Mercury I6 140hp 1979 running on 5 cyl.

[madgadget]

Hi All,

Just thought I would give this a try and open it to the experts for some advice.

I have a 1979 Mercury I6 140hp. I took it out yesterday and it didn't quite seem what I thought it should be. (I'm new to boating). Anyway today I did a compression test on all 6cyl and they came up all around 9 bar ~ 135 psi. Cyl 6 tested no different to any others.

All other cyl are fine, all sparks plugs look the same except 6 which was clean in comprison.

So then I did a spark check and cyl6 seems fine. Ignition coil primary and secondary resistances were also the same across all coil packs.

So I am a bit stumped. Could it be fuel even though cyl 5 is running fine? Cyl 5 and 6 share the same carb so I would have thought if one worked the other should too?

Anyway Where can I go from here ? Any checks or anything people could advise even from the beginning would be very welcome.

Thanks,

Ed

 

[Chris1956]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Ed, If you have spark on #6, and #5 is working fine, and you have a clean spark plug on #6, it is likely water intrusion. This water steam cleans the spark plug, and puts the fire out.

The place where water normally intrudes is either the lower crankcase seals in the lower end cap of the block, or the water jacket covers over the exhaust ports. The best thing to do is to pull the block, replace the crankseals and inspect the inner water jacket cover and the exhaust baffle. if you pull off the outer exhaust cover, you can inspect the baffle and inner cover. Beware, the bolts will break quite easily, if you are not careful with them. Use some penetrating oil, a propane torch and an impact driver to coax them out. The inner water jacket cover bolts are even more stubborn...

The crank seals can usually be replaced after removing the 3 or 4 endcap bolts, and loosening some crankcase bolts. They are a press fit into the endcap.

 

[madgadget]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Chris that's brilliant thanks. It would make perfect sense. I'll get that sorted sharpish then as I really don't want to ruin anything within the engine. Thanks for the pointer.

I guess now the fun begins!

 

[turbinedoctor]

Re: Mercury I6 140hp 1979 running on 5 cyl.

I would just like to say that Chris has an excellent point there. I am in the process of a rebuild due to the lower bearing coming apart and taking out # 6 cyl. Before this happened I noticed that when it was idling it was not quite as smooth as I thought it should be and every now and again it would seem to pick up a extra cyl and then drop it again. I had spark on all of them and it ran good when above idle. Looking into it after the tear down I figured the seal was worn out causing the missing on # 6 and then the bearing went. I have some pictures of what it looks like when balls from the bearing get into the #6 cyl as it is running if you care to see them. Keep in mind you need a strong stomach for them.

http://www.wellcraftv20.com/gallery/Motor-Torn-Down



Durwood.

 

[madgadget]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Hmm interesting thanks for that. I kind of figure that if water has got in there there HAS to be damage. As much as I REALLY REALLY DONT want to have to totally pull it apart I have a feeling its going to be inevitable I guess I will not know until I have pulled the power head off the engine...

We shall see... I must admit im half tempted to take it out one more time but I know i shouldn't before I pull it all apart as it will most likely be the last time I use it this year otherwise.

 

[turbinedoctor]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Roll the dice if you wish but mine was running as good as ever and with out any warning I started getting a bumping noise at the rate of 4200 times a minute. At 8 miles from the dock it was a long tow back.

It's not that hard to get the power head off and then you just pull the lower end cap. The seals are in there. There should be two in the lower and one in the upper. Orintation of the seals going back is most important. You can inspect the lower bearing while you are there to determin if further tear down is needed.

Best of luck,

Durwood

 

[madgadget]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Sensible advice thanks for that. I am going to pull the motor this weekend and take a look.

Thanks,

Ed

 

[Chris1956]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Ed, Don't be too pessimistic. I ran mine with water infiltration for quite a while. You may be OK, but inspect bottom main bearing for wear. Replace Orings on lower end cap, and try to fit 3 crankshaft seals into lower end cap.

 

[madgadget]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Cheers Chris. I am going to make some calls tomorrow morning to try and order some seals and gaskets. If the bearings look ok then I may manage to get it all done this weekend.. I'll see how lucky I get haha I don't want this to get expensive as I have my eyes on another boat with a merc 220xri lump on it which I am also hoping to view this w/e

 

[CVX20SPRINT]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Ed, Don't be too pessimistic. I ran mine with water infiltration for quite a while. You may be OK, but inspect bottom main bearing for wear. Replace Orings on lower end cap, and try to fit 3 crankshaft seals into lower end cap.

Sorry if I'm hijacking this thread.
Are you saying to install 3 seals...2 with the lips facing out and 1 in?
I maybe into the same problem with a 1500 Merc.Just purchased this motor with new plugs,so new that I can't get a read on them.Trying to eliminate the all the external first,before I pull the power head.

 

[Chris1956]

Re: Mercury I6 140hp 1979 running on 5 cyl.

I think all the seals should have the lip facing in. You need to pull the powerhead to get to the lower end cap.

 

[turbinedoctor]

Re: Mercury I6 140hp 1979 running on 5 cyl.

I think all the seals should have the lip facing in. You need to pull the powerhead to get to the lower end cap.

I will have to double check with my manual, but I think the seals point out to keep water from getting into the crank case.

 

[emckelvy]

Re: Mercury I6 140hp 1979 running on 5 cyl.

Both seals in the lower bearing end cap of an Inline Merc are installed with the lips facing downwards.

Be sure to pay attention to the position of the old seals, in relation to any oil bleed passages which may be present in the end cap.

You want to install the new seals in the same spots the old seals occupied. This'll ensure you don't inadvertently block any of the bleed passages.

HTH..........ed

 

[turbinedoctor]

Re: Mercury I6 140hp 1979 running on 5 cyl.

While we are talking about this area of the engine, what is the small hose that runs from the bottom end cap up to the top end cap used for?

 

[Chris1956]

Re: Mercury I6 140hp 1979 running on 5 cyl.

TD, That is the oil bleed line. It had one way valves that "pump" oil to the top bearing.