1984 Johnson V4 90hp

[Chinewalker]

I recently bought a boat with nothing but a 20-inch mid-section and cowling on the back. The mid-section is from a 1984 Johnson 90hp. I'm not sure if I want to find a complete motor to replace it, or take my chances and find a lower unit and powerhead on eBay over the winter to bolt up to this one..<br /><br />Anyway, if I do take the piecemeal approach, what is the range of years that will work with this tower housing? I know that with the 3-holers they changed crankshafts and driveshafts about 1986. Any similar changes to the V4s? Will a bubbleback powerhead fit on this flat-back tower? I know 1984 was the first year of the VROs, but I don't think that will be a problem one way or the other, as I will probably convert it over to a regular fuel pump when I assemble it so that it'll run mixed gas.<br /><br />Just trying to get some information so I can pick a direction with this thing. Thanks!<br /><br />- Scott

 

[Dhadley]

Re: 1984 Johnson V4 90hp

Any V4 crossflow block/powerhead, including the bubble back, from 1978 on will bolt up. So will a 1977 140 or any block from a 1977 25" 85 or 115. Just not the 1977 20" 85 & 115. Nor anything older.<br /><br />All crossflow V4 blocks 1979 & newer have the large center main and parts like the block and crank are easier to find. When youre looking at blocks, ones with the cast-in front lower pan mounts are 79 & newer. If the front lower pan mounts bolt on, the block has a small center main and is 78 or older.<br /><br />Hows that for confusing???

 

[Marc J.]

Re: 1984 Johnson V4 90hp

If I were you I'd send it to me and look for a complete running motor. My 88spl needs a T&T unit. I'd even pay shipping.

 

[rodbolt]

Re: 1984 Johnson V4 90hp

there is a bit more to it than that<br /> in the early 90's the lower crank bearing housing changed along with the top of the drive shaft. about 93 or so the length from the lower unit mating surface to the crank changed some to. I just had a friend destroy a nice 87 110powerhead mounted it on a 97 frame. the powerhead he said laked about 1/4" of seating so he pulled it down with the bolts. less than an hour later the bottom bearing destroyed itself.<br /> so if ya start mixing and matching it can be done but careful measurements MUST be taken.

 

[Dhadley]

Re: 1984 Johnson V4 90hp

There are ways around the lower unit differences depending on what year crank and driveshaft you use. Sometimes what hits is not the splines bottoming out but rather the area right below the splines themselves. Its ever so slightly larger and can hit the crank. That area can be turned to the same OD as the splines and it will work. <br /><br />Like Rodbolt says, it can be done but you have to be careful. Let us know what year powerhead (crank actually) you use and which driveshaft. I had a V4 gearcase with a V6 propshaft in it that we swapped between a V4 crossflow, a V4 looper and a 60 degree 150. Talk about acceleration! A 60* motor with 2:1 gears!

 

[KilroyJC]

Re: 1984 Johnson V4 90hp

I'm a fan of picking up parts & putting things together...<br /><br />Within the last two weeks, I got on ebay:<br />-A complete lower unit, with shafts & prop - $75<br />-A complete intake-side for my motor: airbox (both halves), carbs on the maifold, complete reed assembly, fuel pump, and all the bolts; starter; choke solenoid; motor hood - $40<br />-complete electronics set (p-pack, coils, and the mounting frame and whatever else is attached to it)- $10<br /><br />I was just looking for a couple spare parts, but at this rate I will probably build a complete motor before long!<br /><br />So my vote would be for the winter project to build a Franken-motor from all the graveyard parts.

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Thanks for the help, gentlemen! I'll beat the bushes locally and see what falls out. If nothing, then I'll keep an eye or two on eBay this winter and see what comes along..<br />- Scott

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

UPDATE TIME... <br /><br />Okay - I picked up a good clean lower unit off eBay and had another parts motor given to me. The parts motor appears to be a 1979 (model # 85995) and it's missing a few items (starter motor, carb airbox, etc.). The guy I got it from has some other bits and pieces to various year V4s and offered to help me out as the project moves along. <br /><br />So, first order of business is to tear into the 85hp powerhead and see what we've got. It came off a buddy's workboat (he's in construction) and I suspect the motor coked up and cooked as the engine was often lugged down.<br /><br />Would I be better off looking for a later set of carbs that use the primer system or leaving it as is with the mechanical choke system? Anything else I should consider updating?<br /><br />Thanks!<br />- Scott

 

[Dhadley]

Re: 1984 Johnson V4 90hp

If you can find later carbs easily and cheap, great. If not, you can always add the primer syatem to your existing carbs. No big deal.

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Well, I got into the '79 85hp powerhead that was given to me. Not real sure where to go with it, though, as it has already been rebuilt once (all .030 oversize pistons) and the one piston that went took a good chunk out of three of the port openings. Best I can describe it is that the top edge is not severely "chamfered" over. I don't think going to the next bore size will take it out. <br /><br />On the upside, I've got a good, clean crankshaft, three good clean .030 oversize OEM pistons, four good rods, good bearings top to bottom, electronics, and fuel system. this motor came off a work boat and I am pretty sure it was lugged quite a bit, as there was coking on all four pistons. I don't think the motor had much time on the rebuild, as the three unmarked bores still had the crosshatching from the last rebuild. <br /><br />So, I guess I'm looking for another block...<br /><br />- Scott

 

[Dhadley]

Re: 1984 Johnson V4 90hp

Or sleeve that one if .044 or .064 wont help...........<br /><br />If you do decide to use that one, you can easily open the ports to the 115/140 size.

