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compression failure

6K views 53 replies 14 participants last post by  spencely 
#1 ·
oh boy...I think I have painted myself into a corner again...have an older rebuilt engine that was never run and after installing it I find no "0" compression at all in cyl#2 of this 350sbc. All Others tested to 135psi except one leaky intake at 90 and this seemingly dead cylinder #2. I static lashed the valves twice and tried oil in the cylinder to find no change. So off comes the head only to find nothing apparently wrong there...head gasket good and took the head to a machine shop for test which it passed other than the leaky valve on #6... Valve action has been obsereved for both intake an exhaust...not measured but visually opening and closing as they should. Tried filling pistons with oil with head off and #2 cyl will leak down over a day or two while the adjacent cyl#4 has no perceptible loss. Pulled the engine and removed the piston...rings all look fine. Now what? Could these rings be bad...they were not stuck in any way to the ring lands but I did give it a treatment of atf too to try to loosen if it was stuck a week prior to removal.
 
#2 ·
Even engines with rings that are very worn or broken will usually have some compression. Zero compression should not be hard to find. My first guess is valve adjustment. I would start by backing off the rockers in that cylinder at tdc so they both have a little play in them. This will assure they are not to tight.
A long shot would be the intake runner is plugged and no fuel air mix is getting in to compress.
 
#5 ·
hey guys..thanks for the response... And I agree that it should be relatively easy to pinpoint the problem here but i really did try everything...there are no obstructions...i checked and rechecked the lash and checked that cylinder at least 5 times at seprate occasions. with and without oil...once i filled the cylinder good it wold hold pressure till it started blowing by the ring gaps or "stuck rings" as i was led to beleive. I also Found that difference in the fluid leakdown so something is up with those rings even though I can't believe that would result in a zero compression reading. The engine is new old rebuild....probably ten years sitting..i had it two years waiting till the engine finally croaked in my el camino. I am no ring expert and maybe my leakdown test dosent' prove anything that isnt' normal but it was the only thing i could come up with. I had a competent machine shop check the head over and it is ok. I would assume they would have found a broken spring if it were present... maybe not. I will look more closely. I did do my lashing at tdc but had fully adjusted them to half travel as instructed in my chiltons. I fuly loosened each rocker on the second round relash too. All were adjusted to same condition so in my mind they'd all leak if any was going to. Got any feedback on the leakdown and how serious that might affect? It's looking more like I will need to add a new set of rings. I guess there's a first time for everything. Very slowly one at a time... slow learning curve.... beware craigs list.
 
#6 ·
Bring the suspect cylinder up to tdc both valves closed, put some compressed air into the plug hole and see where is is coming out.
I dont understand "half travel. Could you elaborate on this.
normal adjustment is to make sure the cylinder is on tdc, back off lock nut. Start to tighten and stop when there is no more up and down play in the push rod. If the engine was not run after the rebuild the rings are probably not seated. With no compression at all I would think if you poured anything into the cylinder it would go right into teh pan in a few seconds. If the engine is still apart you could rtv a piece of plexiglass with a whole in it over that one cylinder to seal it and put some compresses air into it and see if it just blows right by. The only other thing I can think of, if it is leaking by the pistons that bad is that you have one piston that is the wrong size. A standard piston in a .060 over hole will leak pretty good.
 
#8 ·
. There are two top dead centers for every cylinder... the crank rotates two times for each one time the cam rotates... you prolly adjusted some of the valves on the wrong top dead center for #2 cylinder because the cam was holding the lifters up... rotate crank one turn and try again... don't try to feel for drag on the pushrod while turning it, move pushrod up and down and tighten nut until the click is no longer felt, then give a half turn more... lock the nut down unless it is self-locking... when done, rotate the crankshaft while watching the rocker arms and make sure all the rocker arms rock back and forth the same amount as engine turns two whole turns of the crankshaft...

. The pistons are in with rings... the machinist said the heads are good... that leaves the problem being the nut behind the steering wheel... LOL! ... (I assume you bolted all the rod caps on the rods and all 8 pistons are going up and down)...

. BTW, the rings should be installed with the ring end gaps of top and 2nd ring on opposite side of each piston...

. Compression test is done spinning the engine with the starter, all sparkplugs out, carb. WOT or removed... spin over about 5 times for each cylinder...

. Good luck...
 
#9 ·
Sounds like a collapsed ring, have you tried fitting the rings in the cylinder without the pistons?

Not that it matters, its out now...repair that cylinder with a ball hone and new rings...might as well do them all since your in there.

