B&S question - repair or replace?

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  #1  
Old 05-14-10, 05:26 PM
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B&S question - repair or replace?

The story: I was using a standard push mower that I purchased used off of craigslist. I was using it for the first time in an area that is moderately wooded immediately behind my house. I had done the same thing in recent years but my old craftsman mower deck had finally given out and I scrapped it. While I was mowing I hit a very low stump. Apparently this mower's height was not the same as the older one. The engine stopped instantly. It restarted but with a vibration. The blade did not look bent. I was suspecting the crankshaft key was partially sheared. The problem was that I do not have air tools to remove the large nut on the top of the crank, (or on the blade) for that matter. I took it over to a local small engine repair shop. It turned out that I bent the blade, partially sheared the crankshaft key, AND bent the crank. The shop replaced the blade and the crankshaft key (and he showed me the old parts). He tells me that about half of the vibration is out of it but that eventually it will chew up the seal on the bottom of the mower.

So the question: Should I attempt to rebuild the engine myself? I have never done a small engine before but do work on my own cars. Look for a used (or new) short block? Look for another craigslist mower?

Here is where I stand today. I used it for 20 minutes this weekend. It vibrated enough to numb my hands. It will get used about that much weekly. The small engine repair shop suggested I use it for the remainder of the season and bring it back in the fall for full service. I have found the same model mower with an engine that will not start that I can have for nothing. The engine is not seized but the internal condition of the mower is otherwise unknown. This other mower may or may not have same engine on it. The manufactures web site suggests that two different engines were used on the mower.

The engine is a B&S with the following numbers: 12F702 0616 01.

Thanks for your opinions in advance.

Steve
 
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  #2  
Old 05-14-10, 05:47 PM
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Originally Posted by 2ndgencamaro View Post
The story: I was using a standard push mower that I purchased used off of craigslist. I was using it for the first time in an area that is moderately wooded immediately behind my house. I had done the same thing in recent years but my old craftsman mower deck had finally given out and I scrapped it. While I was mowing I hit a very low stump. Apparently this mower's height was not the same as the older one. The engine stopped instantly. It restarted but with a vibration. The blade did not look bent. I was suspecting the crankshaft key was partially sheared. The problem was that I do not have air tools to remove the large nut on the top of the crank, (or on the blade) for that matter. I took it over to a local small engine repair shop. It turned out that I bent the blade, partially sheared the crankshaft key, AND bent the crank. The shop replaced the blade and the crankshaft key (and he showed me the old parts). He tells me that about half of the vibration is out of it but that eventually it will chew up the seal on the bottom of the mower.

So the question: Should I attempt to rebuild the engine myself? I have never done a small engine before but do work on my own cars. Look for a used (or new) short block? Look for another craigslist mower?

Here is where I stand today. I used it for 20 minutes this weekend. It vibrated enough to numb my hands. It will get used about that much weekly. The small engine repair shop suggested I use it for the remainder of the season and bring it back in the fall for full service. I have found the same model mower with an engine that will not start that I can have for nothing. The engine is not seized but the internal condition of the mower is otherwise unknown. This other mower may or may not have same engine on it. The manufactures web site suggests that two different engines were used on the mower.

The engine is a B&S with the following numbers: 12F702 0616 01.

Thanks for your opinions in advance.

Steve
Scrap it, save the blade, air filter, etc. and anything else of value and get another mower. The mower is going to come apart, it is just a mater of time. Have a good one. Geo
 
  #3  
Old 05-14-10, 06:29 PM
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I agree on scrapping the engine. The crankshaft costs around $75. Remove the carb, gas tank, flywheel, coil, & sell them & maybe tear it down and sell the crankcase & cylinder. Those are the only items worth anything. you can buy a new engine for around $110.
 
  #4  
Old 05-15-10, 07:31 AM
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Can you point me to a site where I can pick up a new engine for $110? Do you have a part number?

Steve

Originally Posted by indypower1 View Post
I agree on scrapping the engine. The crankshaft costs around $75. Remove the carb, gas tank, flywheel, coil, & sell them & maybe tear it down and sell the crankcase & cylinder. Those are the only items worth anything. you can buy a new engine for around $110.
 
  #5  
Old 05-15-10, 07:57 AM
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  #6  
Old 05-15-10, 10:35 AM
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Thanks but can anyone translate the number on my engine into a suitable replacement part number?

My engine is marked 12F702 0616 01. It appears that the part number on the small engine warehouse web site should be SBxxxxx or something similar.

Steve

Originally Posted by indypower1 View Post
 
  #7  
Old 05-15-10, 12:39 PM
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When you go to Small engine warehouse, click on Repower Old Equipment, then click on the brand of lawnmower you have.
Or you could call them. It's a 1-800 number.
 
  #8  
Old 05-15-10, 01:09 PM
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i have straightened several lawnmower cranks.
take sparkplug out
lay mower on side
remove blade & adapter flange
make some kind of pointer out of a coat hanger wire
use pointer to find high point of crank runnout/where flanfe was-mark it
use about a 2lb hammer-whop! it on the mark
repeat-/repeat
the cranks are soft enough that they don't crack.
 

Last edited by newtofta; 05-15-10 at 02:20 PM.
  #9  
Old 05-15-10, 07:09 PM
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I think they reccomend against straightening cranks for the most part, but I can't say I've never done it successfully.
 
  #10  
Old 05-15-10, 08:17 PM
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YES,from 'my' standpoint 'I' do not impose any liabilaty isuses on any one,or on my self!
Just a thought from my past experience!
(do not want to get any one hurt)
But it does work!
Sorta-like/if god gives you lemons-make lemonaid!
(make do - with what you got)
 
  #11  
Old 05-15-10, 08:39 PM
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Originally Posted by newtofta View Post
i have straightened several lawnmower cranks.
take sparkplug out
lay mower on side
remove blade & adapter flange
make some kind of pointer out of a coat hanger wire
use pointer to find high point of crank runnout/where flanfe was-mark it
use about a 2lb hammer-whop! it on the mark
repeat-/repeat
the cranks are soft enough that they don't crack.

You are using the pointer to mark the high point of the adapter flange so that you pound above that and don't get it out of round?
 
  #12  
Old 05-15-10, 08:51 PM
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Originally Posted by SeattlePioneer View Post
You are using the pointer to mark the high point of the adapter flange so that you pound above that and don't get it out of round?
Just DON'T DO IT, the metal has been stressed, it is going to fail, it is just a matter of time. You have a blade spinning at 3,000rpm, it's going to come off, some time. Would you like that to happen around your kids or grand kids, or anyone's, whatever. Have a good one. Geo
 
  #13  
Old 02-03-11, 08:32 AM
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Final results of the bent crankshaft - fixed.

Someone gave me an identical lawn mower - a JD 14PZ that would not run. It too had a B&S engine on it but the crankshaft was a different diameter - bent one was 7/8" and the free mower had a 1" crankshaft. The 1" crankshaft engine had a different engine number on it but was identical on all other aspects to the old engine except for the crank and the adapter that the blade bolts to.

I took the 1" crankshaft engine apart and could not find anything wrong with it internally. So I put it back together and transferred all the external parts like the ignition, flywheel, spark plug, carb, shroud, head, etc from the running engine to the non-running engine. Assembled with new gaskets; fueled it up and the engine started on the third pull in my cold garage. I let it idle for 15 minutes, stopped it, let it sit for 15 minutes, and it started on the first pull. So the push mower goes back into service in the spring. The replacement engine smokes for about 15 seconds on cold start but not at all on warm start.

And, I also policed my wooded area (around 1/4 acre) and removed all stumps and roots that were above grade.

Steve
 
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