The results are posted as a graph.

I have posted here before with leak-down test results in December, but at that time, I wasn't sure how I wanted to interpret them (i.e. I wasn't sure what to attribute any leakage to). In trying to reduce the number of variables involved and finding where exactly any leakage was happening, I have since:

-- Pulled both heads
-- Cleaned all head bolts and gasket surfaces
-- Had the machine shop look at my heads: they re-magnifluxed them, and they ran a vacuum test to make sure all valves were sealing. Everything checked-out.
-- Pulled any "suspect" pistons (#1 and #6) and had the machine shop check them. They said that the rings were properly installed and in good shape.
-- Reinstalled heads with GM head gaskets (was using Felpros) and a different thread sealant

After all of this, I have re-run a complete leak-down test on all cylinders at top-dead-center. The pushrods and rocker arms were off for all cylinders.

When I last ran this test in December, I was concerned with cylinders #1 and #6 being relatively low. Much to my disapointment, those same cylinders are still low (even after having the pistons/rings inspected). Moreover, since I ran this test with the engine out and the oil-pan off, I could definately tell that the leakage was past the rings in some way.

For those of you who don't know, what I am ultimately trying to find out is why my engine overheats (without getting into any details, I will just say that it overheats badly enough that my car has not left my house since the engine has been rebuilt in April, 2002--and it's not due to simple cooling or timing issues). My only guess at this time is that the overheating and those "low" cylinders must have something to do with each-other.

I was getting ready to drop my engine back in on Sunday, but now I'm not so sure. Remember, the bottom-line is that this engine is overheating badly, and that's what I'm trying to fix. So here are my questions (don't feel like you need to answer each one):

1. What are the odds of consistiently bad results on these cylinders (#1 & #6) would cause engine overheating? That is, is there any correlation between my test results and the fact that this engine is generating too much heat?

2. Assuming that the rings are heads are good (which I am told that they are), might this just be "ring seating" issue--i.e. something that will go away with more mileage? Or, if not, and the problem is with my block, what are my options?

3. Do my leak-down test results indicate any problem at all?

I'm just looking for some opinions as to what my next steps should be. If it seems like I still have some "unfinished business" left to do with this engine, I don't want to take the time and effort to drop it back in this Sunday. I'm just nearing my wits-end with this thing--in a month or so, we'll be approaching a *one-year* anniversary since my dad and I set out to tackle this rebuild, and I've yet to be able to drive my car since then. That's just to long a wait and too much money for a high-school kid--especially for something that could have been finished with in a week.

Thanks for any and all relevent suggestions (and I'll quit my ranting now)...

 

With a new eng, pressures should be within 10% of each other.

Did you bore the cyls during the rebuild? Can you measure them to see if they are truely round and within spec?
Did ya used the correct ring-seating procedure?
(i.e. heavy throttle at low-mid RPMs a few times)
Has the eng been idled excessively since the re-build?

I kinda doubt the low compression is causing a serious overheating condition.

 

You didnt mention this so I will ask you did you check the block deck for trueness at those cylinders comparing them to others. Did you replace the rings on those 2 pistons while they were out?. Did the shop crosshatch the cylinders right when they honed it? Did they accidently over bore those 2 bores during machining? Did you measure the pistons for the right size for the bore? Did the machineshop check for cracks around the spark plug holes? This is a site most often overlooked. What did the pistons look like when you took them out, were they oily, clean as if steam cleaned, burnt, did the 2 pistons look different than the others?

