Trying to figure out why this engine has no compression.....I have spark, fuel and no compression. I have checked the valve lash and everything seems to be correct. So I removed the head and attached pictures to see what the experts out there think? I have before and after carbon removed. Please advise would love to hear your thoughts?
Briggs & Straton OHV Plastic Engine No Compression
- Thread starter Montecore
- Start date
Looks like the exhaust valve is not seating properly. Heavy seat on one side and thin on the other? It also appears to have some "gouges" in the seat (picture isn't clear). I would have put the spark plug back in before you removed the valves and filled the head with some gas to see if it holds the gas or it leaks out (old mechanic trick).
Thanks for the response.....the engine has been removed from the deck and the head has also been removed I can put some gas on top of the the piston and cylinder and see if the gas leaks past that piston rings. What you described where would the the gas leak out? I think you are describing a different way of checking? Maybe this is just a scrap engine now more headache then it is worth.
Yes that's how you'd check to see if the valves are sealing but I'd just junk the engine they're rarely worth the time and effort and parts usually aren't cheap. Chuck it and drop in a harbor freight unit or get a new mower. Looks like you got your moneys worth out of it.
OP I think you misunderstood. Gas will leak past the piston for certain. Put the gas in the combustion chamber of the head after the plug is back in. It will leak out of the intake or exhaust port just like all of your compression is doing. Clean the valves in a drill with brake cleaner and a brillo pad then lap them in. Try the gas to see if they are sealing at that.
It is impossible to say for certain what it is from these pictures. The best way to tell is to do a leak down test. It will tell you where the biggest leaks are coming from. ie. The valves, head gasket, rings. You can buy a leak down tester for under $100. You do need an air compressor to use it. Since you already have it apart, you can inspect the gaskets, valves as discussed above and have rough test of the rings. A bad compression release will actually make the compression higher when starting. If it is stuck on, it will make the compression lower when running. What did you use for the valve lash spec. I think it is .004 to .006 on both. I will have to check it.
What does the cam look like? Plastic lobes? Any wear?
Yes I agree with you sir! There is something causing this engine to overheat and get 600F to make the blue of the valve. The mower was free so I was trying to save it but no compression issues are a nightmare to deal with. This is the first time I have run into this. I am just a small engine self taught guy flipping mowers and snowblowers to save people some money in this tough economy. It is more of a hobby and not a shop. Harbor freight predator engine is $149.99 so would be very hard to turn a profit even with a rear wheel drive toro self propelled deck. People for some reason prefer the push mower not self propelled.
Your camshaft is most likely faulty. These engines are really crappy. The plastic shifts or a gear will break loose from the crank shaft and you will not be timed correctly.
Thanks for the response that is a good thought. Will try
Thanks for the thoughts sorry I am not sure how to do what you said....I have never done that before and I may not have the proper tools
Cam looks great I thought it may have moved but I contacted a parts place and she was nice enough to reach out directly to B&S tech team and confirm the exhaust lobe (top lobe) should be 90 degree from the timing notch. I have seen YouTube videos saying the point of the exhaust lobe should be in line with the notch that is NOT correct. So my cam was in great shape.
Cam looks great I thought it may have moved but I contacted a parts place and she was nice enough to reach out directly to B&S tech team and confirm the exhaust lobe (top lobe) should be 90 degree from the timing notch. I have seen YouTube videos saying the point of the exhaust lobe should be in line with the notch that is NOT correct. So my cam was in great shape.