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cardana24

Bad Compression After Head Gasket Job??

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I have a 1999 mazda 626 with the 2.5 engine. My Dad and I just finished a head gasket job on the car because we thought the head gasket/s were blown. When we first got the car it did not run and the guy said he got it hot and the head gasket/s blew. The rear head obviously got really hot because the spark plug boots were melted to the plugs. Once I saw this, I check the timing just to make sure that was not the problem (timing was fine) and proceeded to take the heads off. When we took the heads off we took them to a local machine shop. They check them, and they were both warped. So we had them resurfaced. We put the new heads on with new gaskets, and I put a new timing set on the car and thought we would be good to go....I was wrong.

I went to his house today to figure out what was wrong with the car, and when I cranked it sounded like it did not have compression so I did a compression check...here were the results

1 3 5

80 30 60

2 4 6

60 30 60

So I put some oil in the cylinders and did the compression test again just on the front cylinders to see if it would make a difference, and it did but it only increased each cylinder by about 10psi....I assume that is not significant enough to say the piston rings are causing this problem?

*also, a few things to note about the compression test. 1) All 6 cylinders held their compression well, even though it was low they were not bleeding off. 2) I did a compression test on the front three cylinders before I started this job and the readings were the same as after the head gasket job 3) On both heads the compression is higher on the outside cylinders than the cylinder in the center...not sure if that points to anything or not....I just thought it was odd

Once I did this I started pulling everything off to check the timing. Once I got everything off, I verified the timing is still set properly...so that's where I am now.

What could cause me to still not have compression??? We did not have the block checked, because we left the engine in the car. Head gaskets on the wrong head (i.e. left side head gasket installed on the right side upside down)? I'm shooting in the dark at this point. Any help??

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It has to be valve timing, even though you checked it. Wild guess: some sort of damage to the crankshafts? But the center cylinders being low is very odd.

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It has to be valve timing, even though you checked it. Wild guess: some sort of damage to the crankshafts? But the center cylinders being low is very odd.

I'm open to ideas, but I lined up the dots on the cams and installed them. Then each cam that has a gear on it has a dowel pin....so you can't put the gear on wrong. The crank pulley has a key way...so that's can be put on wrong. What am I missing?

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1 dowel pin location? Maybe it's different for the 93-97 but mine has 2 dowel pin locations and it is possible to put them on incorrectly. That may not be the case for you I don't know. It is possible however to have put the wrong gear on each cam. That would certainly screw up your timing and compression numbers. If you get no compression loss that means your timing is on though as the valves are sealed and you aren't getting any leakage through the rings. So your mechanical timing as of right now is true. Since you say your ignition timing is set properly too then yeah that's a head scratcher. The loss has to be going somewhere... wait a sec. Have you tried using a different compression tester or are sure that one is good? I remember a similar topic like this not too long ago and have no idea what it was or how it was fixed. Obviously something is not right here. There's no way you can get those low numbers while having your timing correct and not have any kind of bleed off. Just doesn't make sense.

You didn't remove the engine. You resurfaced the head but not the block. What were the warp numbers like? My guess is you could also be losing some of it through the head gasket area simply due to the block side not being trued before reassembly. If you have warpage you have to do the block and the head before putting another gasket in there or of course you'll have issues.

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okay...I cannot sleep, because I think I may have realized what some of my problem could be. As I stated before I verified that all of the timing marks lined up...and they did. But when Initially setting them I never made sure I was on the correct rotation of the crank, I never checked to see if I was on the compression stroke on the number 1 cylinder...I am thinking that maybe I set the heads right but the crank may be 360 degrees off. Is this a possibility or am I not thinking about this right?

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Definitely a possibility yes and people do it all the time. Some of our most experienced enthusiasts have done it. It happens so don't beat yourself up if that ends up being the case. Besides not being on the compression stroke getting the cam gears on the wrong cams will have close to the same effect but I don't think it would mess the compression numbers up as much as being 180 out.

