Engine rebuild input

I have a 1986 J40ELCDE that has been torn down completely due to loss of compression in the top cylinder. I believe old gas was the cause of its demise, otherwise the engine has been a well cared for, low hour, single owner power plant. I have rebuilt of few chevy straight sixes while restoring old pickups but this is my first rebuild on a marine engine. I decided to have the cylinders bored out 20 thousands with new pistons and rings and wrist pin bearings. Before I re-assemble I was wondering if it is normal practice to always replace the connecting rod bearings as well. I am getting ready to place an order for parts and wanted to have everything I needed. I already have a complete gasket set and thermostat on the list.

I have a Seloc manual which has been thouroughly helpful but I also wanted some input from the forum on the re-assembly process that may not be in the manual.

Re: Engine rebuild input

Old gas, by itself won't destroy your motor. Lack of oil will. The old gas may have prompted the use of starting fluid or something like that, which is very bad for any motor. Yes, it is general practice, when you have a motor torn down to that extent, to replace everything including crank bearings. The Seloc manual can be helpful but it will let you down at some point in the re-build. A Service Manual for an '86 40 horse will be the best money you spend on the project. It's totally complete, statrt to finish.

Re: Engine rebuild input

have you sourced the .020 over pistons and rings?...I'd add needle bearing grease and gel seal or loctite 518 to the list to seal the crankcase halves. Definitely new rod cap screws and wrist pin retaining clips. I'd put new needle bearings and cages on the crank end of the rods. If theres no evidence of pitting or overheating on those bearings I don't see a real need to go back with new,it's just something I'd suggest. I'd have the crank polished as well. The crankshaft bearings are another area of choice. If there's any evidence to water intrusion, with pitting and or chatter marks, you'll probably be hunting a new rod along with another crankshaft that can at least be polished. I had to do this with a 18 hp. rebuild recently. Ya know it gets down to how much you want to spend and how many seasons you want out of this motor. If long term I'd replace the upper, center and main bearings as well.

I'd add this ...before you remove the rods from the crank pay attention to the the break seam where the cap and rod connect. Run a pick or pencil point over the chamfered edges of the cap and rod and note there's no mismatch at all. That's what you want to achieve when you reassemble. It's a tedious process, but necessary.

Look on youtube for a vid...small girl rebuilds small outboard...and it will give you an idea of how it goes.

I had my block honed and I think it took 7 or 8 "scrubbings" with a brush and dawn dishwashing liquid to get the bores clean to the point a white paper towel wouldn't be smudged. Coat the bore surfaces with 2 stroke tcw oil immediately after cleaning.

Run into any concerns post back and many members will try to help you out.

Re: Engine rebuild input

Thanks for the input! Exactly what I was looking for to get my parts roundup finished. I just grabbed a service manual from eBay and also ordered the addl parts recommended above. I have always gone with the over and above method while things are apart to avoid problems afterwards! I didn't notice any evidence of water intrusion but I will take a closer look again. The Seloc manual says not to use automotive type gasket sealers...what do you recommend for this?

Re: Engine rebuild input

I use johnson/evinrude gasket sealer < referred to as "peanut butter >...a small can will last a long while

Re: Engine rebuild input

Thanks again for the help.