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79 Evinrude Piston Skirt Clearance

S

stromzilla

Contributing Member
"I'm on a tight budget but

"I'm on a tight budget but I don't want to do anything stupid either. With my engine rebuild I'm hoping to reuse the pistons and install new rings. What are your thoughts regarding max piston skirt clearance for a piston reuse? The book gives a range of .0045" to .0075". My thought is if the clearance comes in at .006" or less, then I might be good to go with the current pistons. What do you guys think?"
 
"My thoughts are that you need

"My thoughts are that you need to get it apart and see what's wrong with it. Outboards seldom wear out. A more common failure is a carboned up piston that is scuffed and scratched once the rings are coked up and stuck. In that case, a piston replacement is warrented regardless of the skirt clearance."
 
"I agree with your comments.

"I agree with your comments. However, in looking at the pistons and crank, I see nothing that says these parts can't be reused. The pistons show normal wear with no scuffing. The compression was also good prior to teardown showing 120 psi or higher on all 4. At this point I'm inclined to believe the gel seal gave out and/or the crank seals crapped out which would not allow the lower end to build pressure thus not getting air/fuel to the topend...but I'm still looking for the culprit."
 
"Burned gel-seal and leaking c

"Burned gel-seal and leaking crank cases are nothing new, it happens from time to time. Most common reason is crank case combustion caused by a lean condition. It might be from fouled carbs, it might be from low temperature (defective thermostats)++++ . It may not have occurred at the time the leakage starts, but at an earlier stage and then developed.
Simply re-seal and assemble, but be sure to really get all old gel-seal removed and surfaces 100% clean!!!
If the pistons are in good shapes, no scores or glazing (shiny spots at pressure areas), reuse them , but install new rings. Rings may look ok, may be within 'specs' but most likely lost tension.
Put it all together with a new impeller/water pump a well as new thermostats. have the carbs properly cleaned out."
 
"GelSeal failure, which is hig

"GelSeal failure, which is highly unlikely, would have the fuel/oil mixture blowing out the sides of the crankcase halves.

A failure of a crankcase upper or lower seal might affect one cylinder slightly but not all as there are crankcase/crankshaft seals between each cylinder.

If you're not getting the fuel/oil mixture to the pistons, the most likely cause is either fouled carburetors, or on that engine, a flawed electric choke."
 
"The Gel Seal definitely faile

"The Gel Seal definitely failed...witnessed the fuel blowing out the crankcase side myself while engine was cranking. Based off various feedback and parts in-hand, I'm betting on Morten Ringvold's assessment...Gel Seal failed over time due to excessive lean condition, probably from dirty jets."
 
It happened in general to cust

It happened in general to customers that kept on running with engines hat should have been taken care of long time ago. The V4 cross engines were the most vulnerable. In general when the by-pass cover gaskets started to leak/blow it would soon be time for splitting the engine and re-seal.
 
"Based on what I'm running

"Based on what I'm running into which includes an unbelievable amount of carbon in the exhaust area, punched out cylinder (1), and the failed Gel Seal, I'm guessing one or more of the previous owners didn't have a clue or didn't care. The carbon buildup is pathetic and very characteristic of running cheap oil...learned the hardway about that, years ago. The punched-out cylinder, probably from a scuffed piston is usually resulting from dirty jets leading to lean-burn because of poor maintenance...failed Gel Seal fits right in."
 
"Have you considered cylinder

"Have you considered cylinder out of round issues?
When I measured my block, I found all six cylinders failing the spec for maximum out of round.
I had to bore all six to .020 over.
It was then that I realized that the motor was definitely "worn out". I don't know how many hours were on it."
 
"David..... The "unbelieva

"David..... The "unbelievable amount of carbon in the exhaust area" you mention.... if that is indeed carbon (regular hard carbon), that's one thing, BUT........

Should that "carbon" be a more soft waxy like build up (a lot of it). That would be the result of a engine condition we refer to as "lugging". This condition presents itself when (usually) a wrong propeller (too much pitch) is installed that prevents the engine from obtaining its full operating rpm range at full throttle.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store"
 
Doug - That's interesting

Doug - That's interesting about your engine being out of round. We measured the cylinders yesterday and there was .001 to .002" wear so I should be good to go for now.