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I can't get my head around it either. But being 360 off on the timing might make sense. The firing order is 123456, so if 2 and 5 are low that means it's symettric, with every third cylinder in the firing order having low compression. Like 1,low,3,4,low,6,1,low,3,4,low,6,1,low,3,4,low, etc.

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I will not get a chance to re set things until this weekend. The car is at my parents house and I will not be able to get to it for a few days. I am really hoping this is what the problem is.

*Also, while we are talking about timing and compression stuff. What is considered a significant increase when it comes to adding oil to a cylinder for a compression test? Like I stated above adding oil only incresed my compression readings by 10 psi per cylinder....I would not consider that significant, but I am just curious what other people have to say. I have never delt with a car that has bad pistion rings, that's why I am unfamiliar with this.

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NickR you're right it's 360 out not 180. I never even realized that till now thanks. Don't worry about the rings right now. Just take one thing at a time. As long as your cylinders don't differ by 15% between each other and you're within the min/max tolerance you're good. Right now just concentrate on getting that timing on.

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Yeah, the crank needs to be turned 360 degrees and that is considered to be 180 degrees off on cam timing (since it takes two turns of the crank to complete one turn of the cam gears)....that's the way I understand it.

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Its extremely rare for a iron block to warp. Ive never once had a block resurfaced from a blown headgasket. The much softer aluminum head usually warps and fails long before the iron has a chance too. I do always check the surface to make sure its true though.

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Its extremely rare for a iron block to warp. Ive never once had a block resurfaced from a blown headgasket. The much softer aluminum head usually warps and fails long before the iron has a chance too. I do always check the surface to make sure its true though.

Wait, our engine block is made out of iron except the head is aluminum!? :blink2: I feel stupid, I didn't know that :ike:

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My bad, i was going off his sig and not paying attention. the FS is indeed a cast iron block, with an aluminum head. But obviously the KL is all aluminum!

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Wow that's still something totally new to me and wondered why Mazda did the iron block and aluminum head on the FS but not the KL engine.

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My bad, i was going off his sig and not paying attention. the FS is indeed a cast iron block, with an aluminum head. But obviously the KL is all aluminum!

yeah sorry guys. My sig is not what I am working on. I had a 98 4 cylinder but it's gone. I currently have a 99, 2.5 and a 2000 2.5

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okay, I turned the crank around 360 degrees. hooked everything back up, and did a compression test again. The numbers came up some but not where they should be. I am wondering what could be affecting my compression numbers? I know the engine being cold with make them a little low, but they are still super low. Some cylinders around 60 others around 100psi. What could cause my number to be low? I added a little bit of oil to a few of the cylinders and compression numbers only went up 10 psi again. Would the lifters not having oil affect the compression? I don't know if putting it back together and seeing if it will start at this point is a good idea.

*Does anyone have a picture of the cams how they should look when cylinder 1 is at tdc? I am almost positive I have the right bank correct but it is so hard to get a good look at the rear marks where they should line up. If the timing is off by 1 tooth would it really make compression numbers that low?

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Hmmm the 2.0 does have solid shims but I've never heard of the shim getting so out of spec. If anything I think it would be harder to push the valve down so your compression numbers would be unusually high and it would have an extremely loud ticking. You've obviously got something wrong there. At this point I'd recommend taking it to a mechanic. When I did my head rebuild I took mine to a mechanic to get it timed correctly. I didn't have the same issue with the timing that you are but I still had to take it to a mechanic for fine tuning because I don't have a timing light so don't feel bad. I think it's time you find some local help.

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Possible that the compression rings are damaged as well. I had a PT cruiser come in for a head gasket job, and after bolting everything together (btw, that job is 11 hours flatrate), I was getting 50-50-180-180. Figured the new used head was warped, I pulled it back off, sent it to a shop, it was true. Threw a level on the block, it was perfect. Disgusted, I dropped the pan and pulled the pistons. The two low pistons had damaged compression rings due to heat. This explains why oil wasn't helping the cause but 10psi. They were cooked, like literally damn near crispy.

