1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

[MadtownChris]

Hey folks,

First time boat owner (3mos or so) and have a 1978 Evinrude 85hp v4 on a 16' Yar-craft tri-hull.

Searching these forums has been super helpful so here I am hoping for some expert answers.

Boat was running pretty well for a while. Had some minor power loss / surge at WOT but infrequent.

Then last Saturday at slow speed dragged my new prop on I think mostly sandy bottom :grumpy:. The engine vibrated vigorously as you'd imagine. Immediately after that, it lost probably 50% of the power and RPMs. I could just barely get the boat on plane and at idle it would die.

Since we were near our destination, we docked for about an hour then got back in and headed back.

Symptoms on the way back were similar but now power loss was probably 75% though engine sounded smooth - the boat went no more than 5-7 mph at WOT - RPMs were similarly low. It took forever (hour?) to get back to the launch.

I checked the spark plugs with a tester and found that one cylinder had no spark. The problem seems to be the connector plug between the wire to the coil and the black power pack (?) thing. If I connect the wires outside the rubber boot, spark tester lights up so appears to be an easy fix. :joyous:

So here are a couple questions:
1. Does it seem like hitting the sand vibrated the bad connection completely loose which is the explanation?

2. Why would I have middling power for a bit, then almost none later? I would think losing one cylinder would result in a consistent speed. Maybe the cylinder was firing a little then not at all?

3. Is 5-7 mph at WOT something you'd expect missing just one cylinder?

4. Should I do anything to the cylinder with no spark before trying to run it? Like replace / clean the spark plug? Are there other effects on the engine from running without a cylinder for an hour I should address?

Thanks!

- Chris

 

[Daviet]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

Welcome to the forum.
1. It is possible for an electrical connection to be affected by a jolt like hitting a sand bar. Make sure all the connections are clean and tight.
2. Again, it is possible for a poor electrical connection to cause intermittent problems, that will come and go.
3. Hard to tell how much speed will be lost with the loss of a cylinder, many things come into account, boat/horsepower ratio, weight of boat prop size.
4. Yes, get spark back to the cylinder, you are not going to be happy with the performance of the boat if it is not running correctly.
It sounds like you have found the problem, a bad electrical connection, fix it properly and enjoy your boat.

 

[emdsapmgr]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

Hitting anything with the prop can cause problems. Possible you have spun the rubber hub in it. If you have another prop, try it. Weak ignition components do tend to fail once the engine heats up to "normal" operating temps. (may run fine when cold, then not well when warmed up.) So-do your testing when the engine is well warmed up. That engine has two identical power packs, one for each head-you can swap them for testing purposes.

 

[MadtownChris]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

Thanks! It turned out power pack was bad. I swapped them and that side ran. Bought a new one today and both sides running.

But now that I had the cover off and was monkeying around... I noticed the right side (failing power pack) had water leaking from the cylinder head gasket. Not a lot but tiny drips. I tightened the cylinder head bolts a little by hand with my smallest ratchet and found that many of them were not even hand-tight. That slowed the leak but did not stop it.

I also had my fingers on all four cylinders while it warmed up on the hose. I noticed the right side getting hotter faster than the left. Water cooling streams seemed vigorous.

Now the right side are the two higher cylinders so maybe on the hose they heat up faster due to lower water flow? Or could it be related to the head leak?

Could the power pack have failed (the resin was all cracked allowing humidity in) due to it overheating on that side?

Suggestions for next steps? It seems to run great despite what I found. We're not running it continuously for long periods - it's a family swim and tube platform mostly.

- Chris

 

[boobie]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

Rent an inch pound torque wrench and torque the cyl head bolts to 168-192 inch pds and see what happens with the leaks. Torque when mtr is cold. To properly check the temp of the mtr you'll need a temp gun.

 

[keefallan]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

I would recommend doing a compression test too. At least then you'll know the condition of the gasket. Worst case scenario is put on a new gasket for 15 bucks and after you run it to get it warm, recheck the torque readings after it cools. I think torque is 20 ft/lbs for the bolts. Torque the bolts in the middle first and then work outward in a circular pattern till they all get torqued. That's it.

 

[emdsapmgr]

Re: 1978 Evinrude 85 v4 one cyl ceased; think I fixed but have questions

Is it the head gasket leaking, or the head cover gasket? That engine has two thermostats in the thermostat housing. One for each head. If one head is running warmer, it may have a bad stat. If you decide to get into the thermostat housing, replace both of them while you are at it. They are inexpensive and may save you having to change the other one in the near future. Always good to retorque the new head gasket after the engine goes through the first few heat/cool cycles.