Air burping z24, already swapped head gasket, ideas?

[nissanrv]

Hi. I have a z24 motor 720 motorhome. One day things went bad. It got hot and started burping air. So i replaced the head gasket. Did a good job i thought. Now its doig the same thing. Anything else it could be? I didnt shave the block nor head. Could it be a coolant or oil pump or front cover gasket or anything? I guess i should get a compression tester and go from there? Its doing exactly the same thing! Air burps. Overheating. Coolant looks like its getting crappy quick. What would you do? I strangely found little evidence of a blown head gasket when i did it. Nothing too clean, nothing looking wrong. But it did come apart easy. I used a straightedge on the block. It showed a pufker between 3 and 4. Does that mean pull the whole motor etc? Sigh.

[AZhitman]

Coolant is getting oil in it?

You put a straightedge on the block, and saw an issue? Then you put a new HG on it, and torqued it to specs, per the FSM?

I'm not razzing you, just making sure I understand. If the block deck isn't perfectly flat, there's zero reason to even TRY to put a head on it.

[nissanrv]

Yup. It seemed to go down between 3 and 4. Looked like less than 1mm which i thought was spec. I torqued it a bit extra too 67 lbs. i prepared the surfaces very well with brake cleaner. I guess im screwed. The motor has only about 70k. Whats strange to me is its doing exactly what it did before i swapped the gasket. I figured i would see some sort of difference??! The car started acting up out of the blue like this too. I can hear the air lumps coming through the cooling system. The heat quit working. The water overflows, then sucks back in. I found coolant at the bottom of the oil before. Can it have something to do with the timing cover or water pump? Things arent lookin too good for me, are they?

[nissanrv]

The thermostat had swelled and gotten stuck. It seems to have been in backwards. So it had zero flow this whole time. Im going to test it soon. Maiden voyage number 2. I had found serious sand onthe valves. I cleaned it all off and it now idles lower. Hopef things go well and i can advance the timing a hair as it detonated too easily betore. Shes a good box. I guess someone had done a head gasket in a bottle. This thing ran for a good few miles before getting too hot... With zero water flow. Another head hasket in a bottle and ill go ez with the amount, and loop past the radiator and also heater core. I bet it wont even get hot , with a lil outside misting on the valve cover.

The block strangely looked exactly like the one on youtube where the guy checks the z24 with a straightedge. It curves down so gracefully, it makes me wonder if its supposed to curve down to compensate for swelling between the cylinders where there is less cooling??? hopeful.

[AZhitman]

Whoa.

If the deck of the head isn't totally flat, you're wasting time. The block is shot. Torquing it down more won't do anything except flex the head, which will ruin it as well. Cleanliness isn't the issue - You're trying to maintain explosive pressure in a container, but that container is not sealed.

No, the deck of the block is not supposed to "curve gracefully" - it is supposed to be completely and utterly flat. Period. There's no "compensating" for anything, and 1mm is an unacceptable variance.

It has nothing to do with the water pump or the timing cover. The block is shot, and the head is most likely shot. The thermostat failed to open, twhich overheated it, and warped the head (likely damaging the block in the process). Don't waste your money on bottles of crap, they'll just clog the cooling passages in a garbage block and ruin a radiator.

"Misting on the valve cover?" Ummm, are you thinking spraying water on the valve cover will somehow cool the engine? That's not how it works - Stop before you waste any more money and time, or worse yet, hurt yourself.

The good news in all this? Z24 engines are a dime a dozen. You can probably find one in a local junkyard for cheap.

[doctor510]

Yup. It seemed to go down between 3 and 4. Looked like less than 1mm which i thought was spec. I torqued it a bit extra too 67 lbs. i prepared the surfaces very well with brake cleaner. I guess im screwed. The motor has only about 70k. Whats strange to me is its doing exactly what it did before i swapped the gasket. I figured i would see some sort of difference??! The car started acting up out of the blue like this too. I can hear the air lumps coming through the cooling system. The heat quit working. The water overflows, then sucks back in. I found coolant at the bottom of the oil before. Can it have something to do with the timing cover or water pump? Things arent lookin too good for me, are they?

LESS THAN 1mm? 1 mm is 0.040"! Max "out of flat" is 0.004"! That is 0.106mm

Block is WAY too warped, go get another motor like AZHITMAN suggested. Early Z24's are known for block issues.

[AZhitman]

Alternatively, a later-model engine swap should be fairly easy in the 720. I'll let the truck guys chime in on that, but I'd think a KA24DE would be a nice upgrade.

[nissanrv]

It seems ok right now. Water is clear. Oil is fine. No bubbles. Im hoping for the best. I replaced thermostat. This motor barely even heats up. Seems to run well. It did have a dip between 3 and 4. How much i didnt measure. I honestly cant see a block warping without major damage orherwise. Its steel vs aluminum. I still wonder if the low point was built into the block to deal with the added expansion at the point between 3 and 4? Ill keep updated but so far, so good. I torqued extra because it felt more proper. Ive had a handful of drives now, ill go back in and loosen each one individually, then retorque each one individually on the head. The difference of 5 lbs torque isnt much. I even had 2 torque wrenches... Each a few lbs different. I used anti sieze as well. It torques higher and easier than just oil. There are many factors in torqueing heads. I never had issues with them. I torque a bit high but like i said, mine keep working. Torqueing heads has alot to do with feel i believe. Also the temp of the metals themselves will change torque values. So shoot me! I cut my egr tube to make this happen. Put it together with some tiger tape and 2 hose clamps and some stainless sheetmetal. I tried heater hose... Hahaha melted soooo bad.

I cant figure how to post pics on my iphone!!! I got some for ya...

