engine valve problems

The backfiring and valve problems at startup were at the dock; inversion could be the problem. The boat ran fine with no problem from 1997 to 2012. Valve adjustment on this engine is done by torquing the rocker arm studs to specifications. 45 lbft, if I remember correctly. It's not set like other engines with either using a feeler gauge or centering the pushrods by tightening down and backing off 1 1/2 turns or so. I was a mechanic years ago and have worked on hundreds of engines, but this has miss stumped. Hy
 
so I am still not clear if you saw a lot of rust on the valves.
 
First, backfiring and detonation are two different things. The most common cause of backfiring out the intake is too lean fuel/air mixture. Backfiring out the exhaust can be valves but valves can also cause backfiring out the intake. Both can cause backfiring as soon as the engine is started.

detonation can be caused by excessive carbon build-up in the cylinder which increase compression and using too low octane gas. Low octane gas wants to 'explode sooner and much more violently than high octane gas. Raising the octane actually slows the burn rate of the fuel so it gives it a better chance of complete burn. Low octane can ignite at multiple points in the combustion chamber. Carbon build-up can also have a red hot point that can also ignite the fuel. Same for the exhaust valves or any sharp point on the piston or head that can get red hot. Soooo, basically, detonation is igniting the fuel when it's not supposed to. Detonation is more likely to occur during high load. This is usually getting on plane or accelerating. Detonation will leave tell-tale evidence like little to large areas of melted aluminum on pistons or exploded spark plugs tips.

Determine which is the root cause of your backfiring (detonation, timing, fuel or valves) and go from the
 
Thanks. There was no melted metal anywhere. Other than being black in color, the spark plugs looked totally normal. Both engines had new sparkplugs with under an hour's use. The plugs on the starboard engine were even replaced a second time. The 'low octane' concept makes sense and could be a result of deteriorated gas. The new gas I added was 87 octane, not the 93 the marina used to carry. They switched gas this season to keep the price under $6 a gallon, at 'only' $5.25 for regular. Mixing that with 3-year-old high test with ethanol may have dropped the octane too low. That would explain the immediate detonation. But again, valves were bent or stuck, pushrods were bent and one broken,soot was on the heads, cylinders, and pistons, but nothing was melted. Nevertheless, Charlie's explanantion makes senses. Thanks again. I think I'll go forward with the recovery plan I put forth a few postings ago. just as soon as I recover from tomorrow's surgery. Hy
 
OK! The black soot is unburned gas. Either tool rich or plugs not firing. Plugs not firing can be anything from timing way off to valves set wrong valve timing off( timing chain set up wrong) or valves set 180* off. Good thing, unburned gas means Too Lean is not the problem.

Now it sounds like valve timing is way off. That can cause valves opening when the piston is at the top of the stroke. Look for a small shiny or depressed crescent on the top of the piston for the valves that got bent.

Cause of valve timing way off is valves set up wrong or timing gear spun/sheared the woodruff key. If nothing was done to the valves since last it ran good, look for sheared woodruff key on timing gear.

Important to give me exact chronology of events of backfiring to the work being done. It's possible the original backfire was just too lean mixture but was compounded by backfire shearing off the woodruff key or maybe valve timing done wrong by mechanic.
 
Wouldn't valves hitting Pistons bend at valve head not top shaft and ding piston tops??
 
..."Look for a small shiny or depressed crescent on the top of the piston for the valves that got bent."
 
I saw that but you didn't comment on how that could bend the top of the stem
 
I can picture the scenario, but we don't know yet if it IS the scenario:

1. Valves rusted to a Stuck-in-Place condition
2. Engine Cranking finds Valves Stuck
2A. Bends Rocker Arm Ends of Stuck Valves
3. Engine Starts
3A. Pistons (possibly) bend Combustion Chamber Ends of Stuck Valves

Scenario with REPAIRED Heads:

1. Forces in 2. and 2A. above damage the Timing Set (sheared Key/Keyway in Camshaft Sprocket)
1a. Valves no longer synchronized with Pistons
2. Valves which are NO Longer Stuck get Bent by Piston Contact
 
FYI, when I had the water reversion issue, multiple exhaust valves rusted at the stem/valve guide and one intake rusted. In fact it had been happening for so long a couple of valves were close to breaking off due to the deteriorated stem just under the valve head. Once the valves rusted enough they stuck in the partially closed or closed position. Fortunately no valve stuck in the full open position. When I started the engine after a long layover of a couple months a few pushrods bent/broke and a couple of valves bent at the rocker end. Because no valve was stuck in the full open position I had no valve to piston contact.

The symptom was poor idle, poor power and lots of backfiring. the piston would pull in a fuel/air charge but with an open valve most of the charge was pushed back into the manifolds. The cylinder with the open intake pushed it all back into the intake manifold. With carbs or TBI the entire manifold has fuel/air in it. Then the spark plug fires in the little bit of fuel left in the cylinder and thru the open intake to the manifold. You get backfire and no fuel available for the next cylinder or two in the firing order since all the manifold has is burned fuel/air mix.

except for a little rust inside the exhaust manifold the only other visible damage was the rust on the valve stems.
 
