Rebuild started but seems like it's been done before

[RX8SE3P]

I started my rebuild recently. Some pictures will be below. Story is that I bought a crap engine without knowing. Blew smoke and here we are.

My dad seems to think that the engine has been taken apart before. It's either that or Mazda never put it together properly. Some of the cam cap bolts were tight, others quite loose. Some of the head bolts were ultra, ultra tight, others rather easy to get out. One of the cam caps was on backwards too. It doesn't affect it but you can see all the numbers faced one way and this one cap was around backwards.

My dad says the engine looks honed recently. Not sure if it is. He cleaned up one of the pistons and you can see it does look quite good. Not sure what to make of all this. They seem high compression ones so I wouldn't think they are aftermarket or new. This is only on the rear head so far (pistons 1 - 3 - 5).

How can I tell if the pistons are standard size when I take them out? Will there be any markings? It just says 21 on it.

[mazdags94]

Geez, if the cam caps weren't torqued correctly (and some were loose) and the head bolts weren't done correctly, then I would question the quality of installation of the piston rings too. It looks like theres some coolant in there. Did it drip when you took off the heads? Also, those heads look pretty gummed up. Looks like the person who did this work didn't like oil changes and wasn't very detail-oriented. Personally, I can't tell if they are higher compression pistons but the cylinder walls look to be in decent shape. If they were honed, judging by what you just mentioned about some areas not reinstalled correctly, I would question the size of the bore. Maybe you were blowing smoke because the bore got a tad bigger after it was honed and there is oil getting by the rings...

It just looks and sounds like the person you got it from didn't know what he was doing.

[RX8SE3P]

Geez, if the cam caps weren't torqued correctly (and some were loose) and the head bolts weren't done correctly, then I would question the quality of installation of the piston rings too. It looks like theres some coolant in there. Did it drip when you took off the heads? Also, those heads look pretty gummed up. Looks like the person who did this work didn't like oil changes and wasn't very detail-oriented. Personally, I can't tell if they are higher compression pistons but the cylinder walls look to be in decent shape. If they were honed, judging by what you just mentioned about some areas not reinstalled correctly, I would question the size of the bore. Maybe you were blowing smoke because the bore got a tad bigger after it was honed and there is oil getting by the rings...

It just looks and sounds like the person you got it from didn't know what he was doing.

I got it from an import wrecking yard. My dad reckons they probably got a crap engine and did a crappy rebuild and tried to flog it off as a good one. He also agrees that they probably installed the piston rings the wrong way around.

Btw yes it dripped coolant during removal, there's no gasket leak. They are high compression pistons which would lead me to believe they are stock sized. As for the hone job that might have happened, I dunno if it's been honed too much. I might need a shop to do some exact measurements or something and fix it up for me.

[mazdags94]

I think you're doing everything the right way. I was very well warned by a local, reputable machine shop not to even try to lightly sand the cylinder walls because they are all an exact measurement. If you cannot ensure that they are all exactly equal, and to spec, then it will throw it off balance (and your rings wont do their job effectively). It could even weaken the cylinder walls.

I would definitely have a machine shop measure it all to make sure it is where it needs to be.

[wytbishop]

It's the little details that make your engine perfect. If it was rebuilt previously and done poorly that would explain much. When your assembling the engine pay attention to the ring gap. It's very important and often overlooked.

The oversized pistons will definitely be marked. Those are probably stock. If you buy oversized pistons for your rebuild they will be stamped with +0.5 or something to that effect. I assume you will be sending the block out for machining. They will tell you the original bore and roundness of the cylinders.

[Collier]

Mmmm... delicious sludge.

[RX8SE3P]

More info, took all of the pistons out.

We found that ALL the rings and even the oil ring expander were installed INCORRECTLY!

They had all the gaped parts directly on top of each other. I'll show pics later and you will see exactly what I mean. The oil ring expander was around upside down on 5/6 pistons.

Funnily enough, the piston that looked the cleanest was the one that had the rings installed the best. The rings were also sloppy on some pistons. We could EASILY take them out of the piston and bend them a lot. Others were quite stiff and hard to get off the piston and did not bend easily.

Definitely an engine that's been screwed around with by complete idiots. The crank looks nice but all the con rod bearings are old. Someone took this engine apart before, screwed around with the rings and stuff, didn't even replace the bearings on the bottom end. It's ridiculous. I'm taking it to a shop to get things measured up and hot tanked.

My dad thinks this is more of a crappy job rebuilding than a worn out engine.

[stoker100]

its good (well sorta) that you have found many small problems that would cause poor performance but nothing serious (damaged), with such a bad job done on it there could have easily been serious damage done. post up some more pics! your making me want to tear down my engine more and more!

[RX8SE3P]

From what I can work out myself, the rings should not have the gap in the same place and should be at least 30 degrees apart or something like that according to the mazda manual. As you can see - the compression rings have the gap right underneath eachother, making a pretty easy path for oil to get past. The oil rings were the same. Correct me if I am wrong but that's what I make of it.