 

ZZ28ZZ: This is something that I should know but have gotten away with not knowing because my dad did it for me; in fact, everything done with the machine shop has been done between my dad and the shop. However, I believe that what they did (I suppose they bored) increased the displacement to 355 ci. I wouldn't know how to check if the cylinder is perfectly round, except that I looked *very* closely at each cylinder and noticed an evenly distributed gap between the piston and the wall. I imagine that's how it's supposed to be since each cylinder was identical in that regard (at least to my eye). As far as the "correct" break-in procedure--I know we varied the RPM. However, I'm sure that we were still pretty conservative with the engine speed--I don't think we ever pulled it past 3,250 RPM. After the first 30 minutes of "break-in" (which was split up into two sessions due to overheating), everything after that was more-or-less at idle. However, it didn't like to stay running unless I had my foot on the gas.

radiateu2: Not sure how many of these questions I can answer, but I'll take a shot...

-- I did not check the block deck for trueness; things like that I assumed were done by the machine shop. There were cross-hatch patterns on each cylinder from the machine shop.
-- I did not replace the rings on the suspect cylinders because the guy at the machine shop said that they looked just fine.
-- Bore and piston size were also things that I left to the machine shop--I basically gave them a disassembeled long-block, they machined the heads and block, and gave it all back to me with an assortment of mid-high grade parts, most of which they selected.
-- I don't think the spark-plug holes were checked, but I would think that any problem there would have been found during the vacuum test they did on the heads. Also, the leakage that I'm having is definately comming past the rings somehow.
-- All of the pistons looked exactly the same: black. The blackness wiped off easily with some carb cleaner. A few of the pistons on the passenger's side had oil on them (#6 included).

 

Sancho,

Sounds like blow by to me You shouldnt se any oil on top of the pistons. If your dad works in a mchine shop ask him to bring a mic home and check the cylinders for you. I definately would have replaced the rings on those 2 pistons. possibly something wrong with them the naked eye cant see. I dont think that is the cause of your overheating. with rebuilds valve lash would cause that as well as a rich carb condition. Do the headers or exhaust manifolds glow?

 

radiateu2: I completely agree about the blow-by...

I think that the oil was probably comming from the heads, though. The only reason why I say that is because, for the cylinders that there were "wet" pistons, the corresponding combustion chambers were also oily. Since the engine was always sitting right-side-up (duh), then the oil in the cylinders must have been comming from above (the heads).

My dad doesn't work at the machine shop, but he might be able to get his hands on a mic. I'm not too sure if I want to do that, though, because I *just* got finished putting the heads on. If, however, I do decide to mic the cylinders and thus, yank the heads again, will I be able to reuse my head gaskets (they're GM gaskets)?

On a side note, the machine-shop's impression of this sitation is a little different than mine. First off, when the guy at the shop first saw my leak-down test results, he was suprised that they were actually as high as they were. He said that for rings that haven't yet had a chance to fully seat, it's a little surprising that the numbers were that high to begin with. Plus, since moly rings take even longer to seat, his impression was basically to not worry about it since nothing has really had the time to seat. His reasoning was pretty-much the same with regards to the oil on the pistons: the rings haven't seated, so there's going to be some oil in the cylinders.

I'm not totally sure that I agree with him, and that's only because only two cylinders are specifically problematic.

But it seems like you guys think that the overheating and the "bad" cylinders might be separate issues, so I'll split things up a bit. Speficically with regards to the overheating and things that might cause that (so nothing to do with my leak-down results), here's a little checklist of things that I've done or checked:

-- New high-flow water pump and new 3-row radiator. Everything is "hooked up" and operating as it should be in that department because there was definate flow in the radiator when we were filling it up. So no problems there.
-- We took special care when installing the rocker arms in the first place. But after the overheating, we thought that might be the problem, so we went back and re-adjusted each one with the engine running. So no problems there.
-- Everything is pretty-much new in the engine-timing department as well. New A/C-Delco plugs, Bosch "Gold" wires, Bosch distributor cap, rotor, and rebuilt distributor. My dad went at it with an inductive timing light, and we made sure to use the proper method of setting the timing with the little brown wire disconnected.

