1987 Force 125 - Knocking Sound/90PSI

[Max_Florida]

I have a knocking sound coming from the motor and the compression on Cylinder 1 is 90psi(others are 135psi).

History(Sorry it's long, I tried to be as thorough as possible):

Before we went out yesterday I ran it on the hose - I noticed what I thought might have been a QUIET ticking noise. Not having a lot of experience with outboards I didn't know if it was normal or not, so we went out anyways.(STUPID STUPID STUPID)

Pulled away from the dock, idled out, hit the throttle and it chugged up to about 2700rpms... ran horrible and very underpowered. We stopped the boat and messed with the motor for a while, finally got it running. Limped back to the dock, the motor was running awful.

Trailer it back to the storage lot. Run it on the hose and it's shaking and running very poorly.

Take out the spark plugs(they were rusty, we were thinking the problem was ignition related) - the bottom 3 have what I think is the typical black oily "wet" residue on them. The top is dry and a light brown color(uh oh).

Compression test all 4 cylinders - top is 90psi, all of the others are ~140psi(all of the cylinders were 140psi a few months ago).

Put in new spark plugs and start it up - motor runs smooth on the hose but the knocking sound is very noticeable.

Took the plugs back out, sprayed a 1-1 ratio mix of fuel/oil into the spark plug hole on the top cylinder. Rotated the stator on the top to get the cylinder to cycle. Put the spark plug back in.

Then we took apart the top carb and made sure everything was good to go - nothing was stuck in there. Put the carb back on, but took the cover off.

Started the motor up and gently sprayed the 1-1 fuel/oil mix into the top carb as it ran. I was hoping that as I lubricated it the knocking would go away and compression would come back up. No such luck.

I am thinking that the problem was caused by(obviously) that cylinder running lean. I am planning on rebuilding the fuel pump this week.

Here is a video we made so you guys could hear the sound: http://www.youtube.com/watch?v=BnOqlBLKOmM&feature=youtu.be

I am thinking that I will need to probably at least partially rebuild the powerhead? Any advice would be greatly appreciated!

Thanks in advance!

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

Its time to pull the head and inspect for damage. You "could" have a rod cap coming loose and causing a tapping sound, but not likely. I bet money #1 has scoring and the rings are stuck. If its just #1 thats bad, that doesn't necessitate a full rebuild. Also, you said rust on the plugs. This usually means water intrusion, and could be a bad head gasket or exhaust gasket. Let us know what you find.

 

[Jiggz]

Re: 1987 Force 125 - Knocking Sound/90PSI

A rusty spark plug? Well, that is the indication of water or worse yet sea water. With 90 PSI you might get lucky that it's only a cracked head gasket. Open and inspect the head gasket and also #1 cylinder. Refrain from running the engine until then.

 

[Max_Florida]

Re: 1987 Force 125 - Knocking Sound/90PSI

A rusty spark plug?

To clarify, the outside of the spark plugs were rusty, not the inside. I should have phrased that better.

We started taking the motor apart today. We have the nut off the flywheel on top, now I just need to figure out how to pull it(I know there is a special tool, but I don't want to buy it). I will post back later tonight and update you guys as to what I found.

 

[Jiggz]

Re: 1987 Force 125 - Knocking Sound/90PSI

Do you have a Harbor Freight store nearby? You can buy a set of pullers for less than $20 to save you headaches and frustrations not to mention stress due collateral damage of not using the proper tools.

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

Why are you pulling the flywheel off? The damage will likely be a gasket or scored cylinder. You need to remove the head and inspect, then you can figure out what route to take.

 

[Max_Florida]

Re: 1987 Force 125 - Knocking Sound/90PSI

First off, thanks for the replies guys - I appreciate it.

To answer your question in regards to the flywheel - I knew that the motor would need to be disassembled to find/fix the problem, so we went ahead and did that.

Found this on all 4 cylinders:


It looks like all 4 rod ends are hitting the block. What the hell? What could cause this?

I identified 3 distinct issues with the motor:

1) Underpowered - Believed to be caused by cylinder 1 running lean(burnt spark plug and lack of oily residue) - I believe it is running lean due to a bad fuel pump(reeds look good). What else could cause it to run that lean?

2) Knocking Sound(Solved) - Caused by rod ends impacting the block - what causes that? What else should I look for and what do I need to fix?

3) Low Compression on Cylinder #1 - Not sure yet. The piston looks good, the cylinder wall passed the finger nail test. How do I tell if the rings are bad? They seem free from carbon for the most part, but they are sharp(cut myself - stupid hurts)

 

[pnwboat]

Re: 1987 Force 125 - Knocking Sound/90PSI

There are definitely some marks on the block, however, the flats on the rods are ground like that at the factory to aid in rod cap alignment. I do not see any evidence that the rods were hitting the block. If they were hitting the block, you would see the whole inside of the block covered in metal flakes/shavings.