I'm a mechanic by trade, I've seen it all (well, almost), and I can tell you you're probably looking at a re-ring if your timing is spot on. Not to worry though, the head gasket kit is only $90 off ebay with bolts, $60 without. If your bolts are new, you can reuse them as the car hasn't heat-cycled. Rings aren't expensive either, though if it were me, I would just search a good used DE, swap over appropriate sensors and accessories, and go. All depends on how much time and money you have. If money outweighs time, get a motor. If time outweighs money, get a rebuild set. With the heads off, you can do everything with the block in-situ.

Good luck, you'll probably need it.

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There wasn't bleed-off in the PT.

I've seen this kind of issue come up a couple times now and still haven't found an answer. If that's what you experienced in the PT then my understanding of faulty rings is wrong which is entirely possible because I'm still learning. That would be nice if it does turn out to be the rings because honestly we see these kinds of compression numbers come up a couple times a year now. There's got to be an explanation for it and if the rings are responsible for making compression numbers like this well honestly it would make sense. I don't understand why there wouldn't be any bleed off though. If massive compression is lost but it's able to hold 30psi in the rings just seems unlikely to me. Blown would be blown.

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Possible that the compression rings are damaged as well. I had a PT cruiser come in for a head gasket job, and after bolting everything together (btw, that job is 11 hours flatrate), I was getting 50-50-180-180. Figured the new used head was warped, I pulled it back off, sent it to a shop, it was true. Threw a level on the block, it was perfect. Disgusted, I dropped the pan and pulled the pistons. The two low pistons had damaged compression rings due to heat. This explains why oil wasn't helping the cause but 10psi. They were cooked, like literally damn near crispy.

I'm a mechanic by trade, I've seen it all (well, almost), and I can tell you you're probably looking at a re-ring if your timing is spot on. Not to worry though, the head gasket kit is only $90 off ebay with bolts, $60 without. If your bolts are new, you can reuse them as the car hasn't heat-cycled. Rings aren't expensive either, though if it were me, I would just search a good used DE, swap over appropriate sensors and accessories, and go. All depends on how much time and money you have. If money outweighs time, get a motor. If time outweighs money, get a rebuild set. With the heads off, you can do everything with the block in-situ.

Good luck, you'll probably need it.

Yeah, thanks man. I really don't know what to do at this point. The car is not in that great of shape over all so I was trying to fix it as cheap as possible. I currently also have a 2000 2.5 with a bad engine and I bought an engine out of a 96 626 to put in it. If that goes over well then I may do the same thing with this car...I just more work. But quite frankly I can change the engine quicker than I can do a head gasket job/re ring....it's kinda a money thing at this point.

If the rings are cooked it should show up on a leak down test right? I took my cylinder leakage tester over to my parents house and dropped it off with my Dad. I have not talked to him in a few hours so I am not sure if he got around to using it. I am guessing that will shine a light on what my problem is.

There wasn't bleed-off in the PT.

I've seen this kind of issue come up a couple times now and still haven't found an answer. If that's what you experienced in the PT then my understanding of faulty rings is wrong which is entirely possible because I'm still learning. That would be nice if it does turn out to be the rings because honestly we see these kinds of compression numbers come up a couple times a year now. There's got to be an explanation for it and if the rings are responsible for making compression numbers like this well honestly it would make sense. I don't understand why there wouldn't be any bleed off though. If massive compression is lost but it's able to hold 30psi in the rings just seems unlikely to me. Blown would be blown.

I was thinking about this, and I am thinking there may be a check valve in the compression tester, if that is the case then a compression test would never show bleed off if that is the case. Does anyone know if this is the case? I could try blowing in it to figure out, but I did not bring the tester home with me.

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Here's the link to a doc file of ProbeTalk Leska's write up on replacing the timing belt. IIRC it has some photos of the timing marks: http://home.comcast.net/~mmunoz70/z/leskatimingbelt.doc

I thought that there had to be a check valve in the compression tester. Otherwise measured pressure would drop to zero on the exhaust stroke. (But I may be misunderstanding the question.)

The 1999 2.5 has solid lifters. But I don't ever remember reading about anyone needing to adjust the shims.

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