Spark issuse solved, now low compression in one cylinder

[83ebbtide]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

I'm no expert but I would think you would want to correct the top end issue before rebuilding the carbs and potentially creating additional problems. Assuming your sure it isn't fuel. I've seen the tip here of using a timing light and checking each coil to see if you get a consistent and steady spark on each coil. You can do it on the hose at idle or on the water just be careful as you get up to speed, don't want your buddy to fall out.

 

[Craig-]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

I'm no expert but I would think you would want to correct the top end issue before rebuilding the carbs and potentially creating additional problems. Assuming your sure it isn't fuel. I've seen the tip here of using a timing light and checking each coil to see if you get a consistent and steady spark on each coil. You can do it on the hose at idle or on the water just be careful as you get up to speed, don't want your buddy to fall out.

The timing light test won't show a bad coil unless it is completely dead. 7/16" spark test will show a weak coil which can get worse when hot. I have seen brand new coils that will spark a plug but not spark a tester. I test new coils on a spark tester before hooking the plugs up, just to be sure.

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

The timing light test won't show a bad coil unless it is completely dead. 7/16" spark test will show a weak coil which can get worse when hot. I have seen brand new coils that will spark a plug but not spark a tester. I test new coils on a spark tester before hooking the plugs up, just to be sure.

I'm getting a spark tester and compression tester this weekend to start with the simple tests to determine if I can fix it myself or wait till I can get the funds and take it to a marine mechanic.

Just knowing there are a few things I can do to help determine what is going on is a big help! Thanks everyone!

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Ok, the boat is in the garage, I've got the $7 adjustable spark tester, compression tester, etc.

I must be missing something on the "how to" for the spark tester. How do you use it? I've adjusted the spark gap to 7/16" as noted, I assume you plug the tester into the plug wire and then clamp the other end to the back of the plug to complete the circuit?

"Do a spark test with an adjustable spark tester set to 7/16th inch gap.
Spark has to jump the gap, see directions for spark test in the top secret FAQ files."

Is that right?

I found the "how to check compression" in the FAQ but not the "spark test".

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

I also have a new replacement coil (Sierra). What kind of solder do you use to solder the plug wire to the plug clamp/connector? Acid core or rosin core? Does it require a heavy duty solder iron?

 

[Daviet]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

The spark checker goes from the plug wire to a good ground, like the block.
I think that the plug wire just screws into the coil on your engine, I have never seen a plug wire that had to be soldered on to the coil.

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Ok, here is what I have discovered based on the spark test and compression tests. I don't know the cylinder #'s so as you look at the motor from the back of the boat (prop side), the cylinders are described below:

Spark test
- upper left cylinder, good spark
- lower left cylinder, no spark at 7/16" gap, weak spark at 1/4" or less
- upper right cylinder, good spark
- lower right cylinder, weak spark at 7/16" gap

Compression test
- upper left cylinder, 110psi
- lower left cylinder, 70psi (not good!)
- upper right cylinder, 100psi
- lower right cylinder, 110psi

So, bottom line, it looks like I need 2-new coils and I have low compression in the one cylinder. Last year, the compression was up around 110-120 I think.


So how expensive is it to fix the low compression and what all has to be done?

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

The spark checker goes from the plug wire to a good ground, like the block.
I think that the plug wire just screws into the coil on your engine, I have never seen a plug wire that had to be soldered on to the coil.

I used the spark tester like an "in-line" tester. It worked, maybe not as good as using a ground though.


The new Sierra coil requires you to solder the snap connections to the plug wire, then slide the boot covers over them. I was a bit upset that it wasn't ready to go straight out of the box like most plug wires. It's an exact replacement for the OMC coil for my motor too so I know I have the right one.

 

[Daviet]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

You might want to pull the cylinder head and check the low compression cylinder. Look for defective head gasket, damage to piston and/or cylinder wall.
Maybe retry the compression test with a little oil in the cylinder, maybe defective rings.

 

[Craig-]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

I used the spark tester like an "in-line" tester. It worked, maybe not as good as using a ground though.


The new Sierra coil requires you to solder the snap connections to the plug wire, then slide the boot covers over them. I was a bit upset that it wasn't ready to go straight out of the box like most plug wires. It's an exact replacement for the OMC coil for my motor too so I know I have the right one.

Always ground the spark tester to a known good ground, not to spark plug.

Your existing plug wires will not plug onto new coils?

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Your existing plug wires will not plug onto new coils?

No, the original coil wires are built into the unit itself and only has one connector for the spark plug, not at the coil.

They don't make the OMC coils like I have any longer. The OMC coils are much like the Sierra coils I believe.


Regardless, my fears have come true. Low compression. That generally means lots of money or at least a $300-$500 for the mechanic I'm sure. I'm not comfortable looking inside the motor so my mechanic will have to take it from here. If it were just a bad coil, I'd be on the water.

 

[AlTn]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Cane..on a '79 model motor...it doesn't take long, labor-wise...to start throwing good money after bad...pulling that head yourself isn't real dfficult..unless this is a saltwater motor which can bring on "complications"

 

[Craig-]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

No, the original coil wires are built into the unit itself and only has one connector for the spark plug, not at the coil.

They don't make the OMC coils like I have any longer. The OMC coils are much like the Sierra coils I believe.


Regardless, my fears have come true. Low compression. That generally means lots of money or at least a $300-$500 for the mechanic I'm sure. I'm not comfortable looking inside the motor so my mechanic will have to take it from here. If it were just a bad coil, I'd be on the water.