If everything is fairly new from a recent rebuild a quick ball hone and re-ring won't hurt anything from a clearances point of view.

Make sure you check the ring clearances in the ring lands and the pistons for proper fit in the cylinder, sounds like the previous rebuilder made a mistake or the engine was abused.

Consider this a fresh rebuild instead of trying to diagnose a problem which may end up being worse later once its reassembled.

Don't take anything for granted, check everything.
 
#10 ·
I have not removed the rings from the piston. they expand considerably from the installed position...excepting the oil control ring which seems to hold close to the stock bore size...I dont' know if that is correct but it is pretty obvious that that ring would have nothing to do with compression. I ran that engine for 3 -15 minute runs to break in cam s a minimum...it would not run under 1200 rpm...any lower and it would start missing and stall out. Put it in gear and the miss was quite pronounced. What exactly is a collapsed ring? there is no indication on cylinder wall of anything different from the other cylinders. Honing hatch is still visible in all cylinders. Yes, I think I am tempted to try to just replace the rings on that one piston as all the others were better than normal at a healthy 135psi.. 90 is an acceptable number in the info I have read. I would be a little worried about rehoning an assembled engine without being able to clean out the grit created by it. The suggestion is noted tho as I will probably have to buy a full set of rings? Everything is new from an unrecent rebuild. Pistons are new flat top 345nd std bore. I was told the engine was a low mileage core from the start. 96 block with center bolt 192heads. is there a free state measurement for the ring diameters? To see if maybe they have lost their tension tho I can't imagine them opening up much more than they are as they would fall off the piston at some point. I didn't think about the ring gap orientations till after I already screwed with it... I have doubts that that could make much difference, nothing prevents that from happening as a normal condition in a running engine, rings are free floating and will find their own balance. I may remove another piston just to compare.

Actual TDC is easily found with one finger on the plug hole. If you have pressure you are at TDC with both valves closed. I could actually hear the difference of the starter motor when checking that cylinder...no resistsance at all. you could hear a cyclic pattern in all the other cylinders checks. I did the compressed air check and that was the only way I could build pressure in the cylinder with 80 psi applied. I could hear air escaping but could not tell from where...my hearing sucks. I proceeded to test with reinstalling head and adding 1/2 qt of oil and gave it the pressure which it would hold for a few seconds till it started blowing by the rings. Had to be the rings as there is no oil in the head at all. Half travel is the designed position for the lifters to be adjusted to...one whole turn after tightening to the point of removing the freeplay. granted in this case I might have tried leaving them loose...too late now. Head was checked and ok'd by Hunts machine in Sch'dy...they are competent. And most definitely there is something wrong with the nut behind the wheel. Something serious I think.

I think that I shall re-ring at least that one piston... If not all. Like everybody else...I am trying to do it on the cheap or I wouldn't have bought an engine on craigs list in the first place. It's going into my 83 camino daily driver.... I thought some real power might be good for it if I can get it to go. As it is, I am already close to the cars value with my investment...dont' want a 6g car that cost me 10g to build. Next we'll be onto the built th350 I put behind it which may or may not have been a good investement.... if I can get the motor to run right.
 
#12 ·
hey t-bucket,,, my chiltons manual would disagree with you...one full turn is what they say...and all the others were adjusted to the same with no ill affect to them.

The piston is new and it is factory marked as I indicated which is the 350 std bore piston. I dont' think they make undersized pistons for the 350. I can measure it with my verniers ....as soon as I find out what size its supposed to be. Visually it is a pretty tight fit in the cylinder...maybe .015-.020 clear each side it seems.
 
#14 ·
Hmm..you know ...you may be right...i just googled valve lash proceedurs and they also said 1 turn is too much...wtf? Since when is chiltons givning out bogus info? I guess my 45 minutes of run time in 15 minute intervals was not enough to burn a valve if thats what was happening.
 
#16 ·
I will be honest , my preferred method is to adjust with the engine running on a hydraulic lifter engine. Cut slots in an old pair of covers. Start engine, back of rocker nut until they clack, turn down until the clack just goes away, turn another 1/2 turn in 1/4 turn increments.
I have done it this way since the 70's. As long as your initial adjustment is fairly close this works every time.
You can do it without old covers if you slow the idle way down to keep the oil from going everywhere. They also sell clips to deflect the oil while adjusting but I dont like them.
 
#17 ·
What was your method of finding zero lash?? The "spin pushrod until you feel resistance" method, and then set preload?? Or did you back off adjuster, "shake/wiggle" pushrod up and down until you feel all slop is gone, then add preload??

