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Turning down a crankshaft and bearings

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YngwieL

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If you turn down a crankshaft say .010, is it even possible to get the rod bearings oversized? Tore my 1989 Evinrude 90HP apart finally today, and an pretty sure I can get it bored out .030 and get a rebuild kit for it.. but the rod bearings were trashed on the #3 cylinder piston.. looks like it could be turned down, and .010 would clean it up.. their was some scoring in the lower 2 inches of the #3 piston bore, no lip at the top at all. And am pretty sure .030 will clean it up. Other then that, everything else looked in good shape..
 
Not aware of any practice to turn crankshaft and oversize on these. Try Tim's Outboard in Hackensack MN 218 682 2331 for a used crank/rod.
 
There are no O/S rod bearings with matching cages.-----Good used cranks / rods are readily available if you shop.----Easy to find in my area.
 
racerone said:
There are no O/S rod bearings with matching cages.-----Good used cranks / rods are readily available if you shop.----Easy to find in my area.
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Quick ?, When looking up a crankshaft for my motor E90TLCEM , are their multiple size and year engines that used the same exact crankshaft/part#? ,
 
Sheesh, this is harder then you would think when it comes to checking for bare powerheads / Engine blocks.. seems like everything I have seen, always have issues with the cylinder on the starboard side.. wonder if this was a manufacturing flaw in these motors, or something else is causing it.

not so sure .040 / 2 = .020 will clean up the bottom of the cylinder scoring. if I may ask, is the bottom 2 inches of the bore as important if its at least cleaned from boring and honing? so if the scoring doesn't clean up 100%, do the rings actually become an issue with the bottom 2 inches of the bore? I never really paid much attention.. think the scoring came from the bottom section of the piston that failed for whatever reason. so basically, if the scoring is below the piston rings, is it as important?

here is a picture of the fried piston / rod bearings, for your laughing pleasure-- > https://photos.app.goo.gl/b8qNkJfh1fdPurGH7

Here is a picture of the bore, the scoring is down in the bore, if you look at the right bottom edge of the 3rd port hole down in the picture, you'll kinda see it halfway between the port, and the bottom of the cylinder. --> https://photos.app.goo.gl/JthwsrYm4M8LawaE9
 
I have said it so many times that EVERY one of these engines will end up in the scrap heap / rebuild bench with broken piston rings.-----Just a poor design of the top piston ring !!!-----But they must be pretty tough since I find some that have broken rings on 2 cylinders and not just one.----Obviously they start and run with a damaged piston until the second one lets go.-----There is a line-up of these on the shop floor if I ever get time to work on them !----And the bottom of the bore is important , which has to do with crankcase compression.
 
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racer said what I was thinking. Many/most people don't realize that on a two-stroke engine the piston skirt acts as a valve of sorts, isolating the exhaust ports from the crankcase. The closer the damage is to the ports, the shorter the leak path.

I know I'll catch all kinds of flak for saying this, but depending on how deep the score is, it may be possible to cheat a bit and move the bore off-center a few thous (within reason) to clean up the damage. Done it many times.
 
The whole concept of this 2 stage " air processing machine " and the 2 stroke process at the bottom of the cylinder is not well understood.-----Add to that the confusion that comes along with oil the gas and how that works !
 
good info.. thanks! I found some pistons that are .064 and may see if going that deep helps eliminate the scoring completely. .032 off the wall doesn't appear it would hurt. only actually piston kit sizes i found are .010, .020, .030, .040, .044 and .064 - I Figure Wilkersons NAPA should be able to work their magic since they run Funny Cars, and I only live 1/4 miles away. said it would cost about 300 for all 4 bores.
 
Go for as small an overbore as damage will allow. Might want to rough bore first...look things over.....then order pistons. I managed a machine shop with 7 workers here in Duluth for 1 year. Toughest job I ever had. Good machinists are hard to find....hard to keep. I'm back to spinning wrenches and running a chain saw. If something goes wrong....ITS MY OWN DAMN FAULT.
 
Speaking of something going wrong, if a machinist goofs up, it can get mighty expensive, mighty fast. Some call it a train wreck.
 
Oh yeah.....your "preaching to the choir", brother. Racers.....they expect a warranty on everything too, eh?
 
I worked on diesel motors for yrs. , ran machine shop for about 6 yrs. at International dealer . I decked blocks, rebushed wrist pin bushing on connecting rods, had 2 Tobin-arp boring machines 1 for wrist pin bushing ,1 for crank bore with cap grinder. I could bore wrist pin bushings on Cummings and 3406 cats a&b to bring my piston 1 1/2 to 2 higher if. I cleared my upper on rod for crank bearing. Worked alot on the old 53's, 71's and 92's Detroit's turboed and both superchargered and turbo. I know the 2 stroke outboard is a different animal. I'm just not understanding with the older v4-v6 jonnyrudes. Is there a problem with piston skirts?
 
No---Not at all.-----The shape of the ring is the problem.------Even a new piston is tapered correct ?-----So draw a picture of the bottom ring in a groove.---Draw a picture of the top ring in a groove.-----Now think about what happens when the ring wears.----And the cylinder wears.----And the piston wears.-----And the ring groove wears.----Should be easy when you draw the pictures.
 
timguy said:
Go for as small an overbore as damage will allow. Might want to rough bore first...look things over.....then order pistons. I managed a machine shop with 7 workers here in Duluth for 1 year. Toughest job I ever had. Good machinists are hard to find....hard to keep. I'm back to spinning wrenches and running a chain saw. If something goes wrong....ITS MY OWN DAMN FAULT.
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I agree, I took it to the shop down the street.i gave the the 5 sizes of pistons I can buy and they said they will work the bad bore first, and let me know what it took to clean it up. Like I mentioned, their machine shop is top notch, I actually talked to Tim Wilkerson who is the driver of a NHRA Funny Car.. So I imagine if anybody knows how to work on a motor, it would be his shop. He said he's done about 15 of these motors over the years.
 
In other words , piston are short so stability in short bore moving fast, if talorance of bore , if bored at .010 over know if same piston were used on rebuild and new rings . ??? Can it work
Or do you go to oversized weisco pistons?
 
Mikey is confused.----If you bore out 0.010 ( 3.510" ) you have to fit a 0.010" o/s piston and o/s rings.----Not sure what you mean by a " short " piston and " short " bore.
 
Think ole Mikey is wondering if replacement pistons, like Wiseco are going to correct the problem.with the initial engineering. That would be bore, stroke, vs. length of piston. I believe that modifications have been made that will prolong motor life by implementing improved piston and ring configurations.
 
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Mikey----Draw a picture of the bottom ring in the groove.----Draw a picture of the top ring in it's groove.-----Now look and see what happens to RING SIDE CLEARANCE as the parts wear !!
 
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