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Salthart

Ever thrown a rod ? Please post here !

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Salthart
Being the type person that thinks most everyting happens for a reason, And seeing whats been said in another topic, And seeing as there are over 4000 members to this club.... This is a chance like no other to compile data on connecting rod failure.. What I'd like to see are posts by anyone who has repaired an engine with a broken rod. Info that would be needed.... Engine make and model #'s Oil used use when rod failed noise made when rod failed tell what was found.. IE was the rod broken in the center, is the bearing cap still intact, Was the block damaged , was the crank damaged, How did the bore and piston look ? Lots of things we know already. Like lack of lube will cause a rod bearing to seize on the crank, Inertia keeps the crank in motion, breaks the rod, Rod is now used as a club against other engine parts. Info like this may go a long ways in helping dodge the failure after rebuild.. But may be to much trouble. Up to you all ! Salt

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tractormike
I have worked on quite a few small engines over the years, mainly on briggs, 3 1/2 horse up through 12 horse and almost every rod I have seen broken was due to lack of oil or using the engine on a steep slope for an extended period of time. The rod is starved for oil and locks on to the crank, snaps the rod in the middle and usually breaks the block behind the electric starter on the right side of the block. Everyone that has brought them to me must not have heard enough unusual noise to stop the engine because they were still running the engine when it blew up. Not much choice, do they what to buy a new engine or not. At least this is what I have seen over the last 25 years or so.

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sun41bird
a rod snaped on me a couple of years back on a 917h with a kohler kt enginei always checked the oil i didnt repair it i put a 18hp magnum in funny thing was just before it blew it never ran better a friend of mine who work at a simplicity dealer said it probebly was an engine defect

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SQUEAK911
I have a 14HP Kohler that the rod was thrown threw the Side. Welded a piece in place. Ive had a KT17 and 20 Threw a rod. Just broke side of the cylinder wall. I replaced the rods in my 16HP kohler engines with Vogel Rods. The Rods never broke but I have broke two crankshafts and one Flywheel. Most of these engines were in pulling tractors so they were pushed a little bit.

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arjr111
The rebuild I did on my 12 HP Briggs 300421, was to repair a thrown rod. Chewed up the crank journal pretty bad to. She is now sporting a new Piston, Rings, Rod, Valves, and Crank. Believe fellow owner Rob-B, was using it in his puller when it went south.

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JimC_Vt
I have repaired all kinds of makes with broken rods ,all are do to lack of oil and filthy oil or both ,some have been easy to repair some just weren't worth repairing ....I had one wisconsin SD-7 that I thought the rod was gone ,but the cap bolts vibrated out,none the less a pain to repair,but no internal damage .... I just started to tear down this 12hp wisconsin in my bolens 1254 ,theres a lot of vertical lines in the cylinder,but if she has not been oversized,she's about too... see ya Jim

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PatRarick
There are always exceptions, but here are the general rules: A connecting rod that is broken in the center, or near the piston, has been broken by overspeeding. A connecting rod that is broken at the crankshaft journal is caused by lack of lubrication, poor maintenance (infrequent or no oil changes) or mechanical failure (loose connecting rod bolts). In all cases, the connecting rod and crankshaft journal will tell the story. If the journals are clean and shiny, and the rod was broken in the middle or near the piston, chances are it was caused by overspeeding due to incorrect governer adjustment, faulty governer, incorrect governer spring, or manually overiding the governer. If the journals are clean and shiny and the rod was broken at the journal, the most likely cause is loose connecting rod bolts. If the journals are dull and have fine scratches, then poor maintenance (infrequent or no oil changes) is most likely the cause. This will cause the rod to break in almost any location, but near the crankshaft is the most likely place for the break to occur. The scratches and dull finish are caused by wear by contaminated engine oil. The connecting rod bearing clearance is increased by this wear. That causes the crankshaft to "hammer" in the connecting rod. At first there will be no noise. If the rod manages to hold together, the clearance continues to increase until a knock is heard. The hammering elongates the connecting rod bore until fatigue causes it to break. If the journals show transfer of metal from the rod to the crankshaft, lack of lubrication is the cause. The rod can break anywhere. The engine can overspeed, breaking the rod near the middle or near the piston. The softened metal of the connecting rod creates "super lubrication" causing the engine to overspeed. The rod can also break near the journal as the rod heats and the metal weakens. None of this takes manufacturing defects into account. In most cases, manufacturing defects will cause failure in the first few hours of use. Pat