The "spin method" and just a single bled down lifter plunger has fouled up plenty of people, we find it is a common problem here at the Hotrodders Forum. lots of guys make that mistake. By the time you feel resistance to spin, the plunger in the lifter is at the bottom of its travel, and not the top. You then add preload, which forces the bottomed out lifter to push the valve open slightly. Once it has been run, the lifter pumps back up and the valve is held even farther off the seat.

You description of it not wanting to run below 1200 rpm and rough running/miss leads to this conclusion...you got one valve adjusted too tight and kept one valve from seating. That's the way it sounds to me anyway.

Check for a ring installed upside down on the piston. You may have to pull another cylinder apart to see what the correct orientation is, as some rings are marked with a dimple, some with a chamfer on the inside edge...and different brands put dot or chamfer up, some put it down depending on ring style...if you don't know the ring brand or have the original instructions you'll have to campare to a good cylinder.
 
#18 ·
Flat hyd cam and lifters...cam is fine, I can see it with the pan off. I don't believe it is anything to radical tho I dont' know the specs. Again...all new stuff. I am now leaning toward the over adjusted valve... tho that one cylinder did leak down the fluids where the other ones didn't. So I am still going to change the rings at least on that one piston if I dont' find anything else to point to the problem.
 
#19 · (Edited)
. OK... Forget swapping pistons or rings... forget collapsed rings, whatever the hell that is... forget swapping springs..

. You simply have the lash adjusted wrong on #2 and maybe partially wrong on another one... as Eric said, you have the exact symptoms of misadjusted valve lash... engine won't run at low RPMs because #2 is exhausting fire into the intake manifold mixture via a held open intake valve, which is messing up all the cylinders... (one way to find correct TDC is watch the lifters for the cylinder you are adjusting and make sure neither one is in up position at all... not in the slightest...)

. Before the valves are adjusted, the valves all stay closed, and you will, thus, feel pressure in the cylinder on both the wrong and correct TDC rotation of the crankshaft, which confused you... simply need to get #2 on the correct rotation and adjust the valves... same for any other cylinder which isn't exactly correct... you can do it... you got 6 1/2 or 7 of them correct (with prolly some luck on a couple)... you can finish it... if you don't understand anything I wrote, just ask some more...

. 1 turn lifter pre-load is correct, so is 1/2 turn, so is 1/4 turn, so is 1/8 turn... they're ALL correct... nobody was 'wrong'... it just depends on what you're doing... I use 1 full turn (as does the factory) on a slow revving stock engine with a stock cam so the lifters will prolly never need to be adjusted again despite normal wear... which is one of the reasons we went from solid lifters to hydraulics... on a bit of a performance cam, we use 1/2 turn to limit amount the lifter can pump up, prevent valve to piston hitting, and speed its recovery from pumpup if engine is overrevved... on higher performance engines, we may go 1/4 or 1/8 turn for MORE of the same reasons... however, as go less than 1 full turn, more and more likelihood that normal wear will cause lifters to eventually start clicking and need the dreaded re-adjusting...

. BTW, don't know what HP was claimed for your engine, but a SBC 350" can make up to 300HP on the stock/standard/basic cam (~194/~202 durations)... above that a performance cam (GM option or aftermarket) of some sort needed... although some poorly designed 350's, such as GM Mexican crate engines, use a big cam and yet still under 300 HP...
 
#23 ·
hey fellows..sorry to dissappear,,i needed a break. frustration is not my strong suit. I am as of this moment about to reassemble the engine as i removed piston number two for a comparison and find nothing obviously different about them so I am convinced that my problem must have been as our most learned friend buzzlol described. Tho i am certain of the tdc position by probing the plug hole. Everything looks great and as it should be. I will try my hand at lapping the leaky valve on number 6 if i can observe some leak ,,,maybe it just needs to be broken in. I hate to mess with them but the shop said a leak and 180 for a valve job was more then i was wanting to do...they can't just do one valve you know... doesn't matter that it's all new. I can do one valve. A more involved lash will be performed and we shall see what happens.... i've done my crunch already and it didn;'t pan out so the project will not be centerstage for a while...got other things that need doing. I'll get some stuff done on it a little at a time..have to get all new gasket set arranged fo the mishmosh of parts I have. 87 centerbolt heads maybe with a 96 block...I cant' identify it by the numbers on it. I researched it a couple of years ago but it's not that clear anymore. I do remember it is the same block they use to create the zz4 version.. or something like that...it has no roller cam but the same block....good potential. Adding the roller would be nice if it didnt' cost more than the whole engine cost. Daily driver budgets dont' warrant roller cams. Anyway...thanks for the ideas and support and i will keep you posted of developments. Especially if I find the idiot that took my engine apart. :)
 
