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Subject: "No compression on new engine????????" Previous topic | Next topic
kballard81Jun-28-09 06:27 AM
Member since Jul 07th 2008
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#126304, "No compression on new engine????????"


          

I build like my 10th engine and this one is giving me like 40psi in all cylinders........bored .020 over new everything......not sure why its doing this.......i tried another head and that didnt change anything.......any suggestions on where to look?

  
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Replies to this topic
RE: No compression on new engine????????, Mike431635, Jun-28-09 07:48 AM, #1
RE: No compression on new engine????????, kballard81, Jun-28-09 07:51 AM, #2
      RE: No compression on new engine????????, ModeratorCorbin, Jun-28-09 04:19 PM, #3
           RE: No compression on new engine????????, Moderatorbullettdsm, Jun-28-09 04:57 PM, #4
                RE: No compression on new engine????????, 420agreenvilleSC, Jun-28-09 07:54 PM, #5
                     RE: No compression on new engine????????, kballard81, Jun-30-09 10:03 AM, #6
                          RE: No compression on new engine????????, AdministratorCODE4, Jul-02-09 07:12 AM, #7
RE: No compression on new engine????????, kballard81, Jul-02-09 05:22 AM, #8
RE: No compression on new engine????????, Moderatorbullettdsm, Jul-02-09 11:19 AM, #9
      RE: No compression on new engine????????, kballard81, Jul-02-09 01:11 PM, #10
           RE: No compression on new engine????????, Moderatorbullettdsm, Jul-02-09 02:07 PM, #11
                RE: No compression on new engine????????, kballard81, Jul-02-09 06:35 PM, #12
                     RE: No compression on new engine????????, AdministratorCODE4, Jul-02-09 08:21 PM, #13
                          RE: No compression on new engine????????, kballard81, Jul-02-09 08:32 PM, #14
                               RE: No compression on new engine????????, AdministratorCODE4, Jul-02-09 09:39 PM, #15
                                    RE: No compression on new engine????????, 420agreenvilleSC, Jul-02-09 10:05 PM, #16

Mike431635Jun-28-09 07:48 AM
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#126305, "RE: No compression on new engine????????"
In response to Reply # 0

          

Assuming both heads aren't losing compression through the valves, I'd have to say you may either have the wrong size pistons or the rings are installed incorrectly.

  
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kballard81Jun-28-09 07:51 AM
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#126306, "RE: No compression on new engine????????"
In response to Reply # 1

          

thats what i was thinking......maybe the block wasnt cut properly......whats the correct way to install rings? i put the first ring at 12, the 2nd ring at 6, and the oil rings at 3 and 9.........??????????????

  
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ModeratorCorbinJun-28-09 04:19 PM
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#126310, "RE: No compression on new engine????????"
In response to Reply # 2

          

You did check the ring gap on all rings and all cylinders, correct? If you know what size rings you have (std, 0.02"+, 0.04"+) and checked the gap of each one in the cylinder bore, then you know the machine shop bored the block about the right size. A supplier once sent me 0.04"+ rings with 0.02"+ pistons. I was suspicious when the ends of the ring overlapped when checking the gap. If you tried to fit std rings in a block bored for 0.02"+ pistons, the gap would be way big. If your compression tester is two pieces, you may be able to connect an air compressor to pressurize the cylinder (my tester used an air chuck fitting to connect the gauge to the hose). Pressurize the cylinder with 90 psi or whatever you can get. Rotate the crank or cam until you hit "top dead center". If you hear air rushing out the throttle body, your intake valves are leaking. If you hear air rushing out the muffler, your exhaust valves are leaking. If you hear air rushing out the dipstick tube, your rings are leaking. You will probably get some noise from all three sources, but the key is to check out the one that sounds worse than the others.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki

  
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ModeratorbullettdsmJun-28-09 04:57 PM
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#126311, "RE: No compression on new engine????????"
In response to Reply # 3
 Jun-28-09 04:59 PM by bullettdsm

          

Originally posted by Corbin
You did check the ring gap on all rings and all cylinders, correct?


Not such a silly question. You'd be amazed at the amount of people that think the rings are pre-gapped (a lot like the spark plug people). It is an automatic red flag if the ring gap seems goofy.

If you are running right around 40psi consistent, then I wouldn't lean toward cam timing. If your cam timing is off a tooth you generally get a fluctuation between the comp in the cylinders (as well as the fact that you have done a few of these before).

The rest of Corbin's description is precisely what my next step would be (also, keep in mind that there is a possiblity that your comp tester is nutso).

Originally posted by Corbin
A supplier once sent me 0.04"+ rings with 0.02"+ pistons. I was suspicious when the ends of the ring overlapped when checking the gap.

You think? lulz...



Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

wiki home page:http://www.2gnt.com/index.php?d=bullettdsm

  
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420agreenvilleSCJun-28-09 07:54 PM
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#126312, "RE: No compression on new engine????????"
In response to Reply # 4



          

i forgot to gap my rings on my first engine. result? 500 miles of burning oil (smoke), and over 200 compression across the board. eventually, it sealed nicely. boosted on it just fine too for well over 2 yrs. emoji

___________________________________________



http://www.2gnt.com/quote_db.php?id=278

Outside of Corona: "That sucks, peace out..." (jamie walks away)... "Sweeet, what we doin?" -Zac
Tim's garage (prior to motor install): "Im gonna smoke real quick, that way if you fuck up I am already nicotined up" -Tim

  
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kballard81Jun-30-09 10:03 AM
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#126325, "RE: No compression on new engine????????"
In response to Reply # 5

          

can someone explain to me how to correctly check the gap on the rings?

