Tell me, did your engine seem to be "making" oil, whenever you checked the oil level in the crankcase!? If it did, your carburetor might have been leaking gasoline into the crankcase(Where the oil goes), which would dilute the oil to the point where it lost its lubricating powers, hence the noise.
Seems to me, if you keep running it, soon you will learn what is making the noise! (To the tune of much moola, to have it replaced!) A fuel shut-off valve, at $% is a cheap price to pay to avoid engine blow-ups!

The price on the fuel valve was s'posed to say $5, but my aging finger didn't let go of the shift key soon enough!
Rustyj

My friend blew up his 10HP tecumseh that way ( they were prone to overflow) - thinned the oil with gas n boom! The clanking sounds like my fathers 12HP motor after he messed with the governer ( he wanted to race me on my 5HP Toro) - his lasted about another month before blowing both sides of the block open. Since you have the motor open, id check the rods, i think the twins have an acess panel on the back of the motor( well my 18HP Twin briggs does) - one other thing to check? Motor bolts to chassis. A freind gave me a 12HP Briggs motored tractor cause he thot the motor was gonna blow, turns out only one bolt was holding it on the tractor and the engine was rattling all over, once i put new bolts in, was quiet again.
Good luck
Kidd

I am not clear if the loud bang you heard was a combustion bang or a metallic bang.

Anyway, sounds to me like you need to see if compression is good on both cylinders then pull the head of a weak one or pull both heads and see what is going on.

Could be a screw out of the carb butterfly, could be a chunk of carbon, but doubt it.

Walt Conner

I'm kind of wondering if the ACR might have broken off????

You can download a parts manual from the link

Here is a link that might be useful: IPL

"I'm kind of wondering if the ACR might have broken off????"

There is none on this engine.

Walt Conner

Should have looked closer. I saw part# 47 (oil slinger) and my fingers started typing:-)
Unlikely that broke off?

Oil Slingers do very rarely come apart but a loud bang from that would generally mean a thrown rod which apparently didn't happen. Problem is we do not have every little detail as to just what happened before and what happened afterwards. It is my impression that the engine was still running and was shut down after the bang but sounded funny for 4 - 5 minutes before (that was the time to shut it down). A pc. of the oil slinger going thru the cam gears might make a loud bang, never heard of that though but could happen.

Pulling the heads still sounds like a good start based on what we have so far, he has already pulled the inspection plate and apparently found nothing out of the ordinary.

Just had a thought, what if a flywheel magnet came loose?

Walt Conner

thank you for the parts manual
the sound is a continous banging when the motor is running very loud nothing like a back fire it sounds to me as if a part is loose somewhere inside.sounds like a hammer hitting the aluminum case rapidly. any advice if I need to take the motor off to work on it what is the best way to do this. right now i have defaulted to the old push mower 20 plus years old and starts on the 2nd pull every time. any advice what i should do. I have many thoughts at this time do i replace the motor, buy a new mower, or try to fix it local shops want 60.00 per hour to work on it, i would like to fix it myself if possible.
thanks again to all out there offering help

Could the fan be making contact with its housing or is something loose near it? I'm thinking
if all that banging came from something internal, it would not
turn as freely as you said it does. Something would have jammed.

"I have many thoughts at this time do i replace the motor, buy a new mower,"

Remove heads!

A new engine will be $1200 - $1400 IF you could even find one. These are out of production. Some places are offering conversion kits for Honda engines for example. Expect price to be in that range.

I have two rebuilt 18 hp B&S Vertical Shaft engine which would be a direct fit, $295 & $325 exch. but have no desire to ship which would be prohibitive anyway.

Walt Conner

The first post said the heads were removed.

I am not that technical i took the valve covers off I can see the top of the pistons and the tops of the valves I also took off the access panels to the springs at the opposite side of the valves i think its the rockers only a guess not real good with the names
I have the housing off and it still makes the noise
where would i look for a flywheel magnet
walt thanks for the engine update I have found some new brigs 17-20 range on ebay for about 700.00
also found a used 19.5 for 200 local off a craftsman 6-7 years old the broke the frame
oh well I try to look for the fly whee magnet
thanks again

Maybe bang on the flywheel with the heel of your fist, a few nice solid thuds. Twist the flywheel a bit and bang again. That might give you a rattle for a loose magnet or instantly show a loose flywheel.

