't think '91 had a tilt only option. Get a new relay in there and then see what happens. Your problem description is a little off. A bad trim system will pop up out of water in reverse. Slamming down in reverse would mean that the engine is mounted backwards.


What does engine mounted backwards even mean?

As far as the motor slamming down in reverse, the perception is just that when it happens. The reverse lock doesn't catch/work, so motor is put into reverse, engine lifts until the prop gets so shallow that it grabs enough air to slip/ventilate and lose its bite on the water.....then the engine slams down onto the transom. Then the prop bites enough to repeat the sequence, over and over, and very quickly....depending on how much power is being delivered to the motor while in reverse, and the perception is that the motor is slamming the transom, over and over, while in reverse.
 

RRitt

Captain
Joined
Mar 30, 2006
Messages
3,319
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

The prop shouldn't come out of the water until over 20 degrees of tilt angle. If it slams all the way back down to transom then the motor isn't deep enough into the water.

As regards the trim circuit. Complete failure to hold reverse on a 1991-1994 is usually accomapnied by a complete failure to hold forward. It is almost always caused by Mercury being too cheap to spring the extra $0.25 to use decent hydraulic fluid. The use of ATF in a high pressure system leads to oring hardening and cracking. Yes, always after warranty. But no, not nearly as long as just plain non detergent oil.
The fix is a complete rebuild and seals for both rams and pumps as well as a thorough flushing of oil tubes. The entire system must be taken apart to remove all debris. If not, intermittent pump failure is likely as debris passes through and gets caught in valves.

could be something else and this is such a pain that its worth checking. Not too likely, but it could be.
 

Thames_Outdoors

Seaman Apprentice
Joined
Dec 13, 2010
Messages
40
Re: Is my mechanic correct or am i? Repairs to 1991 150 hp Mercury Force!!!!

I have never owned a boat before now and I have a 1988 Bayliner Bass Boat with a 1988 Force 125hp motor. I to have never worked on outboards but will help from here as well as a friend and a MANUAL I have my motor running. These guys on here have given you good advise and I would go with that. The thing I want to ad is the: Here is a number 902-929-5040 which is to Mercury Marine and you can order a FACTORY shop manul for that motor from them. You will need to the model number off the motor when you call so you get the right manual. YES this will cost more than on ebay or oline but you will know you have the right manual for the right motor based on the model and year of the motor. Cost me twice as much as online but I got the right manual the FIRST time and thats what matters.. So far everything I have had to do has been easy and saved me $$$$$$ from having to pay someone else to do it. GOOD LUCK and hope all works out.
 
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