Outdoor Power Equipment and Small Engines - Briggs and Stratton 12HP Clanking/Tinkling Sound

Briggs and Stratton 12HP Clanking/Tinkling Sound

Its a long story, but I'll try to sum it up. This is a B&S 281707-0415-01 12HP engine for a riding mower from 1992.

My engine wasn't starting well and burning a lot of oil. First I replaced carb parts and cleaned carb. Soon I had a really hard time starting it, so I took it apart, replaced the piston rings (which were badly worn), lapped the valves, cleaned, and reassembled (with new gaskets etc) and proper torque values.

I was finally able to start it (with the aid of carb cleaner again) but much quicker. It is not idling well (but this is less of a concern for me). There is a faint sound (like metal-buttoned overalls in the dryer, but quieter). The reoccurence of the sound is around every half a second (not very fast). I ran it for 20 min in hopes that the piston rings would seat better. In addition to this strange clanking sound, I am getting gas in my oil (but only since I ran it for 20 min). I have had the gas hooked up for many days after putting it back together without any leakage into the oil.

Any ideas for either of these problems?

Here is the parts diagram if you are interested:
Engine Model # 281707-0415-01 Illustrated Parts List (http://www.briggsandstratton.com/maint_repair/manual_and_more/docmanualdetails.aspx?showpdf=MS8987_LO.pdf)

Might pull the engine shrouds and see if it is full of straw, grass and filbert(or nut shells that may grow in your area) shells :)
This could be part of the oil consumption and even the "tinkling".

You still may have carb or other issues which can be addressed after insuring the engine is cooling.

I had the whole engine apart 2 weeks ago and haven't had it on the grass. There is nothing like that here. Thanks though.

Did you have the flywheel off, check your valve clearances?

Likely that long story summed up is the confusing part.
Just what are symptoms now

For startup, is the choke closing completely?
Are you still getting gas in the oil? What carb parts were replaced?

I would check valve clearance as well. Since you lapped them during the re-build. It sounds like they might be a little loose??
Be sure the key-way holding the fly wheel is very secure. Did you use a new one?

The valves are probably too tight since lapping them. That can account for poor running and difficult starting problems. The noise sounds like wrist pin knock or piston slap from your description. Could also be the rings hitting the ridge in the cylinder if you didn't remove it.

The valves are probably too tight since lapping them. That can account for poor running and difficult starting problems. The noise sounds like wrist pin knock or piston slap from your description. Could also be the rings hitting the ridge in the cylinder if you didn't remove it.

What is piston slap?? If the rings are new is that possible?
Removing the ridge with a ridge reamer is a good idea.
How did the cross hatch look in the cylinder?

Piston slap is when the piston skirt is worn enough that it allows the piston to wobble a bit in the cylinder. It rides up one side of the cylinder on the upstroke, and down the other side on the down stroke, and if it has enough wear, it will slap from one side to the other. It makes a tinny sounding knock...not heavy like a rod. More light sounding like a small rock in a coke can. It doesn't matter if the rings are new or not as far as piston slap is concerned.

Thanks for your replies.

The choke is fine. Startup wasn't much of a problem. I haven't started it again since though. I've drained the oil.

It is possible that the piston is wobbly at the top of the cylinder, but it didn't seem too badly worn when I had it out. I don't think the sound is coming from there, but its possible the way you describe the sound. The thing is that I didn't get that sound with the old rings. Also, for all's info, I did hone the cylinder before putting the new rings in.

As far as valve clearances, I meant to check the gap between the valves and the tappets, but forgot to. I have to remove the carb and breather to get to them. But I did take a look at valve/piston operation from the head before I put the head on. They seemed to be closing ok. (But that could be something that you can't tell for sure that way.)

I could be wrong, but the sound almost seems like it is something light repeatedly hitting the crankcase wall.

I didn't buy a new key for the keyway, but I should check it again. We did take the flywheel off so that we could remove the crankshaft. In retrospect, this probably wasn't necessary, but it made it easier to clean the old gasket off of the crankcase.

I need to have a more trained ear listen to this sound. There is someone I know that I can haul the mower to. I think it'll come down to that. If you have any other ideas, feel free to respond.

Thanks!

Did you cut the ridge in the cylinder? If the rings were as badly worn as you say, I usually find that there is a ridge in the cylinder and a good bit of piston wear when the rings are worn down badly.

I'm not sure what you mean by cutting the ridge. I did inspect the cylinder and honed it.

At the end of the cylinder where the rings do not quite go to the end, there is usually a ridge where the cylinder has worn down except for the little bit at the end. If it is not cut down to the same plane as the rest of the cylinder wall, it can break new rings.

I'm not saying that is your problem, but if you rings were worn badly it probably had a ridge. It may or may not be a problem. Lost of things could cause the noise (rod clearance, wrist pin, piston slap, counterbalancer, pre-detonation, etc...). It would be just guessing without actually taking it apart and measuring all the parts to determine if they are within acceptable tolerances or not.

Yeah, I think thats what its going to take, I'll need to get some measurements done. I do know that there wasn't a ridge though, so that's good. The sound is heavier sounding than a broken ring.