I remember, however, that we could barely get it to idle at the factory spec. However, if we were to turn the engine off and let it cool down, restarting it would be a PITA--and I had to keep giving it gas to keep it idling, or else it would die. It wasn't until it warmed up that it would stay idling. If we intentionally over-advanced (or over-retarted, I can't remember) the timing, it would never have problems idling or starting up, but the "idle" speed wasn't much of an idle at all--I think it liked to stay somewhere around ~1,500 to 1,700 RPM. Also, even after we could get it to idle with my foot off the gas, I can remember putting the car into gear would immediately kill the engine. So keeping it at idle with the car in gear would require the tricky task of giving it gas while putting the transmission into drive--and if I managed to get it into gear, I would have to keep my foot on the gas (with an engine speed of ~1,500 RPM), or else it would die again.

BTW -- I rebuilt this engine with all stock-equivlent components (with the exception of some of the internals). So that means that one would expect to run "to spec" with the factory computer--so I don't think we're looking at any programming issues here...

 

Sancho,

The overheating is not at all uncommon on a fresh build. The two issues may be related, or maybe not. The problems could even be deeper than just some ring leakage. However, you have definitely identified at least one problem through your leakage test, so there is work to be done.

Regarding the assembly, I have a few questions of my own:

• How many total hours has the engine run since rebuild?
• When you removed the #s 1 & 6 pistons, did you pay attention to ring gap position?
• Ditto for reinstall?
• What was the finished ring end gap (if the shop did it, ask them?
• What oil are you using?
• Did you examine the head and deck surfaces, and gaskets when you removed them the second time? Anything unusual?
• Were the heads machined flat?
• What final torque was applied to the head bolts?
• Did you torque the head bolts in the proper sequence, and in incremental steps to the final torque spec?

There is a test you can perform without removing the heads again. Apparently, you have access to a cylinder leakage tester. Retest the cylinders. If you get similar (low) results on any cylinders, remove the tester, pump in a couple ounces of heavy oil (gear oil is great for this, and the tapered spout comes with the bottle), cycle the engine a few revolutions, then retest. If the leakage decreases, you definitely have ring sealing issues. At that point, you'll unfortunately have to remove the heads again. Don't plan on re-using your head gaskets. You already have problems, and don't need to compound it by installing already crushed gaskets that may not seal again. $40 isn't a good, economical saving in this instance. New GM or FelPro gaskets should work great for you.

When you get the heads off, remove the pistons. Carefully remove the rings and place them into their respective bores to check end gaps. You shouldn't have to check you shop's work, but since you have a problem, you have no choice.

Also, it would be very advisable to check the bores for both taper and out-of-round. You'll need either an inside micrometer, or a telescope gauge and larger mic or caliper. A caliper graduated to 0.001" is close enough for these measurements, since a thousandth or two won't cause the type of problems you are experiencing.

I'm suspecting that your case may have had some stresses, and boring relieved them to some extent. If the machinist did not employ a torque plate when boring the holes, there is a chance that they are not straight or round. Since you don't know, and it was done almost a year ago, we can't assume they did. While the heads are off, you should also get a 24" straightedge and flat feeler gauges to check the case decks and head surfaces for warpage. Again, if they didn't deck the case or failed to use a torque plate in boring, it could be waving like a pond, or as twisted as a Mitsubishi salesman.

I'm sorry that you're going through this, but I'll bet you want to get this resolved and reassemble the engine for one final time. Since 11-3/4 months has alreay passed, don't shortcut it now.

 

But what says that the oil isn't coming from the valve stem? And if oil is coming down the stem and the valve isn't closing due to hydrolic lifters or cam....

Hey, my dad's 302 has that same problem where it doesn't want to idle. With his, it's the EGR vacuum. You start it from cold and it will want to die all the time. Once then engine runs for a little bit you can cut it off and let it sit for about 10 seconds. Then when you craank it again the idle problem goes away.

 

Vader,

First, I'll try to answer as many of your questions as possible...

