1990 Force 50 hp - Bad Compression 1 cylinder

[N2Motors]

All,

I could use a little help! While I?m mechanically inclined, I am intimidated by outboards. I?ve read hundreds iboat posts trying to learn from others, but now need some specific advice so this is my first post.

I bought a 1990 Force 50 hp for a great price as I wanted to swap out my exisiting 35hp force and simply connect the 50 to my existing controls for 43% more power. While it sounds simple, I have bad compression (tested cold because I cannot seem to start engine at this point) with one cylinder showing 60 pounds and the other showing 90 pounds.

While my engine may have other problems (TBD), my understanding is that poor cylinder compression can only be caused by one of three things, beyond an obvious crack in the power head (Ring problems, Cracked Piston, Bad Head Gasket). Seeing no cracks in the powerhead, I finally worked up the courage to take of the head cover and take a look.
I was actually amazed by how clean everything looked (maybe I was just too worried after reading about some horror stories from other members). However, the good news at this point is that there are no broken cylinder heads (whew) and the rings do not appear to be stuck. Having never looked inside an engine before I?m not exactly sure what to look for, but the cylinder walls appear to be in great shape (see photos).

Based on what you see in the photos and your experience could I be 'lucky' enough that my problem is limited to a bad head gasket? Could that really cause such a dramatic drop in compression? Would that really causes my engine not to start? After reading all the other posts, I?m nervous about deeper issues (e.g. poor crank case compression). What am I missing?

Thanks in advance for your help!

 

[Jiggz]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Nothing obvious from the cylinder pics although it's really very hard to tell. However, the head gasket is obviously out of the norms. I say, replace the head gasket and reinstall without using any gasket paste or adhesive (so you can reuse it if required). Test for compression again and if the compression is still the same you would have to check the reeds make sure they are still fully closing. In fact, you can also see if the reeds are not fully closing by noting any back pressure (blowback) from the carb during starting.

 

[dutch420]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Hello and welcome to iboats....

First ur compression readings seem very low.. This could be one reason the motor will not start , not enought compression. But im more worried about the cylinderwith the brown/orange color, almost looks like rust in the pic and that would suggest water in the cylinder to me. if it is its most likely from the head gasket being bad or not tight. Now i hate to tell u but u cant check rings from looking at the top of the piston. For that u will need to pull the pistons, and with the look of that one cylinder I would prob pull them just to have a look at the piston/rings/cyl bore to see what shape everything is in but thats me... But ur one big prob is compression and ur lacking it 10% between cylinders is acceptable but u just seem to be lacking it . u could try just a head gasket and be hope for luck . But i would dig a lil deeper and have a look before i tried my luck.
U may hear the same from more people. Any other questions dont be afraid to ask lots of people to help on this site

 

[Frank Acampora]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Do not attempt to re-use that head gasket--it is trash. That is the reason for the low compression numbers on both cylinders. It is difficult to tell because the gasket is black but damage like that can be due to overheating. I would be willing to bet that with a new head gasket the numbers would come up to 120 or better on both cylinders.

Because of the possibility of overheating, check that the water pump is delivering a good flow and the thermostat is opening fully. If you have had the engine for a couple of years or if just acquired with no history, replace the water pump impeller as a routine maintenance item.

The cylinders do appear to be in good shape with only minor scoring One cylinder does appear to be discolored, possibly rust. I would check the exhaust cover and gaskets for possible leaks. Also, it does apper to be a bit "dry" Once you get everything together, clean the carb and set it so the engine is not running lean. Usually about one turn out on the low speed needle.

When you do install the new head gasket, if the head uses 5/16 bolts (1/2 inch head) then borrow a torque wrench and torque them to 220-225 inch pounds in three steps. Use a spiral pattern working out from the center two bolts. After running the engine and heating it to normal operating temperature, re-torque the head bolts. If the head bolts are 3/8 inch (9/16 heads) then torque to 280-285 inch pounds.

 

[N2Motors]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Wow. Thanks Jiggz, dutch420 and Frank Acampora. All your comments are very helpful!

I?ll definitely be buying and trying a new gasket. Sounds like if that doesn?t work, I?ll be able to take off the gasket and address other items and then re-use the gasket? I?ve always been Leary about re-using gaskets, but perhaps it just OK if all I?ve done is tested the motor for a bit?

Jiggz - If the gasket alone doesn?t solve the problem I?ll check for blowback due to faulty reed valves. I did peer into the carb at the reed valves and didn?t see any obvious deformations, but admittedly this was very much a cursory look.

