1996 johnson 70 h.p. Compression ?

[onemotion]

Checked compression on recently purchased motor.<br />#1-135<br />#2-92<br />#3-135<br />I am new to all of this so if someone could please help me out and give me some suggestions on what steps I should take next I would appreciate it. Thanks.

 

[phatmanmike]

Re: 1996 johnson 70 h.p. Compression ?

#2 is a bit low... they should all be within 10 percent of each..<br /><br />try doing a "decarb" and see if it free's up some stuck rings or sumthing.. you can by the product at west marine, boaters world or any marine parts store... just ask for decarb..

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Yep, a decarb is in order. Lets hope that helps. E/J wants them within 15 lbs from high to low. <br /><br />#2 runs the hottest and can stick a piston while cruising in the mid range. There are several upgrades for that series motor. One thing we have found is to richen the mid range on that carb slightly. <br /><br />Make darn sure that motor runs Champion plugs only! And fresh 87 octane.

 

[clanton]

Re: 1996 johnson 70 h.p. Compression ?

After the cylinder is bored, piston is replaced, do what DHadley said and prop to 6000 rpms.<br /><br />DH, doest look like Im ever goimg to have time for a visit.

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Clanton -- I know what you mean. There's never enough time in the day. My son took on a boat project because he was bored after work. Naturally he hasnt touched it yet. I have a feeling hes thinking (mistakenly) that I will do it so he can get paid. Ha!<br /><br />Lets hope Onemotion can get this deal revived with a decarb. I was hoping to hear back from him by now.

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

Thanks for repling and helping out. I de-carbed, but did nothing. I have a friend/mechanic who is going to take a look at it for me this afternoon. My luck is that it needs to be rebuilt, but lets hope the head gasket needs to be re-torqued or something minor I overlooked. Thanks again.

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Thats not what we were hopin for. Lets pull the head and take a peek. <br /><br />Let us know what you find. Good luck!

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

BTW -- what plugs were you running?

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

Well hopefully everything will turn out ok. Took the heads off and there seems to be nothing wrong with the pistons. The previous owner, why he did this boggles my mind, took a steel brush or file, and scraped the inside of the head down. He also had the bolts toghtened way too much. Hopwfully the scratches wont leak any air. Next step is to try and replace old head gasket and re-torque correctly. If not, I do not know what else to do besides take the engine apart? What do you think. Oh yeah and he was running champion plugs which seemed to be new, but who knows he probably just changed them the first time right before i bought the boat.

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Move #2 piston to the bottom and feel the cylinder with your finger.<br /><br />Whats it like?

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

Did this already and noticed that the piston is not as loose as other two, but not extremely tight. There is some play in it, but definately not as much as the other two. What does that mean?

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

The cylinder in #2 has minor scratch to it. When i say minor i mean that you can barely feel it with a finger nail. The other two are as smooth as can be!

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Well, thats good. <br /><br />Lets just clean her up and try a new head gasket. The minor scratch concerns me but lets try the new gasket.<br /><br />Make sure you run a cool plug like a QL77JC4. And richen up that mid range too.

 

[ob]

Re: 1996 johnson 70 h.p. Compression ?

Make doubly sure that your carbs are free from any restrictive fouling deposits and you look into #2 carb before running the engine or your problems will likely worsen.

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

Got a new head gasket today, but before attempting to try it out, we measured the head and in the center of it is warped. I read that it is not supposed to be more than 0.002, unfortunately mine is 0.009 off. Also measured the block and that is also warped. The head is worse than the block though. I think I am going to take it to the machine shop and see if they can flatten it down for me. Then I am going to try and put the new head gasket on and pray that does the trick. Any other suggestions?

 

[ob]

Re: 1996 johnson 70 h.p. Compression ?

Just make sure after machining work is done that you torque the head cover back down to the proper value in the sequence embossed on the head cover.Make sure that the machinist doesn't remove any more material than is necessary to restore a true surface.<br /><br />Then I would determine the cause of the warpage.Lean #2 cylinder,head not torqued properly,head not retorqued at the maintenance interval,etc.

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Ditto. .010 is about all I'd feel good about taking off. And that's if I was sure it hadn't been cut before.<br /><br />Most auto type places will just take a big cut so they only have to do it once.<br /><br />Just be careful.

 

[Dhadley]

Re: 1996 johnson 70 h.p. Compression ?

Did we ever figure out what spark plugs were in it?

 

[ob]

Re: 1996 johnson 70 h.p. Compression ?

Champion QL78YC gapped at .030" is what the manufacturer recommends.

 

[onemotion]

Re: 1996 johnson 70 h.p. Compression ?

Came with new Champion QL78YC's when I got it. Anything before that I have no idea.