-- Very rough guesstimate for total running time: ~1.5 hours
-- I'm currently using Quaker State 10w30 oil
-- The Felpro gaskets that came off were completely in-tact (i.e. the metal rims were in perfect condition); however, they were both wet in some areas (like a third of one was soaked). That might have been because I loosened the head and left it sitting overnight. But one thing that I did notice was that the threads on a couple of head bolts were rusted, probably due to insufficient sealing.
-- All of the heads were torqued to 65 ft/lb
-- I used the "proper sequence" for torquing the bolts, starting at 25 ft/lb and increasing in 20 ft/lb increments to 65 ft/lb

-- Can't say for sure wether the head and deck surfaces were machined flat, but I can check into it
-- Anything regarding [ring] gaps: I, myself, have measured nothing. I assumed that all of the precise/critical measurements were done by the machine shop. Beyond that, I did visually inspect everything for gaps (i.e. making sure that the gap between the piston and the cylinder wall looked uniform for the whole perimeter of each piston)

Now, here's the other part...

I just tried you suggestion and used gear oil in the suspect cylinders. The graph is attached. Obviously, the numbers went up, and I couldn't hear any leakage whatsoever from the bottom of the engine (until the oil started bubbling out).

But this is what I find interesting: on both of those cylinders--and only on those cylinders--there was obvious leakage (hissing) comming from the exhaust ports on the heads. You might remember that when I posted my last results in early January, I said that I heard leakage from the EGR ports on the suspect cylinders. Well, now that the engine is out and the exhaust manifolds are off, I can confirm that leakage. I tried covering the holes with my hands, but the pressure was too high and the air just escaped.

Remember that all of the rocker arms are off.

So what does that tell you?

 

As usual I agree with Vader, he basicly told you in greater detail what I had told you. If you hera hissing on the exhaust valves you may have a bent valve or a valve that may need to be lapped in to the port or even a broken valve train component. That will definately cause your over heating problem. I do think Vader makes the point about ring gap and postioning. Poor end ring gap and poor positioning will cause leakdown. Like Vader said do it right do not reuse head gaskets its more headache than what they are worth. Definately check the decking on the engine. Never take for granted for what someone said they have done. Definately check those bores and compare them to a known good bore. I think you will find that the rings have poor ring end gap as well as ring end gap position. Let me tell you when I did my rebuild I had the rods reconditioned and after installing them I found 2 bent rods. So, you never know unless you check and double check even triple check. You already know it has ring sealing issues when you put the oil in the cylinders and saw the bubbles. I think you can figure it out from there.

 

Sancho,

You've identified another problem - the exhaust valves. Now, the heads are coming off for sure.

 

Yeah, I pretty much know what I need to do. I actually more-or-less knew before I even posted, but I just wanted to make sure that I laid *everything* out on the table for other, more experienced people to see to make everybody is in agreement. I'm just tired of the guessing games.

Crap.

I think that I'm just going to take everything (block included) back to the machine shop and have them confirm what the problems are. I don't have the tools to make precision measurements or do valve work and, moreover, the measurements and head work were their jobs to begin with.

Thanks for all of the replies.

 

Sancho,

I think I would find another shop to ayleast look at the heads. Especially those exhaust valves. From what you had told us they already did some sought of vacuum test or leak test on them and found nothing. The exhaust valves leaking make sense for your over heating problem, and quite possible your leak down test. If you have a bent valve quite possibly you may have prematurly worn a valve guide causing the oil to leak into the cylinders of those to problem children cylinders you have. Start there and see what ANOTHER machine shop has to say. Where did you see the oil "bubble out" of the cylinders at?

 

radiateu2,

I didn't actually see any bubbling. Basically, what would happen is that, from the bottom of the engine, I wouldn't hear any leakage. Then, as the gear oil eventually started running out, I could hear an intermittent hissing that sounded like bubbling. Eventually, I could see the oil running down the rod and dripping onto the ground. It looked white at first, meaning that there were bubbles in it.

