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Evinrude 70 mid-section knocking

J

jn1440

Contributing Member
Might be nothing but I was curious anyway. Like the title says I get a knocking/klacking noise that seems to be coming from the midsection where the engine meets the mid-section at low rpm, any higher than 2000 it is drown out. Does it in and out of gear with no change.

First thing I did was check all the pistons for any type of play by taking the spark plug out and poking them with a wooden dowel, didn't get any play in the direction of motion on any of the pistons but the middle piston has some side to side play in it, piston slap. Not very much but enough that it will clunk a little if you push the piston sideways. I also wonder if this will go away at operating temp due to the aluminum piston in an iron bore.

I cant really imagine what else might be in that area to cause a noise? What else should I check? Kind of concerned because I never really heard anything different when my wrist pin disintegrated..... somewhat paranoid about engine noises now haha.

Here's a link for a video of the engine running at idle. Its more apparent when the camera is lowered closer to the engine,(fast higher pitched ticking noise) its hard to tell over video but I thought I would give it shot. Thanks anyway to anyone who has some input!

https://www.youtube.com/watch?v=K0uQyXgVyEo
 
Sounds like piston rattle, what are the compression readings and did it start over time or all at once? I see no smoke, what is your mixing ratio and what kind of oil do you use?
 
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Can't really tell you when it started, these engines are kinda noisy to begin with so it may have been there before not sure. Compression reads 115-120 across all cylinders and I use Pennzoil XLF mixed at a 50:1 ratio using a mixing bottle. It definitely does smoke may not have shown up in the video though it was late. Is there a way to tell if its the lower crank bearing with pulling it apart? Thats the large ball bearing one right? Just trying to visualize.

I can replicate what I think is the sound without the engine running by rocking the crank back and forth rapidly, doesn't sound as sharp as running but its coming from the same area. Which really sounds like a loose piston it knocks once in one direction and then again in the other like a loose connecting rod or wrist pin. But I really pushed on those pistons with dowel and didn't get anything, rotated the full 180* and tried them along the way too.
 
Did some more messing around with that middle cylinder seems like there is some movement in the direction of the bore but only at the bottom of the stroke and when the piston is coming up all other times its solid. Can't tell if its the rod or the piston moving side to side when pressed on. There's a lot of play at the bottom of the stroke side to side and virtually none at tdc. This is the cylinder I replaced the wrist pin on last year, I used old parts and slapped it together so it doesn't surprise me it failed again.

That cylinder is definitely the cause of the noise, when the piston is pressed to one side of the cylinder and the crank is turned the noise is gone. So its either piston slap or thrown wrist pin in that cylinder.
 
Also have a head bolt broken off now, I don't know what happened just noticed the head of the bolt broke clean off. Never had any luck getting these things out once the head breaks off so does anyone need any parts?
 
If the bores are good its still a fairly cheap fix yourself. Bolt is easy. Pull head off and then you have something to grab. Little heat and good to go, use nice set of vise grips. I just did a 60 hp. Sometimes you can just spin or rotate the whole head around as the shank of the bolt is stuck, not the threads.
 
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Head is off and bolt it out, went fairly easy as the bolt had seized in the threads instead of the head. Looks like there's some places on the block that allowed salt water to leak, one being around that bolt. The surface is pitted probably not allowing proper seating of the head gasket. Could some sealant be used on these places? they will not be in contact with where the cylinders seal.

Bad news is that the wrist pin on that middle cylinder is gone again, there is definite movement in the direction of the bore that doesn't move the crank and that noise is definitely caused by it. If the piston is pressed on the noise goes away and all the other cylinders have the same amount of slop between the piston and bore and don't make any noise. Doesn't surprise me though I reused the old piston from the last one that failed so probably some issue with the piston itself. Now the question is run it till it drops or begin tearing down to replace the piston, pin and bearing, the rod too? Mind you I am a college student with a budget of 200$ to do this haha.
 
What are you studying? There is an extremely high demand for marine repairmen, depending on where you live. The sharper you are the more work will funnel your way. I charge 50 per hour and work at home. All fresh water motors here in Minnesota, nice work. Allows me to still fix 50 year old stuff if I want, people still run 'em here. Need other work for 5 months of winter, however. I sell firewood at 180 per pickup load. Still run a Stihl 880 magnum, keeps a guy in shape. No need for the gym.
I would get a used piston and rod from Tim's Outboard in Hackensack Mn. (not me). Make sure your bore is good. Check no. on piston to see it is stock bore. Calibrate carb butterfly openings when done, as they will change every time they are r&r'd. Gasket sets are available at your local auto parts store. Sierra has a complete inventory of popular sets, or go on line of course. EBay has most as well. Be sure to replace crank seals. You have a good bore? You should make it at 200 bucks. Switch to Amsoil 100 to 1 pre mix oil and go 64:1 that's 2 oz per gallon non oxy fuel only. Check the 55 Evinrude thread on carb info. Clean up head and block surface with nice flat piece of iron or hardwood and 220 wet/dry and mixed gas or WD40. Little high performance silicone you might dap on pitted surface, keeping it away from cylinder sealing area of course. Get another head bolt from Tim's Outboard. Or as many as you might need. Wire brush and lite anti seize threads and under the hex where it meets outer head surface. Good luck. Tim
 
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I'm working on a degree in mechanical engineering and a minor in naval architecture I do work part time during the summer at a boat repair shop, not much of the mechanics more along the lines of fiberglass repair. There is definitely a demand for that time of work the boat yard is swamped all the time.

