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Zero Compression?
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raygreenwood
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PostPosted: Fri Dec 08, 2017 2:08 pm    Post subject: Re: Zero Compression? Reply with quote

Wildthings wrote:
WhirledTraveller wrote:

5) Valve that doesn't close all the way. This could be caused by a really bad valve adjustment (i.e. someone did it very wrong) or by the valve being help up by a piece of carbon or something between the valve and the seat.


I used to see this a lot back 30 years ago. The fuel that was available then would cause lots of carbon to build up in the intake port and when the engine sat for a long while the carbon would come loose and fall down on the intake valve. When an attempt was made to get the engine restarted the carbon would hold several of the valves open causing very limited compression. Even if one or two cylinder would fire, the engine might still not clear itself of carbon all that fast. It might take a couple of minutes to get all the cylinder on line.


Its also really common that an engine that was running rich and parked.....can have the rings siezed in the lands from fuel varnish so they cannot pressurize on the topside and ecpand outward ro seal. Ray
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Wildthings
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PostPosted: Fri Dec 08, 2017 2:21 pm    Post subject: Re: Zero Compression? Reply with quote

Goach2 wrote:
Lots of good suggestions. I'm going to start with a good battery tomorrow. I like the idea of the air pressure in the cylinder to when valves should be closed. perhaps I'm not getting a good seal with the gauge too. I don't know how everyone gets it down under the shielding on 2 & 3, but I did it by feel Smile

Abscate, I'm about 20 mins from the border. You're welcome anytime!


Your gauge may just use standard pipe threads, so the piece that screws into the spark plug hole likely can easily be lengthened with stuff from your local hardware.
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SGKent Premium Member
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PostPosted: Fri Dec 08, 2017 5:32 pm    Post subject: Re: Zero Compression? Reply with quote

is this a screw in compression gauge with an O-ring, or a push and hold style with the rubber nipple?
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Goach2
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PostPosted: Mon Dec 11, 2017 12:57 pm    Post subject: Re: Zero Compression? Reply with quote

It's the screw in. I pulled a valve cover off to see if it looked like a stuck valve, but I can see all the springs moving in/out. I'm probably doing something wrong with the gauge... it's so hard to see inside of all the cooling tin!
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williamM
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PostPosted: Sat Dec 16, 2017 7:34 am    Post subject: Re: Zero Compression? Reply with quote

Very Happy OK- time for an update.
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Goach2
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PostPosted: Sat Dec 16, 2017 8:00 am    Post subject: Re: Zero Compression? Reply with quote

Well, I've chalked the compression tests up to user error for now, and am continuing on with other repairs. One question I have is in regards to what you can see through the plug-hole. I can only see one valve opening in closing near the hole, is there any way to see the other one to confirm? All the springs are compressing and releasing, so I don't think any are stuck...
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airschooled
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PostPosted: Sat Dec 16, 2017 9:54 am    Post subject: Re: Zero Compression? Reply with quote

If the engine is installed, I’ve only ever been able to see T4 intake valves through the plug holes. The plugs are at just a kooky enough angle to hide the exhaust valves.

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Harleyelf
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PostPosted: Sat Dec 16, 2017 10:45 am    Post subject: Re: Zero Compression? Reply with quote

Try the hippie-tech compression check: get four wine corks, put them in the spark plug holes, and have someone crank the engine over while you watch and listen to see which cylinders pop the cork out and which are weak.
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SGKent Premium Member
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PostPosted: Sat Dec 16, 2017 11:08 am    Post subject: Re: Zero Compression? Reply with quote

Quote:
Well, I've chalked the compression tests up to user error for now


did you finally get good compression numbers?
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Last edited by SGKent on Wed Dec 20, 2017 9:16 am; edited 1 time in total
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Goach2
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PostPosted: Sat Dec 16, 2017 3:07 pm    Post subject: Re: Zero Compression? Reply with quote

Not yet, if there wasn't so much engine tin I would be able to see if the rubber washer is seating on it... I'm leaning towards the cork-test. Good thing Christmas is coming with lots of wine!
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williamM
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PostPosted: Wed Dec 20, 2017 9:09 am    Post subject: Re: Zero Compression? Reply with quote

I bought the harbor freight inspection camera and it really takes the guess work out- you should have some pretty serious scuff marks on cylinser walls if you have zero compression -- just a thought.
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