#24 ·
Tho i am certain of the tdc position by probing the plug hole. I will try my hand at lapping the leaky valve on number 6 if i can observe some leak I do remember it is the same block they use to create the zz4 version.. Adding the roller would be nice if it didnt' cost more than the whole engine cost.
. Thanks for the kind words... I don't doubt you had the cylinder you were adjusting the valves on at TDC. I just want to repeat there are TWO TDC's and you have to be on the correct one... the one where both valves are closed and nowhere's near opening... Leaky #6 may also be simply a valve misadjustment... I realize nowadays they say don't lap new valves/seats, but I always do to make sure there is a perfect seal, because if it leaks it can start burning the valve and seat... and/or allow fire back into the intake manifold full of air/gas mix... Yes, ZZx block is good block... On a street car we often look for a low mileage 'takeout' roller cam and use the economical stock-type roller lifter setup...
 
#26 ·
yes...I plan to become a valve expert inthe near future too. I need to see what the issue is and try to handle it. I will be sure to be extra careful verifying where I am at the next time ....thought I was on the first time around too. It never ran right so I kept checking and rechecking. The distributor was loose when I got it so I had to start from scratch from the getgo. So I had concerns about everything... was the cam installed properly? I couldnt' even get the timing mark close to where it was supposed to be and have it run. Some scerwball didnt' check the carb settings till after trying to run it and finding one idle screw all the way in and the other about about a half turn. Then a bad spark form a bad module in the new distributor. Can anything else go wrong? I guess it is to be expected when dealing with an worked over engine that has been lying around too long. Ha ...someday I'll find something that actually is plug and play.
 
#27 ·
At long last I am back ... engine is back in car and running but still not right. I went thru the valves several more times and ended up having to adjust them as tho they were solids to get to the point of best settings for it to run...I was able to push down on the pushrod side and get clacking noise which to me indicates that I do indeed have hydraulic lifters and not solids. I had them out of the engine but I coudlnt' tell one way or the other. I have some other issues yet but I am finally pulling good vacuum and running halfway decent..and new headers and exh installed so no more wondering if the old stock exh pluggin it all up...it was somewhat...had to richen up carb. Any attempt to lash the valve past 0 results in open valves it seems. I have driven it and it seems to rev up and have great power in the upper rpms with no valve float so I am assuming that removes weak valve springs as a possibe culperite. Can you cause a clatter on mech lifters by pressing down on the rockers pushrod side? Sorry...I have no experience with solid lifters so I dont' even know what to look for...the searches i have done have given up little for me. So I'm thinking I should not be able to compress anything on a solid lifter. Oil press and temp running normal, idle is too high but too big edelbrock carb has no more adjustment to bring it down more...another thing to be worked out. Cam seems lopey when it brings down the rpm in gear. Kick down cable has slack and the th350 trans does not kick down at lower speeds into first again but seems to operate fine at 50 kicking back into 2nd and has good power at wot. I guess now I need to know if there's is supposed to be some slack in that cable.

Don't know if any of you original responders will see this but thanks for the feedback and would appreciate any further reflection on the mystery. I also dont know much about how this site works. Had to look a long time to find my origianl post.

In retrospect...yes...it was the valve adjustment that started this whole problem... and it is still not solved.
 
#28 ·
.
. Welcome back my friend to the show that never ends... LOL

. Glad to see we nailed the problem by the first posting response... even if it was a bit hard to convince you... at least you have lots of good instructions on properly adjusting the valves now...

. Yeah, solid lifters (properly adjusted) lightly clack all the time... apparently you didn't see any roller on the bottom of the lifter? I don't think solid lifters have the piston or snap ring in the top of them like hydraulics do... sounds like you're close to getting it all adjusted correctly...
.
 
#29 ·
Hey Buzzy... seems like the wires are crossed...I am still in the courtroom trying to figure out if I have solid lifters or not. As I said,,,i have them adjusted like solids but i am pretty sure they are hydraulics...i can cause slack inthe system while running by pressing down onthe pushroad side of the rockers. after perusing the internet trying to find any differences i can find none...i have seen purported solids with the same spring clips up top as the hyds....Making my seat of the pants test the only way I can determine this,,, a mech lifter should not experience any compression by me pressing on the rocker. I am taking my chances right now as I had no way of setting a .015 gap at the rockers for solids...i may be burning valves as we speak... I just adjusted them till the clatter stopped. 0 lash to me.

