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AC712H

no compression on cast briggs question

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Ronald Hribar

pour a little oil down sparkplug hole and check compression

if you have none, valves are problem, if you have compression

rigs may be problem

And did you check to see if block and head surfaces are flat, level

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Willy

If you remove the head check to be sure it isn't warped.

Lay it on a flat surface, I use a piece of 1/4 inch glass

with a piece of sandpaper, lay the head and work it back

and forth a few times then check for spots that didn't

make contact.

If you have a low spot sometimes you can true it up by

rubbing it until smooth.

Wet dry or crocus cloth works better if you need to take

much off.

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Paulcurtis3

My dime is on the valves. I have this engine on my 7116 and it lost all compression instantly. For whatever reason, the valve was not closing all the way. I adjusted the velve stem and it has run perfect for several years.

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timflury

A "wet test" is difficult to do on these flathead engines.

Your spark plug hole is closer to the valves than it is the cylinder.

I would say that the exhaust valve is no good. Either ready for a regrind, or replace it.

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B10Dave

A wider than spec valve lash will not cause a loss of compression. However the condition that caused the wider lash will. Check for a piece of carbon holding that exhaust valve slightly off its seat. If it can't close tightly on the seat the lash will be wider and a no or low compression will be the result.....Dave

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Willy

If you pour a little carb cleaner in the plug hole

and let it set a few min. then turn it over a few

times and see if you have any compression.

carb cleaner should soften any carbon under your valves.

You may want to change your oil if you use much cleaner.

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MrSteele

Be certain to CLEAN all the lapping compound off before assembling the engine. Wipe with a rag, then with a rag soaked in solvent, then with a clean rag with light oil. If the last wiping shows anything off color, wipe again with a clean section until there is nothing visible. Lapping compound is stupid, it will continue to cut while an engine is running if left in place, and it will cut into things you did not intend to compound, such as rings and cylinder walls.

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simple_stan

How did the cylinder cross hatch look? After you lap the valves, are the valve seats even? I had an engine recently with seats that needed to be cut, but the cylinder walls were a bigger issue, with no cross hatch.

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AC712H

Yeah, I looked at the cylinder walls again and it looked like the PO took some sand paper to it or something. Honestly, I should probably move my attention to the cylinder now. I really don't want to put much into this engine as I was hoping to sell it.

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powerking_one

Nick,

You stated there was about 0.030" exhaust valve clearance (I assume this was measured with the piston at TDC on the compression stroke). With these cast iron Briggs, there is no way to reduce the clearance back to the .017-.019" range without replacing the valve. Since Briggs uses Stellite exhaust valves, they should never be ground/re-faced. If you replace the valve go slow on the grinding/filing of the valve stem end to not go over the spec. Once there is some gap, then use the grinding compound to lap it, then go for the final gap.

Tom (PK)

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