Re-ringing 1968 40 hp

[Redwing4900]

Hello everyone I found a broken ring on my motor and am getting ready to put on new gaskets and rings. Luckily the cylinder walls weren't damaged from the failed ring and my local mechanic will be honing them for me. I don't want to screw this up, so any advice you can pass on from your rebuild or a "don't forget to do this step" I would appreciate. I am currently cleaning the carbon from the pistons and cleaning up the block to get ready for the new gaskets. Am I going to put any of that silicon from the tube on these gaskets to help seal it when I get to that step? I can't help but look ahead to that. I see when I took it apart that some gaskets had it while some did not. Any help would be appreciated.

 

[1946Zephyr]

Re: Re-ringing 1968 40 hp

There is a special sealer for the block halves. I would get that. The head gasket goes on dry. You can use a very thin coat of sealer on the other gasket surfaces. I usually use Permatex, but some will recemend the 3M 847. That is usually used on the lower unit though. Someone else will chime in and give you some ideas too.

 

[HighTrim]

Re: Re-ringing 1968 40 hp

I personally always use 3M 847 on the crank halves, along with the spaghetti seal.

Tips? Keep everything clean. Dont rush. Ensure proper torque, especially on critical items like the rod caps. Ensure the pistons are in the right way. (Obvious I know, but has been done!).

As stated, the new head gaskets dont need sealer, they go on dry. I would dress the head though before re installing to ensure it is true.

For items like exhaust gasket, bypass covers and such, a thin coat of OMC gasket sealing compound is needed. I like to use a magazine with the shiny pages, apply the compound, put the gasket in the magazine, close it, then open. Applies a perfect even coat everytime. Next gasket use a new page

 

[Redwing4900]

Re: Re-ringing 1968 40 hp

Just completed the work of the rings, very proud of myself for putting everything back together without any extra parts(!). Sealed everything as prescribed new gaskets, installed. I finished the initial ten hour "break-in" for the new rings as suggested by my mechanic with double the oil in the fuel mixture. I was disappointed today though when I checked the compression and found it to be 110 in each cylinder...it was 90 psi with the broken piston ring. Am I wrong to think that I should be up around 120 or 130 psi? Also I think the shop manual says to re-torque the head, does that sound right? Would that re-torque give me more compression anyway? I know that the shop manual says that as long as the cylinders are within 10 psi they're acceptable, which I have, maybe I was shooting too High?

 

[HighTrim]

Re: Re-ringing 1968 40 hp

Yes, I would re torque now.

Nothing wrong with 110 per hole. All meters read differently as well.

 

[jbjennings]

Re: Re-ringing 1968 40 hp

What was the compression in the good cylinder before you re-ringed? It should have been at least that good. Maybe your rings haven't finished seating yet, or you had a cylinder a little worn in the middle.
Either way, if it runs like you want, why worry about the compression.
SOunds like a successful fix to me.

 

[Faztbullet]

Re: Re-ringing 1968 40 hp

What was the ring end gap in cylinder???

 

[Redwing4900]

Re: Re-ringing 1968 40 hp

The good cylinder had 90 psi as well which was puzzling to me...I had equal pressure in both but one of the rings was broken. She ran good even with the broke ring on a different boat,much less weight. Now i have that motor on a much heavier boat so I was considering selling this motor and upgrading to a 60 hp as I believe this 40 hp is maxed out on my 16' slick craft. You are correct though she runs perfectly since the fix which I am quite happy about.

 

[Redwing4900]

Re: Re-ringing 1968 40 hp

What was the ring end gap in cylinder???

I didn't check this dimension...I did put the ring in the cylinder without the piston to check this, but didn't actually measure it. The ring ends were so close I was satisfied with it.