No compression on cylinders 1 & 2

[geekeasy]

It's been a long and slow struggle with this boat. But I've finally rebuilt the engine bed from scratch, I replaced the head gasket, I've replaced a bunch of studs, and I've reinstalled the engine.

I tried to start her up, but I've got no compression in cylinders 1 & 2.

The valves are definitely moving.

Any advice on what the likely problem is and what the next steps are in trying to get her running?

[geekeasy]

Oh... and I'm pretty sure the engine didn't have this problem when it was pulled out and the head taken off about a year ago.

[edwardc]

Sticky valves could still be the problem. The very top of the valve stem gets the most gunk built up on it, so the valve may move up freely but fail to seat fully closed.

Try an MMO soak in the 2 affected cylinders.

[Dave Neptune]

What Edward said. You can try to start with some "motor crack" (starting fluid) as the A-4 will run on 2 but rough, this roughness will often get the valves shook loose and the additional RPM's will get them moving faster which can shake them loose. You may hear some lifter noise.

Put a bit of MMO or TCW-3 (best) in the fuel at about 100:1 ratio. This oil in the gas will be delivered PAST the valves aiding in lubrication and "cleaning" the stems a bit.

NOTE it does not take much "off the seat" of the valve to kill compression.

Dave Neptune

[geekeasy]

I'm leaning toward the leak being a problem with the head gasket. I had to put it on and take it off a bunch of times while working on replacing studs. It's _possible_ that it was damaged in that process.

Right now, I'm ordering a compression tester.

Am I right in thinking I can simply remove the gauge and blow into it hard to see if air is coming out of the other cylinder?

As for the MMO soak, that's probably not a bad idea no matter what. Can I have some specifics on how to do that? Is there a specific phase the engine should be in when I pour MMO into a cylinder and let it soak? How much to pour in?

[Mo]

Head gasket usage:

I'm leaning toward the leak being a problem with the head gasket. I had to put it on and take it off a bunch of times while working on replacing studs. It's _possible_ that it was damaged in that process.

Right now, I'm ordering a compression tester.

Am I right in thinking I can simply remove the gauge and blow into it hard to see if air is coming out of the other cylinder?

As for the MMO soak, that's probably not a bad idea no matter what. Can I have some specifics on how to do that? Is there a specific phase the engine should be in when I pour MMO into a cylinder and let it soak? How much to pour in?

You should not use the same head gasket twice. Once on and torqued that's it. If the head comes off again for some reason a new head gasket is required. That said, I'd try the oil soak as suggested just in case you got away with it

[geekeasy]

Still a bit confused about how to do that oil soak.

Just pour a bunch of MMO into it? How much?

Or should it be at some particular engine cycle when you do it?

[sastanley]

I use an 'old school' style oil can and squirt a couple squirts in each spark plug hole..then if you have a hand crank, crank her over several revolutions and let it sit..or blip it with the starter for a couple seconds (plug wires off so it won't start) to swirl the stuff around for the soak.

[sdemore]

FWIW, I just went through the 2 stuck intake vales scenario a few months ago. I tried an MMO soak, but the oil just ran through the intake manifold and into the carb. I got a can of Seafoam (the spray version, not the liquid) and shot the offending valves and within seconds, everything was fixed. MMO in the oil and gas as a follow up and haven't had a problem with them since. For me, the valves were moving, but they weren't moving far enough to seat.

[tenders]

As Shawn mentions, the "old style" oil can is the kind with a flexible spout and perhaps with a lever that you actuate with your thumb. I got one at Harbor Freight for a couple of bucks several years ago. The valves are not under the spark plugs, they're off to the port side for your traditional installations (starboard side for my v-drive setup), so to get whatever you're spraying in there to the valves you need to spray sideways.

I think of Seafoam as more of a solvent than a lubricant, at least in the pour bottle - but maybe the stuff in the spray can is slipperier?

[sdemore]

Tenders, I concur with everything you said. Seafoam is a solvent that will clean up the gum in the lifter and valve stem, not a lubricant. Spraying it works best through the side cover, so it can get to the lifter and valve guide.