I've seen stroker motors where there wasn't enough rod clearance. Motor ran fine below 3000 RPM. No interference. Motor was reved up to 5500 - 5800 RPM, a little more flex on the crankshaft and it was almost instant destruction. There were a couple of loud raps and pieces started to fly everywhere.

I listened to the motor in your video. Not sure but it sounded pretty normal to me

 

[Jiggz]

Re: 1987 Force 125 - Knocking Sound/90PSI

Did you check the bearings for any play? From the color of the rod caps and ends it seems to be out of lube for awhile. Any play could have resulted in what seems rubbing against the block. How does the head gasket look?

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

Running lean has nothing to do with the fuel pump or reeds. Your top carb air screw is set incorrectly. It needs to be 1 to 1 1/4 turn out from lightly seated.

Your rod ends look normal, as do the marks on the block.

Are the rings stuck in the grooves of the piston? Is there any scuffing on the piston skirt? Any aluminum rubb off on the cylinder?

If the pistons and cylinders are clean free from damage, rings aren't stuck then you have a bad head gasket or exhaust gasket.

 

[CoffeeHound]

Re: 1987 Force 125 - Knocking Sound/90PSI

What i am seeing is a Crankshaft thrust bearing in the case is wore out or has a ruptured flang , and has let the crank drop about 1/8th + inch to eleminate the case clearance to the Rod !!
Check it out !!

 

[Jiggz]

Re: 1987 Force 125 - Knocking Sound/90PSI

Since #1 & #2 cylinders share the same carb (top carb), it will be illogical to assume only #1 is getting a lean mix while the other is not. Coffeehound does bring up some logical point since it's only #1 having the hit marks but then I can't tell from the pics if those rub marks are rub marks or made by the company prior. If they are shiny it would indicate they are rub marks.

 

[Max_Florida]

Re: 1987 Force 125 - Knocking Sound/90PSI

How does the head gasket look?

Head gasket looked alright, except for some "burn marks" around the #1 Cylinder. Would that be what a blown gasket looks like or am I looking for obvious damage?

Running lean has nothing to do with the fuel pump or reeds. Your top carb air screw is set incorrectly. It needs to be 1 to 1 1/4 turn out from lightly seated.

I have to respectfully disagree with you. The fuel pump forces fuel into the fuel lines. If the fuel pump pressure was low it would make sense that the top carb would be the one that was receiving inadequate fuel supply. I have set and re-set the idle mix screws according to the directions in the Clymer's manual. As much as I would like it to be, the idle mix is not my problem.

Your rod ends look normal, as do the marks on the block.

I did not clean those areas whatsoever. Those were a shiny silver color when I opened the case. Those 2 surfaces ARE making contact. Is that normal for the rod ends to make contact with the block?

Since #1 & #2 cylinders share the same carb (top carb), it will be illogical to assume only #1 is getting a lean mix while the other is not.

I would agree with you that it would be illogical that one cylinder would receive more fuel than the other, however, I have read in several posts that for whatever reason the carbs on these engines do not distribute fuel evenly - even when everything is set properly. If there was a serious lack of fuel to the carb, I think that the problem could be compounded.

To Clarify - All 4 rod end caps are impacting the block.

What i am seeing is a Crankshaft thrust bearing in the case is wore out or has a ruptured flang , and has let the crank drop about 1/8th + inch to eleminate the case clearance to the Rod !!
Check it out !!

I will check this out and report back.


The piston rings, piston skirt and cylinder all look alright to me. I have never worked on the internal parts of an engine before so I'm not sure about coloration or exactly what to look for, other than obvious scratches, marks, cracks, etc.


Would an exhaust gasket failure cause low pressure on a normal compression test? I would think that at the point the pressure is reaching it's highest point the exhaust ports would be closed and an exhaust gasket failure would not affect the test?

I appreciate all of the replies guys. If I disagreed with what you said, I am not trying to be disrespectful or ungrateful.

Thanks again guys.

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

If the rods are indeed contacting the block, then I would think every main bearing on the crank would have to be bad allowing the crank to wobble. That doesn't sound possible to me, but hey who knows? Did you rotate the assembly to see before you tore it down all the way? If the crank has any movement side to side or up and down you have issues.

As for the lean running#1. The air fuel mix is set on the carbs themselves, and if improperly set is what causes piston damage. If the fuel pump was not properly working then the #1 and #2would have nothing to burn thus would have not damaged anything? You can run on just 2 or 3 cylinders. Even if it had little fuel being delivered, a properly set carb would not cause a lean situation. I have torn down multiple motors with the identical damage you have described. It is indeed possible to burn up #1 with #2 receiving little damage. We need to see some pics of the cylinder, head, and pistons. Then we can tell you what happened.

