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Replace Connecting Rods on 20 HP B&S, Engine tight hard to spin.


Rain Man av's Avatar
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TX

03-26-08, 04:57 PM   #1  
Replace Connecting Rods on 20 HP B&S, Engine tight hard to spin.

B&S 460777, Type 2276 E1, Code 9803265A. The engine seized after running low on oil. Open the back plate and took off old rod caps. Rods and caps showed signed of severe wear. Condition of rod on cylinder two at journal made motor almost impossible to turn. Removed cylinders and using caliber determined both journals to be ok, ie. not rejected according to specs. Specs are from a B&S repair manual I bought at Sears for L-Head twins.

Purchased new connecting rods and purchased a new in-lb torque. After torquing to B&S spec of 190 in-lbs, the motor is hard to turn. If I loosen the bolts at the rods, the engine spins freely. The pistons, rings, walls all look very, very good. No scoring, no nada, pistons move up/down freely, so I know they no be da problem.

According to B&S manual, rods should have some up/down movement on the journal after torque, is this true?. After proper torqueing, they don't and engine is hard to turn.

I polished journals with emery cloth and wiped clean before connecting rods and caps. even put oil on the caps before tightening. Is something wrong or is this "tight" situation common after new connecting rods?

There was no visible damage to the journals, i.e, scaring or gouging. The connecting rods on the other hand had severe scarring. Do I need to treat the journals with muriatic acid, I didn't see signs of aluminum transfer. Or should I start over and polish the heck out of the journals.

Any info/input would be helpful.

If da motor requires da new crank, send flowers.

 
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03-26-08, 06:27 PM   #2  
It appears you have checked out all possible problem areas and also done everything by the book and assuming you purchased the correct connection rods (Briggs part number 498314 (std. size)) then i'd say your crank journal is not within specs. If you so choose, you could have the rod turned down to match your new rods or go undersize using Briggs part number 498541. With what tool did you measure the journal? And do you trust it to be acurate? For curiousity sake and to eliminate a potential bad, new Briggs part, have you measured the rods for proper specs?

 
Rain Man av's Avatar
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03-26-08, 07:41 PM   #3  
Connecting Rods ordered and received is P/N 498314. I used a brand new dial caliper purchased at Harbor Freight just for this purpose. I trust it to be accurate. Oh god, I've got to take her apart.

What is the spec for the standard rods.

here is the really odd thing about it. Before I tore into the motor, only one of the rods was seized. The other moved freely up/down on the crank. I remember that because I thought that movement odd. Then I bought the B&S book and read.

I did not measure the new Rods. I assumed they would be pristine and within spec, out of the box.

I'm real good about making assumptions, let me now share some of them with you.

Ass #1 - that the reject spec published by B&S for the journal means that if my measurement is larger than their reject, then my journal is OK.
Ass #2 - That over time the journals would wear done. NOT get fatter.
Ass #3 - That if I install std size connecting rods, all other things being equal, then there should be possibility of more, not less, play.
Ass #4 - that the specification for 190 in-lbs for the connecting rods printed in B&S book is correct.

I'm hard pressed to understand why a standard size rod on a journal with some age would be tight. Unless it is the freakin rods.

Let me know your thought on those assumptions above.:mask:

 
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03-27-08, 12:46 AM   #4  
I'd venture a guess that you've got aluminum on the crank, especially knowing the fact that it siezed due to lack of oil. This transfer of metal can be hard to see to an untrained eye, but it will make the crank journal larger and cause the rod to bind when the bolts are tightened. It should be free to move and slide up and down with no effort.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
Rain Man av's Avatar
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03-27-08, 02:13 PM   #5  
I'm spending too much time with my hands inside my motor

I took the connecting rods off, purchased muriatic acid and cleanded the journals, there was some fizzing initially, but then it stop. Applied it liberally, rinse and repeated. I again used emery cloth to polish the journals, cleaned, and then applied liberal coat of oil and put connecting rods back on.

I used my dial caliper on one of the Connecting rods, I came up with 1.625 on the nose. Is this the correct spec for the standard rod ?

Here is the funny thing, after reinstalling and torquing the bolts, it is impossible to turn the motor. I've taken two steps backwards.

 
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03-28-08, 03:29 PM   #6  
It does appear that there was more alum xfer from the connecting rod to the journal than I thought. Using dial caliper journal was 1.627 before I started anything. Then I came here, got advice and after all was done, journal was at 1.622, which is right at reject.

This is what I did to git 'er done.

Purchased some emery cloth, rolls, not sheets, medium, fine, and extra fine. I played shoe-shine boy with the journals Started with medium and ended at extra fine (hey, I can see myself) I started with the journal pointing at me, did the shoe shine boy thing, and then turned the crank about 15 degrees, played shoe shine boy, turned the crank 15 degrees, shoe shine boy, turn, shine, turn, shine until I went through one revolution of the crank.

Wiped it down and repeated with fine, and then extra fine. Put fresh oil on connecting rod/journal, bolted together, and voila, I have the requisite rod play at the journal like B&S says in their book that it should.

Now, cylinder one was not very cooperative, after I did all that work, it did not want to play nicely, so I used a screw driver and gently nudged it up and back down on the journal, after three or four times of doing this, the journal played freely in my hand. I guess it needed some light persuasion. Nothing two heavy as I did not want to break nuttin.

Thank you so very much, now it is time to get out the engine mounting bolt that broke off. Yeah me !

 
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03-28-08, 11:06 PM   #7  
Let us know how it goes.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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