  
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AdministratorCODE4Jul-02-09 07:12 AM
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#126347, "RE: No compression on new engine????????"
In response to Reply # 6



          

Originally posted by kballard81
can someone explain to me how to correctly check the gap on the rings?


http://www.circletrack.com/howto/1818/index.html

---

2012 2500HD LML

  
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kballard81Jul-02-09 05:22 AM
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#126346, "RE: No compression on new engine????????"
In response to Reply # 0

          

ok so i checked the ring gap and its all good......so whats the deal with this thing......pistons are new, rings are new and gapped good, blocked was bored, head was resurfaced, new valve seals, new head gasket and bolts......where else can i look?

  
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ModeratorbullettdsmJul-02-09 11:19 AM
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#126360, "RE: No compression on new engine????????"
In response to Reply # 8

          

Originally posted by kballard81
ok so i checked the ring gap and its all good......so whats the deal with this thing......pistons are new, rings are new and gapped good, blocked was bored, head was resurfaced, new valve seals, new head gasket and bolts......where else can i look?

Originally posted by Corbin
If your compression tester is two pieces, you may be able to connect an air compressor to pressurize the cylinder (my tester used an air chuck fitting to connect the gauge to the hose). Pressurize the cylinder with 90 psi or whatever you can get. Rotate the crank or cam until you hit "top dead center". If you hear air rushing out the throttle body, your intake valves are leaking. If you hear air rushing out the muffler, your exhaust valves are leaking. If you hear air rushing out the dipstick tube, your rings are leaking. You will probably get some noise from all three sources, but the key is to check out the one that sounds worse than the others.


What happened when you did this? If you only have 40psi on crank, the hissing will be obvious.

Also, not to question your ability, but what were your numbers on the rings?



Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

wiki home page:http://www.2gnt.com/index.php?d=bullettdsm

  
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kballard81Jul-02-09 01:11 PM
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#126363, "RE: No compression on new engine????????"
In response to Reply # 9

          

what numbers on the rings are you referring to? i put the engine together like i have the past dozen ive done......some reason this one gave me trouble.....it builds compression, just not alot at all....only 40psi cold.

  
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ModeratorbullettdsmJul-02-09 02:07 PM
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#126364, "RE: No compression on new engine????????"
In response to Reply # 10

          

Originally posted by kballard81
what numbers on the rings are you referring to?


How did you do this then?

Originally posted by kballard81
ok so i checked the ring gap and its all good......


Please make note of these points;

Originally posted by Corbin
You did check the ring gap on all rings and all cylinders, correct?


Originally posted by bullettdsm
Not such a silly question. You'd be amazed at the amount of people that think the rings are pre-gapped


Guys there are a couple o' few reasons to do ring gaps. Not the least of which is that this is THE most important area of your engine. This is where it all happens. Yes, you could have gotten away with putting in rings without gapping them, but that doesn't make it right. Without setting proper ring gap, you are setting your engine up for premature failure (or quick catastrophic failure). There are a multitude of thoughts and reasons for doing ring gaps (having to do with expansion and contraction of metals and gases, variances and tolerances of product, machine shop inconsistancies etc.) and I'm just not going to go into the explanations.

Now on the other hand, I would never do a cold crank compression test on a rebuilt engine that hasn't been fired up yet. There is no seating on the rings per cylinder, you should have assembly lube (at least I do) within the cylinder bore that would queer the numbers etc.







Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

wiki home page:http://www.2gnt.com/index.php?d=bullettdsm

  
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kballard81Jul-02-09 06:35 PM
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#126366, "RE: No compression on new engine????????"
In response to Reply # 11

          

does anyone know the ring gap for the top 2 rings...they are stock and i checked the top ring in cylinder 4 and it was over .025 not sure if thats way to big or not.....if it is, how do i shrink the gap or did they bore the block to big? had it bored 20 over stock

  
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AdministratorCODE4Jul-02-09 08:21 PM
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#126367, "RE: No compression on new engine????????"
In response to Reply # 12



          

You do not shrink rings. If the gap is beyond spec you buy new ones.

---

2012 2500HD LML

  
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kballard81Jul-02-09 08:32 PM
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#126368, "RE: No compression on new engine????????"
In response to Reply # 13

          

ahhhhhh that sucks.....how about jb weld? lol......do you know the ring gap specs?

  
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AdministratorCODE4Jul-02-09 09:39 PM
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#126369, "RE: No compression on new engine????????"
In response to Reply # 14



          

Ring gap specs are dependent on piston and ring brand/manufacturer. Also the builder's preferences - some, depending on application will gap further than others.

JB weld? How about you play Russian Roulette with a semi auto pistol?

---

2012 2500HD LML

  
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420agreenvilleSCJul-02-09 10:05 PM
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#126370, "RE: No compression on new engine????????"
In response to Reply # 15



          

Originally posted by CODE4
Ring gap specs are dependent on piston and ring brand/manufacturer. Also the builder's preferences - some, depending on application will gap further than others. JB weld? How about you play Russian Roulette with a semi auto pistol?


lolllllllllllll

___________________________________________



http://www.2gnt.com/quote_db.php?id=278

Outside of Corona: "That sucks, peace out..." (jamie walks away)... "Sweeet, what we doin?" -Zac
Tim's garage (prior to motor install): "Im gonna smoke real quick, that way if you fuck up I am already nicotined up" -Tim

  
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