Mazda 2.3 DISI MZR Spun Rod Bearing Advice

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PAoutdoorsman

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I recently picked up a 2007 Mazda MazdaSpeed 6 that had an engine knock/noise. Here is a video that I took of the engine on a cold start. Hammers for a short time then goes nearly silent followed by some light tick noises.

Video of cold engine start

I pulled the cylinder head off and found that the right most piston has indication of getting intimate with the cylinder head. Just enough to clear the carbon from the surface.

pistons1.jpg

pistons2.jpg

So I then dropped the oil pan and pulled the piston from that cylinder to find a spun rod bearing.

rodbearings1.jpg

rodbearings2.jpg

rodbearings3.jpg

I'm hoping to get some advice from people with a lot more knowledge than me. Could I possibly re-bearing onto this journal from what you can see? I'll mic it tonight and compare measurements to the factory service manual specs.

rodjournal1.jpg
 
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Originally Posted By: PAoutdoorsman
Originally Posted By: madRiver
What makes you think its a spun bearing?



Pics in post above.


I saw a video of motor....Pics are clear and better you posted them.
 
How deep is the imprint of the piston on the cylinder head?
If the piston has been contacting the head, there have been a lot of abnormal forces stressing the engine that it wasn't designed for. The picture of the crankshaft shows some heat discoloration, so it has probably been weakened. The big end of the rod has been hammered on by the loose rod bearing and probably wouldn't have adequate crush on the replacement bearing. If you can buy a remanufactured shortblock and finish building it with your upper end, I think that is the best way to go. If you try to rebuild what you have, it will probably fail again, and end up costing you more in the long run.
 
Don't just mic the crank in one place...if the piston has been hitting the head with a spun bearing, there's a good chance that journal is out of round. If you mic it in several places, you might be able to see that the crank is out of round. In which case, you junk that engine.

As A_Harman said, even if it mics OK, this might end up being a heartache job...where the crank is now slightly bent from all the abnormal impacts and no matter what you do, it'll just fail again and soon.
 
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To repair this properly you need to pull the engine and crank. Have the block checked and if necessary align bored and crank checked for straightness, have it ground and balanced.
I would have the bores checked and bored/honed if needed and put new pistons and at a minimum check the rods dimensions and magnaflux or just put new ones in it.


By the time you do all that, do the head, replace the oil pump, etc a good used low mile engine might be a better and cheaper alternative, certainly faster.

49.gif
 
Originally Posted By: A_Harman
How deep is the imprint of the piston on the cylinder head?


There is no depth to the imprint. Just like the piston, it has the carbon cleared, but that's about it. The previous owner had it roll backed from where it started making noise. Of course myself and a few other potential buyers started it to listen to it to get an idea of what we were up against.
 
Originally Posted By: Astro14
Don't just mic the crank in one place...if the piston has been hitting the head with a spun bearing, there's a good chance that journal is out of round. If you mic it in several places, you might be able to see that the crank is out of round. In which case, you junk that engine.

As A_Harman said, even if it mics OK, this might end up being a heartache job...where the crank is now slightly bent from all the abnormal impacts and no matter what you do, it'll just fail again and soon.


Thanks. I'll get measurements at as many locations as I can, as well as measurements from the guys next door for comparison.
 
Originally Posted By: Trav
To repair this properly you need to pull the engine and crank. Have the block checked and if necessary align bored and crank checked for straightness, have it ground and balanced.
I would have the bores checked and bored/honed if needed and put new pistons and at a minimum check the rods dimensions and magnaflux or just put new ones in it.


By the time you do all that, do the head, replace the oil pump, etc a good used low mile engine might be a better and cheaper alternative, certainly faster.

49.gif



I'm not sure there are good used low mile engines out there. This model was only built in 2006 and 2007. And I think only about 10,000 units each year. Maybe the MazdaSpeed 3 used the same engine for a time. The non-turbo version of this engine was used in a lot of stuff, but it has some subtantial differences.
 
The CX-7 had a turbocharged version which I believe was the same engine attached to an automatic transmission.

Although the Mazdaspeed6 was only made for a few years, the Mazdaspeed3 had a much longer production run and you should be able to source an engine from those much easier than perhaps finding a speed6 engine. The problem with these is that you want an engine that was not abused by the previous owner...

I own a mazdaspeed3. Check mazda forums as they should be able to confirm the engine fitment accross different models.
 
Trav's way is the best way, but it will live a long life if you don't find any obvious problems after a close inspection.

First off, the crank is done. You don't munch a bearing like that and get away with re-using the crank (not long term). Send it off and have it re-hab'ed. Before you do though, pull the remaining rods/pistons and spin the crank in the mains. Does it "feel" smooth? Even, no catches or roughness? Remove the crank and VERY CLOSELY inspect the journals and bearings. Look for even wear on all surfaces.

If:

1) all bearings are into the backing, the block and crank need to visit a machine shop

2) Parts of the bearings are considerably more worn than other parts- like the edges being worn into the backing, the block needs to visit a machine shop

3) One whole bearing is toast, the block needs to visit the machine shop.


If the crank spins nice and the bearings look good, then in all likelihood, it'll be okay for many thousands more miles.

If all you have is superficial marks on the head of the piston, I'd personally run it again- but only if the skirt looks the same as it's friends in the other holes. Hone the bore with to the appropriate finish for the rings.

The rod will need re-conn'ed... no two ways around it... PERIOD. Unless it's a fractured cap, then you may simply have to replace.




Two of the engines powering the cars in my sig have been re-done in the same way I detailed. One died from a MASSIVE intake leak- I hand polished the cranks=, new bearings, blah blah and ran it. It currently has 50k miles on it. Runs fine, burns no oil. The other was ran out of oil and pounded a rod bearing out of it. That one took a piston and rod, new bearings. Crank needed turned too. It now has almost 30k miles on it. Runs great, does not burn oil.
 
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Another thing to look into if you go forward with the build would be tuning options. These cars really need a quality aftermarket tune for longevity. It seems like the speed6's are really plagued with motor issues. From my understanding a big killer is a long highway drive and then heavy throttle to pass or similar situation.

Also I believe engines from Mazda are about $3500 or there's other options out there like CP-E that have short blocks.

Either way good luck with your adventure! They are very cool cars.
 
Sorry I neglected to include the history I did have on the car. The previous owner owned it for just under 2000 miles. He bought the car and was not aware it was burning oil. Of course he wasn't checking it, and as such he ran it low. I assume to the point of the oil pressure light coming on. After that he started checking and adding oil as needed until it began making noise. So this damage is likely a result of the low oil. He thought it was dropping almost a quart every 200 miles.

Looking at the oil rings, the expander rings are completely coked shut. I suspect this is the reason it was using oil in the first place. Not sure the oil could make it to the oil relief holes in the ring groove. Would you agree? Take a look...

expanderrings1.jpg


expanderrings2.jpg
 
I pulled the rest of the pistons. Here are some pics of all the rod bearings. The rod journals for cylinders 2, 3, and 4 all look beautiful, and mic identically at all locations. The journal for cylinder 1 measures .006 less than all the others on the left side of the journal, and .008 less than all the others on the right side. Strange as that sounds, but the right ~1/3 of the journal is worn slightly smaller.

To me, it looks like the bearings have gradually less wear as you move from the one side of the engine to the other. With cylinder one having the spun bearing, and cylinder two showing deeper wear in the bearing than 3 and 4.

rodbearings4.jpg


rodbearings5.jpg


rodbearings6.jpg
 
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