No compression after rebuild

[golden boy]

So,according to Hughes engines, you don't fill lifters with oil or presoak them. and you preload them 15 thou. this did not work for me as it kept the valves open ever so slightly. i will go back to doing it the way i always have. 0 preload. start the engine and let the hydraulics (pressurized oil from oil galley) take up the slack. at least to get it started. the no compression thing floored me. as i have never checked this after assembly and i would imagine that not many people do. this engine was originally built by Blueprint in 2011. they set ring gap at the recommended spec provided by Keith Black at the time 22-26 thou. Every engine builder i have talked to since mine popped the crown of the piston off on 2 cyl has told me that these hyperuetectic units generate so much heat that the ring gap closes and jams in the bore snapping a corner off the top of the piston. more common with iron heads i'm told. This is why all engine builders now gap the top ring @ 32 thou minimum when using these pistons. unfortunately , i paid the price for this new found info. cyl wear was minimal. Used 220 grit stones as opposed to ball hone. Used washers under head bolts as did not have torque plate

 

[Dartfreak75]

So I'm I the only one thinking rings is the problem??? He said it was leaking into the crankcase wouldn't it have to be something with the rings. If it was a valvetrain issue it would be leaking out the valves back into the intake exhaust not the crankcase. It has to be ring related right?

 

[Dartfreak75]

So! as it turns out , a little thought goes a long way. Thanks to those who quickly pointed out it had to be the valve train. it seems that i had all the valves adjusted just enough to keep them barely off their seats. this causes the engine to sound weird (like a broken timing chain)when it turns over . but the interesting thing is that i checked #1 with rockers backed off @ TDC and 0 compression /leakdown was air pouring out of the crank case. So ,for those who are curious. freshly rebuilt engines have no compression until they run enough to seat the rings. who new? got it going last night sounds great!!!

Oh I missed this ignore my last comment lol! Glad you solved it.

 

[67Dart273]

So I'm I the only one thinking rings is the problem??? He said it was leaking into the crankcase wouldn't it have to be something with the rings. If it was a valvetrain issue it would be leaking out the valves back into the intake exhaust not the crankcase. It has to be ring related right?

He could be wrong. Sometimes a leak past a valve "you missed" can SOUND like noise in the crankcase.

 

[Dartfreak75]

He could be wrong. Sometimes a leak past a valve "you missed" can SOUND like noise in the crankcase.

I didnt finish reading the thread he solved it. Oops I guess it was a valve train issue. I was wrong.

 

[MoparLeo]

Rockers too tight, valves not closing. Only reason for "0" compression is a valve train problem.

From post #

 

[nm9stheham]

Every engine builder i have talked to since mine popped the crown of the piston off on 2 cyl has told me that these hyperuetectic units generate so much heat that the ring gap closes and jams in the bore snapping a corner off the top of the piston. more common with iron heads i'm told. This is why all engine builders now gap the top ring @ 32 thou minimum when using these pistons. unfortunately , i paid the price for this new found info. cyl wear was minimal. Used 220 grit stones as opposed to ball hone. Used washers under head bolts as did not have torque plate

As for the heat on the rings, it is due to the KB rings being quite high on the piston, not because they are hypers. Place the top grooves high on any piston, and the top ring will get hotter. Makes sense that iron heads may be more problemematic since their chamber surfaces run hotter than AL heads. I'm gonna guess the honing process left a few tiny high spots that let the pressure out.

Regardless, good to hear it it running.

 

[furrystump]

but the interesting thing is that i checked #1 with rockers backed off @ TDC and 0 compression /leakdown was air pouring out of the crank case. So ,for those who are curious. freshly rebuilt engines have no compression until they run enough to seat the rings. who new? got it going last night sounds great!!! So I trying to learn here. I have never heard of zero compression until the rings seat, but if you had the rockers back off and the piston was a TDC with a screw in compression tester. Then you turn it over there will be no compression because the cylinder is sealed and the first motion is down on the piston creating a vacuum. No valve movement, so up the piston comes returning the cylinder to atmospheric pressure. This is assuming no valve movement.

 

[AJ/FormS]

but the interesting thing is that i checked #1 with rockers backed off @ TDC and 0 compression /leakdown was air pouring out of the crank case. So ,for those who are curious. freshly rebuilt engines have no compression until they run enough to seat the rings. who new? got it going last night sounds great!!! So I trying to learn here. I have never heard of zero compression until the rings seat, but if you had the rockers back off and the piston was a TDC with a screw in compression tester. Then you turn it over there will be no compression because the cylinder is sealed and the first motion is down on the piston creating a vacuum. No valve movement, so up the piston comes returning the cylinder to atmospheric pressure. This is assuming no valve movement.

This is all messed up; if rebuilt engines had no compression ....how would anyone start them to break in the cams? Compression testers work by trapping a sample of the compressed air at the top of the compression stroke. Sometimes it takes a couple to several pulses to stabilize the reading on your gauge because on each compression stroke, a little more air gets pumped into the gauge. On the intake stroke, your gauge has a little valve in it to isolate it from the cylinder so it cannot suck the air out of the gauge. That is how they are built, and that is why I posted back in #8;see below
As for leakage into the CC, the only connection between the chamber and the crankcase is past the rings. If either valve leaks, the path is back to atmosphere.For air to be pouring into the CC; either the rings are leaking, or the fire ring/headgasket is, or there is a serious mechanical issue.
Well I suppose, if you did the LD test on split overlap, and the air was pouring out the valves in both directions, then some of it could enter the PCV system and flood the CC from there,lol.

