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Atikin9000

78 620, L20B foreign matter in combustion chamber.

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lRjpRdk.jpg

 

 

Valve seat?

 

Get a piece of fence wire and bend a hook in the end and try to fish it out. This will tell you more.

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lRjpRdk.jpg

 

 

Valve seat?

 

Get a piece of fence wire and bend a hook in the end and try to fish it out. This will tell you more.

 

 

 

Thanks man, it's looking like a valve seat, gonna attempt to fish it tomorrow, just wondering what my next approach should be lol.

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If it is a valve seat one of the valves will likely be a lot higher than the others, and the rocker arm will be tight against it.

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Leak down test. If it is a valve seat you will have a leak on your tester.

 

It will either be blowing air out of the exhaust or out of your carb.

 

 

 

I know this does nothing to fix the concern, but diagnosis is fun.

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Do not run the engine. It may already have already pounded the seat area to shit and the head in not repairable.

 

Seats fall out for at least these two reasons...

 

The engine was severely overheated.  The valve seat and the head seat area are an interference fit. The heads are baked to 350F in and oven to expand the seat hole. The valve seats are frozen to shrink them and then assembled. When at room temperature they cannot be removed.

 

The were replaced previously by an incompetent shop that didn't know how to properly do this replacement. When you remove the head, look in the combustion chamber around the valve seats. If they were staked in place and punch marks are showing this is why.

 

ValveSeatsStaked.jpg

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Do not run the engine. It may already have already pounded the seat area to shit and the head in not repairable.

 

Seats fall out for at least these two reasons...

 

The engine was severely overheated. The valve seat and the head seat area are an interference fit. The heads are baked to 350F in and oven to expand the seat hole. The valve seats are frozen to shrink them and then assembled. When at room temperature they cannot be removed.

 

The were replaced previously by an incompetent shop that didn't know how to properly do this replacement. When you remove the head, look in the combustion chamber around the valve seats. If they were staked in place and punch marks are showing this is why.

 

ValveSeatsStaked.jpg

PO said he checked the plugs and that they were fouled told me the carb just needed messing with,and he was running it when I showed up to buy it, I took his word(my bad), then spent all day yesterday turning it over and getting it to fire a couple times cause I was messing with the carb. Then comes today I took the plugs out and found that. Engine spins free and the piece of what ever it is is loose in there.

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What I meant is I haven't ran it since discovering this, but idk if I have much hope now. Regardless going to have to take the head off. I'll try and fish it out tomorrow too.

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Have you done this before? If not, you may want to watch hainz video on YouTube. He goes by banzai510 here. Good luck.

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I took the plugs out and found that. Engine spins free and the piece of what ever it is is loose in there.

 

It's unlikely that it is loose but would be loose during the time when the valve would be open. If it is loose it may be broken into pieces or something else. Try to fish it out.

 

As wano? said take the valve cover off. This cylinder likely has a depressed valve spring because the valve seat is jammed under the valve.

 

If this is not the case, it should be investigated further before jumping in and taking the head off.

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Have you done this before? If not, you may want to watch hainz video on YouTube. He goes by banzai510 here. Good luck.

So type L series head replacement instead.

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Have you done this before? If not, you may want to watch hainz video on YouTube. He goes by banzai510 here. Good luck.

 

Yea I watched the dude with the headband lol.

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It's unlikely that it is loose but would be loose if the valve were open. If it is loose it may be broken into pieces. Try to fish it out.

 

I will attempt, I'll take some more pics too if you're curious to see. Hopefully I'll have some success. I'm working outside right now with Oregon weather.

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Yea I watched the dude with the headband lol.

...may seem funny but he has and specially his video helped a lot of people put their L series back together.
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A valve seat won't make it past the installed valve, until the head breaks off of the stem.  That looks more like someone let debris get down the carb throat.  Either way, the piston and cylinder wall will likely be pretty beat up - not to mention the combustion chamber, valves, seats, etc...  Focus on pulling the head to make repairs.  

 

If you want to see what's wrong, lower the piston in the cylinder around an inch and take a look.  

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It looks more like a piece of piston ring rather than valve seat, radius isn't tight enough.  First step is getting it out, either a small magnet telescope tool or maybe you can grab it with a hemostat.  Once it's out, it can hopefully be identified.  If it's not a piece of the engine broken off, but something ingested through the carb, maybe source a borescope to check for FOD, you might luck out and not have to tear it down.

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510-head11.jpg

 

Agreed the seat won't come off the valve unless something breaks but you might still easily see it through the plug hole. If it came through the carb and got past an intake valve it can only be so big to fit.

 

If a seat, (I don't think ring fragment because a lot of piston would have come with it, someone wound have noticed the smoke and blow by)  take the valve cover off. That cylinder will have a compressed valve spring because it can't close. The rocker arm and lash pad may also have flown off.

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Pop the head off and lets see who's right.

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I was thinking it could be a valve seat, but it seems like the seat would have to be broken and caught in the valve for it to get that far over to show in the spark plug hole as the valve shaft is fairly large down low, it would then hold the valve down and make the rocker arm very loose, if the seat had broken and not got caught in a valve then the valve would be very high compared to the others like what happens when they sink into the head and you lose all adjustment.

If it was a ring piece I would have thought it would have less curve to it, same if it were a piece of the top edge of the piston.

Is the piston holding that piece up there, or is it caught in the valve?

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Pop the head off and lets see who's right.

 This !

No matter what, it has come off anyway....

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I only had a minute to look over it this morning and upon further investigation, it looks like a valve seat and it's in one piece, turned it over by hand so the piston would drop and the ring stayed in one place looks like it's hanging off the valve, valve spring worked though, the supposed ring seems jammed hard now, tried to fish it out but it won't move and seems very whole to come out of the sprarkplug hole. Piston had some scaring.

 

When I have some time next I'll pull the head.

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Pull the head it could have scored the cylinder wall and or beat up the head and the piston.

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"Will have" scored the piston, likely won't have touched the cylinder walls, definitely bent the valve, definitely beat up the head.  The piston may be fine, but the head is going to get expensive to repair.  Likely welding to get a seat to take after it released then pounded against the head every time the valve opened and closed.  You'll need someone who can weld aluminum AND has a Serdi head bench to cut the head for a new seat.  Valves are cheap.  

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