'77 85hp - Update and confusion

[iwombat]

'77 85hp - Update and confusion

Well, I've got the carbs off and they're ready to get all sklorbed out. In the meantime I'm looking at the block and thinking hey, I'm basically a handfull of bolts away from opening the crank. So, I'm thinking I may just do a ring-job while I'm staring it in the face. Compression is still hovering around 90psi after de-carb.

Is it a simple to tear the rest of it down as it looks? Looks like the intake manifold should come off as a unit, as well as the lower part of the crankcase. I'm hoping the latter comes apart with all the various linkages attached. The parts list I'm looking at is:

1 - manifold to crankcase gasket
1 - seal cylinder to crankcase port
4 - retainer set (aka big-end rod bearings)
4 - std ring sets
2 - head gaskets

That look about right?

 

[ezeke]

Re: The new revised maintenance plan '77 85hp

Re: The new revised maintenance plan '77 85hp

I think everything [seals and gaskets] is in the kit 388602 except the cylinder head gaskets. Sierra # is 18-4301.

Scroll down on this for the list:

http://www.iboats.com/mall/partfind..._row=40&keywords=18-4301&session_id=675237807

 

[iwombat]

Re: The new revised maintenance plan '77 85hp

Re: The new revised maintenance plan '77 85hp

That seems like a lot more gaskets than I'll be needing though. I shouldn't need to touch the exhaust side, or any of the leaf plates, or cylinder covers.

Still, maybe it's cheaper to go with the kit.

 

[iwombat]

Re: The new revised maintenance plan '77 85hp

Re: The new revised maintenance plan '77 85hp

After pricing out the parts for a ring job I decided it was just too much $$ for what would probably amount to a band-aid. Instead, I decided to pop open the side covers and heads and see what I was dealing with.

This is where it gets confusing.

The pistons, bores and rings all look immaculate. I can still see the cross-hatches from the last honing. I'm assuming it was re-ringed since I can see some minor scoring on the pistons, but none on the cylinder walls. So, what in the world could be causing the low compression evenly in all cylinders? The bores all check out within spec.

I'm puzzled.

 

[ezeke]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Can you tell if the rings are free?

 

[F_R]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Are you sure that 90psi is low? I really don't know what would be expected, but since they are even and given the general condition that you describe, I wouldn't be tearing it down unless you verify that there is ring sticking (thru the ports).

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

The rings are nice and free as seen through the side ports. They're brandy-new shiny looking as well. At this point I'm not planning on doing anything besides button it all back up and run it. The bores are right on the edge of being in spec. Next winter will probably see a full rebuild, more for piece of mind than anything else. I'm still scratching my head on this one though.

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

All that being said, it could be my pressure gages (I tried two). They're cheapies, but they both read nearly the same.

 

[jimmbo]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

When you are doing your compression tests, how long are you cranking the engine? 1 or 2 revolutions? or are you cranking it until the gauge stops rising?

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

I cycle it for about 5 or 6. Enough to stabilize the pressure gage for at least two cycles..

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

I think the last one I did like 15. Enough time for me to pick my jaw up off the ground.

 

[F_R]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

By picking your jaw up off the ground, does that mean you are rope cranking it? Maybe that accounts for something.

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Cranking with the electric starter.

My jaw was hanging open in sheer disbelief as I read the still freakishly low psi on what looked like brand-freakin'-new cylinders with a brand new head gasket installed.

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Really guys, this is baffling. I've gone through a lot of motors of various sorts and types and rarely have I seen one so undeserving of a disassembly as this. I mean, even the piston tops are just ever so slightly roasty colored, and could probably be shined up nice and silvery with a minimum of effort. Looking at the sides of the pistons, they're bright and silvery. Finding a even a trace of carbon around the rings would take some very close inspection. The only thing I can think of is I measured the bore wrong and these things are just totally out of spec. But looking at the edge of the rings, they're not riding very far out of the ring grooves, so I have to believe it's all good. I still have gaskets for the port side, so maybe I'll break into it and double check.

Then again, maybe I'll just run it and forget what the gage tells me.

 

[jimmbo]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Position the piston rings so you can see them through the intake ports.Take a blade screwdriver and push on each piston ring. it should push in a bit and rebound with a springy action. If it doesn't the ring is probably broken.
You say the crosshatch pattern is still visible in the cylinder walls. Perhaps the motor wasn't broken in properly, the rings never fully seated, now the cylinder walls have glazed and the rings will never seat properly, at least in our life times

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Rings are springy. Remember ALL cylinders are just about dead even ranging from 88-91psi. So, unless each cylinder has the same kind of damage, I doubt anything is really amiss mechanically.

Cylinder walls _are_ glazed and there's decent cross-hatching visible, but it's not like it's a fresh hone I'm looking at or anything. An improper break-in is about the only theory that makes sense so far.

I wonder if I can break the glaze with solvent or something and maybe get the rings to seat better. Honing with the pistons still in there is something I wouldn't want to even try.

 

[iwombat]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

Are the rings on this motor the same, or is there a top and bottom side? I wonder if they went in upside down or got the bottom and top reversed.

 

[jimmbo]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

The top ring is a wedge shape and so is the top ring groove, It can only be installed one way. The theory being that combustion pressure will push the ring harder up against the cylinder wall. The second ring looks like a regular ring.

A flex hone can be used to break the glaze. However you must remove the pistons and while they are out, you might as well rering it.

 

[Dhadley]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

There must be more to this story, like another thread - no? All 4 are around 90 psi. Why is that bad? Given this is a small bore V4 crossflow (3.375" std bore) with 1977 85 hp port timing, why is 90 bad?

You seem to indicate it's still standard bore. The motor is 30+ years old. Regardless of what it looks like, have you measured the cylinders to see how much out-of-round there is? Ring wear? Skirt collase?

Which head gaskets are on it? Standard or thick?

I'm thinking that 90 psi (static compression) ain't all that bad for a motor with port timing that low.

How does it idle?

 

[F_R]

Re: '77 85hp - Update and confusion

Re: '77 85hp - Update and confusion

DHadley just said what I said way up yonder somewhere in this thread. Why do you think it's bad? I think it's just fine from what you have said so far. The original factory crosshatch should still be there. If it's gone, then it's gone from wear. Since it isn't gone, the cylinders are not worn and are just fine. Now go to bed and stop worrying about it already.