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Hi all,
I am new here and have a bit of a problem. my craftsman riding mower with a Briggs and Stratton 18.5 HP OHV engine died on me. The engine shut down and now wont turn over. I tried turning the flywheel, but it wont turn. The oil was a little low, but not too bad. I pulled the head off and was able to push the piston down with little resistance. once i did this i was able to turn the flywheel till the piston reached the top, but no further. After the piston is pushed down the flywheel will spin in reverse for a while and stop, I can then go foward with it, but only till the piston gets back to the top. What might my problem be, can it be repaired?

Any help greatly appreciated.

Thanks, Jim.

Almost sounds like your rod cap is making contact with your camshaft, but if it did that at working speed the insides would have piled up.

Is your flywheel making contact anywhere on its revolution?

Anymore details you can provide?

Flywheel is not making contact anywhere. the flywheel key apperars to be two pieces, not sure if that is how it is supposed to look, but it is still aligned anyway. when it died i was mowing on a flat surface and did not hit anything with the blades... it started to run really rough for a few seconds than just abrubtly shut down. when i removed the oil dipstick, seconds after death, there was steam coming from the dipstick tube.. Oil was a bit dark, smelled a little burnt, but not all to low... when i turn the flywheel with th episton set at the bottom, it will spin easily till piston reaches top, then stop with a metallic sounding bang which sounds like it is coming from inside the cylinder, but i cant really be sure.

thanks for your response :smile:

jimkerr12 said:

Flywheel is not making contact anywhere. the flywheel key apperars to be two pieces, not sure if that is how it is supposed to look, but it is still aligned anyway. when it died i was mowing on a flat surface and did not hit anything with the blades... it started to run really rough for a few seconds than just abrubtly shut down. when i removed the oil dipstick, seconds after death, there was steam coming from the dipstick tube.. Oil was a bit dark, smelled a little burnt, but not all to low... when i turn the flywheel with th episton set at the bottom, it will spin easily till piston reaches top, then stop with a metallic sounding bang which sounds like it is coming from inside the cylinder, but i cant really be sure.

thanks for your response :smile:

Click to expand...

Man, I had to look to see where Maryland was. Mowing in March? We're still under three feet of snow up here. We won't be mowing before the end of April mid May for sure.

Back to the engine,
- if the piston will travel when you turn the flywheel then the connecting rod is ini tact ( that's a good thing).
- If the flywheel key (little one 3/16" or so square by about 1/2" long) broke for some reason then your timing is out. The internal timing on your crank and cam is fine but your ignition time is thrown out.
- starting with the cheapest route is always the best way to start a repair. A flywheel key is about a buck and and a bit. change that first. I've had motors in my shop that had a stretched keyway on the crankshaft which made the key slack which screwed up the timing. We changed out the crank and away it went.
- any chance you can post pics or send some to me?

robertw@fvsd.ab.ca

I have a 18.5 briggs hp in the shop now that I might be able to compare it to if you could.

I will try and post some pics later... It appears that the key is sheared and the nothches are off about 1/8 of an inch right now.. i dont have a flywheel puller, but after attempting to pry up on the flywheel while smacking it with a hammer it is now spinning freely ( Starter will spin it non stop, piston moving up and down.), I need to put the head back on and relace all the parts i removed to see if it will start or not. any suggestions on removing the flywheel to replace the key my method didnt work too well.

thanks for all your help so far

oh and yeah, grass starting to grow down here... :thumbsup:

That key is designed to shear off when your blade hits something hard like a boulder or a side walk. I saves the connecting rod from taking the torque and snapping.

Over years of mowing and hitting "not so hard" things the key takes some abuse. If your key is off by 1/8" that is more than enough to bugger up your igntion timing.

If that fly wheel has been on for a while it'll be tight. You can make your own puller if you have some tools and if not maybe a buddy has a puller he can lend you for 5 minutes. Pullers are a bit pricey for one time use.

