McDonnell Miller 61 LWCO leaks with new gaskets

nybigapple

I was doing my basic maintenance of cleaning the LWCO. When I opened the LWCO the previous gasket completely split erraticaly and was fused to both sides. They don't even look like a gasket anymore, just black gunk. This is both on the head gasket, and the main body gasket. Scraping was very difficult. Sometimes a big pieces would come off, but a lot of small bits was leftover and near unscrapeable.

I scraped off as best as I could and replaced with new official gaskets. The main body would leak on cold water. I re-opened, scraped again, another new gasket. It still leaks just on cold water. When I look at the sides, they are fairly clean. I spent a lot of time scraping, and there is little to no obvious bumps.

I tried putting a coating of pipe dope with the gasket. The leaking on cold water finally stopped. Testing the heat however, as soon as the pressure builds up, the LWCO leaks from both the main body and the head gasket.

Is there something else I can use here? The LWCO works find except for the leaking. I fear I must have gouged the cast iron or something with scratches while scraping, but that was the only way to remove the gunk.

I'm tightening as much as I can where I think I would start stripping the bolts if I tried any harder. Ironically, the first two years, I opened the main body, and didn't even bother scraping/replacing the gasket. I just reinstalled and no leaks. Last year I put in a new official gasket which worked instantly. But in a year it fused and turned into this black gunk.

Big Ed_4

You can use a sander and resurface the contact area or replace …

retiredguy

If the gasket surface is clean there will not be a leak when the head is re-installed with a new gasket. IF it leaks, there is still something on the gasket surface or the body has cracked. Here is how I serviced those units. Remove the head, clean and flush both the head and body, clean both surfaces with a 4.5" angle grinder with a "cup brush" on it, , brush on anti-seize compound, add the new gasket and tighten the bolts as per specs. Job done!

nybigapple

Interesting. I understand a sander, but you angle grind the surface every year? Probably a lot to do with experience, but how do you manage not to make any uneven shavings or accidentally gouge the surface?

I had purchased an extra one severtal years ago, which I just used to replace. I was hoping to save this one since it was working fine though.

Jamie Hall

Take it apart. Get the mating surfaces clean — and I do mean clean, not just kinda. Shiny bright metal. No bumps. No scratches (run your fingernail over the entire sealing surface). Using a mechanic's straightedge, make sure that both faces are plane — no warps.

Then try again. A very VERY thin coat of automotive gasket sealer might help. But isn't a band-aid.

retiredguy

@nybigapple , you only need to use the angle grinder with the cup brush when the gasket has attached itself to the cast iron. Usually, after you reinstall the head piece and use antisieze compound you may never again need to use the grinder. The need to use a mechanical wire brush comes with experience.