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1994 90 hp s/n oeo93538 motor rebuild

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bassmaster59

Regular Contributor
I'm trying to help my brother rebuild his motor. found #1 piston had pre-igniton melting & rings gone with small amount of scoring on cyl. walls. think we can get by with .010 over size kit & rebore. should we rebore all three to balance engine or will it matter if we replace 2 bottom pistons original? I saw where someone said to chamfer the port holes? how much chamfer? Are there any more details we migh be needing to know? I've never rebuilt an outboard but doesn't look much different from other 2 cycle motors. I hope I didn't just stick my foot in my big ol' mouth! I also read a post that someone was able to find complete rebuild kits with piston sets. where could I find those? would the kits include top & bototm crank bearings & seals If any one has any little tricks to make this easier, I would greatly appreciate any & all input. thanks in advance.
 
Re: 94 90 hp s/n oeo93538 motor rebuild

oh, i forgot. would the timing or rich/lean mixture be the most likely culprit for pre-ignition? thanks
 
Re: 94 90 hp s/n oeo93538 motor rebuild

The gasket kits could be found possibly on this site or e-bay.Just do 1 cylinder,champer is not needed.Just clean up the inside.The bearings usually don't come with the kit.But they aren't usually bad.
The reason it went bad could be, bad reeds,the carb not set right.clogged cooling on that cylinder bad head gasket????
Boats.net will have most of what you need if you can't find it here, or on e-bay.Just be careful what you buy on e-bay/J
 
Re: 94 90 hp s/n oeo93538 motor rebuild

thanks for the reply, we didn't unassemble the carbs &intake just pulled pullled block halves apart. inside of reeds ,what we could see looked ok. what is rod bearing, bottom plate, block, & head torque supposed to be? bro don't want to buy man. but I may git him talked into it. thanks
 
Re: 94 90 hp s/n oeo93538 motor rebuild

Head 20# connecting rods 170.in#.Main bearing bolts 270 in# top ring 10-20 thou clearance bottom ring 6-16 thou.
If you have 3 rings then you need to get a manual.Should have one anyway.The library has books.J
 
Re: 94 90 hp s/n oeo93538 motor rebuild

thanks jerrry, it has 2 rings. still can't find pistons for this motor. wiseco, marineengine,iboats,boats.net all are out of stock. mercury says obsolete. so? I'm thinking we are going to have a good parts motor minus pistons, any one interested? if you know of anyone who might have the pistons (834797a5 merc. # ; 3151p1 wiseco # ) .010 over, 3.385 bore I'd greatly appreciate it if I could get them somehow , rather than scrap this & buy a new one. thanks, jeff
 
Re: 94 90 hp s/n oeo93538 motor rebuild

ok, decided to replace motor. We have all good parts or complete motor for sale. except pistons. Rods, mains, and everything else is in perfect working order. hope someone needs this motor for parts. thanks, jeff
 
Re: 94 90 hp s/n oeo93538 motor rebuild

hey jerry, I was wondering if you could tell me. I found the pistons, part # 3151p1 here. but it says you have to use wrist pin bearing part # w5216 with these. I don't have the old pistons handy to measure the wrist pins diam. will these bearings fit? I may have to drive out & put the calipers on the old ones to make sure. but I still won't know what the new bearing diameter is. maybe I can find it on wiseco site if your not sure. thanks, jeff
 
Re: 94 90 hp s/n oeo93538 motor rebuild

took block, crank,& pistons to machine shop today. they said sometimes the manufacturer's bore the cyl. at an angle to the head surface. I've never heard that. does anyone know if this model is like that or if it is exactly bored at a right angle. will help give them a heads up before they start to set it up to bore it. I've known them for a long time, & they do good work on all types of emgines. but specilize in racing motors. they just weren't sure about the merc. force motor bore angle.thought it would be less time consuming if some one here knew for sure.thanks, jef
 
Re: 94 90 hp s/n oeo93538 motor rebuild

got cyl's bored .010 over, looks good, will know more when gasket set arrives to begin putting back togather. any comments on anything I might need to know during this process? can't find fac. manual, so will try to make due with seloc. hope it is informative enough!
 
Re: 94 90 hp s/n oeo93538 motor rebuild

When you assemble it use assembly grease on the bearings.It melts and disolves quicker.Use a good grade oil to assemble.Don't use a magnet on any bearings.
Make sure the bearing and the crank holes line up.If not it will be harder to turn over.It should have little resistance when turning.
There was a reason it took a crap try to figure it out before you start and do it again.
Make sure the ring end gap is correct.I think?? It's top ring 10-20 thou bottom .06-16 thou.
Head bolts 225 in# Connecting rod 170in# Flywheel 90 ft# Main bearing 270 in# The local library should have this info.
Good luck,J
 
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Re: 94 90 hp s/n oeo93538 motor rebuild

thanks, jerry. I went ahead & seperated the head & cover today. wasn't going to but glad I did. found massive buildup of mineral deposits on both surfaces. will take to machine shop to be sandblasted & lightly resurfaced. found exhaust gasket twisted during teardown. can't find any blockage, but I think the buildup under cover & head wasn't allowing the water to contact alum surfaces hence no heat dissipation & incoming water being heated from exhaust tube was causing it to get hot at times. carbs were rebuilt this spring, but will double ck them before running & pouring $$$ down the bottomless pit.What could cause rings to break? old, worn out, or maybe alittle heat over time? pistons were not melted. they looked like the rings broke & got caught between the exhaust ports & pistons on top 2 cyl. only damage was about 1 1/2 inch wide on exhaust side of pistons. shoulder between rings was broken about 1 inch long gap. top edge of top 2 pistons were bent on that side also. cyl's had very minor scratches with small gouges inside exhaust ports edges. Would running a little lean or running right on the edge of overheat for short periods of time cause them to break? Really don't want to experience this again if i can eliminate the source of problems. thanks for your patients? & advice, jeff
 
Re: 94 90 hp s/n oeo93538 motor rebuild

oh yeah, cked reeds today & they all looked fine.look brand new. I was wondering, do they ever stick closed? we didn't try to open them for fear of damaging.all were closed evenly & looked the same from the intake side.
 
