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quantico

broken connecting rod questions...

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quantico
I finally had a couple days to pull a non running magnum engine out of one of my tractors. The connecting rod broke and chipped the jug. I am cleaning some of the icky metal off of the crank carefully. A bit of metal polish seems to clean it up pretty well. The clean side and icky side measure the exact same, so I guess I will be ok once I get the crank re-polished. Do you ever reuse a jug with a couple chips out of it ??? it should still seal up ok , but will the chip be a weak spot or cause uneven heat issues ??? What seals the jug to the engine block ??? it seems to have no gasket... just an RTV like product arount the sealing edges... thanks Scott




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olcowhand
Muriatic acid (brick layers clean mortar off bricks with it) will, dissolve (eat) the aluminum off that journal. Get it at any building supply store. Use full strength with brush. You'd hafta be very careful to just brush a tiny bit on with the crank still in cases, as it loves eating ALL aluminum. You could wipe off after a few minutes with a wet rag, then do again if needed. Makes noxious harmful fumes, so use very carefully so as not to breathe the vapor. Final polishing with very fine emery cloth. I like to at least use a good dial caliper to check journal for any out-of-round when polished. The only Magnum I had, a MV20 had a thin gasket, but many engine makers use just silicone gasket goop. I wouldn't worry about the chips in cylinder bottom, just be sure there are no hairline cracks leading from chips.. But use a round file or the like to chamfer the edges of the chipped spots. By the way, be SURE to check the oil pump screen. The one given to me had a tossed rod too. The screen was pretty much totally clogged with silicone sealer bits. It couldn't pump hardly any oil. The engine was never taken apart, so all the excess silicone was from factory. Put just enough to seal so none will squeeze into case.

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quantico
can I check out the oil pump screen without seperating the engine case halves ?? I prefer to leave it in tact as everything I looked at looked great... thanks Any special silicone gasket goop ??? I have used form a gasket and high tack.. etc but never used any silicone on an engine before ??? thanks

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olcowhand
I use only Permatex "Ultra Grey"....think that's the name. I'll check in shop later to be sure. Funny how you can use something every day & not remember it's name. VERY good at sealing & much better than regular silicone. It may have some silicone in it, but it's nature is much different. Any overage of it that may slide/run into case will stay on the case & not come loose to clog anything. I figure with a small mechanic's mirror you oughta be able to peer inside & look at the screen. You could likely get it clean without splitting cases if it has stuff stuck on it.

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quantico
Thanks very much. I will get out a few of my little mirrors and poke around... Is just swapping out a connecting rod when one breaks a fairly common solution to the problem??? The cylinder walls and the other rod and piston set all look perfect. Everything inside the case looks beautiful and clean and nice. The only thing that worries me is that it seemed like there was about half gasoline inside the crankcase instead of engine oil. The oil was thin, but I don't know if the last owner was using 30 weight oil... or 10-w -30 oil or something. The engine fins and air fan were completely clogged, so my guess was that the high heat caused the failure..... I have cleaned everything well and have no issues with how any part looks now. I am not planning on pulling apart the valves... although since I got the engine not running I have no compression to go on... The engine is only three years old...however. Here are a few pictures to show how clogged the air cooling system was... YUCK






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olcowhand
quote:
Originally posted by quantico
The only thing that worries me is that it seemed like there was about half gasoline inside the crankcase instead of engine oil. The engine fins and air fan were completely clogged, so my guess was that the high heat caused the failure.....
[img]/club2/attach/quantico/clogged air fan 2.jpg[/img]

You just supplied the needed info. The oil was thinned by gasoline. Look for either a bad diaphram in fuel pump, or if fuel supply is higher than carb then a bad float/needle could fill combusion chamber with fuel that leaks past the rings while sitting. Likely it's the fuel pump diaphram. The very thinned/compromised oil along WITH the clogged cooling is a definite for engine failure. Either one alone is bad enough, but both......very bad! Lucky it's not MUCH worse.