[AZhitman]

I won't even begin to go into how many inaccuracies are in that last post, but if it runs, God bless ya.

Time to go camping.

[nissanrv]

well, im still rolling. dont have a timing light, but, it seems the timing winds up right in the middle between the end and the slant... any feedback on this?

i live in the RV. my back is screwed up and im very far from 'home'. otherwise i would have gone further with this. i found it so strange how the block had a low point between 3 and 4, as if it were intended to be there. i mean, wouldnt have other things melted before the steel block? i didnt overheat it, but someone else might have... which was probably why the valves were coated with "sand"... the dribbles of the "head gasket in a bottle" the previous owner had used.

this thing is running smooth! only 70k on it. it never ran so well. the power pulls linear and screams on top. i couldnt time it properly before, because the sand on the valves made the compression too high i guess. it doesnt ping now. i stay running premium and havent tested fuel otherwise. this thing will lug 4th gear at 25 mph now! its pretty awesome of a motor...

come on, my post wasnt too bad! its true, anti sieze and oil will produce different results upon torqueing... its been tested by others.

thanks for the help, everyone. it really means alot.

[AZhitman]

Keep rollin', brother. It's just a testament to how robust and sturdy those engines really are.

How about some pics of this beast?

Side note: I predict the 60's / 70's RVs will be the next big "trend" - I'm already seeing young guys buy them, rat them out, drop them, and make 'em awesome... Kinda the "shag van" for a new generation!

You might be living in a gold mine.

[nissanrv]

Hey. I would post ics but i dot see how. I push the image button and it gives me html code. I dont know what to do with it. Pics are good...

[AZhitman]

You place the url of your image between the [img]and[/img] tags.

Example: [img ]http://ww.photobuket.com/720RV.jpg[/img ] (without the spaces).

[nissanrv]

[nissanrv]

for the scraping of the gaskets,,, i used a drywall blade, a regular razor and a regular razor with a scraper holder. it seems i would switch off and get through different sections when i got stuck. the head gasket area required me to positively scrape the whole surface, inch by inch, looking it all over, and wiping with rag and brake cleaner. its got to be perfectly dust and everything FREE!!! you have got to remove every smidgen of gasket off the intake as well, and its not always completely flat... you got to get in there, and also not remove any metal!!! take your time, dont make a groove which will equal failure later on !!!! scraping much of the time means more like sqeeking the blade along the surface, because you DO NOT want to make even a single scratch! where the gasket is thick, you have to go down layer by layer, wetting it the best you can with (i used brake cleaner) and going down a bit more, patiently. dont rush it and make divots and scrapes in the soft aluminum head nor intake!! the steel block can handle a bit more harsh scraping... be sure to scrape along where the steel head gasket part will go, but NOT from bore out! scrape AROUND the bore... imagine if you made a scratch... and compressed gasses started following it and blowing the gasket out!! so make sure your scrapes are in intelligent fashion just in case it makes a tiny scratch !!!

you can see what i had to take off... not much. i took out the o2 sensor for safety, as it is brittle ceramic. i put a block and a brick under the exhaust to hold it up so it doesnt bend down over time while disconnected.

i started it all out by setting to TDC, spinning off the crank clockwise and catching TDC while spinning clockwise so the slack remained on the correct side of the cam chain...

i wedged the wedge with a bit of oil on the wood only, and put it with hammer taps on a helper block as i kind of wiggled it back and forth so the wedge wouldnt push down the cam chain and cause it be too taut. the wedge securely wedged and required double shoelace with a hammer handle as a handle to yank it out of there! your wedge should be about a half inch thick material so you can get the sprocket off right in front of it more easy... thats how mine worked out anyways. it was all very close and i had to remove the wedge to sand down its trouble areas... it took some time to get it correct.

i put the egr tube together with a bit of tiger tape muffler repair. the stuff is total crap unless you put some sheet metal and a couple hose clamps over it... then it seals up nicely and is unable to blow out. if you can find some high enough temp hose, it would be easier, but i didnt have any and am not sure its even available.

i somewhat soaked my intake gasket in synthetic oil and rubbed it in. same with the paper exhaust gaskets. it helps things seal up and crush down nicely. and it will remove easy later and possibly not even tear up the gasket. next time i may use spray copper gasket sealant, as i understand its basically like a gasket anti stick. i wouldnt use anything on the head gasket though, and the felpro i used was already coated in something probably akin to the copper coat.

the intake comes apart easy with an open end/box end wrench. take your time torqueing the whole deal. i put a tiny tiny bit of RTV where the front cover gasket meets the head gasket, after i cleaned up its protrusion with a sharp razor. also use rtv on the half rounds, but, dont let it get in the oil! it can clog tiny and ultra important oil passageways! take heed.


torque the valve cover in same pattern as head. unbolt head from outside bolts then in, torque head from inner bolts then outer, starting at the exhaust side.

i cut the egr tube instead of attempting to take it apart. a 4 inch angle grinder just barely fits down in there... i cut through and then inserted a blob of grease to catch errant metal pieces... then q tipped them out.

the head bolt holes... first off, i numbered all the bolts as i took them out...

then qtips and brake cleaner in the block bolt holes, and after a fistful of qtips, some full on brake cleaner blasts to blow the crap outta there for the final! then air... if u got it.

be sure all bolts are perfectly clean. then i used a bit of anti sieze and threaded each one in , and even a touch of it on the washers... which fit on the bolts only one way, so pay attention! i torqued the bolts around more than the few times which is recomended... i went like 7 or more times until they were all dead on perfectly even. i also took it apart in more than 3 steps to help ensure an UNCRACKED head.

[AZhitman]

Well-done sir!

[nissanrv]

Thanks for the help everyone!