Re: 94 90 hp s/n oeo93538 motor rebuild

No they don't usually get stuck.If they are clean then they are probably good.If your worried take a Q-tip and gently push on them.Usually the bend or break.
AS far as the rings, getting hot can do that.Not flushing after using will cause gunk/salt in passages to build up.Not allowing it to cool right.But cooling in spots so the alarm won't go off.
You take pics? Post them.Flushing after each use is very important if you EVER run in salt water.Or think you hit sand/mud.J
 
Re: 94 90 hp s/n oeo93538 motor rebuild

don't think it's ever been near salt water,didn't see any sand or mud during tear down. lake texoma has been it's home for a few years. they usually left it in a slip year round. maybe water not draining out from being raised up & no way to drain like when you put it on a trailer?already got head & cover back from being sand blasted & resurfaced, so no pics. sorry. pistons & gaskets arrived today, machine shop will press new wrist pins & bearings on pistons mon. what is the best sealant to use on block halves, & head cover plate? I thought maybe aviation permatex. don't really care to put silicone inside engine.blue or green thread loc on all bolt threads? manual hasn't arrived yet. is there a torque sequence on block halves? what is torque seq. on head? thanks for all your help, would be stuck or screw something up if I didn't have this site & knowledgable people willing to help.If/ when I get this one going, I may buy a row boat, & charge other people to work on THEIR motors!!
 
Re: 94 90 hp s/n oeo93538 motor rebuild

I used a Black silicone.Black cause I didn't like the other colors.It matches the block better on my motors.
Stagger the sequensce of the bolts.Start in the middle and work out.The manual I have says Locktite#8936-1 Jerry
 
Re: 94 90 hp s/n oeo93538 motor rebuild

motor is back togather!! will finish wiring & retro fit harness in console, & hook up final few things in next few days. thanks for all your help, jeff
 
yahoo!!! motor is running! re-wired entire boat,& trailer. new fuse links,fuel lines,connections,terminal strips,wiring,on/off switches, the works. all electronics are working correctly( I think) except trim gauge. purple wire from ignition to "I" terminal, ground from battery to "GR" terminal, double wires from trim position sending unit,one to ground, one to "SIG" terminal. It works sort of. will register motor completely down but only rises to 2 .5 on the gauge no matter how high I raise the motor. Havn't figured it out yet. any ideas? Ran motor on muffs for about 20 minutes. was really smoking alot I guess from adding double dose of 2-cycle oil to gas. set static timing, idles about 850. haven't reset carbs on the water yet. will get down & dirty with all carb & timing settings in couple of days when schedule allows time to go run it at the lake. I havn't found in my manual what the proper procedure is for break-in. I know I can't just take off & run full throttle.would appreciate input here since I've never broken in a "new" motor before.didn't have any pistons or rods or any other loose parts come flying thru the side of the block, so maybe we got this puppy back togather right. Sounds pretty good on muffs without the carbs adjusted correctly,fairly smooth & all. thanks for all your help, jeff
 
can i double ck the timing at wot ? I set it static, but I wanted to ck it dynamic before I ran it very much. should I wait or would it hurt the motor to verify timing is right? Also found issue with trim gauge. The small arm the motor pushes on to send signal to gauge was stuck down. silicone lube freed it up, works fine now.
 
I learned at the dealer where I worked it was too dangerous to check it at WOT.
So we just set it static.
We never did dynamic.My motors ran great for 22 years.
I just bought another boat,just like my other one and I set it static.J
 
welllll,I have a buddy who has some 'nads. He is really good at fine tuning engines,too. We double cked timing on my rude 200 hp on my 21 ft. nitro between 50 & 60 mph. he said it wasn't so bad as he thought it might be! of course we were in an area that was somewhat calm until we made the 3rd lap. By then he had it cked, & luckily we had it dead on staticly.I just didn't know if it would hurt the cyl's if we ran WOT long enough to ck timing. Also I've been reading where most people use merc. regular 2-stroke to break in instead of synthetic or syn. blend. I already mixed syn. blend in my tank & started it on that in my driveway. I guess I'll have to drain that or use a buddy's portable tank with the reg. oil till it's broke-in?
 
ok, ran motor 3hrs. yesterday & 3 hrs. today, just above idle 10 to 15 min. then 3000 rpm for 10 min.,back to idle etc... I tried to get it up to 3300-3500 but prop cavitates. found cavitation plate on lower unit is 3 " above the bottom of boat. Do I need to put some kind of jackplate on it to get the cav. plate level with the bottom of boat? Other than that this motor runs really smooth except after idling for a bit with the 25:1 oil mix. thanks,jeff
 
Post some pics of the transom and the motor where it's bolted to the transom.Then the cavitation plate.
I don't know what boat you have.So pics will help.J
 
will get pics in a couple of days. 1990 18.5 ft kenner center-console. It's really light in the back, plan on adding some fishing seats in back two corners. that will add some balance to back end. had battery for trolling motor & anchor in bow storage compartment, thought bow was going under for a minute. moved battery to back, which helped some. cked waterline & looks as if stern could stand to go down a couple of inches. That still doesn't lower the anti-cavitation plate to the same level with bottom of boat. Thought about a hydrafoil, but not sure that will do the trick either.will get pics on here soon. thanks,jeff :D
 
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