Another question is how my thread made it back to you...is there some way to follow a thread on here? I had to look a long time and then thought none of you guys would get it after this long time.
 
#30 ·
Hey Buzzy... seems like the wires are crossed...I am still in the courtroom trying to figure out if I have solid lifters or not. As I said,,,i have them adjusted like solids but i am pretty sure they are hydraulics...i can cause slack inthe system while running by pressing down onthe pushroad side of the rockers. after perusing the internet trying to find any differences i can find none...i have seen purported solids with the same spring clips up top as the hyds....Making my seat of the pants test the only way I can determine this,,, a mech lifter should not experience any compression by me pressing on the rocker. I am taking my chances right now as I had no way of setting a .015 gap at the rockers for solids...i may be burning valves as we speak... I just adjusted them till the clatter stopped. 0 lash to me.
I've just read this thread for the first time. My advice, for the love of God, find out what you have before you wreck it. To check the lifters is not that time consuming or expensive, and for that fact it is not very expensive to a buy a new set of hydraulics. If they are hydraulic, then perhaps the lifters didn't take 'the 10 year wait to be run' very well, but it does sound as if you have solids from what you've posted - FIND OUT - it will help me sleep better:thumbup:

FWIW, a compression tester has it's place as a diagnostic tool, but if you would have leaked down the cylinder when you found the one low (90) and the other with zero, then you would have known where the air was or was not going. It would have saved a ton of your time, money and frustration.
 
#31 ·
I just read the entire thread as well.
Glad your making head way on your problem.
One thing I could suggest about adjusting hyd lifters while engine is running.
Back of each rocker until it clacks and tighten just till the rocker quits making noise. Adjust each rocker this way.
Once you have adjusted all of the rockers basically at zero lash shut off engine, go back and turn each adjuster another 1/2-3/4 turn.
As you have probably seen, as you adjust the rocker/lifter past the zero lash point the engine will stumble/miss as the valve is now being held open until it can bleed off some oil in the lifter to the proper point.
When you shut off the engine and go the extra 1/2 turn and then restart, each lifter will self adjust before full oil pressure is reached.
Hope you can understand what I'm trying to say here.
To subscribe to a thread:
there is a box of additional options below the box your writing/editing entitled thread subscriptions. Open it up and select how you would like to be notified.

Best of success with your project.
 
#32 ·
Cut the tops out of an old set of valve covers to prevent getting oil all over the motor and bay when adjusting the valves with the motor running. This photo shows the cut being too wide. You only need it wide enough to get a socket on the adjusting nuts. If you keep a rag wetted with solvent handy, you can wipe off the top of the cover occasionally so that a piece of tape will stick to the cover to further prevent the egress of motor oil onto everything.
http://www.route66hotrodhigh.com/images/TopEnd/vavlecov.jpg

Yeah, I know they make those little clip things to attach to the rocker arm, but in my experience those things ended up most anywhere except on the rocker arms.
 
#34 ·
well i must have done something right that i am getting responses to this old thread , thank you site designer. I just didnt' want to leave it unsolved.

Yknow i did do a valve lash exactly as you describe and couldnt' help myself and turned them in a 1/4 turn more..not...now no compression in 6 and weak on 8. No2 now ok and complete driver side ok. Take it all apart again for the millionth time and reset them to 0 and left them...i can hear some valvetrain clicking but not bad. but i am experiencing some popping at idle in gear i suspect is some that are too tight. I dont' understand how these tweaks can move around the problems. I am all for finding out what the hell i have there...i have seen them and had them in my hands..they looked like regular hydraulics to me. I am not taking them back out again so there has to be some other way to tell. Tonight i had some major improvement with the carburation ....mech issue... throttle adapter lug nut on back of throttle plate hitting idle screw and preventing the carb from closing all the way. Doh oh! Nice now that I can bump the timing up where it belongs and still shut the car off. The lifters are still a mystery..they have all been adjusted in the same manner and should have all been leaking or all not leaking...not here and there... not changing form one spot top another...something is not kosher here. I can compress the valvetrain using the handle of my ratchet onthe rocker arm while its running....is this not a valid check for determining what they are? I will break them eventually if thats what it takes to get what i really want... A new cam and lifters and springs and god know's what else.. just keep throwing money at it till it runs right. At this moment it is still 100% better than the 305 pos that was in it. I think the original owner thought it was a good thing to keep the original oil in it...or what was left of it. This weekend I am going to take the valve covers off yet again for you know what again to try to chase down anymore tight ones..id really rather not burn the valves...with my hydraulic solid lifters.
 
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