What I'd really like to do is to take the whole engine (well, the longblock anyway) as it is to a machine shop. I don't know if that's a good idea or not, but it'd be nice for them to be seeing the same thing that I'm seeing. I wasn't there when the vacuum test was done on the heads, but I doubt if they were able to get as much vacuum on the combustion chambers as I was able to get compression.

 

Hey Sancho,

Keep us informed on what you find. I am sure Vader is as curious as I am. I think that you may have found the problems.

1. I am sure taht you have a sealing issue with the rings/pistons and cylinder walls.

2. I willing to bet that the exhaust valve problem you found on the 2 cylinders isnt helping anything and maybe the cause of your overheating.

3. Never use the head or intake gaskets over. You will be cursing yourself for doing it (even if they say reusable on the package) its not worth it.

4. Taking the long block to a mchine shop maynot be a bad idea.

5. When you said you found rust on the head bolts, I wondered if you used sealant on them and what kind? Most of the head bolts protrude into the water jacket and if sealant like teflon is not on them they could cause a head gasket leak and overheating.

Good luck my friend I hope we were able to help out.

 

RE: Head Bolts... I did put sealant on all of the bolts, but after doing some reasearch (and speaking with some Permatex reps), I figured out that what I used was not intended to be used in the envrionment that I used it in and could have become brittle under those conditions. I just reassambeled it with some Permatex "aviation grade" sealant that the machine shop guy says that he always uses to seal head bolts with. Guess I'll have to wait and see how well it works...

Thanks for the advice. I'll keep you all posted with what I find out.

 

So Sancho what did you use on the head bolts? I am curious now. I used Permatex teflon sealant that you brush on like pipe sealant

 

Permatemakes a couple of good sealants, but LocTite PST or Pro-Lock are excellent in those bolt areas:



It isn't a "regular" Teflon pipe joint compound, but an anerobic sealant, so it will not creep under pressure.

 

Just thought I'd give an update on my progress with this issue (or "these issues") so far.

I went down to my machine shop yesterday (the same one that did the work) with a printup of this this whole thread, as well as some of the graphs. My dad and I spent a good half-hour talking with him after closing-time about what we've done and what we've found. Basically, we're agreed that we think there must be issues with the rings on the bad cylinders.

While I got the impression that he was a little surprised with the results overall (including the good cylinders), he, like us, was concerned with the fact that two cylinders were nearly 25% lower than the rest. Once I told him about putting gear oil into the cylinders and the new results that came from doing that, he also agreed that it must be indicative of bad rings. So he went ahead and ordered me some new rings right off-the-bat, and suggested that I changed the rings on the bad cylinders and re-run the leak-down on them again. So once I get the rings (hopefully Friday), that's going to be the next step.

One interesting thing I also found out: he told me that he did not use a torque plate. He took some time to explain what it did and why he would use it, and basically he is of the opinion that it is not necessary for street applications like mine. He said that the only time that you really have to use a torque plate is on racing applications or anything that is going to be nitroused. We asked him if the bad leak-down results might be due to cylinder-wall distortion from not using a torque plate when machining, and he said that it *could* happen (though not likely), but in that case I would have likely seen bad leak-down results in more cylinders (i.e. in the cylinders next to the bad cylinders). So since my bad cylinders stick out like isolated sore-thumbs, our blow-by issues aren't likely to be due to cylinder wall distortion.

Also, we talked about the leaking exhaust valves, and we're all (he, my dad, and I) still stumped on that one. It doesn't make much sense why he could of magnifluxed, vacuum tested, and checked the valve guides on these heads and still have exhaust leakage. He said that before any running time, immediately after the rebuild, is about the only time when leakage might be acceptable because of the way that the valves are ground. Something about using one stone on the valve and a different one on the head because of them being different materials, and the resultant grinding patterns don't match until the engine has been run for a while. But since it has been run for a net time of >1 hr, that shouldn't be an issue. So I don't know where we stand on that issue; we'll probably take the heads down to the shop one more time since we'll have to have them off to change the rings.

