Briggs 6.5 pressure washer engine won't start, compression questions

[TerdFerguson]

Hi folks! My name is Matt, and I'm an alc..... wait a minute :laughing:. New member here, but been lurking these forums for a long time. This site has provided me with a wealth of info relating to my old Ferguson, so I figured I would see if you guys have any idea what's up with my pressure washer engine. I received a Craftsman pressure washer for free that the previous owner said ran, but would bog down and surge when the trigger was pulled on the wand. It has a Briggs and Stratton 6.5 Intek OHV engine, model number 120312 0143. He took it to a local shop and they told him it needed a new valve "or something like that". Well, when I got ahold of it, it would not start at all.

So I took it apart, expecting to see a stuck or damaged valve, but to my surprise everything looked pretty good. The gasket was still intact, and the valves moved freely and smoothly, so I put it back together and tried to start it with some starting fluid shot into the spark plug hole, thinking maybe the carb was just gunked up. No dice. Not even a sputter. I did notice the starting fluid fog pulsing out of the muffler as I pulled the cord though, so I presumed it had compression (I can also obviously feel the compression when pulling the cord). Next I checked for spark by pulling the plug, laying it on the metal housing, and pulling the cord. It's definitely sparking.

At this point I knew I had both fuel and spark, so I moved on to check compression. This is where I get lost. When I screw the gauge into the spark plug hole and pull the recoil cord, I get 0 reading on the gauge. Not just a low reading, but zero. I then removed the gauge, and put my finger over the spark plug hole and pulled the cord. It tries to suck my finger into the hole, but never tries to blow it away from it. The valves appear to be moving up and down as they should, yet the piston doesn't ever seem to push any air out of the spark plug hole. This doesn't make any sense to me. Has anyone else ever seen this? I read a little about the compression release do-dad on the cam, but it doesn't seem like that would cause it to have zero compression, it would just be lower. Am I way off base?

I also do not understand why the staring fluid did not at least cause it to sputter and/or backfire. If there's both fuel and spark in there, something should eventually go boom, right? Any help would be greatly appreciated, thanks in advance.

I hope I put this in the right section of the forums. If not, sorry fellas, new guy here.

 

[oldnslo]

What did you take apart to inspect? Did you fully remove the head or just the valve cover? If just valve cover you could have a valve partially stuck open or burned. Was there any freeplay between the rocker and valve stem? If yes how much?

Compression release usually keeps the exhaust valve open until a certain RPM is reached. Below this RPM the valve may not close properly.

Is the spark coming at the correct time? I.e. sheared flywheel key throwing the timing off?

Lots of newer small engines have problems with surging RPM's thanks to the excessively lean mixtures required to meet EPA regulations. This has lead to more and more pistons being ruined from lean full mixture, cylinder walls scored, etc.

 

[/pine]

you should have least gotten a pop...did you try a different spark plug ?

 

[TerdFerguson]

Thanks for the reply oldnslo! I removed the entire head, pulled the valve springs and keepers, and pulled each valve out of their guides to inspect them. They seem relatively clean, undamaged, and appear to be opening and closing as they should. There was a little freeplay between the rocker and the valve stem, but I didn't get a feeler gauge out to check how much. I would guess just a few thousandths. I assumed at the time that they were still adjusted the way they were when the engine still ran.

So, even if the compression release is holding the exhaust valve slightly open, it should still fire, right? It just wouldn't develop 100% of the power/compression it does when that feature is disengaged? If that's correct, I don't think this sounds like my problem, because I'm getting no fire at all.

I'm not sure how to go about checking the spark timing. I'm not familiar with how the ignition system works on these engines. I'm more of a 60's Chevy type of mechanic haha. You might be onto something though. I will google "sheared flywheel key" and see if I can find some more info on that. Do you suppose that would cause the weird "no blow" condition at the spark plug hole when the plug is removed?

And yeah, I've experienced the same surging symptoms with another older Craftsman pressure washer, so I assume that's pretty common. On that one though, it would continue to run, it just surged and sputtered until it got warmed up. I can't even get this one to start in the first place. If the piston or cylinder wall was damaged bad enough to kill the compression, wouldn't there be less "tug" on the recoil cord? It's definitely much less when the spark plug is removed, and with it installed I can feel the tension become greater and lesser in different parts of each rotation. Pretty much like I would expect a "good" engine to feel. And I presume I wouldn't have felt a strong vacuum with my finger in the spark plug hole, right?

 

[TerdFerguson]

Yeah Pine, that's what I was thinking too! I didn't get any sort of pop or sputter whatsoever. That's what prompted the compression test, which still has me befuddled. I didn't try another spark plug because the only others I had handy are from a VW dune buggy, and I think the tip that goes into the plug wire end is different on those. I may have another one in an old tiller down in the barn, I'll have to check. The one that's currently in the pressure washer looks to be in good shape. It's fairly clean, not bent, burnt, or covered in oil. Is it possible that the spark is too weak to ignite the fuel mix? Is there a way to test the coil (or whatever it's called on this type of engine)? I pulled the plug, laid it up against a piece of metal, pulled the cord, and checked to make sure it was sparking. I didn't do any real scientific investigation beyond that. Any suggestions would be appreciated.

 

[Coyote machine]

Start with the most basic things, known good, fresh fuel. New correct spark plug. Get a spark tester tool at local auto store. Make sure if there is a fuel shut off valve it's turned on, and you're getting fuel delivery. Is the s.plug getting wet when you spin the motor with the cord? Then, if none of the aforementioned fix it look at timing of spark, it could be off as mentioned.

And, you sprayed starting fluid and saw atomization of same- this does NOT mean you have fuel delivery. I would also advise against using starting fluid at all. This is not the way to diagnose an engine.....

 

[TerdFerguson]

Good points Coyote. I'll pick up a new spark plug and tester. I started this whole process with fresh gas after I verified the condition of the valves, and checked for spark at the plug. I realize that shooting starting fluid into the plug hole does not indicate I am getting fuel to and/or through the carb. That was not my intention or belief. My thought was, if I put a shot of starting fluid directly into the engine and it fires, it proves I do NOT have fuel delivery. If it still does nothing when I pull the cord (which was the case), it would indicate the problem lies elsewhere and I need to dig a little deeper. Which brings me here.

 

[jlgurr]

Maybe grasping here, but did you check the crankcase for pressure that might indicate excessive ring blow-by?

Sent from my iPhone using TractorByNet

 

[TerdFerguson]

Maybe grasping here, but did you check the crankcase for pressure that might indicate excessive ring blow-by?

Sent from my iPhone using TractorByNet

How would I go about doing that? Honestly I didn't really pay much attention to the piston, rings, or crankcase since the previous owner said it was running when I got it. I should have inspected that stuff closer while the head was off. I did notice that the oil looked extremely clean. I would expect it to be dirtier if the rings were allowing much blow-by.

I did, however, notice air being puffed out of two small holes in the plate the rocker studs go through in the head. I assume that is supposed to work that way though, because there is a rubber hose that comes off the valve cover and runs back to the air filter box. I assumed it was some kind of recirculation type of setup.

 

[jlgurr]

On my B&S I simply unscrewed that tiny oil fill cap (two button heads on the top) and put my thumb over it while pulling the starter rope. Spark plug must be in of course.

The rings were so bad it blew oil out of the fill hole.

Sent from my iPhone using TractorByNet