#3 cylinder, good spark - no fire

[MikDee]

Re: #3 cylinder, good spark - no fire

IMO, I'd get rid of the surface gap plugs! Then pick up a standard gap comparable heat range "resistor" plug. The resistor tends to keep the spark at the electrode tip, rather then any outside surface of the plug, especially if you have solid core metal (non-suppression spark plug wire!). No wonder you keep getting shocked!

There should be a comparable plug you can gap to replace this, maybe from a plug chart, OR, from an older, like 89' 125 Force outboard like I had.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Jiggz, the plug is not new but it works fine in the other 3 cylinders. The coil and wire are good they work fine on the other 3 cylinders. I have replaced the stator, and the regulator. The part that I don't know is, will the water cause the plug not to spark while it's installed? With good even compression can the head gasket be blown? How do you suggest I ground the plug with it uninstalled?

MikDee, thanks for your input but I'm not sure that's the best advice. The motor was engineered to use these plugs, if the plugs you speak of work better without damage to the motor then that would be the factories recommended plug. I have read on this forum that the heat range is very different between the 2 styles of plugs. If I use to hot of a plug it most likely will destroy my pistons. I do appreciate your advice though.

 

[jerryjerry05]

Re: #3 cylinder, good spark - no fire

Keep the surface gap plugs.Nothing wrong with the plugs.
Millions of they motors are using them.If the motors setup right it will need nothing changed.
If you have ANY moisture in the cylinder you either have a bad gasket or a cracked block possible the exhaust system leaking back into the cylinder?
The reeds IF they were bad you's get some blowback from the carb as it runs.
I had a gasket go bad.The compresson was at 150 all 3 cylinders but the bottom cylinder had a very tiny hole in the cylinder allowing water in and a miss..
Your motor the compression I believe in the top and bottom cylinder was designed to be lower than the 2 center ones.
At 120=123# your gauge isn't reading right.Try another it should be 145 1/4 and 155 2/3.
Remove the head and check the gasket.

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

Well if you have verified the #3 plug to be working by switching it over then there is no need to verify it visually. But to answer your question, NO, water or moisture will not prevent a known good working plug not to spark or arc. So the next move now is to verify fuel mixture in the affected cylinder. You basically need three factors to have combustion on these motors, i.e. air-fuel mix, compression and a spark. So far you have validated the last two and all you need is to validate you actually have air-fuel mix going into the cylinder.

If you have all these three factors, even with slight water leak you should have combustion (albeit it will steam clean the cylinder), unless the said water leak is so great it prevents combustion, but then that would probably result in a hydrolock also. As mentioned before, I verify fuel mix in a cylinder using a rag placed in the plug hole and cranking the motor. With proper fuel mix you would see wetting on the rag.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire



I noticed a new leak coming from the fuel pump area.
The photos are a picture of the leak and the reed test
I also purchased a brand-new compression gauge and the sooners read 155 160 155 160 top to bottom.

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

Looks like either #3 or #4 by-pass cover is leaking. There is a gasket under each of the by-pass covers. Maybe something as simple as tightening up the four bolts that holds the cover in place. Red arrows point to the four bolts on each cover. There are 4 covers, one for each cylinder.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

That"s the best news I've heard all week. I can't wait to get home!

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

Looking at the fuel in the cylinder tests from the 4 pics, I surmised it was taken from top to bottom of #1 and down to #4 with the #3 having no trace of fuel. If this is correct, there is an indication the reed might be faulty or as mentioned by PNW, you could be sucking air from the by-pass cover. I would personally open and inspect the cove gasket before tightening as it may already have a tear on it. Anyways, fix that and test again and hopefully that is just the cause of the problem. If problem persists, you will have to open and inspect the reed on #3.

 

[Lone Duck]

Re: #3 cylinder, good spark - no fire

Well if you have verified the #3 plug to be working by switching it over then there is no need to verify it visually. But to answer your question, NO, water or moisture will not prevent a known good working plug not to spark or arc. So the next move now is to verify fuel mixture in the affected cylinder. You basically need three factors to have combustion on these motors, i.e. air-fuel mix, compression and a spark. So far you have validated the last two and all you need is to validate you actually have air-fuel mix going into the cylinder.

