Briggs and Stratton crankshaft bearing surface

pointer33 · #1 09/11/13, 04:13 PM

I have an early 80's Troybilt Horse. 8HP electric start Briggs and stratton. I received it in a non-working state. Upon opening it up the connecting rod broke apart on the bearing surface of the crankshaft. Looks like a case of low oil. So what I see is aluminum smeared on the bearing surface. I tried to attach a photo of this.. I was able to knock some of the aluminum off with a screw driver. Much remains and my question is this. Since aluminum and steel absorb heat at different rates can I use a propane or a cutting torch to heat the aluminum to expand or melt it off without destroying the shaft? This crankshaft is no longer available through Briggs and Stratton nor is the shortblock. Any thoughts or suggestions appreciated.

plowjockey · #2 09/11/13, 04:42 PM

It will take 1200 degrees to melt aluminum. I'd be concerned actually softening the crank surface.

Also since it was run out of oil, I'd be concerned what else is damaged.

You can get a new replacement engine for as low as $300

That is what I would do.

pointer33 · #3 09/11/13, 04:57 PM

PlowJockey,
Thanks - I bet you are right, I may have to ultimately replace it. Right now while it is off the tiller and I have another B&S on the tiller without the electric start....it never seemed to be a very good motor from the start I took it off a cheaper made tiller to use as a temporary substitute for the engine in question. Just was hoping to keep the original motor with e-start before getting another one. My running B&S seems no better than a harbor freight clone I bought a few years ago for another application so maybe I will shop them soon.

flewism · #4 09/11/13, 08:20 PM

Muratic acid will do it without damaging the crank journal any worse, then get a mic on it and see where you stand.

simi-steading · #5 09/11/13, 08:35 PM

More than likely, the surface will be scored even if you could get the aluminum off.. You might check with some of the local shops, they may have a used crank in decent condition for a decent price.. I kept them on the shelf for sale when I'd find a good one from a scraped out an engine... I'd sell one for an 8 to 12 HP for around $50..

More than likely though, that engine is shot inside.. the valve guides are probably messed up too.. A lot of metal would have traveled through that engine before it stopped.

**alleyyooper** · #6 09/12/13, 06:13 AM

Just do a overhaul on the engine. Take the cylinder and crank to a machine shop and get it turned. get the cylinder measured and olny honed if need be or bored if it needs it. I did a 10HP B/S a bit ago with new piston turned crank bearings and all the gaskets for less than $100.00

the habor Freight 212cc engine on a horse tiller, You need to tilt the engine when filling it with oil when changeing it. That engine isn't designed to work at the angle the tiller will put it in when tilling. Isn't a big deal lots of them in use just tilt to fill it with correct amount of oil.

Al

pointer33 · #7 09/16/13, 09:53 AM

Guys - I appreciate all the thoughts you have given me as I am unexperienced in dealing with this sort of thing. I so far picked up some muratic acid and went that route....at first I was happy to see it worked like a champ! Then as I was looking closely I saw a small gouge on the shoulder of the bearing surface and a small area in the center of the field I could not feel with my finger but I could feel it with my fingernail.....so priced an undersized connecting rod assembly from Briggs and Stratton .020" gee they want about 20 bucks more for the undersized rod assembly.
It may seem like I am penny pinching here....I already have another newer B&S that seems to be a piece of junk that I may put on this tiller....it would work....but I still like the idea of this older electric start flathead if it works out. Got the name of a local shop that may grind the surface...will check with them.

plowjockey · #8 09/16/13, 01:14 PM

IMO there's a difference between a small engine, that needs an overhaul, verses one that was run without oil, to the point of failure.

Motor oil cools the engine, as much as it lubricates it, so I'd be concerned with warpage or fatigue, not corrected with re-machining.

Seen good money and work, go into these rebuilds, only to have the engine, grenade or seize after 10 minutes

Good luck, though. It's cool to have an old engine with elrctric start.

simi-steading · #9 09/16/13, 02:02 PM

Quote:

Originally Posted by plowjockey

IMO there's a difference between a small engine, that needs an overhaul, verses one that was run without oil, to the point of failure.

Motor oil cools the engine, as much as it lubricates it, so I'd be concerned with warpage or fatigue, not corrected with re-machining.

Seen good money and work, go into these rebuilds, only to have the engine, grenade or seize after 10 minutes

Good luck, though. It's cool to have an old engine with elrctric start.

I agree with this.. I was a B&S Master Tech for years... The bearing surfaces for the crank in the block may be bad, along with the cam bearing surfaces... the valve guides may be messed up, the head and or block could be warped enough that milling would be the only fix.. and there's not really much there to mill.. Stress fractures from overheating could be present and it's just a matter of time.. .

Johnny Dolittle · #10 09/23/13, 09:57 AM

Those Troy Built tillers were flawed in their design in that the engine is tilted back when tilling deep. Those engines were not made to operate constantly in that position. Many of the Horse models were powered with a 6 hp Tecumseh which had a reputation for locking up and breaking the rod. I have an 8 hp "90's model Horse with Briggs. I keep the oil level on the high side and check it often.

davel745 · #11 09/23/13, 10:05 AM

If the connecting rod broke I suggest the case be magnafluxed. more than likely cracked.

Johnny Dolittle · #12 09/23/13, 10:16 AM

The engine could be the old cast iron block but probably is the aluminum block and if so I would not be willing to spend much to repair it.

oneokie · #13 09/24/13, 03:36 PM

The discoloration of the crank throw and the areas on either side indicate that it hot hot enough to change the temper (hardness) of the throw. It also appears that the cheeks of the throw have been damaged.

pointer33 · #14 10/06/13, 01:52 PM

I sure appreciate this blog. Many of you guys have brought up thoughts and or issues I have not thought of! While I am nostaligic for the idea of rebuilding what I think of as a motor that is of higher quality than what is available inexpensively now I think I have decided what I will do. I am carefully placing the assorted pieces and parts on a shelf in my shed until I am willing to spend the nickel and dime money that DOES add up to get the motor going again at the risk it might not work out and ....just be a learning experience. Meanwhile I have mounted a newer slightly smaller B&S motor without electric start I already had....seems kind of unimpressive in the quality department but it works

And now in my spare time I focus on replacing some seals and gaskets I bought for the tiller. Thank you again for all the responses!