 

[Max_Florida]

Re: 1987 Force 125 - Knocking Sound/90PSI

I finished disassembling the crankshaft and pistons.

The two Main Bearing Races between Cylinders 1&2 and 2&3 had some play in them. The third was tight.

There are no thrust bearing on my motor, the Main Bearing Races ride directly on the block and cylinder cover. Those areas(which I will refer to as "thrust bearing areas" for lack of a better term?) are worn. There are ridges where the grooves for the snap rings on the Main Bearing Races were riding. They are high enough to easily catch a fingernail.

(I labeled all cylinders so that it's easy to tell what area you are looking at)

Pic of top 2:

I also found a crack/hole in the top "Thrust bearing area"(Can someone tell me what that is actually called? haha)
Pic:

Pic of lower one:

There was also wear and significant ridges had formed on the cylinder cover:

Lastly, rust had formed on the edges of the area of the crankshaft where the connecting rod rides:


I checked my fuel pump diaphragms and they seem okay. The reeds look good and I serviced both carbs recently.

What do you guys think?

I will pull the exhaust cover today - I am letting the bolts soak in PB Blaster as I already sheered one off when I was trying to find a ground for the voltage regulator I installed.

Obviously there is a lot of rust for an area that is supposed to be highly lubricated. I am thinking that there is either a serious lack of fuel getting to those top carbs or serious water intrusion, maybe both.

I am thinking blown head gasket. I will re-inspect. How noticeable will it be?

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

Thats a gasket failure. All of the other wear in the bearing saddles is normal. Your main bearing race will have a split that looks like a crack but it is normal. The main bearings are held in place with the locating pin in the saddle. A little play is normal, just as long as there is no rust or pitting. You may be able to save the crank if the rust can be removed with crocus cloth. However the rod end bearings will need to be replaced for sure.

If you are careful, you should be able to clean up everything, reassemble with a new gasket set and rod bearings and be running again. That is if the cylinders are ok, it was hard to tell from the pics. The fuel pump needs to be rebuilt as they can look fine, but still cause problems. Plus its cheap to do, and easy to boot. Then do the link and sync in the FAQ section at the top of the threads.

 

[pnwboat]

Re: 1987 Force 125 - Knocking Sound/90PSI

If the crankshaft has "shifted", most likely culprit is the top main bearing. It is pressed on to the crankshaft and keeps it from moving back and forth from end to end. It should be sitting flush up against the shoulder of the crankshaft journal. It sounds like maybe the crank has slipped down out of the top main bearing. If you can press it further on to the crankshaft, then it has definitely slipped. It should be removed and the journal where it is pressed on to inspected. If the journal shows no signs of galling or discoloration, tuned blue from overheating, then it should be OK and the bearing should be replaced.

The hole that you mentioned looks like a casting defect in the block. Kind if hard to tell from the pictures but it's probably OK.

Looks like a lot more rust on the crankshaft than I would expect to see. Water intrusion is most commonly caused by a bad head gasket or exhaust cover gasket. Take a close look at the roller bearings on the rods. Make sure they are not pitted and discolored (blue) from overheating.

 

[Max_Florida]

Re: 1987 Force 125 - Knocking Sound/90PSI

Still working on removing the exhaust cover.

Two of the pistons have wear on the skirt, here is a pic of #4:

The other one is similar, just not quite as bad. Replace them?

How badly do the cylinders need to be scratched before they need to be bored out? I was getting 130+psi on all of them except for the #1 cylinder. They all passed the fingernail test(except #4) but scratches are visible. #4 cylinder has some scratches I can catch my fingernail on... does that mean it needs to be bored out?


The top main bearing looks fine. But it does seem that the crank has shifted downward as the location of the marks from the rod ends is all uniform. Is this normal wear? Has anyone seen a motor with this before?

Thanks for all the help guys, I really appreciate it!

 

[tater76]

Re: 1987 Force 125 - Knocking Sound/90PSI

#4 should be replaced as that much wear is excessive. If the scratches in the cylinders are light enough you can get away with a hone job. I do it all the time, its quick and generally cleans up all the scratches. Now as for having it bored.... thats going to be a judgement call on your part. I would try a hone first, then if that doesn't clean it up have it bored. You can rent them from local auto parts stores for free. Now the reasoning for the wear on the pistons looks like lean running conditions. That needs to be adjusted before you run it again. Remember, idle speed is set with the timing tower on the side of the block, not the carbs.

I have not run into a crank shifting downward yet. That's not to say it impossible, but I think its really unlikely. I have lost the top crank bearing, and it dropped all the bearings into the case. I got lucky, and they all came out the exhaust while running. I guess if the upper (top crank bearing) had been replaced and not pressed far enough on this could happen. However, there isn't a whole lot of room for play in the other components?