Engine rebuild on a 73 115HP V4 Johnson

[teslaman]

Well it finally did it. Took the boat out over the holiday and as soon as I hit WOT the engine started to kick a little. No crazy sounds, I just felt like the torque wasn't constant. As I turned ouround to head back to dock, the motor seemed to get progressively worse.

I haven't check compression with a guage, but by stcking our fingers in the hole we can feel a possible lack of compression in cylinders 2 and 4. Also, I just topped of the fuel tank with 50:1 mix.

How difficult is it rebuild the engine? Should the pistons be inspected before parts are ordered? What kind of $ am I looking at for parts and possibly labor?

A mechanic with experience in Johnson boat motors is going to look at it later this week.

The motor has been hard to start when cold since I bought it. I know the previous owner used either to start the motor when cold, and I'd say that took its toll. I've starting using a 50:1 mix in a squirt bottle to cold start---works nicely.

 

[Walker]

Re: Engine rebuild on a 73 115HP V4 Johnson

I'd get a compression guage and test it or wait for the mechanic to take a look at it.

 

[tashasdaddy]

Re: Engine rebuild on a 73 115HP V4 Johnson

agreed, that ether wasn't good for it. cross your fingers. maybe just a power pack failing.

 

[DHPMARINE]

Re: Engine rebuild on a 73 115HP V4 Johnson

Bad compression/pistons won't feel like torque kicking in/out.That sounds like a clutch dog /forward gear problem in the lower unit.

Pull all 4 plugs out and do the finger test again.If the response is a LOT weaker on 2 & 4 remove the cylinder head for inspection.Maybe pull both cylinder heads so you can compare.Let us know what you see.

A bad head gasket could let a plug foul to quit off and on,causing the kicking you describe.

As to rebuild ...... what does a 34 year old motor sell for in your area? Next to nothing here in MA. And once it's rebuilt it's still 34 years old.

DHP

 

[ezeke]

Re: Engine rebuild on a 73 115HP V4 Johnson

That could also be a propeller problem. Also, the problem during a turn could be air intrusion - was the tank full?

 

[teslaman]

Re: Engine rebuild on a 73 115HP V4 Johnson

Tank was full. The prop needs replaced, but its in no worse shape than when I bought it. I used it all summer with no problem.

I thought about the lower unit, what is the best way to check for this. Remove the lower unit and inspect the gears?

 

[Chinewalker]

Re: Engine rebuild on a 73 115HP V4 Johnson

Easiest way to inspect the gears is to drain the oil. If the gears are getting chewed up the oil will contain metal filings...

Check powerhead compression with a gauge to get a good read on what's going on inside. Evidence of water on the plugs may indicate a blown head gasket. Hopefully that's all it is...

- Scott

 

[teslaman]

Re: Engine rebuild on a 73 115HP V4 Johnson

The water thing is interesting. We did the compression check after I got the boat in the driveway. No water hose or anything. We removed all of the spark plugs and used our fingers to plug the holes. When the starter was engaged, fuel shot out of the holes -- except that the fuel did not smell much like fuel, it was more like water.

My step father is a car mechanic (little experience with boat motors) and he helped me to do the test. Since we had the wrong guage with us, he used his fingers to see if there was a substantial difference between cylinders. He is the one who noticed that the fuel seemed very watered down. I'll have to ask him later if only one cylinder produced this result or if there was another also. We plan to have a mechanic with more experience with Johnson boat motors look at it some time this week.

 

[h_lankford]

Re: Engine rebuild on a 73 115HP V4 Johnson

look at the sparkplugs. If there is water, then the steam cleaning may make the plugs color near white, compared to the normal color of the other plugs. Same for the top of the piston which you should be able to see.

 

[teslaman]

Re: Engine rebuild on a 73 115HP V4 Johnson

The mechanic is going to look at my engine on Saturday. I was browsing around the iboats site, and noticed that they sell rebuilt powerheads and lower units. Has anyone gone this route? If so, how was the quality?

Is the core charge refunded if the old part is sent back?

 

[teslaman]

Re: Engine rebuild on a 73 115HP V4 Johnson

Well, I definitely blew the engine. I had a mechanic chec it out yesterday morning, he and I checked compression and the spark plugs. The spark plug in cylinder #1 was bent in so that the electrode and cathode were touching. This would describe the loss of that cylinder and the unused fuel that we found in there. However, compression did not raise raise any huge alarms although it was lower in #1 than in the other cylinders..

The question is how did the spark plug get bent? We thought the piston may have hit it. So we checked to see if there was any movement (slack) with the piston. There was very little, but not enough to cause alarm. So I took the boat out--It ran smoothly at first, but about 8 mph less at WOT than usual. Finally, #1 went out again and violently. It destroyed the spark plug and post mortem revealed a molten piston head. To make matters worse, the cylinder walls have some pretty deep groves now.

Looks like I'm going to get a rebuilt powerhead from iboats now. I plan to call them on Monday to see how long delivery takes and perform the installation over Xmas break. I asked about these rebuilds on another thread, and folks out there seem to have the upmost confidence in them. They also come with a 15 month warranty, something I probably couldn't find on ebay.

 

[funpilot]

Re: Engine rebuild on a 73 115HP V4 Johnson

I don't think I would invest in a new powerhead on a 1973 motor. I might try rebuilding it for fun, if the gouges could be machined out, but I think if I were going to spend the money, I would try to find something a little newer. There won't be a lot of difference in buying a powerhead for a non-functioning motor which is 10 years old as opposed to almost 25 years old.

 

[teslaman]

Re: Engine rebuild on a 73 115HP V4 Johnson

I thought about that but by time I spend money in parts and the time it would require for the rebuild, I may as well get a professional rebuild for <$1,400 that has a 15 month warranty.

I'll have to swap out the powerhead which may take a couple of days. If I get a 10 year old engine, then I stand the chance of inheriting more problems which may end up in another future rebuild.

 

[funpilot]

Re: Engine rebuild on a 73 115HP V4 Johnson

When I was checking on power head choices for my 90hp I think the least costly was about $1800. I rebuilt mine for $600, but if I had replaced bearings it would have been about $900. I thought my bearings were fine. The newer engine suggestion was based on buying one that was bad, and rebuilding it (since you are spending money on a rebuild anyway), figuring that the lower unit would be good, and ending up with a newer engine with VRO, better ignition and the like.

Your best warranty wil be your carbs and fuel delivery. Any engine that is properly rebuilt will last 15 months if it is fed right.

good luck with your decision!
fp