For some reason I missed where you said the valves were stuck so I went past that scenario to a sheared key in one of the timing gears. Now sounds like Happyhour's problem mirrors yours. Ask for his fix which hopefully is less involved than yours.
 
If this is the actual failure scenario, then it makes a good case for the Merc dry joint system or better yet a one piece stainless steel exhaust system as made by Hy Tek marine in Australia. Very expensive, but eliminates the Achilles heel of inboards (that thin riser gasket). Although if it was because of reverseration, higher riser height is the main part of the solution.
Also brings out the importance of fogging at winter lay up, despite the fact that fuel injected engines need a different technique than carbed engines, it is still very important...
 
Yeah, for about 10 years now, I have been welding up the water passages in my center riser manifolds and risers that are full fresh water cooled. Hundreds of times cheaper than the dry joint system...BUT, That only cured one of the water ingestion problems. The other problem is 'Water Reversion'. Water reversion is the raw water exiting the riser being sucked back into the riser and down the manifold. This happens at low RPM's where the cams are ground so that the intake and exhaust lobes overlap. This overlap creates a scavenging effect in the flow of the incoming F/A and exiting exhaust gasses. There is a little point when the piston going down on the intake stroke will suck a little of the exhaust gasses back into the combustion chamber. This effect is what pulls the exiting raw water back into the risers.

I made SS risers that are water jacketed the full length of the exhaust system so the exiting raw water is some 23 inches 'down river' from the manifolds and not at the high point of the stock systems.

Some of the Hy-Tek exhaust systems have a similar looking feature (extended exhaust pipe), though I don't know for sure from just pictures.
 
The exhaust system has 6" spacers to raise the risers even higher. The system had worked for 17 years. Why the inversion problem all of a sudden? A snapped woodruff key might be a source if it were only one engine giving me problems, but it's both engines. Likelihhood of a broken key, jumped timing chain, etc. in both engines is slim. I won't be able to get to the boat for at least another two weeks. I'm probably going to have o pay the marina's mechanic to put the engine back together because of the limitations of my knee surgery. We'll take it from there. Thanks for all the suggestions. Hy
 
Reversion has been around for decades but was first identified in the 1960's for Flagship engines.

http://www.michel-christen.com/ExhaustElbows.pdf

Though I don't agree with all of their findings or explanations.

I believe it was Merc that made a clear exhaust and made a video of water actually being sucked back up the exhaust. I haven't seen it personally but I first heard about it around 10 years ago.

Some may think I'm being repetitive in my explanations and overly wordy in that replies go beyond the original problem. The fact is, I do try to explain a little more than just the basic problem. If you notice, the number of replies as compared to the number of views to each posting, you'll understand there are many people interested in every subject and depend on this forum for help in identifying and fixing problems.

There are many RO's that recognize this and and are identified by their involved replies. Most notably in the 'Engines...' department, Sandy and Bruce and OHB and don't let me forget Alien and others.
 
I spoke to a senior mechanic whom I know about the valve problems. His recommendations, assuming there is no leakage in the exhaust manifolds, are to put the engine together, leave off the valve covers and sparplugs, and leave the pushrods loose. Then, using a rachet and socket on the crankshaft bolt, run the engine though a few cycles just to make sure there's no mechanical interference caused by a timing chain problem. He doubted that would be a cause because the problem's in both engines. I should then bring #1 to TDC and check that the rotor is pointing to #1 firing position. I should then rotate the engine a little to bring all pistons somewhat down from the top of each cylinder. At that point, I should torque the rockers to set clearance. Then, once again, rotor the engine by hand. If all is clear, which it should be, I can then install the plugs, flush the fuel system, change the fuel separator filter, and connect a 6-gallon can of premiun gas. That's the plan for once I'm cleared to work again. I'm doing really well with recovery and am not using a walker anymore. I can even walk a bit without the cane, though I won't push it. Climbing down into the engine bay and lifting engine parts is still a few weeks away. To be continued. Hy
 
Charlie:
Your posts are thoughtful and supported by information. Diagnosing problems on the web with only a few sentences and incomplete reporting of the symptoms is difficult at best. Theories often exceed the details provided and it can get frustrating trying to solve problems when the root cause is not identified.
 
That reversion issue was an amazing bit of detective work. I certainly would have never considered valve overlap as the cause and would still be searching for low risers.
 
The amazing thing is my 1973 searay with a 302. It has log type manifolds with end 'risers' and is only a coupla' inches above the water level. Never had an ingestion problem ...but a backfire would probably suck a couple of quarts.[:O] Just lucky it never happened while I had it.
 
Risers are about 2 1/2 feet above water level.There are 'can' mufflers between the exhaust hoses and the thru-hull exhausts. When I pulled the hose off one of the input-strainer canisters, no water came into the boat even though the thru-hull feed valve was open. The canister was above the waterline. The canister is about 2 1/2 feet below the riser. I have to agree with Bruce, diagnosing problems over the internet is difficult. I have tried to be as complete and accurate as I can be with my descriptions. When I do get back to the boat, I will check everything that has been suggested both here and via the mechanic I know. Hopefully, I can solve this problem without more money, work, and aggravation. Hy
 
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