1971 Johnson 6hp (6R71G) loss of compression in one cylinder

[jsngendron]

Recently lost power with my 1971 Johnson 6hp. No compression in the second cylinder. Besides the obvious hole in the piston possibility, what else would be a likely cause here? The motor is in superb condition and has run flawlessly for 40 years and I really want to fix this so the family can continue to enjoy it.

 

[jtexas]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

blown head gasket? ...only one way to find out...

 

[Chinewalker]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

I concur - if it came on suddenly, without any obvious mechanical issues (ventilated crankcase, metal parts laying in the belly pan, etc.) then it is likely a blown head gasket.

If it's something worse, you have to pull the head off anyway to check it out, so might as well pull the head and look...

 

[jbjennings]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

Recently lost power with my 1971 Johnson 6hp. No compression in the second cylinder. Besides the obvious hole in the piston possibility, what else would be a likely cause here? The motor is in superb condition and has run flawlessly for 40 years and I really want to fix this so the family can continue to enjoy it.

It only ran good for 40 years????? Geez, you should have bought a better brand of outboard!!!
Just kidding, welcome to the forum. You have already gotten answers from experts--I've nothing to add.....

 

[nwcove]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

i concur with all of the above.....had the same problem with a bit newer 4.5 rude. 15 bucks or so, you get to see if its a another issue.....but most likely all is good and yer back on the water!

 

[jsngendron]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

Great, thanks for the help guys. Head gasket never crossed my mind. Was just assuming it was more serious.

 

[jsngendron]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

Update: Head gasket was blown, new one on the way. Anyone know of a place to find torque sequence/specs?

 

[tx1961whaler]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

60-80 INCH-lbs. Start on an inside bolt and spiral your way around.

 

[cajuncook1]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

60-80 INCH-lbs. Start on an inside bolt and spiral your way around.

What tx1961whaler said!!! Here a general diagram to get the general idea. Make your first pass at 50% torque and then second pass with 100% torque value. After you run the engine for a bit, stop it. Let it cool a bit and then re-torque the heard screws at 100% torque 60-80 INCH-lbs and not foot pounds. Click on thumb image to get a better view!

 

[jsngendron]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

One final thing. I figure at least a couple of these bolts go into a water jacket...which would mean they'll need sealer on them when I re-install. Anyone know for sure if this is the case and maybe which ones?

 

[nwcove]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

hope someone else chimes in, but i have never used sealer on any bolts for a head gasket replacement, it might be a good idea....or a bad one? ( are you sure that any of the bolts actually are into the water jacket?.....push a small piece of wire into the holes and see if it bottoms out.)

 

[jsngendron]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

I am not sure, but a couple of the bolts do appear to have had a sealer on them...Thanks for the reply.

 

[jay_merrill]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

You don't need sealer. None of them "go into" a water jacket.

 

[cajuncook1]

Re: 1971 Johnson 6hp (6R71G) loss of compression in one cylinder

I am not sure, but a couple of the bolts do appear to have had a sealer on them...Thanks for the reply.

In the Johnson service manual, there is a recommendation for applying a thin coat of non cement sealant to the threads called Perfect Seal No.4. This recommendation was specifically was made regarding motors being exposed to salt water. It helped prevent intrusion, corrosion, and striping of bolts and threads.

Perfect seal #4 has given way to BRP "Gasket Sealing Compound" PN 317201 or 508235

Here is a link to order some if you wish.

http://www.go2marine.com/product.do?no=78394F