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Al
Hi, Right on Pat, I might mention that failures that show 2 overlays of metal transfer to the crank, usually indicate a dry start condition with a delayed failure. This situation usually shows up when mass merchant mowers come for "warranty". Dry start symptoms are not warrantied. The dry start will start a layer of metal, and may stall the engine. Often oil is then added and the engine restarted. Shortly heat will cause more transfer and as the metal sticks to the crank, temperatures sky rocket and the pressure on the inside of the rod journal cause the rod to "explode". Another clue on vertical shaft engines if the rod fails is to check the upper main bearing, if it is galled, indicates lack of lube. If it is good and the rod fails, it may get warrantied. On the Briggs "DU" bearings the lack of oil won't show up before other failures. We are just short blocking a Kohler 25 that broke the rods. The journal on the lower rod had metal transfer, and the adjacent rod portion of the journal was mirror smooth. The engine was well out of warranty, and I called my Kohler rep and asked him to look at it, because I felt it should go more hours, and the clues didn't indicate neglect. They provided the short block, and the customer stands the labor. Now the details of why it was a warranty issue. The welch plug in the oil pump had blown out, this allowed the oil pump output to spill in the crankcase. Since the oil flow to the rods it from the top down, the bottom rod was the first to oil starve. There are books written on failure analysis, and many companies are having failure analysis classes, to teach techs to determine if a failure is warranty or owner neglect. Plugged fins can cause rod failures when the oil breaks down. We sold a new engine to a customer for a Grasshopper, he took it to a part time guy for a deal on a cheap installation. This application requires changing the blower housing and the old flywheel. The guy took the plastic fan off and changed the blower housing. The customer called us about 3 weeks later and wanted to know why when he changed the oil only part of it would come out and it was lumpy like gun grease. I told then I needed to see the engine, well it croaked, and when they brought it in the block was all yellow colored aluminum. We found the problem, the part time guy has no insurance, and no money. They are out $1350. engine and install. Anyway if the aluminum turns gold, it has been overheated to excess of 500 degrees. The list of clues goes on. Didn't mean to get carried away. Good luck, Al Eden

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Salthart
Al hit on what I'm looking for in a way. When you know the oil is there, and when you know the engine wasn't turning to many RPM's and the rod fails. This was the case with my powerking's 12 hp Kohler. And I have yet to do a tear down on it. I was on it when it went and I know from the sound the rob bearing gave up. But with all that mass in motion, Even though I was reaching for the kill switch at the first tap I was far to late and will have more powder than rod left to check out. I was ploughing and the unit had been under a heavy load. Add the fact that it was in the 90's and I think I'm gonna find that the piston seized just enough to get things started. If i find this to be true, Yours truely will go to straight 50 weight in all cast iron engines..Just for the peace of mind I'd get from the higher temp protection..Likey a little tough on cold winter starts for you northern boys ! Salthart

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Leroy
Another thread that makes a magazine subscription worth the money paid. My Kohler lost the rod at the top but not on the piston. i was ideling while i was moving lawn furniture and it poped. It was not wound out but it was not under an obvious load either.

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BigSix
What a great thread! I learned more here in a shorter time than I can even say thanks for but..thanks. I think this would be an excellent beginning to a "Failure Analysis" file, like the "Do It Yourself" one. Then people could search for their particular failure, like at any time, and not wait for advice to come in, and possibly not need to even ask. One could follow the successful course of action already documented, and perhaps documenting their own failure carnage photographically, and their related experiences, to build the reference. A section for engines, decks, etc..., could be opened as they come in. Always makin' work for Kent....:D

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dlcentral
Broke one while checking rpm speed on a14 koh pulling motor,saw extreme vapor coming out of breather,then SNAPPO!,reason of failure was determined that motor was humming around 6000??rpm,no metal on crank broke about at mid point,put new rod in, RESET rpm to 4000 ,trophy winner now,,

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SmilinSam
You guys ll' like this one... Had a 917 with a KT17 twin in it. Had a friend overhaul it. He decided to be cheap and not to buy new rods and re-used the old ones( Good man huh?) I was about 1/4 mile from the nearsest place I could possibly get a trailer into when I heard a loud thunk!(like a hammer hitting a slab of aluminum) and the engine stopped. I knew what had happened immediately. As I didn't care to push a hydro 1/4 mile, I gave it a shot to try and restart on one cylinder and by golly it started after a couple of tries. ( Rod broke at the cap and came off clean from the crank)Drove it to the trailer, though you can imagine what pumping all the shavings and metal flakes through the system did... at least I didn't have to push, and I figured a KT series wasn't any great loss anyhow..

