Question for (Old) Gearheads....

[Rick D]

The Engine thread got me to thinking about a problem on one of my boats. This is a 92-year old launch with a 22 hp Grey Marine four cylinder gas side-valve engine. The engine is a rebuilt with maybe 200 hours on it. (We own it in a partnership.)Early this year, we diagnosed a problem as broken valve springs on #'s 3 and 4. Three springs were broken and another replaced because it looked bad. All were corroded to some degree. After that the engine ran well for about another 20 hours and then went bad again. We found two broken springs. The intake on #4 was broken in four places. The top of the exhaust on #3 was broken. That may have been broken by the missing keeper pin from the #4 exhaust, but we don't know for sure.There was not enough time for there to have been corrosion. One of the valve gaps is a bit loose, but not the one that failed. I found an Atomic Four site in which it is said that the aft (#3 and 4) valve springs tend to fail because the engine does not get hot enough to burn off condensation. I believe this is relevant because I think they are both marinized versions of the same Continental block. They did say to use Marvel Mystery Oil as a gas additive as well as adding a half-pint to the oil, which we did despite being a skeptic on additives. Another problem is that this generation and model of Grey has no thermostat. Having said all that, it is still a mystery why the damn springs broke again after only 20 hours. The engine is rarely run hard. The hull will go to hull speed at a few hundred RPM over idle.So... any thoughts? We will look into adding a thermostat, but can't figure the lack of one has anything to do with the last failure.Rick D.

 

[JoeD]

I am an old gear head

Really need more information to help you. Mystery Oil will help lube the valve stems. Not sure why they broke, were the valves tight in the valve stems? Where did you get replacement springs, were they to spec?The old side valve engines were designed to run on leaded fuel. That being said the lead was also a lube for the valves. I would be glad to help if you want contact me.email cycleshopinc at aol.comJoe

 

[KennyH]

I would think two possiblites

I would think either the valve springs are the wrong size for the motor or the cam profile has been modified at some point for special springs. I guess the third possiblity would be spring manufacturing defects. My first guess would be springs that don't meet the spec for this engine even if they where sold for this engine. Take off the springs from valves not breaking and compare carefully to broken springs.

 

[JerryA]

Interesting

I don't think I'm old yet, but I've rebuilt many of my own engines. Valve springs usually fail from coilbind or excessive heat buildup. I would doubt you are experiencing coilbind unless you have the wrong springs or retainers. Valvesprings use the engine oil flowing over the coils to remove heat buildup from the spring. Springs will get really hot fast without oil acting as a heatsink. They can also fail due to destructive harmonics at certain RPM's. The inner spring wound the opposite direction, usually smaller and sometimes flat, will greatly reduce the harmonics. It could be a problem at constant RPM's, but I doubt it in an engine like this.I wouldn't be surprised if you were given the wrong springs for the application. Also I didn't see where you replaced the same spring twice, just that you had a problem with valvesprings twice. As a general rule, if you find one bad spring - the others should be replaced as well.Good luck and nice boat,JerryA

 

[Pete]

thoughts on thermostat

not sure about the thermostat either but just a thought. I seam to remember some of the older foreign cars used to have a thermostat built into the radiator hose ,maybe this type of set up might work for you. No experience with this but just a thought. NICE launch by the way !

 

[Benny]

You do not mention how old is the rebuild.

This could corroborate or not the diagnostic of corrosion for the original failure. 200 hours of use is not a whole lot if the launch is used frequently but it could span a number of years if used infrequently. I would think for it to be a corrosion failure it would need a number of years. I would look into the thought that the original failure may not have been due to corrosion but to another problem and that the same problem persists and likely may have caused the failure of the replacement springs after just 20 hours. This problem would need to be found in the valve train; I would inspect the valve stems, the valve guides, the camshaft lobes. There may be an underlaying reason for that problem and it will also need for it to be looked at, was there a lubrication failure? Was there a cooling passage obstruction? The usual cause for broken springs is excessive heat either self generated or transferred from another componenet. Friction in the valve stem or the cylinder head overheating could just be two possibilities. I would discard corrosion as a likely cause and I would not install a thermostat if the original design did not ask for one. By all means verify that the replacement springs were up to speck and that they were properly installed but if it all checks out you may be left having to do an engine teardown. Beautiful launch, whatever work is needed will be well worth it. Good luck. I'm not a proffesional mechanic, just a problem solver.

 

[Dan Johnson]

Rick...

I think Jerry A hit it on the head. In the older engines, oil played a major cooling role. There might be an oil gallery or passageway that's blocked and preventing cooling oil from being squirted on the spring assembly. I've broken a lot of things in racing but they were due to over-revvings or lacking oil, not lazy chugging about in a nice picnic boat...

 

[Fred Ficarra]

Drat!

I just hate it when these guys cover all of the possibilities!