Grass? the kids were snowmobiling yesterday and we are planning an ice fishing trip three weeks from now ha,ha

good luck

ok, flywheel key is certainly not in it original shape... it is now like 2 halves fused together offset by about half its width. (that would explain the 1/8" the notches were off) gonna pick me up some new keys, you think this should get me back up and running? also, I think while I ws removing the head a small circular object (about 5/16" diameter, not sure of correct name) came out of where the valve lifters seat into the block, any trick on getting this back in place?

jimkerr12 said:

ok, flywheel key is certainly not in it original shape... it is now like 2 halves fused together offset by about half its width. (that would explain the 1/8" the notches were off) gonna pick me up some new keys, you think this should get me back up and running? also, I think while I ws removing the head a small circular object (about 5/16" diameter, not sure of correct name) came out of where the valve lifters seat into the block, any trick on getting this back in place?

Click to expand...

If your key is offset that much, then your sparkplug is definitely confused.:confused2:

As far as the other part, 5/16" eh?

Is it like a mini cylinder/sleeve? Some manuf's use sleeves on some holes to help allign and reinforce bolt holes.

Have to take the head off to re-inspect for that. A pic would do wonders here. You might not have to take the head off. It might be a part of the valve train.

You might have done this already, but if you need to re-install the head, it should be torqued down in three installments.
1st at 75 in.lbs, 2nd at 150 and third at 220

Well... Flywheel key replaced, however, I was wrong about the piston moving up and down. Still only moves to the top then stops untill i push it back in. flywheel spins forever, valves are both doing their work... sounds like I may be screwed huh? Any Idea why this is happeniing?

Thanks for all your help so far :smile:

If when you push the piston down and if the flywheel does not turn while pushing, you are right. QUOTE:sounds like I may be screwed huh?

jimkerr12 said:

Well... Flywheel key replaced, however, I was wrong about the piston moving up and down. Still only moves to the top then stops untill i push it back in. flywheel spins forever, valves are both doing their work... sounds like I may be screwed huh? Any Idea why this is happeniing?

Thanks for all your help so far :smile:

Click to expand...

:frown: Push it back in? Uh, oh. That means the rod is pooched. The valves are working because the rods doesn't effect their operation. Sounds like the crank throw catches what's left of the rod and pushes the piston up but when the throw (crank pin journal) goes down to complete the revolution theres nothing to pull down on.

Sound like its time to pull the engine apart for a look see.

An online over-haul:licking::thumbsup: Are you up for an over haul?

HI
SOUNDS LIKE MAYBE LOW OIL & THE VALVE SEIZED OPEN STOPPING THE PISTON. SAID YOU HAVE HEAD OFF, WHAT ARE THE VALVES DOING? YES CAPS LOCKS - I CAN SEE WHAT I TYPE, KINDA:laughing:
STEVES

missed post of flywheel, yes sounds like crankshaft/rod issue! time to tear down.
this capslock thing!
STEVES:confused2:

Sounds like wristpin fell out. Rods in cylinder pushing piston up and thats why piston stays up probably messed up bottom of cylinder also.

So jimkerr12, what were the results of your engine seized issue? I am having a very similar situation.

Hello,

I'm having same issue and have my entire engine in pieces. I will post the pics of where I think the problem is a and the parts affected. I definitely see wear on the cylinder and metal chips fraying away on the inside. My questions is going to be: Why did this happen? What parts are still salvageable and which ones do I need to replace? How to fix this problem?

All answers will probably come easier once you see my photos. I'm referring to same engine, I believe.

jasonchiefoil said:

My questions is going to be: Why did this happen?

Click to expand...

The list of why can be a bit of a puzzle, but here's some ideas,


- low oil
- oil not serviced properly (viscosity breakdown)
- metal fatigue ( wrist pin is steel and con rod is Aluminum. Eventually wear is going to occur no matter how well it is serviced)
- Heavy use
- A ring break (jam the piston in the sleeve)
- Sudden stop on crank and flywheel key doesn't break way
- Break-away key replaced with a piece of steel key stock

I'm guessing here of course, but as easy as these little engines seem to be, sometimes figuring them out takes some time.

I had a little 3 1/2 hp engine one my bench one time that met specs, everything went together the way it should have, but it wouldn't fire.

Would just fart every now and then.

Long story short the keyway on the crankshaft was worn so the there was some slap when the flywheel was turning. Threw the timing out. We changed out the crank and vroom.

The crank is harder than the flywheel key so what would cause the wear? Flywheel nut slack off a bit and the flywheel wobbled? Rough use?......Will never know I guess. Sometimes I think it's best to learn thinking outside the box......lol.

Course that will never happen again..............lol