The Stovebolt Site Forums The Shop Area Engine Shop Rear Core plug on 235

Took the engine off the stand today to replace the rear core plugs. Got the one behind the cam, but the other one didn't move when I was tapping on it. Does that one go up against a ridge or something solid inside? Do I need to drill a hole in that one to get it out, or just beat on it a little harder? It doesn't have a flange, so thinking it runs up against something in there.

Also, is this the one I've read can accumulate a lot of gunk behind it? Every other plug I replaced was clean as a whistle inside.

Yes, that upper core plug on the block has a ridge inside. Drill a hole and use a sheet metal screw in the hole to pry it out. It uses an expandable plug that's dome shaped. Insert the new one in until it hits the ridge, then tap the center dome to expand it so it seals. You may find a considerable amount of gunk behind that. The pics are from my 216, but a 235 is similar.

That big upper plug is the back of the cooling system- - - -the lower one seals the camshaft bore. A little bit of brush-on gasket sealer like Permatex Super 300 is a good idea when installing the new plugs.
Jerry

Thanks Kevin and Jerry.

Pulled the plug today, and at first I didn't think it was all that bad. Then I started cleaning it out and realized how deep that gunk went down and how much there was. Spent two hours digging it out with a screwdriver, a large allen wrench, and anything I could use to get in there. The drain hole on the back of the block was clogged up too. I used a screwdriver and a piece of TIG welding rod to open that up again. I got a LOT out but there's still some in there. Now that I've broken it all loose I'm concerned about it getting into the radiator.

Is there anything I can pour in there that will sort of dissolve that stuff? I'm thinking maybe I can do it in a few stages. Let it sit for a few days, drain it, and do it again. Thought I saw that discussed here one time.

Are you dealing mostly with rust, or grease-based sludge? Trisodium Phosphate (concrete cleaner) with HOT water dissolves greasy deposits. Phosphoric Acid is the classic rust dissolver, but it can be hard to find. Muriatic acid (used for cleanup of masonry jobs, bricks, etc. is very aggressive, but it works quicker than phosphoric. Most anything that we used to use back in the dark ages to clean up engines before rebuilding has been outlawed by the tree huggers- - - - -like an Oakite solution in a boiling tank, for instance. They claim if you use that stuff, all your kids will be born naked! I've built a wood fire around a 55 gallon drum of water, with a heavy dose of laundry detergent and sodium hydroxide (lye) in it, followed by a boiling water rinse and/or a pressure washer.
Jerry

It's a greasy sludge. Some of it toward the bottom was semi-hard, kind of gritty. Could get that out in big chunks. The stuff on top as a little softer, slimey kind of stuff.

Phosphoric acid is actually readily available. The big box hardware stores carry it in the paint department, It's called Ospho. LINK

I had basically the same greasy sludge you had. After mechanically scraping it out, I used a pressure washer, then after installing the core plugs, filled the block with commercially available coolant system cleaner, which I believe contains Trisodium Phosphate. Let that set in there for a couple days and rinse it out again. Heat helps, but I didn't have a way to do that, and it seemed to do pretty well.

Kevin, do you remember what cleaner you used, and how much it took to fill the block?

Here's a one pound box of the pure stuff- - - -with free shipping. It's the same degreaser I use, mixed about half a pound to 3 gallons of water, to hot clean firearms prior to bluing. Dissolve it in 180-200 degree water, and pour the block full of the solution. You can drain and reheat it if necessary.

www.ebay.com/itm/205303005338?

Jerry

I don't recall. I just went to the local parts store and got something off the shelf. Jerry's TSP would work nicely as well, also available from your local hardware store.

OK, gonna try Jerry's TSP first, then probably also use a coolant system cleaner. Going to try to clean just the rear area of the block first with the plug still removed so I can still see in there to determine how well it's working. Then install the plug and fill the whole block.

My biggest concern with the TSP is a cold engine block in the winter sucking the heat right out of the water fast. Especially a small quantity in just the back, but I'm gonna give it a try. I'll replace the water often.

One of those kerosene-burning tornado heaters aimed at the engine would warm it up sufficiently for the cleaner to do a better job, if you happen to have access to one. Mine keeps my drafty shop at least tolerable, if not comfortable to work in, and it's 24 X 40 feet with a roof over 12 feet tall.
Jerry

You could try a magnetic block heater it will warm the area .i have one were I am just in case in the winter extra heat or if the block heater kicks the bucket but maybe not feasible if you only need it once.

Warning: OTS (old timer story) alert.

I had a 235 engine that was as you described. I bought the engine ($25) for parts. Many decades of rust in the coolant system seems to settle around the rear cylinder. Even worse, radiator stop leak additives can migrate there as well (like digging in a coal mine). I ended up removing the head to gain access to the other coolant passages being careful not to punch a hole in the cylinder jackets with a cleaning tool. Then I tried different cleaning acids (respirator required) which helped. Once I had clear flowing water out the rear drain plug, I put it all back together and flushed the engine on the stand. More rust comes out. I put the engine on my engine test stand with an adapter to a garden hose and let the water exit onto the ground. I got the engine running at idle. More rust comes out as the engine heated up. Eventually the water started running clear. After all that work, the engine overheated after about 30 minutes. I finally figured out (brain spasm) that this is why the old engine was removed in the first place. The head warped from an overheating block because of the rust buildup restricting coolant flow. I installed a head from another parts engine, and this fixed my overheating problem. It took a month of my labor to get the engine in running condition. What did I get in return? A worn running engine but...it's running now cause, I fixed it. At the time I was young(er), eager to learn by doing it myself and had a limited budget. It was absolutely fun. Today, time is precious. I would strip it all down and have my local engine shop to boil the block/head and check the if the block/head need resurfacing. Go on to the next problem.

I'm going back to my easy chair now. My apologies to the forum.

After 65+ years of tinkering with worn out engines of all sorts, I've come to the conclusion that there's only one surefire way to clean up a water jacket- - - -strip the thing down to the bare block and use a rotary table hot water jet washer with a strong cleaning solution to flush all the crud out of the cooling system passages, the crankcase, the oil galleries, etc. I just bought one of those jet washers- - - -which will arrive sometime later today or tomorrow. A good condition used one can be purchased for $6,000.00 or so, which is why most hobbyists, and very few commercial shops don't have one. A new one will cost about $8K-12K or so.

www.ebay.com/itm/336264730196?

Jerry