Tool

[Patriot Services]

Personal theory on testing at past TDC. If there is any ridge at the cylinder top it can interfere with the ring to cylinder contact. I have an OTC model that's probably 20 years old. This is important info. Guys throw tons of parts at a problem when only to find out its lacking enough compression to even start.

But that's what Motor Honey is made for. Right?
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[andy35321]

So patriot where do you go 1/4 past tdc. Thanks for all the replies.
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[piston slapper]

Originally Posted by Patriot Services

Personal theory on testing at past TDC. If there is any ridge at the cylinder top it can interfere with the ring to cylinder contact. I have an OTC model that's probably 20 years old. This is important info. Guys throw tons of parts at a problem when only to find out its lacking enough compression to even start.

But that's what Motor Honey is made for. Right?
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If there is a ridge at the top of the bore...there is probably another just like it at the bottom of the bore..The ridge is a result of worn rings and/or a "Piston Slappin' "..As the purpose of the leakdown test is to best figure the internal condition of the valves and rings without taking it apart..The more info you can get...The better...

[BigFish]

Originally Posted by Bashby

Why go past tdc? Both valves should be closed, right? I've used a leakdown tester once, but couldnt justify buying one. I take the schraeder valve out of my compression gauge and hook the quick coupler directly to shop air at TDC. I have an adapter since the coupler on the compression tester is different than the one I use for my air tools. I have used a rubber tipped blow gun before when I didnt have the adapter available. I cant figure peercentage of leakdown, but I can tell where the leak is and how bad by how much air is flowing.

Hey, that works! I've used the ol' blowgun trick many times! Either way, ya gotta get past the point where the ACR is holding one of the valves open. Usually you have to bring the piston PAST top dead center by about a quarter inch or so. On OHV units, you can check the rockers for play and go with that.

[BigFish]

Originally Posted by andy35321

You have to go 1/4 past tdc to do leakdown.
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Yes, both valves have to be closed.

[piston slapper]

Just loosen the rocker arms...pop them off the pushrods...and put the air to the cylinders...
Keep it simple...
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[Patriot Services]

Originally Posted by piston slapper

Just loosen the rocker arms...pop them off the pushrods...and put the air to the cylinders...
Keep it simple...
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Your assuming the person loosening the valves has the skills to readjust them. But that will be another thread.
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[andy35321]

I like to keep it simple. Most times when I adjust valves I just open one then adjust the other. And do the same for the other.
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[piston slapper]

Originally Posted by Patriot Services

Your assuming the person loosening the valves has the skills to readjust them. But that will be another thread.
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Another thread indeed....
Exposing the people with leakdown testers that don't know how to adjust valves..
By the time I have to perform a leakdown test....the head is usually coming off anyway...for one reason or another...
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[Bashby]

Originally Posted by BigFish

Hey, that works! I've used the ol' blowgun trick many times! Either way, ya gotta get past the point where the ACR is holding one of the valves open. Usually you have to bring the piston PAST top dead center by about a quarter inch or so. On OHV units, you can check the rockers for play and go with that.

I'm used to working on cars, no compression release. So the acr holds the exhaust valve open at tdc on compression stroke?