Export thread

Howdy everyone,
For starters, here is what I am working on: Briggs 128M02-0926 from Troy Bilt 725EX 190CC mower. I believe the serial said it was from 2011. Anyway, my coworker's husband decided to try his hand at some regular maintenance. He installed a spark plug that's almost twice the thread depth as the stock plug. I'm fairly certain it bottomed out onto the exhaust valve. Needless to say, it wouldn't start when he tried to pull start it.

Here's what I've done so far: I've got the correct plug in there now (good spark), I've cleaned the carb, pulled the exhaust, and pullded the head to check out the valves. I wasn't able to see any light behind the valves, but I'm guessing the exhaust valve is bent or worse.

I've cranked the flywheel with my hand, and I do meet resistance during the compression stroke. I unfortunately do not have any way to test the compression. However, I can hear a little hiss through the oil fill hole and a squeak noise through the breather assembly hose (where it meets the air filter). Also, there is a big push of air out of the intake before a small intake of air. The exhaust purge seems small too, but I am not experienced enough to know what is normal.

I guess what I'm trying to figure out, before opening up the crankcase, is what's most likely damaged from the spark plug bottoming out on the exhaust valve? Thanks in advance, and I hope I was thorough enough in my explanation.

I mean my train of thought on this is that it's either a bent valve or something with the timing. I'm leaning towards something with the timing because the spark plug was limiting the range of motion of the exhaust valve not the intake valve, but the intake is not closing and allowing a big push of air/fuel out through the carb. Can anyone chime in to let me know if I'm even close? Thanks!

Spark plug would hit the piston top. I would pull the head and look at the piston.

BlazNT said:

Spark plug would hit the piston top. I would pull the head and look at the piston.

Click to expand...

On a Side valve engine ?


You analysis is probably correct so you will have to pull it apart again and remove the valves, both of them and check the valves are strait.
Before you pull them out check that they both open to the same height as the cam shaft itself can be bent if your hubby is a bit of a hulk with the starter.

bertsmobile1 said:

On a Side valve engine ?


You analysis is probably correct so you will have to pull it apart again and remove the valves, both of them and check the valves are strait.
Before you pull them out check that they both open to the same height as the cam shaft itself can be bent if your hubby is a bit of a hulk with the starter.

Click to expand...

It got someone smarter than me over here to help the poor guy.

I'm fairly certain it's a camshaft issue. The exhaust valve could be bent, but it seems to be true just from casual observation.

I got the head off and applied a little pressure (my desk-jockey thumb isn't that strong) to the exhaust valve and was able to keep it from opening while rotating the flywheel with my other hand. Looking at this makes me think the gear and lobes are plastic!? -> http://www.ereplacementparts.com/images/part_p_1733640_2242276042.gif from http://www.ereplacementparts.com/br...engine-parts-c-16758_17347_229369_229406.html . I'm planning to open the bottom up tomorrow morning to have a look.

weekendmechanic said:

I'm fairly certain it's a camshaft issue. The exhaust valve could be bent, but it seems to be true just from casual observation.

I got the head off and applied a little pressure (my desk-jockey thumb isn't that strong) to the exhaust valve and was able to keep it from opening while rotating the flywheel with my other hand. Looking at this makes me think the gear and lobes are plastic!? -> http://www.ereplacementparts.com/images/part_p_1733640_2242276042.gif from http://www.ereplacementparts.com/br...engine-parts-c-16758_17347_229369_229406.html . I'm planning to open the bottom up tomorrow morning to have a look.

Click to expand...

Yes they are so it sounds very much like open heart surgery

Open heart surgery performed and a success. The camshaft gear had a crack in it at one of the "spokes" and mangled the metal fork that I assume keeps the gear from rotating freely on the shaft. Luckily, I found one for sale in my area. It's running great but is having trouble starting when the engine is hot. Starts right up cold.

It has a new spark plug and new air filter. When I undo the air filter and start it hot, it starts right up. I can then screw shut the air filter and it continues to run fine.

It looks like there is an excessive amount of fuel collecting on the air filter too. I made sure to line the the camshaft notch up with the crankshaft notch for timing... hmm.