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  #1   IP: 68.238.229.208
Old 08-23-2007, 10:52 AM
rods a4 rods a4 is offline
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Question Lower compression in non-adjacent cylinders

Fuel problems this year had me troubleshooting the engine. Hopefully I have solved the fuel issues (at least for this year). Pulling the spark plug wires at idle and in neutral showed variation between cylinders. The engine becomes very rough when the #2 or #4 wire is pulled but little change in engine sound is noted with the #1 or # 3 wires removed. Pulling the spark plug wires while in-gear and at medium throttle results in a large loss of power (runs very rough and almost stalls) with either the #2 or #4 wire removed, a very slight power loss with #1 wire removed and almost no change with the #3 wire removed.

The results above caused me to run a compression test. I did test compression in earlier years with a borrowed tester. The data are below. The values are an average of at least two readings. The second values are with two teaspoons of 30wt oil added. The 2005 & 2007 testing done with open choke, full throttle, and all plugs removed

2000 #1) 108/- ; #2) 109/- ; #3) 99/-; #4) 107/- (not sure I tested correctly this year)

2005 #1) 90/117; #2) 100/112; #3) 90/120; #4) 107/-

2007 #1) 83/110; #2) 100/-; #3) 67/92; #4) 106/-

I did the one-quart of MMO added to oil supply procedure and ran the engine for about five hours, mostly at fast idle or at low-medium throttle under load. I noted no change when doing the spark wire removal test again. Changed the oil back to all 30wt.

The engine is a 1977 V-drive and has never had the head off or valves adjusted. I installed FCW in 2005 after one year in brackish water (now in Rock Hall, MD) - before that time the boat was kept in fresh water at the head of the Chesapeake Bay. The engine temperature runs at 150-175F. The engine uses some oil, at most, a quart per 30-40 hours, and there is some bypass haze/odor in the cabin after a long motor. I see almost no noticeable smoke coming out the exhaust.

Obviously, the compression in two cylinders as gotten worst. How do I proceed from here?

If a mechanic needs to remove the engine from its cave for the repair, (not a simple job in this boat), should I have the engine overhauled at the same time? Cost: ring and/or valve job vs. complete overhaul? In other words, how do you know _when_ (if) the engine needs a complete overhaul? – What symptoms do I look for?

OR simply - IT’S TIME for an overhaul – my best guesstimate is about 1200 hours on this 30-year-old engine.

Rod
C&C 33-1
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  #2   IP: 71.168.72.224
Old 08-23-2007, 01:22 PM
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David Masury David Masury is offline
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Depending on what you want to do.... a valve job by itself is not a bad job....I did mine with the engine in the boat. If you have room to remove the exhaust manifold, the head, and room to easily play in the valve adjustment area then I would recommend that.
The valves can be touched up at you local auto machine shop and lapped in place on the. New gaskets are inexpensive,and the only tool you may need to buy is the spring compression clamp... you should be able to do the job in a long day, not counting the machine shop time.

Good luck,

DHM
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  #3   IP: 38.118.52.41
Old 08-24-2007, 09:24 AM
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Don Moyer Don Moyer is offline
 
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Rod,

In spite of the strong circumstantial evidence suggesting that compression is causing your power loss in cylinders one and three, I'm bothered by the fact that 83 psi does not usually cause power concerns. We talk to a lot of owners who have compression in the 80's on all four cylinders and claim to have good performance in all respects. This makes me wonder if there might have been some other issue historically (like a weak spark to cylinders one and three or perhaps tight valve clearances) that has led to their poor compression by creating more carbon build-up than normal in those two cylinders.

Before giving up and pursuing major work, I'd check valve clearances to be sure that they are all a "generous" .010" for intake valves and .012" for exhausts. Then check for a strong spark to each of the cylinders, and finally treat cylinders one and three to massive treatments of Marvel Mystery Oil (MMO). Put 6 or 8 squirts of MMO into each of those spark plug holes, trying to aim the MMO away from the manifold side of the engine. Burn the MMO off under load at normal operating temperature and repeat at least 5 times. Then repeat the compression check (without adding additional MMO for the check). If you find that you're gaining compression, repeat the procedure until compression levels off.

If this procedure leaves you with 60 psi on cylinder number three, I'm afraid nothing will improve it short of new rings and probably re-boring.

Don
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  #4   IP: 71.126.120.234
Old 08-24-2007, 11:05 AM
rods a4 rods a4 is offline
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Thanks Don,
I will test for spark strength and do the MMO thing the next time I’m at the boat since I can easily do these things myself. However, the spark plugs, wires, and tune-up kit (all Moyer parts) are all new this year so I doubt that is the issue.

I know this is not in the order you stated above, so would the MMO procedure be a waste of time to do before checking (and maybe adjusting) clearances?

Checking the valve clearances might be beyond my skill level and my sore knees. By the way, does checking the clearances require head removal or can it be done by the just removing the valve inspection side plate (and exhaust manifold)?

Rod
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  #5   IP: 38.118.52.41
Old 08-24-2007, 02:40 PM
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Rod,

I don't think the order of things is that important. It is not necessary to remove the head to check valve clearances, but access to the valve side of the engine is quite problematic on most boats, so checking the valve clearances may well be beyond your reasonable capability.

Don
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