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olcowhand
If that engine is stuffed so tight you can't get your hand in to wipe off the flywheel screen then I'd cut a couple inches from one of the side shields so you can. This screen should be checked before every use. Oil level too.

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quantico
Checking on fuel pump right now... the fuel tank is above the engine height wise... so I will have to look the carb over as well... Lots of work on this project... You can see that the tank is quite high above the carb... the tank is slightly higher than the battery...


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olcowhand
quote:
Originally posted by stevenj
Even after you replace the fuel pump, install an in-line fuel shut off valve between the tank and the carb to prevent it from happening again.
I put one on most all my tractors, unless fuel tank is low enough it's not needed. Worth it to not have to worry about changing oil. One or 2 of my tractors would fill block while not running (no fuel pump) no matter what I did to the carb. Started putting the valves on everything after that. Never had gas in oil since!

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PeppyDan
With that much stuff packed in the engine, I would be concerned with the overheating cooking the governor gear. From what I have read in other posts on this site, this is one of the biggest reasons the magnums come apart. I have a magnum 18 I am rebuilding and also don't think you will be able to see the screen without splitting the block. I would also urge you to split the block to make certain that everything can be thoroughly cleaned and inspected. Here are a few pics of the inside of mine. This is not a new governor gear but it did seem to be light in color so I am using it. The other one is from a kt17 that I also have apart. These gears appear to cost less that $20 and to me that would be cheap if there is any doubt. Think what it would cost for a different engine if this one blows because of a $20 part! Dan








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DMedal
how would one break a connecting rod without damage to the cylinder walls or bearings? Only by overrevving it seems to me, governor failure. I can see throwing a rod because the piston siezes but other than that, what else but too high RPMs or a bad rod could cause it. The oil being too thin is bad news, might cause cylinder/ring failure, or bearing failure, but not I think a rod. So perhaps the governor is already toast due to poor lube, and the rod failed secondary to that. Am I wrong? -Don

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olcowhand
Once that rod started galling due to bad lubrication, the rod keeps fusing aluminum to the journal until it just locks solid to it or loses enough material to create a loose hammering rod. The rod has to break at this point. I've known of rods throwing at very low speeds. The rod is a bearing itself where it meets the crank journal.

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andrewk
quote:
Originally posted by olcowhand
I use only Permatex "Ultra Grey"....think that's the name. I'll check in shop later to be sure. Funny how you can use something every day & not remember it's name. VERY good at sealing & much better than regular silicone. It may have some silicone in it, but it's nature is much different. Any overage of it that may slide/run into case will stay on the case & not come loose to clog anything. I figure with a small mechanic's mirror you oughta be able to peer inside & look at the screen. You could likely get it clean without splitting cases if it has stuff stuck on it.
If I use anything, I usually use a very thin coat of either Loctite 515 or Permatex aircraft sealant. Don't remember the permatex number, but it comes in a can and is applied with a brush. Stinks too, but works well. I used to be a big RTV silicone fan, but time and experience have taught me that they are not all they are cracked up to be.

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olcowhand
quote:
Originally posted by andrewk
quote:
Originally posted by olcowhand
I use only Permatex "Ultra Grey"....think that's the name. I'll check in shop later to be sure. Funny how you can use something every day & not remember it's name. VERY good at sealing & much better than regular silicone. It may have some silicone in it, but it's nature is much different. Any overage of it that may slide/run into case will stay on the case & not come loose to clog anything. I figure with a small mechanic's mirror you oughta be able to peer inside & look at the screen. You could likely get it clean without splitting cases if it has stuff stuck on it.
If I use anything, I usually use a very thin coat of either Loctite 515 or Permatex aircraft sealant. Don't remember the permatex number, but it comes in a can and is applied with a brush. Stinks too, but works well. I used to be a big RTV silicone fan, but time and experience have taught me that they are not all they are cracked up to be.
The Loctite 515 is almost just like "Yamabond" sold at Yamaha dealers. Also much similar to "Ultra grey" except the above is thinner. I use Yamabond & 515, but just have ultragrey right now. Anything except RTV or other pure silicone sealers.

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