Here's the pics. See the piston ring picture with the compression rings gap in the same sort of area, oil would have been running through here and I'd imagine that I might have lost some compression as almost all the pistons were like this. (explains why spark plugs got so black). The oil expander ring is that crinkle shaped one in the middle. I took the oil rings off this piston. But the oil expander ring was upside down on all piston but one.

Crank looks ok. No visible damage at all. My dad thinks the crank looks ok too. Am still taking the bottom end to a shop to get it cleaned and whatnot.

[stoker100]

can you do me a favour and measure the knock sensor resistance (one of the wires off the know sensor is a shield so you need to measure accorss the red wire and then to the block to get a reading) correct reading should be 560ohms, i got 570K ohms today. cheers.

::EDIT:: actually you dont have to worry about it, apparently the haynes manual is wrong, its supposed to be 560k ohms.

[RX8SE3P]

can you do me a favour and measure the knock sensor resistance (one of the wires off the know sensor is a shield so you need to measure accorss the red wire and then to the block to get a reading) correct reading should be 560ohms, i got 570K ohms today. cheers.

::EDIT:: actually you dont have to worry about it, apparently the haynes manual is wrong, its supposed to be 560k ohms.

Ok no worries. Hey you know the plug right in the middle of the engine (forgot what that sensor is called- is that the knock or crank angle??) - has a broken wire! I just noticed it today. I wonder if that was killing my performance.

Btw, my piston rings and gasket kit arrived today and I'm picking them up tomorrow from the wreckers (who paid for them).

Other good news is that my friend knows a guy who builds up drag racer engines. He's getting me the hookup. Reckons he will hotwash my block and heads etc for virtually bugger all. I'm gonna try get him to check out my valves and do a bit of head work just to make sure everything is good.

[stoker100]

yeah the sensor inbetween the V of the engine is the knock sensor, it should only be 1 wire (coax) and then splits into 2 wires at the connector, if one wire is broken you would get a code 5. you should definitely replace/fix it if the main shielding is broken while the engine is out, as you can imagine taking the IM and coolant tube wont be fun to remove later. (take a pic of where its broken and post it up).

you can test the knock sensor by measuring AC voltage across the two pins and lightly tapping the engine, you should see +50mV when you tap the engine. theyre not cheap ($150+) so i hope its just the single wire on the connector thats broken. let us know how you go.

[Inodoro Pereyra]

RX8: You're right, the ring gaps are wrong. Depending of who you learned from, you should stagger the gaps either 30, 45, 60 or more degrees. Personally, I use 90 degrees in all 4 rings (including the 2 oil scrappers), but others use different angles. The blow off on the piston skirt is a dead giveaway of the quality (or lack of it) of the job performed. Also, even when a picture is not the best way to judge something like that, the hone job looks awfully deep to me, more like sandpaper than honing stones...
I wouldn't be surprised at all if you needed to overbore your cylinders.
Being that you already disassembled your engine, this may be a good time to think about a complete blueprint. If you send your block to be machined, you can get them to align bore your main bearing saddles, and deck the block. Also, even when the crankshaft seems to be in good shape, being the kind of work these people did, I wouldn't trust it without miking every journal to death, and checking it for straightness..
A good blueprint job is not really difficult, just tedious, and you'd end with an engine with better than factory specs.

Anyways, just my 0.02. Hope it helps.

[RX8SE3P]

Thanks for the info, Inodoro.

I took the block to a guy who does drag race motors. They said the bore is ok and we checked with new rings etc. They gave it a proper hone (my friend and the rebuilder). Everything has been hot washed. I'll post some pics up soon, even the piston look almost new.

He's gonna do both my heads for $250 which is cheap. (hot wash cost me nothing because my friend knows him). I'll have to give my friend some money for doing all that for me! Even washed out the oil pan and all these other things. They washed my oil pump too and greased the gears somehow so it's good to go.

Basically they said that there was a crappy rebuild attempt done and they must not have cleaned out the piston properly when doing the rings. That combined with the crappy gaping caused the rings not to seat well and made it blow smoke.

@ Stoker100 - They said my knock sensor is pretty buggered and the wires are heaps screwed. I'm gonna steal the one off my K8 instead, I'm pretty sure that one is good.

[Inodoro Pereyra]

Great, you just saved a ton of money (and work)!

I'm guessing (hoping) you're gonna replace the rings, so here's a little tip: Before putting the oil ring on, take a drill press and drill a few holes on the inside wall of the ring race, radial to the piston, all around the perimeter of the piston. Eight holes at even intervals would be perfect. Make sure the drill bit never touches the lateral walls of the ring race (the walls the scraper rings sit against).
Those holes will provide a path for the oil that splashes on the inside of the piston to get to the oil ring, greatly improving cylinder lubrication. It's not much, but it's a cheap and easy way to make your engine a little better...