Joe - I never realized that a lugging engine can develop the soft-like carbon. I would classify the carbon in my engine being the harder variety...and it was thick. The prop on this engine which is hanging on the boat at the moment and I've been assuming has always been with this boat (Carlson CVX-16) is actually under-pitched (13"x19") because it over-revs @ wot. I'm fairly convinced that a combinatin of time and low quality oil has contributed to what I believe to be an excessive amount of carbon buildup.
 
Fuel blowing out the side of t

Fuel blowing out the side of the crankcase while cranking? Sounds strange to me. More like a bad fit between crankcase halves. Gel seal will only hold if the surfaces are a very good match. It will not bridge any gap at all.

Leaking piston rings or timing that is advanced too far will make it worse.

It sounds like the pistons are good enough to use.
 
Note you must check the crankc

Note you must check the crankcase now if its warp. Follow the manual very simple to do..
 
We had "force" (th

We had "force" (theres that word again) that would do that. We switched from Gel-seal to grey seal and never had a problem again. The grey would squish out better and keep the main bearing clearances much tighter. Used this stuff after working on Subaru's and Vw air cooled cases. You still had to scurry as it would set up as fast as the gel-seal. But never with as much dimension as the grey seal.
 
I think I'm screwed. When

I think I'm screwed. When I place the crankcase mating halves together (without crank) I can fit a .004" feeler guage in between at the corner. And I don't think that is a good situation. Any suggestions? I'm already looking into resurfacing/boring but I have a feeling that will be cost prohibitive for me. And I was really enjoying this project. Now it's a total bummer.
 
"No you are NOT , have a machi

"No you are NOT , have a machine shop "plane it down" or build it up !"
 
I think you could get away wit

I think you could get away with using a hard sealer instead of gel seal ( I do this all the time on rebuilds ). Hard setting permatex will do the job. Forget about machining.
 
"Tony - Now that's an inte

"Tony - Now that's an interesting thought. I would not have trust in using gel seal with .004" warp but using a hard seal...at least I'd feel better if I were to forego the machining. You also mentioned leaking pistons...1 piston had a stuck ring (bottom ring) and a second piston with a ring starting to get stuck. This engine had been running lean from dirty carbs, creating excess carbon from using cheap oil adding to the sticky ring scenario, and then the blowby adding to the situation. How the heck did this engine survive this long? Why is it people will spend thousands on equipment and turn around to buy cheap-crap oil for their prized toys only to save a couple dollars? Ignorance is bliss."
 
I don't even bother with G

I don't even bother with Gel Seal on a rebuild. Soft permatex works fine. If I feel the clearance is too great I use the hard setting permatex.
 
"Tony - What do you consider t

"Tony - What do you consider to be too great of a clearance? As I stated earlier, my clearance is .004". Would you use soft or hard Permatex with .004"?"
 
"Have to agree with tony. Gel-

"Have to agree with tony. Gel-seal will cause more clearance problems than it cures. The Spaghetti seal round the case should hold just fine, but if your still worried, spray some paint on one side and do a dry run and see where the paint transfers. Then "draw file " The area for a closer fit. Remember .004 is just 1 stroke of the file. Again I recommend grey seal as it stays runnier longer and seals fine. leaving no excess in the parting line. Have used it for 20 years on VW, Subaru's and all makes of Outboards."
 
"I would NOT use anything othe

"I would NOT use anything other than Loctit 515 it will eliminate a gasket up to 15 thou in thickness. It is the "RIGHT" stuff to use.

Loctite® Gasket Maker 515™ Flange Sealant is a flexible, gasketing material for use on rigid machined flanges with less than 0.015" gap. OEM approved ™ use where OEs specify 515 or ™anaerobic™ gasket (cures in absence of air). Eliminates preformed, pre-cut, paper, rubber and cork gaskets."
 
