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Old 12-27-2012, 12:09 AM   #1
65air_coupe
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Default High compression at cranking speed

In my pursuit of finding why one or more cylinders are missing, I ran a compression check and found pressures from 215 to 235! That seems excessive and was wondering if my lifter problems have anything to do with it?

I'm using a set of used V6 lifters in a SBC 406 block reworked to use OEM roller cam components. Compression ratio calculated to be 10.25:1. Trick Flow heads, mild cam (can't remember the numbers right now) installed @ 0 degrees.

I found at least one lifter that was collapsed and my cold adjustment of 1/2 turn was actually lifting the valve off the seat. After I backed off the adjustment, that cylinder's reading went from 0 to 240 psi.
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Old 12-27-2012, 01:53 AM   #2
427Hotrod
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Ought to be a responsive little dude! That must be an awful small cam in there. Any issues with detonation/pinging?

What are the lifter issues? Tried setting them while running?

JIM
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Old 12-27-2012, 03:28 AM   #3
TCracingCA
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Default If you think your lifters are a problem, then I would run some Rislone thru

the system and then change the oil. To avoid taking off the manifold to pull them for cleaning. Thus try to clean the gunk out and then work your valve adjustments. You didn't ID your lifters (on a roller cam?), so I assume that they are hydraulics and I assume they are proper for your set up or you won't have had them installed. The other thing you can do, but it is messy would be to pull a valve cover off and cycle the engine to see if the pushrods are pumping out to the top from a working lifter in conjunction to the function of the pushrod. It sounds like to me your valve adjustments, more than a lifter problem.

Last edited by TCracingCA; 12-27-2012 at 04:28 AM.
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Old 12-27-2012, 03:44 AM   #4
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X2
set them running. should make LOTS more power at 240 instead of 0
don't use 87
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Old 12-27-2012, 09:05 AM   #5
65air_coupe
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Thanks guys, after thinking about it a bit I'm going to find some old steel valve covers and cut them out so I can adjust hot and running.

I inspected the lifters prior to using them but did not dis-assemble them. They were stored more or less dry for several years before being used. I've got a couple that feel soft as well as the one that doesn't seem to pump up.

As for the cam specs, it's a Comp Cam 12-432-8, Xtreme Energy model. Specs in brief are: Duration @ 0.050" 230/236, lift 0.340/0.347, separation 110.
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Old 12-27-2012, 09:38 AM   #6
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cam degreed or just dot to dot?
240 sounds high for that cam w/10.25cr
maybe advanced 1 tooth
? or could CR be higher?
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Old 12-27-2012, 09:44 AM   #7
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Quote:
Originally Posted by 65air_coupe View Post
Thanks guys, after thinking about it a bit I'm going to find some old steel valve covers and cut them out so I can adjust hot and running.
Check out Ebay seller "Autonets". Chrome SBC covers for $26 and no shipping. Hard to beat that deal.

I just changed lifters and went with GM/AC 12371044s, based on many recommendations.
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Old 12-27-2012, 09:55 AM   #8
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No need for an extra set of valve covers. I use tin foil. Just cover the valve train stuffing the foil inside the lip of the heads, poke holes where the adjuster nuts are and fire it up.
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Old 12-27-2012, 09:59 AM   #9
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cam degreed or just dot to dot?
240 sounds high for that cam w/10.25cr
maybe advanced 1 tooth
? or could CR be higher?
Not degreed, just dot to dot. And yes, 240 seems very high but I'm also very confident I'm not off a tooth.

CR could be higher but not sure how. Although it's been awhile since I did the calculations, I am pretty confident of their accuracy. It's the kind of stuff I did in my 30 year career as an engineer but of course, I'm still human and do make mistakes.

I think I'll know more after doing a running hot adjustment.
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Old 12-27-2012, 10:02 AM   #10
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Quote:
Originally Posted by TCracingCA View Post
the system and then change the oil. To avoid taking off the manifold to pull them for cleaning. Thus try to clean the gunk out and then work your valve adjustments. You didn't ID your lifters (on a roller cam?), so I assume that they are hydraulics and I assume they are proper for your set up or you won't have had them installed. The other thing you can do, but it is messy would be to pull a valve cover off and cycle the engine to see if the pushrods are pumping out to the top from a working lifter in conjunction to the function of the pushrod. It sounds like to me your valve adjustments, more than a lifter problem.
When I primed the motor, I got oil out of just about all but not those in question.
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Old 12-27-2012, 10:04 AM   #11
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No need for an extra set of valve covers. I use tin foil. Just cover the valve train stuffing the foil inside the lip of the heads, poke holes where the adjuster nuts are and fire it up.
Yeah, pretty sure that's not going to work...the oil runs down and over the valve cover lip and onto the headers. Did that with just priming it with a drill and modded dizzy.
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Old 12-27-2012, 02:57 PM   #12
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What kind of rings are you using?
What temp was the engine at when you did the test?
Did you add oil to the bores before testing, or not?
I assume that a strong battery was used, carb chocked wide open, and 3-4 cranks to compression cycle.

With calculated 10.25:1 SCR, and assuming your calculations are accurate, then that yields a 8.055:1 DCR with your cam (IVC 67 ABDC @ .006" lift [ADVERTISED DURATION]) and assuming that you used 6.0" con rods.

That is a very conservative DCR, and you could have safely gone to 8.5:1 with a sloppily designed engine and 8.75:1 with a well designed engine.

The cranking compression numbers are very high considering all of this, unless you built it with gapless top rings.