If you have all these three factors, even with slight water leak you should have combustion (albeit it will steam clean the cylinder), unless the said water leak is so great it prevents combustion, but then that would probably result in a hydrolock also. As mentioned before, I verify fuel mix in a cylinder using a rag placed in the plug hole and cranking the motor. With proper fuel mix you would see wetting on the rag.

I have been following this thread with great interest. Could it be that the P O put a type of nonconducting thread locker or some type of material to repair the threads in the plug hole?? I noticed some kind of crude on the spk plug washer and around the plug hole. Is the spk plug grounding in the hole?? LONG long shot I know but stranger things have happend.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Funny you say that Duck, the #3 plug was a little harder to unscrew. I could still do it by hand. This theory would explain why it shocks me and doesn't fire the piston. Whats the right way to fix the plug threads? Don't tell a new head.

Just to add a smile to the thread, my 9 year old daughter suggested I fix the leaking seal by spraying it with some Flex Seal from the infomercial.

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

It is really easy to verify if the plug hole has been re-threaded with a non-conductive material by doing a continuity test (either with the plug hole thread itself or with a spark plug threaded in and taking a reading from its steel hexagonal body) with the engine block and the resistance should be less than 1 ohm. If there is good continuity then you can validate the spark plug is fully grounded and should be working. Most of the time, you get shock from plug wire is mostly due to deteriorated insulation, i.e. cracked, lost of dielectric property, stiffed, water soaked, etc

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

If you verified that the plug hole has been re-threaded with non-conductive material (most of the time the material is conductive, i.e. helicoil, save a thread, etc, except if you used too much of that thread lock material you can lose conductivity) there is no other option except to remove it (existing thread) and do a re-thread using helicoil or save a thread kit. Youtube has many video showing how to do thi.

 

[Big Fish Billy]

Re: #3 cylinder, good spark - no fire

Remove the head and check the gasket.

Ditto...relatively easy.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Well the bypass cover gaskets for both #3,#4 look really good[

 

[bogginyota]

Re: #3 cylinder, good spark - no fire



I know the picture sucks, but do you guys see any thing on the reeds that stands out?

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Is it ok if I replace the bolts on the bypass cover with some that are stainless steel?

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

Yes you can, however, in saltwater environment use lock washers and coat the threads with some anti-seize. Preferably the nickel based anti-seize. If you can't find that, the copper based or just marine bearing grease. The idea is to keep the saltwater out of the threads. Saltwater plus a stainless steel fastener in an aluminum alloy can corrode to the point where the fastener is almost fused to the aluminum. Make sure the By-Pass cover gaskets are in good shape, no tears or breaks that may cause a leak.

Can't really tell if the reeds are OK. Unless there is a piece actually missing, it's hard to tell. Probably have to remove the reed blocks to see for sure. If you're careful, you can usually get them out without damaging the gaskets. Ideally, the reed petals should be laying flat against the reed block. Factory specs say that maximum gap between the reed petal and block is .010 inch. If any are bent up more than that, or cracked, or broken, they need to be replaced. Personally, I replace them if I see any gap, but that's just me.

You can check them by looking inside the reed block and shine a light on the opposite side and look for and light indicating a gap between the reed petal and reed block.

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

As PNW mentioned, you will be better off uninstalling the reed for full inspection.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

I've had quit a hectic few weeks, and plan on checking out the reeds this weekend. Does anyone know of a marine parts place in Port Canaveral area or Brevard County FL. that would stock the parts I may need?

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

I don't know of any places close to you, however, it is a standard Mercury part (P/N 855952T3) that runs about $80 new for one reed block assy. Your motor has 4 of them, one for each cylinder.

I've seen quite a few used ones on the auction sites but most of the ones that I've purchased that came off of 120HP motors were slightly bent and would not lay perfectly flat. It's strange because I've purchased used ones for 1994 and later 70HP and 75HP motors which use the same part and every single one was perfect. Used ones run about $35 - $65 for one reed block assy.