Flywheel is mounted on the very top end of the crank shaft.
The flywheel is what the recoil starter attaches to on walk behind lawn mowers.
Magnets are attached to (and part of) the inner side of the flywheel.

I have an older 11HP briggs off a junked freebie snapper , the inner magnets came loose n locked the motor up ( this was just turning it by hand that they came loose). They made a scraping noise for a while before the magnets fell off , I had to pull the flywheel and pull the stator(since it was wrecked) and the loose magnets , then put it together, since i didnt have a spare 11HP stator. Like i said, i havent had this motor running since i got it, but turning it by hand , it locked up.
It turns free and smooth now.
Kidd

Hey Guy's, He first said that he had the heads off, then later he said" I am not that technical i took the valve covers off I can see the top of the pistons and the tops of the valves I also took off the access panels to the springs at the opposite side of the valves i think its the rockers only a guess not real good with the names
I have the housing off and it still makes the noise "
He doesn't have the Heads off this engine, just the covers. He needs to remove the heads and look for damge caused by a bolt or nut. Then he needs to pull the piston and rod out and check them. A wrist pin could be loose, but I would have to guess that he blew a connecting rod and the crankshaft is shot.
Shane

thanks to all I got it
i pulled the engine off the mower then removed the plate cover and there it was 2 of the screws on 1 of the connecting rods were loose tightened them now i just need to find a new gasket for the plate cover and try to put it all back together
by the way shane for someone who seems to have a sarcastic side there are no heads to remove the block is all connected, and sorry i didn't seem to know what I was talking about.
Walt you are a true champion this is the second time I have been on this fourm and you rock. thank you to walt and all those that added some insight thanks

"and there it was 2 of the screws on 1 of the connecting rods were loose tightened them now i just need to find a new gasket for the plate cover and try to put it all back together"

Did you look at the bearing surfaces for any galling etc.
The fact the bolts came close, may have allowed the rod to "hammer", possibly "stretching" the journal area. Check it for play in every direction you can and compare to the other rod.
Did you check on the other rod bolts to make sure they were tight while you're in there?

When you start it up, I'd go slow at first, listening for any odd noises. If you hear them, you may still be able to save the engine with a less costly repair than taking a chance of "really" breaking something.

You can use the IPL to learn the terminology when not sure what a part is called. (I know I have)

Hope everything works!

Bill

thanks for the advice I checked the other rod it was fine
the one that was loose did come in contact with the back of the I,m guessing is the crank housing the end of the bolts or screws hit it and there are some loose fine shavings. can i just tighten the bolts and go? i,m wondering will they come loose again. also should I replace the rod to be sure and if so how does it come out the easiest?
thanks millions
Yury

To replace a rod, you have to remove the head and push the rod/piston assembly out of the block.
Before you do that though, you have to remove any wear "ridge" that may have formed in the cylinder at the height where the upper piston ring travels. Failure to do so can break rings (possibly piston), since the rings will "catch" on the ridge.

IF one gets THAT involved, it's almost a shame not to install new rings. IF you do it on one cylinder, it pretty much makes sense to do it on both....

What I would do-?
IF the rod bolts didn't thread back on smoothly, I'd probably replace them.
THOROUGHLY examine the rod & crank bearing surfaces for ANY gouging or metal DEPOSIT (on the crank).
IF every thing looks OK, I'd button it back up and use it.

Like I mentioned earlier, I'd start off slow and work your way "up" on the throttle for a minute or so and back for the first 15-30 minutes. Go up to speed a bit more each time and then idle. REPEAT until you are up to full throttle. LISTEN for the start of any noise. If you hear anything "abnormal at any time, shut it down. If not, go mow.
If you make it through the first hour of mowing, you're probably good.