You didn't specify a Leakdown result, so I might assume you did it at BDC, and that cannot work unless you back off all the rocker gear.
But you give a confident big fat zero for compression, and that also is not possible, unless maybe the intake is completely isolated from the atmosphere, but the comment "fires but won't start, precludes that. At least you didn't say backfires and lit the car on fire,lol. So in that case, at least the intakes are closing.
So far we know the pistons are going up and down, the intakes are closing, and somehow with zero compression, she fires but won't start.
Hmmmmmmmmmmmmmmmmmmmmmmmmmm
My guess is your gauges are lying,charge the battery, pull the plugs, squirt a lil oil in each hole, crank it over to distribute the oil and blow out the excess. Yeah it will make a mess so take steps to minimize that. Then repeat the compression test with a different screw-in tester, or do the LD test with the pistons at TDC-compression,each one in it's proper sequence. Or if you cannot get the pistons to hold still, sometimes it's just easier to do the LD test with the pistons at the bottom and the rocker gear backed off. Unfortunately, this does not tell us anything about the valve seal AFTER the rocker gear is re-installed; it only tells us if the chamber can or cannot be sealed, not is sealed.
Then post up the results.

BTW; some LD into the cc would be normal, say up to 2 or 3%, I mean the air will find the ring-gaps pretty quick

 

[Jadaharabi]

Ok correct me if I'm wrong. (something sometimes some of you think I am when I'm not, lol)
You are at top dead center and you had no rocker arms to open the valves on that cylinder. So when you crank the engine over and the Piston starts downward to bottom dead center you are actually pulling a vacuum.
Then the Piston starts back up in the cylinder to Top dead center and you show no compression. You would not show compression because you did not have the valve train hooked up to allow air into the cylinder to be compressed.

 

[AJ/FormS]

Ok correct me if I'm wrong. (something sometimes some of you think I am when I'm not, lol)
You are at top dead center and you had no rocker arms to open the valves on that cylinder. So when you crank the engine over and the Piston starts downward to bottom dead center you are actually pulling a vacuum.
Then the Piston starts back up in the cylinder to Top dead center and you show no compression. You would not show compression because you did not have the valve train hooked up to allow air into the cylinder to be compressed.

There is nothing wrong with your thinking , except
A) nobody does a compression test with the valves not operating. And you figured out why.
The trouble is you reported a big fat zero compression ,
and I said that is not possible.
And we all got messed up because you didn't know how to do a Compression Test.
Oh crap, wrong poster, sorry Jad

 

[nm9stheham]

Ok correct me if I'm wrong. (something sometimes some of you think I am when I'm not, lol)
You are at top dead center and you had no rocker arms to open the valves on that cylinder. So when you crank the engine over and the Piston starts downward to bottom dead center you are actually pulling a vacuum.
Then the Piston starts back up in the cylinder to Top dead center and you show no compression. You would not show compression because you did not have the valve train hooked up to allow air into the cylinder to be compressed.

Which is what furrystump said, I think.... But if you started anywhere else besides TDC, then you WOULD get + pressure during part of the cycle around TDC, and the 1 way valve in the compression gauge would catch that. In reality, if the piston starting at TDC, some small amount of vacuum would leak off past the rings on the each stroke, and the gauge ought show something other than 0.

The one way valve in the gauge may need some minimum pressure to open; that part I don't know.

 

[nm9stheham]

This is all messed up; if rebuilt engines had no compression ....how would anyone start them to break in the cams?

Maybe we could use cartridge fired starting like on the old airplane engines... POW! LOL

 

[AJ/FormS]

Which is what furrystump said, I think.... But if you started anywhere else besides TDC, then you WOULD get + pressure during part of the cycle around TDC, and the 1 way valve in the compression gauge would catch that. In reality, if the piston starting at TDC, some small amount of vacuum would leak off past the rings on the each stroke, and the gauge ought show something other than 0.

The one way valve in the gauge may need some minimum pressure to open; that part I don't know.

They are special, a bicycle valve doesn't read right. I buy them off the tooltruck now,after figuring that out. Mine has read as low as 20psi during diagnostics.

 

['63GT]

220 stones !!??!? plain cast rings ? Not moly's I hope...

 

[RustyRatRod]

So ,for those who are curious. freshly rebuilt engines have no compression until they run enough to seat the rings.

There's so much wrong with this statement, it makes my head hurt. New rings on fresh cylinders are certainly not yet seated, buy they will damn well have plenty of compression.

 

[1994redram]

Isn't compression one of the main ingredients for a combustion engine? It has to have some compression for it to ever start and run.

 

[AJ/FormS]

The last time I went thru my engine, with fresh file-fits and a plasma-Moly second ring, the leakdown was so low with an 80psi test pressure that the gauge barely moved. It was under 2%. And that was on the engine stand.

 

[IQ52]

What the heck! This thread is weird.

 

[AJ/FormS]

a spider-web