Results of overheating

[Marty_B]

Hi All,
I suspect that my engine was overheated at some point in its life before I got it. It is not seized and turns over pretty easily. Right now I know that several of the valves are stuck and I plan on pulling the head this weekend. My question is what should I look for when I get the head off and what are the long term ramifications of an engine that has been overheated?

Thanks in advance.

[Dave Neptune]

Marty, there can be many problems arise after an overheating episode. However since your engine has been running I doubt you have any real "problems" due to it. The A-4 block is made of a "hi-Nickle" alloy and is far superior to most automotive cast iron blocks. Usually the first issue is the head gasket distorting and eventually leaking because of the distortion. The rings can also be stuck and even broken but since yours is running it should be just fine.

The stuck valves can and are probably a separate issue. Todays fuel without the lead and traces of alcohol are very "dry" IE they do not lubricate as well while passing through and burning in the combustion chamber so the valve stems get no lubrication from the newer fuels. I always ran a bit of synthetic 2 stroke oil in my fuel as it is both designed to burn with fuel and lubricate very well. MMO is also good but does not lubricate or burn quite as well but still works. I used about 1 oz. per gallon. I even use it in my cars at a lower mix as the synthetic does not clog a catalytic converter. To loosen valves use about 2 ~ 2 1/2 oz per gallon.

Do pressure check the manifold which can be done while still installed to be sure no water is encroaching from a breach in it's water jacket.

Check the head gasket for any bad spots when you pull the head and get the head and block really clean before reinstalling a new one. While apart it is a good idea to check the integrity of the studs too as they are exposed to water in the block.

Be careful getting the valves loose so you don't bend them. Take a good look at the seats on the valves and the block to be sure of a good seal. Any bad spots should be redone by having the valves ground or replacing them with new ones. The seats in the block can be re-cut with a seat cutter and if they are really bad they will need to be bored out and new harder seats installed and this will need to be done at an engine machine shop.

Dave Neptune

[capnward]

I use 2 oz. of MMO per 5 gallons of fuel. In several thousands of hours of use I have never had to look at the valves.

[Al Schober]

If you have a thermostat installed, I'd check it for proper operation. An overheat incident will damage a thermostat.

[Marty_B]

Thanks to everyone for your help. To be clear, this engine does not run, but does turn over. I have removed the manifold and do not think that it is leaking. I did not pressure test it but while cleaning it, I filled the water jacket with vinegar and left it overnight and the next day the intake and exhaust passages were dry. I am in the process of taking off the head. I have 5 studs that are likely to break and am treating them with PBBlaster and will try to get them out tonight. Once I get the head off, I should no more.

The was told by several people that this engine was in running condition when I got it but I now know that it was not, and quite frankly I am taking nothing for granted now. There were so many bad things that found on this engine, it is obvious that someone made feeble attempts at trying to fix it. The carb/manifold bolts were loose, the gasket between the carb and manifold was missing, the mechanical fuel pump was removed and it looks like a used electric fuel pump was installed but the push rod for the old mechanical pump was not removed, and there was no gasket for the fuel pump mounting plate. There are many issues like this that worry me.

Also I am not sure that the engine overheated, there are just some clues such as peeling paint on the block, discoloration on the head and water jacket cover and things like that. It could be that its just a 48 year old engine that to my knowledge has never been out of the boat until now. I have removed the cover and the ports on the water jacket fitting were almost closed off with rust and gunk. I have since cleaned the inside of the water jacket out and will order a new plate and fitting for the water jacket. The thermostat is missing.

How does one tell if the rings are stuck without removing the pistons? Also, since the valves are sticky, are there valve guides or seals that should be replaced?

I am sorry to be so verbose. Thanks for everyone's help.

[Dave Neptune]

Since it turned over did you do a compression check? If the compression is consistent you should be good to go. If you can still do one before the head comes off "DO IT" dry first and wet the second time. First do a check as she sits the manifold and carb do not need to be attached. Be sure all spark plugs are removed and the battery is fully charged. Record the numbers, twice on each cylinder is a good idea.

To determine the ring integrity do a second "set" of tests after spraying oil into the cylinder being checked each check. If the compression goes way up there may be an issue with either a sticky ring or a broken one. If broken you should see a linear scratch in the cylinder once the head is off if no scratch the ring may just be stuck. Soaking the offending cylinder with MMO and running the engine will almost ALWAYS shake the ring loose~~very common to get them freed up.

Dave Neptune

[Marty_B]

I performed a compression test and got no compression on any cylinder as all of them have stuck valves. I can see the stuck valves through the spark plug holes and I have removed cover that covers the valves and springs.
I attempted to remove the head today but my stud extractor broke on the first stud that I tried to remove. I will get another tomorrow and start again.