General Engine Rebuild Questions

[fmjnax]

Motor is an '84 Johnson V4 115. I was battling a poor idle all last season (but it did run and was usable). I was going to sell the boat and cut my loss, but decided to try and find the problem. The carbs are off and have been freshly rebuilt. The intake manifold is also off (I was checking reeds and such). I ran compression on it tonight and got the following:

90 on top right
89'ish on bottom right
50 on top left
89'ish on bottom left

I checked them all 5 times each, with the same result. So suspecting a cylinder problem, I pulled the head cover and then the head. With compression that low, I was expecting to see a huge mess or a sure sign that something broke or got stuck. I found quite the opposite.

I'm just a shade tree mechanic and have never worked much at all with cylinders and such, so I might be missing something obvious. The ONLY thing I see is a groove in the lower-right of the cylinder. You should be able to see it in the picture. Otherwise, the rest of the cylinder is very smooth.

Nothing else looks out of place, or really any different than the bottom cylinder. Looks like carbon buildup on the piston head, but looks normal to my untrained eye. Back side of the head looked like a little carbon buildup as well, but not bad. The head cover was nasty and had a white lithium grease looking gunk all over it that I have no clue what it would be. The head gasket was intact, albeit obviously old and nasty (same for the head cover gasket). Nothing appears stuck or burnt, again to my untrained eye.

I haven't put any fuel through the block since August, but I did give each cylinder a squirt of premix and a couple hand turns before testing the compression. The batteries haven't been charged since August either, but were disconnected until tonight. If the battery was weak, I would have expected low compression on all 4, though.

So enough rambling, what should I try to look for? What else could cause the low compression? I bought the boat knowing full well it was a project and I'm planning on a full restore, so anything short of a major rebuild, I would like to try and fix it before looking at a new PH or full outboard.

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[Bosunsmate]

Bad headgasket, stuck rings in that 50psi one

 

[schematic]

That cylinder has a bad score and will need boring and oversize piston. Looks like the top ring is also broken. The water deflector is swollen and is constricting flow. You need a overhaul for sure....The nick in the top of the piston also suggests broken ring......

 

[emdsapmgr]

Likely that cyl has been severely overheated and that would have affected the ringsets. If you look at all 3 pics, you will see the rubber water deflector is in the wrong position. It's completely blocking off water flow to the that side of the block . I'll post a pic of what a "normal" deflector positon looks like in the middle position. (the deflector on the right is not in the correct position in my pic.) When this happens on an engine with a good cooling system, you won't get an overheat horn on the head, but internally, that piston can be cooking. That ring may have no spring left in it due to the overheat. Surprised that it did not destroy/throw a ring and do some visible damage.

 

[Brock O]

Hi Fmjnax

Sorry to hear the news, but 100% cracked rings, check out "0" compression on page 2 due to the same heat issue but at cyclinder number 1...there's a good article / thread attached by Bosunsmate as well!.

GUYS....WTF is it with these deflectors and has any one changed other wise, clearly the pick of the new deflector by emdsapmgr is a totally different set up to what we see on this page....and mine, Does rubber swell that much and stay swelled or is it ****!! I've just order 4 new deflectors for my rebuild...but am i potentially going to have the same problem over time...yes its an 84 model here but look at the condition...excellent except for what these deflectors have coursed....or am i way of track here??


Brock

 

[Faztbullet]

OEM deflectors are nothing but 1 side of fuel hose from the old double line hose. Usually they are ok unless engine overheats or fill with deposits and expand,just cause its peeing good doesn't me it cooling on a Johnrude...

 

[daselbee]

Time for some experimentation with some sort of new deflector material.
I have been using this yellow Tygon tubing for fuel primer line, and for recirculation lines.
The stuff is tough!!

I wonder if a piece of Tygon tubing, properly sized, would be a better material.

 

[fmjnax]

Thanks guys. Much worse than I was thinking.

If I overhaul, I should do all 4 pistons and not just the one, correct? I'm not scared of doing the job as I am more than average when it comes to be able to do engine work (I've done just about everything on the automotive side; just not overhauls), so I'm considering it. What would be a conservative cost to do it myself and what would it entail? If it ends up sounding like too much work for what it's worth, I will start shopping for another outboard.

On a side note, I bought the boat from a "friend" for $700 and have another $800 or so in it between electronics and other parts, so I'm not out a whole lot of money. The top right carb was gunked up when I rebuilt it, so I would imagine that was [one of] the cause of the overheat.

