Low Compression - Next Step Confirmation

[Ujin]

Hello,

I've a late model engine in a 1970 Cal.

I noticed low compression and valves ticking ( but not sticking) in cylinder #2.

There is smoke in exhaust (oil is clean) and oil in the intake section of the manifold.

I figure I'll need to pull the head and replace the head gasket, studs, valve springs.

What I'm trying to figure out is if I should replace the piston rings.
I don't want to do the head gasket then still have issues.

Read through the forum quite a bit, so just looking for feedback on the best next step.

What do you think? Replace the rings?

From the engine's maintenance history, I do believe that everything interal is original.

I've cleaned the cooling passageways out as much as possible via barnacle buster and replace the electrical components (except fuel pump and starter), gaskets (except head gasket), and exhaust.

Looking forward to hear your feedback.

Thanks

[Al Schober]

For starters, replacing the piston rings is a major job and requires that the bottom end be opened up so the connecting rods can be disconnected from the crankshaft. This is a job to be done with engine out of the boat and during the off season. Can you get through the season with the engine as is?

[Ujin]

Thanks for the response.

Yes, the engine runs and moves the boat.
I can get through the season.

I figured the engine would need to be pulled for piston ring work.
Just wanted to make sure that was the most logical next step.
Didn't want to pull the head then redo that work later to address a piston ring issue.

[Al Schober]

OK, make it through the season then rebuild.
Couple of preliminary step to take now. First is to buy a copy of the Moyer Manual if you don't have one. Read it twice. It's the Bible. Second is to start to shop for a machine shop that will do the work beyond your capability. If you have a local auto shop that you trust, ask them where they send their cylinder heads for work. Go talk to the shop, tell them what you'll be doing, and see how they respond. You want to be comfortable with them.
My last overhaul, I had the shop do the valves, valve seats, and the Kaminsky mod in the transmission cover. As to the valve seats, my inlets cleaned up but the exhaust seats needed carbide inserts - no extra charge! Goodson is a good source for tools that you may need.
Shop can hot tank the head and block for you. Good time to go to glycol cooling if you haven't - make her last.

[Surcouf]

Before going extreme, spraying your favorite lubricant in the cylinders, on top of the valves as much as you can between 2 days of sailing, and a few high rev operation with hot engine may break loose gunk / corrosion and improve your engine compression / operation. As you can go through teh season like this, I would recommend doing that and checking compression in a couple months, may have improved...

[Ujin]

No problem with sourcing a shop to do the machining work. I'll look into the Kaminsky mod. and cooling.

For lubricant, currently running MMO in the fuel and Seafoam into the top of the cylinder after running engine.
Definitely a fair amount of build-up on the intake valve for cylinder #2. Hopefully, the lubricant will help break that up.

[Al Schober]

Be stingy on the MMO in the fuel. IMHO, the hot intake valves are the first thing the fuel hit, and the heavy fraction of the MMO deposits on the stem of the inlet valves, causing buildup and choking off inlet flow.
Valve and their seats do deteriorate with time, particularly with the lack of leaded fuels. The valves can usually be restored with a shop grinding, but the seats are vulnerable (being in the iron block). My experience is that intake seats may clean up, but exhaust seats may require carbide inserts.

[Dave Neptune]

Curious

How did you determine low compression on #2? If it was from a compression test what are the numbers? And was the compression done first dry and then a second time wet?
How did you determine the buildup on the valve?
You also stated that you found oil in the intake manifold, was it puddling?
Did you notice this all of a sudden as a power loss or did it slowly get worse over time?

A good way to help oil consumption is to back the timing off a little bit. This takes a great deal of "shock" off of the rings and will alleviate some of the oil getting by. May be worth a try.

Worn rings can still operate for a long time albeit not well. However a broken ring can jam, bind and score the cylinder or just go along for the ride.

When adding MMO to the fuel do not exceed a 100:1 ratio.

Dave Neptune

[capnward]

100:1 ratio?

That makes me do the math. Usually, I put 2 oz. MMO per 5 gallons of gas. So, 20 gallons gas would need 8 oz. MMO. 5 gallons is 640 oz. 1% of 640 is 6.4 oz.
So, I am using around 30% of the maximum recommendation for MMO in the fuel. Seems to be working.

[Dave Neptune]

Any amount of "top oil" with todays "dryer" and less "lubricative" fuels is a plus. When the 100:1 is exceeded plug fouling can occur in poor running engines.

I used a "top oil" in my A-4 for 34 years at about the same ratio you described didn't hurt. I do prefer using a synthetic two stroke oil with a TCW-3 rating as it is a modern design that stays in suspension better, burns with the fuel cleaner and lubricates better. I run it in every engine I own and have for over 30 years except my Dura Max diesel. The TCW-3 also will not clog or affect a catalytic converter either.

Dave Neptune

[Ujin]

Hi Dave, to answer your questions.
Yes, it was a compression test. First dry test (cylinders 1,2,3 4, respectively) 90, 50, 90, 90. Second dry test 110, 110, 110, 115 Wet test 140, 130, 150, 160.
Build up on the valve can be visually seen when manifold is removed.
Pudding, no. A heavy coating on the surface and discoloration around ports between block and manifold
Been slowly getting worse.

Great advice about the top oil.

[Dave Neptune]

The numbers don't look bad at all! The first test on #2 could easily of been an anomaly as the second dry and the wet test look excellent.

How do the plugs look? And are you really using/burning a lot of engine oil?

I would check for a good spark on each individual "plug wire" especially #2 as a weak spark can easily cause a poor burn and gum things up. See if you get a nice blue snappy sounding spark not a pale yellow with about a 1/4" gap.

Timing can easily be a factor but will show up on all cylinders not just one which is the reason for how does each of the plugs look? To much advance timing can add to oil burning and to retarded can give a poor burn.
Did you check the centrifugal timing by twisting the rotor to see that it moves freely with no binding, very important to your issue possibilities.

Try opening the idle air screw a 1/4 turn which will lean it down a bit once warm too.

Dave Neptune

[sastanley]

I will 2nd the 'don't rush to rebuild if you don't have to, but do it when you have the time & energy.'
When I got my boat, my PO said, "engine is in pretty rough shape, but will get you in and out of the harbor", when I bought the boat in 2009.

I was seeing like 95-95-90-45 on my compression tests...So the valve was sticky but not zero movement.

About 2011, I got the stuck #4 valve to clear with lots of spraying of MMO oil in the cylinder as Surcouf mentioned and top end oil in the gas (2-stroke/MMO as Dave mentioned)..We were having a fairly joyous evening motoring home in light winds around sunset, and suddenly when the #4 valve started working it was like, "WHOA! Did you hear that..it finally happened"..
The point is I expected an engine replacement in my near future when I got my boat in 2009, and in 2022 the same engine is now spinning 2200 RPM without ever having to remove the head. YMMV, but a lot of that is just learning the motor and listening to the folks here...they've taught me everything I know about this motor.