Dutch420 ? Good eyes on the brown/orange cylinder as I was fearful this was a sign of rust. Oddly enough this is actually the one that has the better compression. Do I need to do anything special here to ?undo? the rust damage or if I just address the root of my problem(s) will this run OK. Just for clarity, is the only way water can enter the cylinders via the head gasket (or do I need to check other gaskets for potential water leaks)? Also, it is possible to check the rings by peering into the intake ports? I think I?ve read about this and I?m fearful about taking the whole power head off. Obviously if it comes to that, I?ll have to give it a try, but wasn?t sure if I could check the rings a big further without complete disassembly.

Frank Acampora ? Is there a difference between water pump and impeller (sorry ? probably a dumb question). I?ve researched how to check the impeller and plan on doing so, but didn?t want to tackle this until I squared away compression as I didn?t? want to throw good money after a bad engine. Thanks to iboats I know how to test the thermostat so I?ll check that too. You mention checking the exhaust cover / gasket for possible leaks. What is the purpose of this as I?m not sure I followed why I would do this? Is this a potential water entry point or cause decreased compression?

Appreciate everyone?s help!

 

[dutch420]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Not a problem everyone here has been in the same "boat" at one point or another .
Um yes u can look at the rings from th intake ports( not sure of the right name... Frank will let ya know lol). And from under the exhaust cover but other then getting a quick basic look in my opinion that wont tell u much about the rings. But before i would mess with that i would do as frqnk said get a new head gasket and give her a try........ Just a question th cyl with the discoloring how does it feel ... Is this rust? Or is it rust dust? . Either way now that u have the head off i would try to cleqn it up if i can. I wonder if the rust could be from the bore it self or the rings and if it has gotten in to the ring grooves and made ring movement stiff...
Anyone else weigh in on this

 

[Frank Acampora]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

You can check rings through the bypass covers but it will probably be a waste of time. damage to rings is usually confined to the exhaust side unless damage is so severe that the cylinder is scored deeply. Your cylinders look so good that I would not bother checking the rings. I have never seen an undamaged engine with worn-out rings (Unless it had really high operating time.) Outboards get a fresh shot of oil with each combustion cycle and rings are too well lubricated to wear

It is VERY likely that water--if any--was entering through the head gasket SO: The first thing you would do is install a new head gasket and run the engine. If it is rust, running will take it off without harm because it is not flaking, only surface discoloration. If it is still getting water, the plugs will be steam cleaned. You only need to look at them to tell-- no disassembly required to diagnose.

If it is rust and the new head gasket does not solve the problem, THEN check the exhaust gaskets. DO NOT check them first because it is likely that a bolt or two might snap.

The water pump is the complete assembly. The impeller is the only moving part inside and it is the part that wears.

And yes, a new head gasket if not damaged can be re-used. It is already compressed and need not be retorqued after running the engine. I re-use them all the time on my personal engines. I take heads off more than I change my underwear---OOOH! Too much sharing!

 

[dutch420]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Lol

 

[N2Motors]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

You guys are great! I just ordered a new gasket so once I get my power head cleaned and the gasket installed, I'll give it another shot. Hopefully I can wrench on it and circle back with some great news by next weekend.

In the mean time, I appreciate you keeping your fingers crossed for me (with or without clean underwear) that it is just a gasket!

 

[N2Motors]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Guys,

Two questions as I await my new gasket.

1) How clean do I need to get the metal surfaces? Might be tough to tell from the photos, but I think I've gotten them smooth enough (with no gasket residue), but there is still some black markings. Thus far, I've simply used my fingernails, carb cleaner and a dishwashing scour pad. I have some plumbing sand paper (to prepare copper), but not sure if that would be too abrasive.

2) Also, I've noticed a slight gap in the middle of the power head (I can fit two sheets of paper between the block and a straight edge. Is this a deal breaker?

Thanks!

 

[Jiggz]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

The straight edge you are referring or shown in the pic is nowhere close to a "real straight edge". So I would not make a call based on that diagnosis. Don't worry too much about cleaning the cylinders especially those that involves sanding. The discoloration as Frank mentioned will go away if you are able to fire the engine back again. Checking the reeds while installed especially with the carb still in place is very inaccurate. The only way to really check reeds is to uninstall them. However, hold up on doing that for now until you get done replacing the head gasket. As Frank mentioned, it's almost a sure thing the head gasket is the source of your problem. Hopefully!

 

[N2Motors]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Guys,

Just an update. I ordered a gasket and it took nearly 3 weeks to arrive. Much to my dismay, after opening the package the gasket turned out to be bent (there is a slight kink in one of the metal rings). I'm sending this back and now have to wait again. Nothing is ever easy....

 

[N2Motors]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Guys,

Wanted to let you know I finally received a good gasket and installed it. I'm blown away, it worked. I now have solid (~120 pounds) compression in both cylinders. Thanks so much for all your help on this topic. Now I need to somehow fix my tilt / trim which experiences slow leak-down.

Thanks

 

[roscoe]

Re: 1990 Force 50 hp - Bad Compression 1 cylinder

Congrats.

Don't forget the impeller !!