Last edited by 65tripleblack; 12-27-2012 at 03:17 PM.
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Old 12-27-2012, 04:24 PM   #13
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keyways are notorious for being in the wrong spot.
i would not have any confidence in dot to dot.
that said, it could be fine,

except without oil in the lifters, it is like having a really small cam.
so start it up, adjust valves, and re-check
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Old 12-27-2012, 07:29 PM   #14
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I checked my compressions about 6 weeks ago. 327/350hp, stock CE motor. I got over 200 psi on all cylinders. Seems like manual called for 160psi? I was surprised that it was so high, but pleased that they were all basically the same (+/- 10 psi). I wrote it up to my starter's unusually high cranking speed, and moved on to other causes for my vibration problem.

Harry
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Old 12-27-2012, 08:33 PM   #15
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If it were me (and it isn't) I would forget about high compression causing a miss. Especially since the compression is higher than normal in all cylinders. I'd prefer to set that part of the equation aside and work on something else. Sometime later, I might get around to checking the calibration on my compression gauge.

So far, I have yet to see any sypmtoms of why the OP thinks he has a misfiring engine?
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Old 12-27-2012, 09:20 PM   #16
65air_coupe
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Quote:
Originally Posted by 65tripleblack View Post
What kind of rings are you using?
What temp was the engine at when you did the test?
Did you add oil to the bores before testing, or not?
I assume that a strong battery was used, carb chocked wide open, and 3-4 cranks to compression cycle.

With calculated 10.25:1 SCR, and assuming your calculations are accurate, then that yields a 8.055:1 DCR with your cam (IVC 67 ABDC @ .006" lift [ADVERTISED DURATION]) and assuming that you used 6.0" con rods.

That is a very conservative DCR, and you could have safely gone to 8.5:1 with a sloppily designed engine and 8.75:1 with a well designed engine.

The cranking compression numbers are very high considering all of this, unless you built it with gapless top rings.
Conventional rings, not gapless. Don't recall the brand but top shelf I'm sure.

Engine cold, no oil added, carb in idle position. Probably 4 revs on average, stopped when gauge stopped moving.

CR was calculated using actual bore and stroke along with manufacturer specs for pistons and heads. Included the volume between piston top and top ring, so yes, I'd consider it fairly accurate.

Eons ago, I had a Ford 406 with 12.5:1 CR and I though its cranking numbers were high at 195. I think the 240 number is because of a lifter problem but the 215-225 numbers are still a concern.
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Old 12-27-2012, 09:29 PM   #17
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Quote:
Originally Posted by MikeM View Post
If it were me (and it isn't) I would forget about high compression causing a miss. Especially since the compression is higher than normal in all cylinders. I'd prefer to set that part of the equation aside and work on something else. Sometime later, I might get around to checking the calibration on my compression gauge.

So far, I have yet to see any sypmtoms of why the OP thinks he has a misfiring engine?
I never said or implied the miss had anything to do with compression, other than the fact that the cylinder that was missing initially had zero compression. This thread is about the unusually high numbers and if there's any correlation to my lifter issues.

And the gauge was one of my suspicions. It's brand new so I have no history with it and intend to run a check on it tomorrow.

Last edited by 65air_coupe; 12-27-2012 at 10:10 PM.
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Old 12-28-2012, 04:35 AM   #18
TCracingCA
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Default I am still concerned with the oil not pumping up on the problem cylinder/cylinders?

Quote:
Originally Posted by 65air_coupe View Post
I never said or implied the miss had anything to do with compression, other than the fact that the cylinder that was missing initially had zero compression. This thread is about the unusually high numbers and if there's any correlation to my lifter issues.

And the gauge was one of my suspicions. It's brand new so I have no history with it and intend to run a check on it tomorrow.
Trust me, don't be running things dry. I don't know if you tried the Rislone yet and sometimes things can be so gummed up that you have to pull it apart. I would fix that first and then move to any concerns about compression. If the car is not misfiring, or doing anything weird when running (except for the oiling situation), then the compression is good enough for now. Basically I have seen valve adjustments set out of sequence or wrong, that caused erratic compression readings. When static setting the valve clearance, you want to make sure you are cycled to the right set of valves. Thus both pushrods should be loose for each cylinder. If you have the adjustment too tight, then you could be causing the lifter to not work. Thus in the cycle of doing the adjustment, you won't get the feeler gauge in that one. Thus run thru the valve adjustment again. I hope you haven't wiped out a cam lobe or something, but then you said that you got the compression to come up.

Also take a rubber hose length, put it to your ear and listen to each cylinder valve train for anything sounding different than the rest. Or one of those doctor heart things. The hose works really good. If that pushrod is rattling around or something is adjusted way off, then you will hear it through the hose.

Basically I am trying to do as many of the simple possible fixes, before giving you the hard recommendations.

Last edited by TCracingCA; 12-28-2012 at 04:53 AM.
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Old 12-28-2012, 04:47 AM   #19
TCracingCA
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Default Also see if the lifters are rolling or contacting the valve in the proper geometry!

On a built engine, you could have thin head gaskets, thick head gaskets, longer pushrods, too short pushrods, a milled head, etc..
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Old 12-28-2012, 06:33 AM   #20
65air_coupe
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Nothing is running dry. And when I dis-assembled a couple of the lifters prior to building the engine, there was only clean oil in them so it's doubtful any are gummed up. I've adjusted the valves 4 times, using 3 different methods and am confident there's no issue there. And I'm the one that built the engine so I know all the particulars regarding heads, gaskets, pushrods etc. I just think I have one failed lifter and no amount of playing with it will get around having to pull the manifold and have a look at it. I guess that's the risk I took when I put used lifters in it.

More to the point of this thread, why might the compression be so high and if nothing's amiss, will it cause problems?

As mentioned earlier, valve timing is a possibility and that could be related to lifters, but I really only have one suspect cylinder and while it does show higher compression than the others, the others are still quite high.

Occum's razor comes to mind...check the gage! I'll let you know what I find. And I'll run through a hot adjustment too.
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