Calling F_R! Johnson 70hp restoration questions

[jbjennings]

F_R,
I know you can easily answer these if you have time, and anyone else is of course welcome to chime in as well!

I got a 1974 johnson 70hp on Sunday. I'd like to restore it into reliable running condition for use on my crappie boat. It has about 122 psi on all cylinders and appears to idle well (I've not tested it on a boat yet). I've read in the past some of your posts that the exhaust cover baffles are bad about warping. Should I remove the exhaust cover and replace that baffle and gaskets as preventative maintenance, or leave it alone since it appears they're o.k. at this point. ALso, what would you do to get it reliable other than carb cleaning, fuel lines, wiring, water pump impeller? Just curious if there's anything else I need to look at that you would have experience with being bad about failing on this model. I'm going to pull the thermostat cover and replace the thermo, and poppit valve and water pump impeller for sure!
Thanks ahead,
JBJennings

 

[F_R]

Re: Calling F_R! Johnson 70hp restoration questions

Sounds like a plan to me. You might take a looksee at the stator under the flywheel (no need to pull the flywheel). Look for goo dripping out of it. It will be hard starting if leaking, then not starting at all.

I'd replace the entire water pump with the newer version with plastic housing and stainless liner. Unless it has already been done. Look before you order parts.

As for the exhaust cover, it's a crap shoot. I'm sure you have heard my rants on it before. I guess it is up to you. Not real easy to do, since the powerhead has to come off for access.

All in all, they are good motors. Much lighter and better performing and a heck of a lot less gas than the old V4 it replaced.

 

[jbjennings]

Re: Calling F_R! Johnson 70hp restoration questions

F_R,
I only remember that I saw you mention it one time and placed that in the ol' memory banks much like every other piece of outboard info I see in your posts. If you don't mind--- What would YOU do? Is the inner baffle the culprit or the cover itself? Will it foul up without the engine overheating? Is corrosion just as likely as an overheat to be a problem with that baffle plate? I don't mind pulling the powerhead although I've exhausted my rat-hole money lately. I will check on the pump and do whatever you recommend. I want it reliable and I don't want the powerhead ruined because I scimped on effort and money for the pump or exhaust baffle. It apparently doesn't need a lot to be a runner. The lower unit oil was black and needed changing horribly, but had no water in it so I'm at least hopeful it's good.
Anyway, I tried the "search" mode on here for about an hour yesterday and didn't have much luck. I had more luck just typing in stuff on google and looking for hits on iboats forums in the address. ---basically I don't want you to think I'm totally lazy in looking up info you've already given.
Just curious what you'd do to it if you were fixing it for yourself.
Thanks for the quick response, BTW!
Oh, and no goo at all on the stator--looks great!
JBJ

 

[kodibass]

Re: Calling F_R! Johnson 70hp restoration questions

I have also been told that the older 70's in addition to the baffle plate may have problems cooling the top cylinder area (i think) & that there is some kind of drill / tap run a extra hose mod to help this problem, ever herd of anything like this on the 70's ?

 

[jbjennings]

Re: Calling F_R! Johnson 70hp restoration questions

Ah, thanks kodibass! I remember from previous posts what you're talking about. I'll research that. I think it's a change in water tube location just as you described. I think I can see a leak trail coming out of the baffle plate area, so I'm really leaning toward pulling the powerhead.
Thanks again,
JBJ

 

[bonz_d]

Re: Calling F_R! Johnson 70hp restoration questions

I have also been told that the older 70's in addition to the baffle plate may have problems cooling the top cylinder area (i think) & that there is some kind of drill / tap run a extra hose mod to help this problem, ever herd of anything like this on the 70's ?

This is for the telltale. I believe Chinewalker has a reference in one of his posts.

I too have a 1988 70hp I'm contemplating a rebuild on. It has a bad crank where the splines have been stripped out of it.

 

[F_R]

Re: Calling F_R! Johnson 70hp restoration questions

JB, the thing that kills those motors here in Florida is all the weeds in our lakes. The guy goes plowing through them and the motor doesn't really get hot but it is hot enough to warp that plate in the exhaust port area. Then it squirts water into the ports. He doesn't even notice that either till it has ruined the powerhead.

Even without any overheat, the design is poor. The plate is very thin, and poorly supported and with the bolts too far from the problem area and too far apart.

So, the question becomes would I tear down one that shows no sign of leaking? Probably not. But if I had the slightest doubt, I would. I don't know what else to say. If there is no sign of any water ingestion, it probably is ok. For sure, check that compression and peer in at the piston tops, looking for any steam cleaning.

 

[jbjennings]

Re: Calling F_R! Johnson 70hp restoration questions

Thanks F_R,
I am most likely going to tear it down, and for sure will look at the piston tops. I noticed that the plate is NLA, although I've located one NOS for 60$ plus shipping. Would you jump on that? I'm thinking that's a reasonable price and also figure that even if mine is not bad as of now, will likely have a lot of corrosion and be on the brink of leaking even though it's never seen salt water. I also figure removing it will possibly warp it and ruin it--not counting the likely broken bolts!
Arrgh! You've spent enough time on me, don't worry about it. Heck, I need to put it on a boat and see what all it needs to be a runner. The prop is absolute junk!
Thanks again,
JBJ