33HP overheating aftermath

[i386]

I overheated my 33hp today. Engine slowed down while running at WOT. My first reaction was to grab the primer bulb but it was firm. Seconds later she stopped running. The cowl cover felt hot and when I opened the little door, white smoke poured out.

Back home I checked to see if the flywheel would turn freely and it did. Next I did a compression check on both cylinders. 60 psi top, 90 psi bottom. Top is low for sure. Bottom is about right if I recall correctly.

After that I pulled the head. All bolts broke free easily thank goodness. I can't tell by looking at the gasket if it failed. The top piston is clean as a whistle. The bottom one has some carbon on it. I'm thinking the gasket failed on the top cyl. and allowed the water to steam clean the piston. There is some slight scoring in both cyls. I don't know how much scoring, if any, is acceptable in a 44 year old engine.

Am I on the right track to install a new head gasket and re-check compression? I could hear and feel something not right in the water pump while moving the flywheel by hand. I expect at the very least for the impeller to be in peices.

Any tips for getting a wrench solidly on that bottom head bolt? Should I use anti-seize when re-assembling? Which gasket sealer if any goes on the head gasket?

Thanks!

 

[kfa4303]

Re: 33HP overheating aftermath

Hi i. I think you're on the right track with replacing the head gasket and impeller. If the impeller broke into pieces make sure none of them go sucked up into the power head. I just had to do the same job on my '66 20hp and I had to remove the power head to access the lower head bolts. You don't need any gasket sealant except for on/around the head bolts themselves, otherwise the gasket just goes on dry. It has it's own sealant impregnated in it. You then torque the head bolts down to the proper spec and run the motor. Bringing it up to temp will help seal the gasket. You can then re-torque the head bolts after a good run on the water. Be sure that you confirm water circulation in your test tank before heading out on the water again. Here are some handy links.


Reviving a Vintage Big Twin - Part 1

 

[i386]

Re: 33HP overheating aftermath

I pulled the LU at lunch time. Impeller was in pieces. I put it back together like a puzzle. No pieces missing so I know none of it's in the engine. I'm optimistic.

Where in North FL? I was born in Port St. Joe. We moved to Ga when I was 8-9 years old.

 

[F_R]

Re: 33HP overheating aftermath

Since it overheated to the point of seizure, the exhaust cover gaskets will be burned and will leak. That can cause catastrophic damage from water ingestion into the cylinders. You should replace the gaskets. While you have it off, you will be able to see the piston skirts and check for heat damage. Yes, powerhead removal is required. So be it.

 

[kfa4303]

Re: 33HP overheating aftermath

yeah, I'd replace the exhaust gaskets too. I just replaced all of the gasket in my powerhead. I was able to get a whole kit for about $100. It was my first time doing the job, but once I got everything put back together, she's running better than ever. I live in Tallahassee and usually go boating on the Wakulla, St. Marks, St. George, Lake Talquin, etc...

 

[i386]

Re: 33HP overheating aftermath

Thanks for the heads up. I'll replace both of the exhaust cover gaskets.

 

[i386]

Re: 33HP overheating aftermath

yeah, I'd replace the exhaust gaskets too. I just replaced all of the gasket in my powerhead. I was able to get a whole kit for about $100. It was my first time doing the job, but once I got everything put back together, she's running better than ever. I live in Tallahassee and usually go boating on the Wakulla, St. Marks, St. George, Lake Talquin, etc...

Cool. My grandad was a shrimp boat capt. in Apalach. I'm pretty familiar with that area. I still have a cousin living in Panacea. I'll be down for the Seafood Festival in Nov.

 

[kfa4303]

Re: 33HP overheating aftermath

Small world i386. There are actually quite a few N.FL guys hiding here in the forums. Can't go wrong with the seafood festival in Nov either. It will cool off a bit by then too. It's been redorkulously hot and wet this summer. Even the mold has mold on it at this point. It's supposed to stop for Sat and Sun, so I think I might hit St. Marks, or something.

 

[i386]

Re: 33HP overheating aftermath

Installed new head gasket. Compression stayed exactly the same. 60psi top 90psi bottom. Exhaust cover gaskets are on order. Is there any point in installing those?


Edit: Installed new impeller and ran it a bit in the bucket. Rechecked compression. 90psi top and bottom. Maybe ring was stuck or just needed some oil. Who knows.

 

[i386]

Re: 33HP overheating aftermath

Pulled the powerhead today and installed the exhaust cover gaskets. So that's new impeller, head gasket, and exhaust cover gaskets. Took her to the lake this evening. Ran like it never happened.

 

[jimmbo]

Re: 33HP overheating aftermath

When you had the exhaust cover off did you rotate the engine and looking thru the exhaust ports, check the piston skirts for scoring, and the rings to see if they still had tension?

 

[kfa4303]

Re: 33HP overheating aftermath

Are the head bolts torqued down to the proper spec? You may also have a bad compression gauge as well.

 

[i386]

Re: 33HP overheating aftermath

When you had the exhaust cover off did you rotate the engine and looking thru the exhaust ports, check the piston skirts for scoring, and the rings to see if they still had tension?

Yes, there is a little scoring visible through the exhaust ports. I'm not real happy about it, but then again the engine is working as well as before it overheated.

I have a spare powerhead for this one that needs rebuilding. I'm thinking about making it my winter project.

Are the head bolts torqued down to the proper spec? You may also have a bad compression gauge as well.

Bolts are torqued to spec. Compression gauge is fine. Not sure if I was clear eariler. The engine is back in business and performing just as well as it was prior to overheating.