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Discussion Starter #1
I am working on a Briggs & Stratton model 12H802-2390-B1. It had a bent crankshaft that made the engine vibrate pretty bad so I figured since I had a spare crankshaft, I would just swap it out. I got the new crank in but when I tightened the connecting rod cap down, it was so tight, that I couldn't turn the engine by hand. So if figured maybe the new crank had a different size journal. I put the bent crank back in and when tightened down, it also made the engine too hard to turn. What is going on here? I tried tightening the rod cap bolts to 100 in lbs per the repair manual and made sure to oil the journal and rod before assembling. The cap only fits one way so it is not backwards. Before I tightened the rod cap for the first time, I did it by hand (without the torque wrench) so is it possible I screwed up the rod so it is too tight now?
 

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Given the parts are the same as before, I would check that you don't have the connecting rod angled. Gravity will try to make the rod drop to one side of the journal, and if you get it cocked, it could be jamming. Check to see that the rod can be moved back and forth on the crank journal.
tom
 

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Is it a Briggs rod for the type number engine you have of an after market replacement? It could be the wrong rod as it doesn't fit the original crank. Manufacturers make running changes on engines that is why it is very important to get the correct parts with the type number. It could also be you got a .010 rod that was put in the wrong box. Roger
 

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What Tom says, plus make sure the bump in the connecting rod bearing is properly seated in the matching milled slot of the connecting rod and cap. If the bearing is angled or has come out of the key that holds it in place, that would account for a tight fit. If it did come out and you torqued the bearing down, chances are the bearing will need to be replaced because it was badly deformed.
 

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Try it with the sump cover slid on, so the crank is held in alignment...and make sure there is oil on the crank/rod...
 

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Discussion Starter #6
For clarity, the rod is the original rod and spun freely before I took it apart. Now, even with the original crankshaft it is too tight. I will take a look at it and see that the rod is straight and can move side to side. I will also try turning it with the cover on. I will update you guys soon. Thanks for the suggestions.

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Discussion Starter #7
The rod moves freely on the piston pin and appears straight (I took it out and put it back in to make sure it isn't binding.) I put the sump on and it is still impossible to turn. When I put the rod cap on hand tight, it turns fine, but as soon as I tighten it to spec, it locks up. I am thinking that I over tightened it the first time around and it warped the rod or something crazy like that. Possible?
 

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Its possible, but Ive seen rod bolts gotten so tight they stripped or snapped, and not deform the rod. Are you sure you got the right cap and rod...Because, you have 2 caps, and 2 rods there...if they got mixed up..it could make problems. If you put the halves togethe,r off the crank, do you feel any flaws where they meet, all bolted together?
 

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Discussion Starter #9
Its possible, but Ive seen rod bolts gotten so tight they stripped or snapped, and not deform the rod. Are you sure you got the right cap and rod...Because, you have 2 caps, and 2 rods there...if they got mixed up..it could make problems. If you put the halves togethe,r off the crank, do you feel any flaws where they meet, all bolted together?
Sorry for the confusion but I only have the original rod and cap. The part I am changing is the crankshaft.
 

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Suspect faulty torque wrench...


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I find it hard to believe that tightening the connecting rod cap bolts could deform the bearing surface. That would mean the the bolts can 'warp' solid aluminum. I would have thought the bolts would snap or the heads twist off before it could deform the journal.
Is it possible a previous job put some shims between the cap and rod, and they were not noticed when taken apart? I haven't heard of shimming mower rods, but it's possible.
One other possibility is that the rod needed some help coming apart after the bolts were removed, and that slight tapping distorted the cap. I would try some Plastigage to check the journal and rod for round and clearance. If the cap is distorted, time to spend some $$s
tom
 

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You should just replace the rod. You've got a new crankshaft, so having a new rod would be money well spent. Your existing rod cap is deformed. A machine shop could resize it for you, but why waste any more time on it when you could purchase a new rod have this thing back together and running.
 

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Discussion Starter #13
I looked around the area where I took it apart and was not able to find any shims so I don't even know what the deal is as far as it being so tight.

Replacing the rod sounds like a good plan. I am going to look around and see if I have one otherwise I'll just order one up (they aren't expensive). I will let you guys know as soon as I get it in.
 

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Sounds like you might have warped or bent it somehow.
 

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A head-scratcher for sure.. Put the doubts to rest and get out the Micrometer and measure both the old crank and new crank's rod journal.. That will tell the tale.. It they measure the same then the rod is tweaked / bent badly and replacement is necessary. To check the crank-to-rod fit, go to your local auto parts store and get some 'Plasti-gauge' and follow the instructions. Examine the new crankshaft's journal.. Look for any deformities or damage..

All I got.. :dunno:
 

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Discussion Starter #18
A head-scratcher for sure.. Put the doubts to rest and get out the Micrometer and measure both the old crank and new crank's rod journal.. That will tell the tale.. It they measure the same then the rod is tweaked / bent badly and replacement is necessary. To check the crank-to-rod fit, go to your local auto parts store and get some 'Plasti-gauge' and follow the instructions. Examine the new crankshaft's journal.. Look for any deformities or damage..

All I got.. :dunno:
I made sure to measure the journals before I swapped out the cranks. They are the same so it has to be the rod.

Sounds like you might have warped or bent it somehow.
If I remember correctly, the sump cover on this was pretty hard to get off probably because of rust and the bent crankshaft. I may have put too much force pulling that cover off or something and did something to the rod.

I will just go ahead and order up a new rod but I would like to try the plastigauge thing WNYTractorTinkerer mentioned first.
 

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No need to waste time plastigauging a rod that is locked up once the bolts are tight....obviously, it has zero clearance.

Plastigauge is useful when building engines, or when checking an engine during tear down, in order to determine that you have X amount of clearance between main bearings (in an automotive engine) and the crank, or rod (rod bearings) and the crank.

If you want to play with that bad rod, and have a good inside micrometer, bolt the rod cap on, and then measure the inside diameter in 3 or 4 directions. I think you'll find that the opening is no longer a perfect circle, hence why it binds on the crank.

A machine shop has a special machine for resizing rods. Basically a hone type of device with an expandable hone. They assemble the rod, and run it back and forth on the spinning hone, until the rod opening is a perfectly round hole, a the correct diameter. If need be, they can cut the bolted faces of the rod, making the hole very slightly smaller and oval, and then machine it back out to round from there. Very handy when building an automotive engine.

But for you, where a Briggs rod is dirt cheap, you wouldn't spend more than 3 seconds to say, "Rod is bad." And then be on the computer with midwestmowerpro.com and have a new rod on it's way....like a week or 2 ago.:hide:
 

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Briggs and Stratton 694691 connecting rod too tight - checked with Briggs
mod 21M414
type 0017E1
Code 100222YD
they gave me the same part number i am using
 
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