125 hp Force low compression

[2-stroke head case]

I have a 1989 19' Bayliner with a 125hp Force L-drive. I was on the bay running strong... I stopped then when I tried to get on plane I couldn't achieve more than 10mph and would not idle (kept stalling). I replaced all the fuel system and cleaned the carbs. Still could not achieve WOT. Only 3000rpm's. I then noticed a spark near the trigger when I tried to get WOT. While testing the cylinders for spark (killing each one individually) #3 seemed to not change idle when shorted. I switch coils... no change. I switch SCR's or CDI boxes and #1 and #3 were dead. Tested Compression and #3 was low with only 35psi. Do you think the trigger is bad also. I know the stator is good it's putting out 210v. Where should I go from here? I was going to pull the head but a mechanic friend said it might be only the reed valves...?

 

[foodfisher]

Re: 125 hp Force low compression

Pulling the plug on #3 wouldn't change the running of the motor with only 35#. Find out what the problem is there.

 

[2-stroke head case]

Re: 125 hp Force low compression

Ok... but when I changed the cdi packs it also killed #1. If a CDI pack went bad that controlled the #3 cylinder, could that kill the piston or rings in #3 cylinder? (aka compression).

 

[foodfisher]

Re: 125 hp Force low compression

No, compression is compression. Spark or no spark. Pull and ground all spark plugs and check compression. If the results remain the same you've got a rebuild ahead of you and maybe an elec. problem I'm not versed on.

 

[2-stroke head case]

Re: 125 hp Force low compression

Sorry... I don't think I explained myself correctly. Do you think lack of spark would ruin a cylinder? Or do you believe lack of compression ruined the CDI?

 

[roscoe]

Re: 125 hp Force low compression

I doubt that either condition is related. Two separate issues.

 

[moparman]

Re: 125 hp Force low compression

you need to be sure you hooked it back up correctly first, if so ,swap back to the original set up and see if it goes back to the original running condition.Is it possible that the coil or cdi unit had some thing to do with the low compression,....its a stretch of probability to think so,but if its continuously dumping raw fuel into the cyl and not burning it ,possibly, but why not cyl #4 also[ cyl below]? The compression reading needs to be done again with all plugs out and wires grounded to verify the first readings. You might also do a decarb on it to see if that helps that cylinder if the rings are stuck. I believe you have mechanical problems myself but your going to have to go further with your checking. keep us posted

 

[2-stroke head case]

Re: 125 hp Force low compression

I got a little anxious this weekend. Here are the pics of the pistons. They are in order #1,#2 etc... It seems that #3 is missing a portion on the top left. Does the cylinder wall look as it needs honed, or would a simple exchange suffice?







Hopefully the attachments come through!

 

[moparman]

Re: 125 hp Force low compression

Pull the piston and see what the rest of the cylinder looks like. It will need to be honed at the very least, possibly bored ,but you can bore just one cyl if it needs to be bored.

 

[2-stroke head case]

Re: 125 hp Force low compression

What do you think the cause was...?

 

[2-stroke head case]

Re: 125 hp Force low compression

I'm now trying to replace the piston that was damaged due to detonation. Do I have to completely split the case? I thought there were quicker ways to replace a piston.

 

[Frank Acampora]

Re: 125 hp Force low compression

First: Stay away from your Mechanic Friend.

Second you can try replacing the one piston but from the little I see in the photo, that cylinder really needs an overbore. Yes! To overbore, you will need to completely disassemble the engine.

However, If you want to go the fast, cheap, and easy way (Don't come to me crying with disappointment when the engine doesn't perform as well as it did before) It is possible to replace one or even all four pistons through the reed valve opening. Removal is rather easy but reassembly can be time consuming and frustrating but I have done it a number of times. You will need a 12 point 1/4 inch drive 1/4 inch socket, An adapter from 1/4 to 3/8, a 3/8 drive torque wrench and a 1/4 inch six inch extension bar.

Buy brand name tools as the cap bolts are on really tight and may split a cheap socket.

Final torque during reassmbly is 180 inch pounds.

Finally, the damage was caused and always is caused by that cylinder running lean. Either the bottom carb was set too lean on the low speed idle needle or something clogged it.

 

[2-stroke head case]

Re: 125 hp Force low compression

Thanks for all of the great info... even the friend comment! Got-it all apart... actually with ease... but it sounds like reassembly is the trick. Anyways... here's a pic of the piston. A lot more damage than I expected, to the piston, but the wall does not seem bad at all. I think I'll try the quick fix! As far as the cause... when i bought the boat early last year the previous owner ran the engine with no water (while showing me the boat)... and seemed to think it was OK to do so. After noticing an overheating and revving issue... I immediately replaced the impeller, which was destroyed. Could that have been the cause... basic overheating?
Thanks again!!!!

 

[Frank Acampora]

Re: 125 hp Force low compression

Please! Please! Please!

With that much detonation damage to the piston it is a given that the cylinder WILL need to be rebored. Don't believe me? Drag the whole boat to a machinist and let him "mike" the bore. Especially near the exhaust ports. Betcha it will be WELL over the .002 wear tolerance allowed. Betcha it will need at least .020 over and more likely .030 over

While severe overheating can lead to detonation, overheating damage would not be confined to one cylinder. So while overheating is not good, the underlying cause in your case will still most likely be running too lean--your piston is a CLASSIC example. And FYI That amount of damage can be done in less than 10 seconds

 

[2-stroke head case]

Re: 125 hp Force low compression

I pulled the engine... it's in the machine shop for evaluation right now. Guess I shouldn't have bought that piston!!! Oh well. FYI... I had cleaned the carbs shortly after the impeller change... because I could not get on-plane... but I'll go through them again. I'll also check the "low idle screw" it seems there's a lot of chatter on these forums to make sure it is adjusted correctly. FYI... When this happened I was about 30mins from land and had to limp it in. Oh yeah... I also lost the CDI module for that cylinder (if that makes a difference).
Thanks again... and again!