Motor Question

[River Rider]

Ok I am about to undertake some major upgrades on my 14' center console semivee. It currently has a 1978 70 horse on it and it is just not running the way I want. I have shimmed it, sharpened it, new coils, just about all I think I could do to it. I am tired of it so I have got a new/used outboard I am going to use to repower my boat. It is a 1989 70 horse. It is the bigger block which Member lil blue rude told me is the way to go. After pricing everything out I am debating a coupel things. First the compression is a little low for this motor. All the cylinders are right at 105lbs, which the top cylinder is the worse. I have pulled the head once and noticed some light scratches but everything else looked fine. The rebuild of this motor is going to be up near the $600 range, and for the new shaft to match my old pump up to the new motor is $170. This was ok, but outboardjets in California is telling me I should get the new bearing and housing with the new shaft for $400 for the complete assembly. My question now is should I go ahead and get the new assembly and just run the motor and see how that works out. Or should I try to break my budget and overhaul it completely? I would not worry about this but I have a fishing tourney lined up in October and I don't want to be stranded with my fishing buddy looking like a fool. Any advise is appreciated. Also I had a question about once I am shimmed out on my impeller which should I purchase first, the impeller or the liner? Does one wear out before the other, or is that something I should replace both at once? Thanks again. I will get some pictures up of the boat tomorrow so you see what I am starting with.

 

[Ranchero50]

I don't understand your question. Replacing one 70hp with another isn't going to make much difference, especially if the new one is low on power.

If you are out of shim then I would replace the liner, it was only $60 with a new impeller key and sleeve for a 90/65, cheap enough to be a maintenance job. I'd replace the liner, then see where the engine is revving wide open and go from there.

I would not swap one 70 for another, doesn't seem like you'll gain anything (on paper).

Jamie

 

[River Rider]

From what I have been told the early 70 horse has a smaller cubic inch motor then the 1989 and newer models. So I would rather rebuild the newer one rather then the older one. I was just curious if I should just try to run it as is rather then go ahead and drop all of this money at once. Hoenstly I have rather rebuild the newer motor, replace the shaft and bearing, and then get a new liner and stainless impeller. The only thing is I didn't budget this much and I thnk this weekend I will see what I can dig up with financially and then decide. I was just feeling out other jetter's thoughts on the subject. Hope this clears up what I am doing.

 

[Ranchero50]

So, is the old engine sick or just not powerful enough? Is the engine revving correctly?

If the old 70hp engine is running correctly and you are not going correctly you either need the pump overhauled (new liner etc.) or a higher HP powerhead. Adding cubes while keeping the same rating is telling me they are either running the newer motors at less RPM or underrating them but at the end of the day 70hp is 70hp. What's wrong with the boat now that you are unhappy with it?

Jamie

 

[River Rider]

I am thinking there is something sick with the older motor. Sometimes it runs fine, and then sometimes it is a dog. This past weekend was a good example, ran great on the way down river, but on the way back up it wouldn't plane my little boat with just me and a cooler half empty in it. Then after it set for a few minutes so I could back the truck and trailer down it ran fine again. It is just random like that. I first supsected coils and wires. Which i was right on the wires, but replaced the coils as well. It ran fine after that. Then now it is doing something else. I can hear the motor and it doesn't sound like it is running right either so I just figured if I am to over haul an outboard I would do one that is newer. Plus the older one had been used in salt in its lifetime so I don't want to deal with finding corrosion. As for the bigger block deal, I was told this by a couple people that the bigger block was better for the jet, rather then the smaller block.

 

[turne032]

hmmm....

the newer 70hp is more powerful than the older 70hp, but...one wore out 70hp is probably not much better than another wore out 70 hp.

I would only be concerned if the difference in all three compressions were more than 10psi. if the top is 90 psi, and the others are 100+ then it needs a rebuild. If they are within 10 psi, I would run it.

Warning: if you pulled the head off to look at the cylinders, purchase a new head gasket. It will seal better and not blow. You can buy one for $20-$30. Good insurance for little $$$ Keep the old as a spare (for those tournament days that you cant miss)

The best and most bang for your buck is a new liner and impeller. In most cases the liner will wear out before the impeller. if it has been sharpened alot, i would go ahead and buy a all new combo impeller + liner.

If you grease your bearing often, I would check the seals in the pump, but would not spend the extra to put new bearings into it.

 

[Lil' Blue Rude]

1. back in the 80's and before the motors where rated at the powerheads and newer motors are rated at the prop shaft. 2. just because to motors are both 70hp doesn't mean they will run the same especially if they're both 2 strokes. Diffrent port jobs bring on diffrent power bands. no 2 motors are ported the same so they alll come on the power band at diffrent rpms. The key to making a jet run good is finding a motor that makes power at lower rpms and makes power up until about 6000rpms or so. That is why the older 70hp isn't as good as the newer one because the 49.9cube 70hp makes good power at higher rpms but doesn't have good torque. That's why the newer motor is worth up grading too.

 

[River Rider]

Thanks for all of the insight guys. This is what I have planned, now that I have gotten some advise. I will start tearing the 1989 motor apart to rebuild. The other motor should limp me along until I get the other one finished as well as afford all the new parts I will need to swap the jet out. Now that is out of the way I get to start working on the boat itself as well. I am about to tear out the console to rewire everything, run new fuel lines, install a new tank and filter, putin the new floor, and then do some reworking on my center console as well. I need to install some gauges, switch panel, and possibly a new stero. Of course this will be an ongoing project as this is goign to get a little costly. I will get some pictures up before I start as well as along the way. Thanks again for the help.

 

[Ranchero50]

I'm curious, did Outboard Jets recommend the same pump setup between motors? Seems it should use at the least a different impellor to work at the new motors RPM's if they are different.

Jamie

 

[River Rider]

Yes sir my pump fits the newer motor but I have to change the drive shaft because the splines don't match up on the lower unit. Otherwise they are identical.

 

[River Rider]

Well I am still waiting to see if I have the money to do a rebuild or not, but as of now I figured I would do some work on the jet pump. I have dropped the foot and pulled off the impeller. I then tried to remove the liner from the jet shoe. I have taken the two bolts out that holds it but no luck. I have tried tapping it with a rubber mallet aroud the outside edge but still nothing is giving. Any ideas on the easiest way to remove the liner? While I have the time I might as well pull the liner and the grates in the grill and get everything to near new condition. Thanks again.

 

[Ranchero50]

The Merc I did had four bolts and took a couple good whacks with a punch and hammer to get it to move.

 

[River Rider]

Thanks I will try that out after this weekend. Dove season opens today so I will spend some shells this weekend and get back to the motor next week.