I checked into the replacement pistons, found some on ebay too. If I went this route what would I do at the crank? a few have mentioned that if swapping the main bearings and rod the crank needs to be ground or death will ensue.

May have some good news, before when thinking there was something wrong with the rod or bearings I was only eyeballing it and using my thumb as an instrument but today I decided I should put a dial indicator on it and really see whats going. After playing with it for awhile I cant find any dead spots between the crank being turned and piston moving. So it could be possible that what i was feeling before was the piston shifting to a side due to the piston slap. The bore looks good, no marks deep enough to catch a nail in or anything but it definitely has some slop in the bore.
 
How long ago did you replace the piston? What kind of piston did you use? Did you put the rod caps on the correct rod? What is your compression? You need to measure the bore, not ideal with the piston in but you can do the top of it. I am going to guess that is a 49 cid block 85 or earlier so it is a 3" bore. You cannot grind 2 strk cranks because no oversize bearings are available. I would look at the lower crank bearing also. I say this because piston slap or a rod knock does not go away it should get louder as it revs up. A lower crank bearing can go away as it revs up, I just fixed one on a 15 hp that sounded like yours. Your video would be better with the hood off.
 
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Piston and wrist pin were done in the spring of last year, so it ran all of that summer with it and up until now this season maybe 100 hours since it was done. I used a piston from an 84 evinrude 70 that failed due to one of the cylinders losing compression (not the cylinder I used the piston from), wrist pin, bearing and piston are from that engine. Compression was 120, 115, 120 before the head was removed.

How would one go about determining if a lower crank bearing was bad? I do have a video of the engine running at high rpm but again the cover is on.
 
Gotta pull Powerhead to check bearing. They usually are not a problem, however. The noise would soften if it is a piston as it warms up. You should hear my old Subaru. Aluminum expands more than the steel lined bore.
 
That's what I was afraid of, I wiggled the crank and didn't read any play in any direction for what it's worth.

Here's a video of the engine running at about 4500 rpm, not the best but maybe something I'm missing.

https://youtu.be/ZmpVohrrwjQ

I am pretty sure the noise is coming from that middle piston slapping around, poured some oil in the cylinder and noticed when the crank is rocked you can see the piston going from side to side as the crank chances direction and the tick follows suit. I will post a video of that later.
 
Yeah the bore measured from the top is 3.02" I did not consider this when I did the piston replacement so I'm not sure what the piston size is.
 
Ok If we take your measurement your bore 3.02 you are .020 over on the bore. Your piston is designed for the stock 3.00 bore. The bore will need to be measured as far down as you can get use telescoping gauges.
 
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Ok yeah I know what gauges you're talking about I will get that and check the piston size. But now I'm thinking it's that lower main crank bearing as I took off the lower cowling and discovered alot of oil that looks like it's coming from the lower seal.
 
Took some more measurements, as I suspect the issue is in the crank not the rods or pistons. No side to side play of the crank shaft but up and down play along its axis of rotation there was about 0.007" of play up and down on the crank. I assume this isn't normal?
 
To me, without checking, that's not too bad, certainly not enough to give a noticeable knock. How did you check it? Dial indicator?
 
Yep, dial indicator base stuck to the starter (only piece of real metal on it haha) and measured from the center concave cone in the top of the crank where the flywheel nut goes. I didn't figure that much play was allowed in the bearings? what would be considered too much?
 
The lower bearing holds the crank in position and is a " C3 " bearing.----------A little extra clearance but I believe 0.007 is too much.
 
Got a better dial indicator base it was kind of precarious on the starter there, and did things a little more carefully. Now getting about 0.005" in axial play, not much difference just wanted to be absolutely sure. What tolerance range would be considered acceptable? For future reference.
 
Well in that case I've run put of stuff to check, for me anyway. Maybe something in the lower unit? The input shaft is always spinning despite being in gear or not. Or maybe I'm just expecting too much from a 34 year old outboard with 2000 hours on it haha.I hate to tear it down because I've learned with saltwater engines this old sometimes there's no going back together. Either way I do appreciate the help as I have learned alot from this diagnosing process.
 
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