But, anyway, that's where we are right now. I'm going to heed my machine shop's advice, as well as responses here, to try to fix this problem once and for all. And, while it's been suggested that I see another machine shop, I really do trust the one that did the work in the first place. This guy has been doing this stuff for almost thirty years, has a great reputation in my area, and has been more than willing to stand by his work whenever I've come to him with these problems. I don't think this is an issue of poor machine work on his part--if anything, it's probably something that I screwed up on because this is my first rebuild, and we've just yet to find it.

I'll post back when I find something else out...

 

Hey Sancho,

I am glad to see he is working with you on this stickwith it. I hope you are able to find out whats wrong with the heads. Keep us informed on the outcome ok.

 

Dude, you should seat every one of those valves once you get the heads off. And I don't think you have to take the heads off to change the rings, having the heads off just makes it easy

 

Sancho,

Fortunately for you, your mechanic seems like a forthright, honest, and knowledgeable person. Your dad chose well. the fact that he is willing to work with you indicates his desire for your satisfaction. This guy will be in business for a long time.

As for the rings, don't discard the old ones as soon as you remove them. They may be your only clue to why you're leaking. When the pistons are removed, note the ring gap positions carefully. Note their orientation. Are they upside down?

Remove them carefully to avoid breakage. Use them to check the gaps at the top and bottom of the suspect bores.

As for the valve leakage, the speculation over the surface finish after grinding is valid. However, this is more reason to hand lap the valves after grinding and before assembly. A few minutes with each valve and a little lapping compound can create a perfect seal.

Good luck on your quest.

 

Okay, I just got back form my machine shop again. This time, I personally took my heads over so that he could look at them. The first thing that he did was to vacuum test the suspect exhaust valves. Both of the valves pegged the vacuum gague (that is, they were holding enough vacuum to max-out the gague).

So the next thing that he did was to remove the springs, and then he vacuum tested the valves again without the springs. After that, he took a penlight (must have been some special penlight, though, because it looked like it was emitting flourescent light), shone it on the valves from the combustion chambers, and looked down the exhaust ports.

I can remember him saying that, at least on #1, he could see a little bit of light shine through. Also, I remember that, although the vacuum gague was pegged, it went up a little slower on #1.

Lastly, before he put the valves back in, he took the exhaust valves to the grinding machine and ground each one a little bit.

Basically, I got the impression that he wasn't totally sure why I was getting leakage through the exhaust during the leak-down testing, given that the vacuum tests came out good. So we kind of left it at a "let's just put it back together again and see what happens".

With regards to the rings, I have put all new rings on the suspect cylinders and put the pistons back in. Honestly, taking the "old" rings off, I couldn't see anything at all wrong with them. The were all on the pistons in the right order and position. My dad even took one of the old compression rings and put it into the top of the bore, visually noting the ring gap (didn't have a feeler gague that was small enough). He then took a new ring and did the same thing with it and, at least visually, I couldn't tell a difference.

So putting it back together again and re-running the leak-down tests are all that I can think to do at this point in time. Once I get some new head gaskets, I plan to put the heads back on and get back to you guys here.

Thanks again everybody for the help!

BTW -- Open_Slot: What do you mean by seating the valves with the heads off? I thought that the only possible seating happened when the engine is run?

 

Sancho,

Lacking any directions from the ring/piston manufacturer, and before you assemble the engine, you should file the ring gaps to about 0.018" on the compression rings (unless you are using "zero gap" rings). On forged pistons, a little more gap is desirable. The ring and/or piston manufacturer should have provided ring gapping instructions, but in case you didn't get any. .018 is a good target.

I'm curious about the vacuum pump being used for the chamber seal testing. Either thay are using a huge pump, or not pulling very much vacuum. If you can see a light past the closed valve, it's leaking, despite what a tester might indicate.