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Okay, we made some progress - I think. I found an identical 1984 Johnson 90hp on eBay within a morning's drive, so I grabbed it. This one appears to have low compression in a couple cylinders, but has never been apart before, so I am hoping I can rebuild it with what I have onhand without investing too much into it outside of boring and a gasket kit and carb kits.<br /><br />I hope to dive into the powerhead this weekend and find out what killed it. I have a hunch someone ran it "dry" as the waterpump impeller was absolutely baked! The blades looked like a pencil eraser after running over sandpaper - really worn down with a serious set to them. Lots of rubber transferred to the stainless steel liner, too. The rest of the unit looks good, so I have a spare lower, mid and trim unit, which will hopefully recoup some of the initial investment. <br /><br />Are the two blocks I've got from the previous motors worth anything? The one had been bored once before (.030 in all four) and has a serious gouge in one bore now. I don't think .064 would do it. The rest of the block looks decent - no rods let go, or anything to damage it. The second one has kind of offset bores - the steel sleeve looks thinner on one side than the other. Looks to be standard bore. Are these worth trying to sell or are they scrap? DHadley mentioned sleeving - are they worth the trouble? Hate to scrap them if they're still useful to someone...<br /><br />Thanks!<br />- Scott

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Got the "new" 90 apart last weekend and discovered two banged up pistons. The bores were a little nicked up, so I took the block in for boring to .030 on #2 and #3. #1 and #4 look pretty good and should clean up with a light honing. The tech at the marina said he'd mic them to be sure.<br /><br />Will be ordering the gasket kit, carb kits, and new rings shortly. I'm pretty sure this thing blew because of overheating due to being run dry long enough to melt the impeller housing. I've also got a regular fuel pump off the '79 to make it an easy VRO removal.<br /><br />"I love it when a plan comes together!" - John 'Hannibal' Smith<br /><br />- Scott

 

[rodbolt]

Re: 1984 Johnson V4 90hp

while he is checking the bores have him check the used piston diameters, no sense in putting together worn out motor, if one side got hot due to a bad pump the other side did to. sometimes when the pistons expand and contact the walls it alters their diameter when they shrink. we call it a collapsed piston skirt, its common. that piston is a cam ground(not round) piston in a round bore and with excesive heat it will permanantly disfigure the piston. check them carefully, but if you already have 3 known good pistons its cheap to buy a another and bore 2 more holes. always use new pin bearings and rodbolts. never reuse the pin circlips. carefully clean all mating surfaces with a 3M type pad, do not wire brush aluminium. use the factory gaskets and sealants, be careful using loc-quick primer on the gel seal surfaces, if your not quick when mating the crankcase halves it will start curing and create a shim rather than a seal. I dont use the primer anymore I prefer to allow it to cure 12 hours before placing it in service.<br /> if your using carbs with plastic bowls carefully check the surface flatness of the bowls, especially along the aft edge where the fuel transfer is. if its warped it will leak and create a rich condition at idle. I prefer the metal bowls and most all since the 70's will interchange if you use the correct jets from the plastic bowl. the intermedite jets on some of the older bowls are on the side and the plastic bowls have the intermediate jet inside the bowl. the fuel does not care as long as the jet size is correct.

 

[Dhadley]

Re: 1984 Johnson V4 90hp

Just a thought -- you might think about leaving the VRO (or OMS) pump on. Even if you choose to block off the oil side and pre mix, those pumps have the capacity to flow more fuel than the standard old style pump.

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Thanks guys! Will look into the existing pistons and see what we find there. Any dimensions I should know for standard and .030 oversize pistons so I can mic them myself? .ie, is there a go-no go number I should be looking for? I know the nominal bore is 3.5", so where do I go from there?<br /><br />- Scott

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Now we're moving! Got my block back this morning from the shop with #2 and #3 at 30-thou oversize. The tech said the bores are finished and ready to accept my pistons, so no additional work needed there.<br /><br />NAPA called to say my rings and gasket kit are in, so I'll be picking them up today. My other pistons all check out okay, so all the pieces are now there - just gotta put it all together. I will also be going through the carbs, too. The worst part is that I won't be able to run it for a couple months yet, as I don't have running water at the shop during the winter months, and the boat ramp is frozen in. <br /><br />I've rebuilt hundreds of motors over the years, but mostly 2 and three cylinder stuff. Never had one of these big beasts apart before, so it has been a fun learning experience. Thanks for all the help and advice!<br /><br />- Scott

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

One more question - will the 1979 crankshaft out of the parts motor work in a 1997 90hp crossflow Johnson? The parts lists show a number change along about 1992. Got a guy interested in the '79 crankshaft if it'll fit his '97. By pics it certainly LOOKS the same, but I don't want to send it to him to find that there's some subtle change that will prevent it from working...<br /><br />Thanks!<br />- Scott

 

[Dhadley]

Re: 1984 Johnson V4 90hp

Yes, the 79 crank will work in his 97 crossflow. HOWEVER -- there wont be any O ring in the spline area. Not a problem if he realizes that and greases the drive shaft splines every year. <br /><br />He'll need to use the same style lower seal plate that is in the 79. Not like the one in his 97.<br /><br />Just make darn sure he has a crossflow, not a 60* 90 hp. The good news is that those arent even close to the same so he'll never get the installation started and then find out its wrong.

 

[Chinewalker]

Re: 1984 Johnson V4 90hp

Finally getting to look at what I've got and tried getting the powerhead together. Discovered that all four bores are .030 oversize, not just two. I have three pistons onhand and need one more. Anyone have a good used .030 oversize piston for a 1984 90? The three I have are OEM and I'd rather not mix in an aftermarket piston, so a good OEM .030 ought to do it.... I already have rings, rods and bearings - just need the piston and I can close this thing up....<br />- Scott