 

[Brock O]

Good luck fmjnax which ever way you go.....I'm going all four..cant see how over sizing one can work. I went through marineparts for me piston ring sets and that's just over $400 there .030' O/S...with full power head gasket set and big end bearings as well...just over $900. I spent a little more on the boat and other things due to living in van dieman land so $900 is on the good side. you may need to way it up as there's machining too.

Cheers for the comments on the deF$%ters...must be something better than the black rubber which ill look into from my end and add to my rebuild thread......if not these are something that would be best checked and or replaced at intervals.

 

[racerone]

The first picture clearly shows that there is a broken ring !!!----Damage around the exhaust port.-----This is a failure that is going to happen to all of these crossflow engines.----See this failure all the time.--A metal water diverter will work just as well.

 

[daselbee]

A metal water diverter will work just as well.

Or a properly sized nylon rod. Anything that will fit in the proper location, will stand 250 degrees max (just an arbitrary value), and not deteriorate with time.

 

[motodave]

Sorry to hear it fmjnax. Such hardwork on your boat restore and now this. I feel for you, good luck and let us know what you end up doing, the ppl on here are obviously willing to help should you rebuild!

 

[fmjnax]

Thanks motodave. This is actually on a different project boat; one that may not be worthy of a restore now. The restored Skeeter in my signature link was the perfect boat, ran like brand new. Saddens me that I sold it.

 

[fmjnax]

Ok, so after a little research, it looks like I have to strip down to the bare block (heck, it's halfway there as we speak) and have a machine shop bore/hone/resleeve it, then I can build it back up with new pistons, rings, gaskets, etc. Anything else major I am missing?

 

[Bosunsmate]

Ok, so after a little research, it looks like I have to strip down to the bare block (heck, it's halfway there as we speak) and have a machine shop bore/hone/resleeve it, then I can build it back up with new pistons, rings, gaskets, etc. Anything else major I am missing?

That should do it unless your crank has a ding or corrosion in it, unlikely but worth checking before you order parts.

Definitely read this thread, its the one Brock mentions.
http://forums.iboats.com/forum/engin...ng-a-tell-tale

The rubber deflectors are possibly the original, Since the head should come off every few years to have the water channels cleaned then they should be replaced then, I have thought it is probably much worse an occurrence on a saltie than a fresh used motor but perhaps the heat does it to fresh water hose too just as quick....

 

[fmjnax]

Thanks Bosunsmate. Checking it out now, and doing a lot of reading. I found a place about an hour away from me that will do anything from a short block build up to a full build still on my boat. Waiting to hear back from them on their quote. If the short block quote sounds reasonable, I may just go that route as I'm not very far from having the PH removed as it sits.

 

[Bosunsmate]

I got a quote the other day for $130 for one cylinder rebore and hone of it, Thats NZ$130 so about $100 US.
They could hone up the other cylinders for it if you wanted, otherwise you can buy a honing tool for an electric power drill for around $20 and its a tool thats good to keep.
If you have time to spare id get a move on on removing the powerhead, If thats a salt water motor then on those rebuilds i often spend 85% of my time trying to remove the powerhead as the steel bolts get seized up in the alloy exhaust casing. Heat, banging and sometimes drilling is required then. Also if they start backing out dont think you have won as the corrosion in the threads will slow down and eventually take the head off the bolt so once its moving its a long process of loosening a few turns then tightening again for a couple to makes sure the threads dont get jammed and seized again.

Nothing goes better for me on a rebuild than if those bolts have being done in the last few years. I back mine out and coat them in antiseize every three years, an hour long job thats more than ever a stitch in time saves nine

 

[Bosunsmate]

If you decide to go with them i recommend getting the crank polished too

 

[emdsapmgr]

It is permissible to replace just one piston (and re-ring all 4.) It is also ok to overbore just one cyl hole (up to .030 over) without carb modifications. A marine machine shop can mic you block to see if it's cyls are tapered and actually need reboring according to factory service manual specs. If it's not tapered or egg-shaped too much and the pistons are not egg-shaped you might be able to reuse some holes/pistons with a re-hone of the cyl walls only. If you've got vertical scratch lines in the liner walls that still show after a rehone, you should rebore that hole. Just depends on how much $ you want to put into it and what your expectations are for that block. I would not mix pistons from different manufacturers.

 

[racerone]

Piston grooves will be worn.---No point in putting new rings in worn gooves.----Best to find pistons that do not use wildly bevelled rings.