"William - I don't believe

"William - I don't believe my engine case uses the spaghetti seal. Can you fill me in a bit more on "Gray Seal"? What is the brand name, and where can you find it? I was in the auto parts store the other day and could not find it.

Jamie - I didn't even know about the 515. I've been studying the data sheet on the 518. By the way the max gap is .0098"...still well within my .004". In looking at both it appears the only difference is in the flex capability of the 515, which I think I'd prefer. Is that why you'd use it over the 518?"
 
"I think 515 and Gel Seal II i

"I think 515 and Gel Seal II is more or less the same. Loc Tite once used to have a similar product called Master Gasket where the 'base' was the same, but they had added micro-balloons in order to make it able to fill a bigger gap. The problem with all of them is that they deteriorate over time and with exposure to fuel and HEAT! In short, if You have a problem with crank-case combustion, it 'burns' out. The advantage with it, is that it handles better the pulsing over-under pressure that You have in a two-stroke crank case. This might be a problem with the other sealing types mentioned. In Your case I would have glued a piece of wet-sand paper (800 grid)on apiece of glass (bigger than the crank-case, and carefully planned both halves. Then use Gel-Seal or 515."
 
"I've been receiving some

"I've been receiving some interesting and enlightning information from many, and it's well appreciated, so I thought I'd update the thread with what my current plans are. It's obvious there are many who feel machining in my application is not the way to go with having a .004" gap. In light of my situation along with my engineering background regarding materials, I've decided to forego the machining and instead choose the best sealant and draw the cases together during torque-down. I get the feeling (but can't prove it) that there are more warped cases on older engines than some are willing to admit, all due to the constant heating/cooling cycle that all engines go through during the course of their life. In talking with a machine shop he thinks he can do it but it's not his specialty. If my case gets messed up then I am truly screwed and so I'm a bit gun-shy about machining. I know it can be done, but between the risk, cost, knowing I only have a .004" gap (some of which will draw out), and available sealant band-aids, I feel that using it as is for now is the better choice. Now I have to choose the sealant. The concern I have is obviously it's capability along with minimizing the unwanted shimming (from sealant) when the parts get mated and torqued. The products I'm leaning on are the Loctite 518, 515, Permatex soft, Permatex hard, and Gel Seal. The only data sheet I can't seem to get my hands on is for the Gel Seal. Please keep the feedback coming. I have learned a lot from all who've responded to my thread and in private. Thanks again. David."
 
Go to the loc-tite side and do

Go to the loc-tite side and download the data sheet of the 515 and 518.( google loc tite 515) Then You might understand my comment about heat and fuel. The biggest mistake done when applying gel-seal/loc-tite is that people make a 'string' and do not even it out thin enough like a film. At the factory they use a 'screen' to apply with which makes it easier. The most important is a clean surface!
 
"Morten has it right when he s

"Morten has it right when he says "clean surface" and my only trouble with get seal was with the people who would string in a bead and just bolt it together, but it would build up a .010 gap of gel-seal which would break down and have big main clearances.

Found the grey-- it's true name is "ultra-Grey. from permatex. item #82194

It does take a day to cure. It was a warrantee required sealant for Suburu back in the day.

If the spaghetti seal didn't jump right out at you -you probably don't have it. It was expensive to put in a design, and apparently not all that effective. The earlier Johnson Evinrudes used it in the crank case parting line seal and on their early lower unit halfs, Chrysler followed suit."
 
".004" is a wide gap for a

".004" is a wide gap for a crankcase. Of course it will decrease when you torque the fastenings, but this will tend to force whatever sealer you use out of the areas where there is no gap.

So, the best approach is use hard sealer, tighten the fastenings just until you feel contact, let the sealer cure for a day, and then torque down.

This is the point where someone usually comments that this will change the clearances of the crankshaft bearings. Go figure."
 
"Have to disagree with tony on

"Have to disagree with tony on that .004 is a wide gap. If you set that engine case 1/2 in the shade and 1/2 in the sun it would warp way more that .004.

So would compare all the sealers, and choose for your self.

Might move to another forum as we all seem to have a favorite here."
 
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