Don't let it scare you, pulling the heads is easy. Just don't break a bolt.
PB Blaster soak them. As long as you don't have a water leak, you can still run that thing, even with the bad compression. Just need to find the cause, so it doesn't get worse.

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Based on my compression test numbers, I called a local mechanic that I've never been to before (i heard he's really good and been a marine mechanic for 30yrs or so).

Here's what I told him:
- I needed a rough estimate for ring replacement or worst case scenario just for ball-park numbers
- year and make
- weak compression in one cylinder
- I had a tune-up and decarb last fall (this is where he stopped me and told me that the decarb was a bad thing)

He told me that the engine decarb on the older motors was bad and could have created a gash in the cylinder wall. He was 90% sure there was more to it than just a bad ring and that I would probably need to over-haul the motor and that was about $3,500-$3,800 roughly with a 1-yr warranty.

He said the V4's are great motors and last forever.


Someone please tell me that I have not ruined my motor by trying to do the right thing, take it to a reputable mechanic and had a tune-up/decarb performed to PREVENT having to over-haul the motor?

I'm about to panic cause this little boat is my baby...



No, I'm no mechanic and don't want to do it myself. I know just enough to do small things.

 

[Rscardina]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

cane..i feel your pain..

I'm a bit puzzled though. I have heard and read numerous post on here that decarbing is a good thing. The coincidence that the decarb cause a score or gash is a bit crazy. Decarbing is a fluid mixed with gas/oil that cleans carbon..where on earth a gash comes from is beyond me.

I guess a long shot is that the carbon was holding a ring snug and the cleaning loosen it...causing a scoring..???

I guess its no different from using mystery oil in a car to clean it and then all of a sudden you have oil leaks everywhere cuz you just clean years of sealer (old dirty oil)...

The experts here should chime in...I'm betting a hunderd posts that say NO WAY the decarb created thi issue...
I'll let them tell you why....

 

[jonesg]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

Based on my compression test numbers, I called a local mechanic that I've never been to before (i heard he's really good and been a marine mechanic for 30yrs or so).

Here's what I told him:
- I needed a rough estimate for ring replacement or worst case scenario just for ball-park numbers
- year and make
- weak compression in one cylinder
- I had a tune-up and decarb last fall (this is where he stopped me and told me that the decarb was a bad thing)

He told me that the engine decarb on the older motors was bad and could have created a gash in the cylinder wall. He was 90% sure there was more to it than just a bad ring and that I would probably need to over-haul the motor and that was about $3,500-$3,800 roughly with a 1-yr warranty.

He said the V4's are great motors and last forever.


Someone please tell me that I have not ruined my motor by trying to do the right thing, take it to a reputable mechanic and had a tune-up/decarb performed to PREVENT having to over-haul the motor?

I'm about to panic cause this little boat is my baby...



No, I'm no mechanic and don't want to do it myself. I know just enough to do small things.

So you asked him to check it out and assess the damage and he said $3500 before he looked at it. And he said decarbing is bad ?
Find another mechanic.

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

So you asked him to check it out and assess the damage and he said $3500 before he looked at it. And he said decarbing is bad ?
Find another mechanic.

It was a random cold call over the phone and I have him very little information. I had been told he was a good mechanic and been around for 30yrs and knew a lot so I thought it would be worth calling. I agree that he sounded like he would "fix it right" which may be the most expensive work possible.

I told him very little and he stopped me when I said, "decarb" and said, "Decarb? Wait, did you take your boat to ___ (Identity to remain nameless mechanic)?" That's what really through me off. How would he know exactly who I took my boat too by simply saying "I had a tune up and decarb last fall".

He said he'd seen that scenario many times before and that decarbing could eat up the rings as well as breaking up large deposits. The large deposits could scratch the cylinder walls and thus an overhaul was probably needed. While saying this from a random call does sound a bit odd, I tried to give him the benefit of the doubt based on experience.

I admit, it really scared me because I paid $2,200 for the boat (1979 model) and now I potentially have an overhaul on my hands if he is right. That's a ton of investment in a 31yr old boat.


I am going to ask my original mechanic what his thoughts are, rough cost estimate, as well as ask other mechanics to check around. My mechanic has a great reputation and lots of folks like him and recommend him no matter what the other guy said about him.

 

[Craig-]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

As I said earlier, pull the heads yourself. It's over 30 years old, do what you can then run it until it gives up. It should run, even with the compression disparity. $3,500 is way too much to put into it. You would be way better off putting that towards a new or newer motor. Spend $30 on gaskets, you've got nothing to lose trying, just don't break anything while doing it. It really isn't hard at all to do.

 

[CaneCutter79]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

As I said earlier, pull the heads yourself. It's over 30 years old, do what you can then run it until it gives up. It should run, even with the compression disparity. $3,500 is way too much to put into it. You would be way better off putting that towards a new or newer motor. Spend $30 on gaskets, you've got nothing to lose trying, just don't break anything while doing it. It really isn't hard at all to do.

It does run, I just do not want to damage it further.

What do I look for once I get the covers off? How do I change the rings? What if it's a warped cylinder? Sorry, I'm WAY New at going inside the motor. I mess with the outside stuff. I've cleaned the starter, replaced brushes, coils, plugs, etc. but when it gets in lower units and motors, I know nothing....

 

[Craig-]

Re: Bad coil or failing power pack??

Re: Bad coil or failing power pack??

No, I'm no mechanic and don't want to do it myself. I know just enough to do small things.

Pulling the heads really is a small thing. It is not like car heads, these are just covers. It only requires a wrench and cleaning the mating surfaces. If you can take out a spark plug, you can do this. If you run into a problem stop and ask.