420 CC question

Going from good compression to none seems strange. A piece of junk that gets caught under a valve will cause those symptoms. Clearance gets set on a valve that is not closing all the way.
 
ILENGINE said:
Going from good compression to none seems strange. A piece of junk that gets caught under a valve will cause those symptoms. Clearance gets set on a valve that is not closing all the way.
Click to expand...

Ah yes. That is an extreme possibility. I was cleaning the top of the valves. There was a lot of carbon build up. This gives me an idea. I can take the valve cover off, and recheck the lash. If it's still the same. Take the exhaust pipe off, and see if I can see the exhaust valve. Maybe shoots some seafoam in there, and let it set for a while.

How about compressed air through the exhaust? Anything that might me keeping the exhaust valve open, or even the intake, would be loose. For the simple fact that there was compression before.
But in thinking deeper into this, once the valves started opening and closing, (when I tried to start it), should've either been sucked in or pushed out away from the valve seat.

Right? Unless maybe it's now lodged in the valve seat.
 
What did you use to clean carbon off the inside of the head and the valves? And did you lap the valves after?
 
This might be irratating but pull the valve cover off one more time. See if everything looks ok. Then while watching the rockers, turn the motor over by hand. Make sure both have the same amount of travel in both directions.
 
dfbroxy said:
This might be irratating but pull the valve cover off one more time. See if everything looks ok. Then while watching the rockers, turn the motor over by hand. Make sure both have the same amount of travel in both directions.
Click to expand...

I took the head back off, pushed the valves open by hand (no spring compressor for this type). And blew it out. Let some seafoam soak on the inside and out of both valves for about an hour. Then blew it off again, scraped a little more carbon off from around the valves. Cleaned it up, put it back together. She cranked this time. Smoked like the dickens on low rpms.

Final diagnosis, these engines are crap.
 
And to answer your question, carbon gets under the valve when the exaust valve opens the exaust goes through the open valve, through the exaust port in the head and out the muffler.
 
dfbroxy said:
And to answer your question, carbon gets under the valve when the exaust valve opens the exaust goes through the open valve, through the exaust port in the head and out the muffler.
Click to expand...

Well, yeah, I know how it gets under an open valve. But it can't get through a closed one. Which is what happens when the head comes off. They close. If I had 150lb compression, before removing the head, seems that I'd have that much after it went back on.

One thing I forgot to mention in the last update, was the keepers. I didn't pay a lot of attention to them, when I put the new head gasket on. Just sort of stuck in the hole and didn't pay any attention to how deep it went, compared to the other one. So when and torque it down, if it wasn't in there all the way, that would explain the loss of compression.

I did notice some tiny tiny air bubbles coming through the exh valve. That's how I check to see if the valves are seated, spray something around the top of the valve, shoot compressed air towards the bottom of the valve, from the inside. The were so tiny, that I don't think that could've caused the extreme loss of compression. So I'm gonna say it was one of the keepers not seated right.
 
A quick test is to remove the carb & exhaust pipe.
In a dark place shine a strong torch down the plug hole and look for light in the inlet & exhaust.
As for your worry about how it gets undr the valve when closed. it dosen't.
It falls off and drops under the valve when it opens then gets squashed into the seat when the valve closes
 
I have been busy prepping some garden beds and repairing some irrigation at our 1/2 garden for the fall and winter garden.

One reason some carbon will get in there is that when you chip away at carbon with a screwdriver and not get it shiny all the way is.................

Combustion in an engine is very powerful, and will cause some flakes and chips to come loose all the time.

Springs on those OHV engines are easily pressed down with some strong man hands. I take the keepers out easy like that myself.

I had to go get me a new BRASS wire wheel today for my drill. I am prepping a 4 HP Briggs for a overhaul. I love doing those 10 and 9 series. Way better than the new E series engines. They are Classics like the old 283 and 327 Chevy engines.

I spend a about 40 bux on new parts and a few hours on one. Get it on a nice frame and get 130 to 150 bux for it......

Hope you get it resolved Mon Ami ~!~!
 
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