B&S 15.5HP 28N707 - Epilog/postmortem


Old 11-20-05, 08:08 PM
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Join Date: Oct 2005
Location: USA
Posts: 62
B&S 15.5HP 28N707 - Epilog/postmortem

B&S 15.5HP Model 28N707 Type 0173-01
Born c.10/96
Died 11/19/05
"It lived for better or for worse...but it's dead for good!"

Well after the high note of it starting right up after replacing the head gasket and running it for 45+/- minutes on Thursday PM (with NO unusual noises, etc), I needed to start it on Saturday AM to move it out of my garage (so I could get my extension ladder out and clean my gutters). Temperature that morning was about 36F (shades of Challenger...) but it started right up and after running for about a minute I decided to engage the mower deck just to put it under some load which I had not done before. Almost immediatly it died, but it still didnt sound all that unusual. When I went to restart it the engine would not turn. So I tryed turn the engine by hand using my hands on the top blower screeen and I actaually got it to move 20 degrees or so and then the same in the opposite. But at the endfof the 20 degrees I could feel that something inside was hitting/binding. Now Im standing on the 'drivers' side of the tractor and I notice that as I turn the engine back and forth this 20 degrees my eye catches something moving on the other side of the blower cover near the starter. What the... So I go around the other side there are some small wires just aft of the starter motor and well you see there is this nice big hole in the side of the engine block starting just aft of the starter motor and extending forward to behind the starter. And sticking out of this hole is a piece of, well I have to pull it out of the hole. And isnt it a nice piece of the connecting rod. Actually a piece of the rod, the rod cap, and one rod bolt - loose! And it was pushing on the wires on the outside of the engine when I turned it by hand and thats what I saw moving. Now I can almost turn the engine completely by hand but at about 3/4 revolution it binds again and I can hear it. So with a small light I look in and there is another nice piece of connecting rod. And my telescoping magnet pickup tool wont attach to it...its ALUMINUM! An aluminum connecting rod, well Ill be. So a piece of coat hanger wire with a hook on the end and with a bit of fiddling out comes another piece of connecting rod, cap, and with its bolt - also loose! With the light I can see a 'stub' of connecting rod still attached to the piston. So my connecting rod broke into 3 pieces! Actually if you unbolt the rod/cap pieces the connecting rod is now actually now in FIVE PIECES!!! From best I can tell looking at my new connecting rod 'parts' and the B&S illustration the rod uses no seperate bearing (like an auto engine does). The rod bearing surfaces were VERY deeply scored and chewed up. Im now sure that 'Stu' (from previous thread) was correct and that my original siezing incedent really did a job on the connecting rod big end. But now the crank turns easily thru 360 degrees rotation and when I position the connecting rod journal of the crank so it is near my new 'inspection window' I can see that the crank journal looks to be in very good shape. I can run my finger across its width and around its surface and I see/feel no gouges or scoring. So the good news is the crank may be salvagable along with every thing else except the upper engine block/cylinder, stater (see below), and obviously the connecting rod. I just could not believe how loose the connecting rod bolts were - each at least two turns from seated - especially considering that for all the time it ran after it siezed and I got it loosened up (45 minutes after the head gasket job plus a short time it ran before the head gasket job) I heard NO unusual knocking or such noises. Maybe this old mans ears are just shot! Also worth mentioning is that when the rod exited the block it must have hit the starter motor (the hole in the block is directly behind and to the aft of the starter), or distorted the motor's mounting/housing, or both as the starter pinion gear no longer aligns correctly with the flywheel ring gear although the pinion gear itself does not look damaged. Either way the starter motor will no longer turn, electrically or by hand.

I'll try to post a few open casket pics, though probably not till after the holiday.

As I stated in the original thread if this engine needed anything more than the head gasket I was opting for a new engine. I think now it needs 'alot' more! I found a few dealers on the net selling new 28N707s for $450 including UPS ground.

The bottom line is the entire episode was MY OWN FAULT. It stated a few years back when it started 'burning oil' (probably the head gasket at that point) and I began to run it with less than a full crankcase of oil as it would not smoke (or smoked less) that way. I honestly thought I must be overfilling it - regardless of the dipstick - and that is why it was smoking, because it would not smoke with less oil. In hindsight, knowing what I now know about these engines, it was a very stupid thing to do and I was sowing the seeds of its ultimate demise. So beware and keep your engines correctly filled with oil. And if they smoke/use oil then get to the bottom of that.

Maybe when my son gets a bit older (he is 2-1/2 now) we will take that old B&S apart and he will learn about engines from Dad's old lawn tractor engine - the way I did, except I did not have a dad - a neighbor gave me an old engine he had that did not work and I took it apart.

Happy Thanksgiving to all!!!!!
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Old 11-20-05, 09:15 PM
v8driver's Avatar
Join Date: Sep 2005
Posts: 767
ahh yes, sad day though parts are salvageable, and can be sold to make up for some of the cost of a new one. or maybe a new block? well as for small air cooled engines..... as you stated, keep em full.....unlike a car and or truck that can be low.......these babies have to be in operating range on the dipstick, if it burns, keep it checked more often and keep it to the full mark! one thing i'm glad of, nobody got hurt!
Old 11-20-05, 11:54 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,818
Well, shoot! You never know. I was hoping it would last awhile. I've seen some sieze and break loose and run for a few more years, and then I've seen some knock and come apart almost immediately after breaking loose. Well, at least you got to have a blast doing the head gasket repair! Lol!

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