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PatRarick
When I purchased my 914H, it had been parked for a year. The owner told me that it used quite a little oil, was very low on power, and was difficult to start. He figured the engine was toast, and was selling selling the tractor with that in mind. The engine didn't concern me as I wanted it for a Vanguard engine conversion. When I got it home, I decided to see if the engine would run so I could test the other components before proceeding with the conversion. Found the points burned to a crisp. Since I only wanted the engine to run for testing purposes, I installed a set of good, used points. Carburetor throttle shaft had a LOT of wear. Had a spare carb, so I switched that. It started and purred like a kitten, but there was a fair amount of smoke. Ran beautiful at idle and wide open. There was no knocking and the engine ran quiet. The tractor would not move. I found the hydro drive idler pivot was sticking. While the engine was idling, I decided on the quick fix of prying the idler bracket to tighten the belt. I walked to the tool box, grabbed a pry bar and headed back to the tractor. Just as a was to tighten the belt, the engine went into "free wheel" mode. No noise, not nothing. Just an instant, quiet transition from idling to free wheeling. The following winter, I tore the engine down. The rod was in 17 pieces, the piston in 4. Lack of maintenance and overheating (a loose head bold had been leaking oil for some time and the cylinder fins were plugged solid with "charcoal") appeared to be the cause. I was just amazed that it ran so well, then stopped without a sound when there was so much damage. Pat

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patrician12
I snapped 2 different rods 1 year apart on a 12hp Kohler for no apparent reason that even the factory store couldn't figure out.That was 8 years sgo.Since then tried a 16 hp Briggs single cylinder on my 912 and running ever since.Sold on Briggs.I now have Briggs 18hp twin,Briggs 16 twin,2 10hp Briggs,2 8hp Briggs and 7 5hp Briggs on various stuff around the farm.I also have Tecumsehs a 10hp ,7hp and 2 5hp.About 24 hours ago I blew apart a10 hp tecumseh through stupidity.I thought it was overreving and sure enough kaboom!I checked and the governor lever was loose and not working.I didn't touch it but that's how it goes. Here's the good news.With ebay I find it doesn't even pay to rebuild anymore.I can buy good running motor whole for cheaper than the parts with a fraction of the aggrevation.You guys remember aggrevation?????? Two Christmas' ago I decided to go motor hunting for a spare 16-20 hp twin Briggs just in case mine went down on my main tractor.You will not believe this,I bought a 1987 Gilson in near mint condition for $125.00 with a deck,weights,snowplow and a beautiful 16 hp twin off ebay!!!The trick is to BUY BEFORE YOU NEED IT,when you get it for the right price let it sit until the emergency hits.You know when you have to have it you're dead.My theory is why people have portable generators,it may sit for years waiting for that one big day. I almost forgot,BUY BRIGGS.Just because other brands can be more expensive doesn't mean they are better.

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bigcountry
quote:
Originally posted by patrician12
I almost forgot,BUY BRIGGS.Just because other brands can be more expensive doesn't mean they are better.
10-4 on that! Briggs is the only way to go for repowers.

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a7117puller
kohler kt-17 started to smoke bad while mowing, (sucked oil all way up throught the intake)so i just shut it down. shop took a look, and rings were paper thin and in some pieces....never did sound right when got it...like a diesel.., usually those first series throws rods from wrong oil or so..but when they blow, they usually take the aluminum block out just in front of the right side cyl. seen some with busted caps, halfway up the rod, take the piston skirt out too and the cast iron lining thats just on the inside of the engine too. crank would need to be redone too, as for some reason on small engines, there are no rod main bearings... picked up a kt17 series 2 for parts too, threw rod too, even though was full pressure lubrication. low oil or wrong oil im guessing. oh well...parts is parts, and thats what picked it up for. so now have couple kt-17's stripped and in parts. also have a i/c cast iron b/s 16hp engine that has a busted rod...at the cap area, took the piston skirt out too, but no visual damage to the cyl wall, but crank, camshaft are shot cause all marred and knicked up on the gears. also took out the oil slinger. ive never dropped a rod, but that smoking 17 was as close as i have come.

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