I just dismantled an S4 13B I recently purchased this week. The previous owner said it was suffering from a blown coolant ring, and that the engine would run for about 45 minutes before requiring a coolant top-up. They never mentioned anything about vibration or any other odd symptoms that would lead one to replace an engine. Upon disassembling the engine, I found all coolant seals to be intact (the water pump was clearly seeping coolant) but found the side plates to be junk.

In trying to diagnose what caused this wear (gouging) on the side plates, I initially thought the eccentric shaft was bent. I measured it as recommended by the FSM. Run-out, as measured at the end of the crank pulley side, was well within factory specification. But now that I think about it, if it were a bent eccentric shaft, gouging would be found around the entire perimeter of the housing and not in the one spot.

I then remembered that the rotor that faced that plate had a significant amount of material removed for balancing. So much in fact that I think they would have broken the surface had they removed any more material. It isn't just a few spot drills, the entire corner of the rotor seal face is milled down. It looks like whoever was assembling this engine *really* wanted to make sure this rotor was used.

I can see how the wear was caused by imbalanced rotor given the wear pattern on the plates... but it's hard to imagine that Mazda would assemble an engine with an improperly balanced part.

Anyone have any idea what caused this?

Pics (sorry if they are too big - I want you guys to be able to see detail)

Front plate:


Intermediate plate - Front Rotor


Intermediate plate - Rear Rotor


Rear Plate


Rear Rotor and Housing:



^ If you look close at the far rotor tip, you can see how much material was removed.

I appreciate the help!

 

was the front cover o ring ok?

 

Man, my eyes must be getting bad because I'm not seeing the damage. Are you talking about the oil seal tracks? I can't see the rotor problem either. Maybe more detailed pics?

 

^ i'm with him on that.

 

Ok... maybe it's not gouging, but there is an excessive amount of wear on the narrowest part of the side plates... directly beside the bore for the stationary gears.

Maybe I'm just being naiive or I have been lucky to have seen engines with mint side plates... but that looks like excessive wear to me. Given that the mileage of this engine is unknown, is it possible that this is just a really high mileage engine and that wear is normal?


If you mean the O-ring that seals the oil passage between the front plate and the front cover, yes it was fine.

 

high wear on the side plates, plus the rotor hitting the side plates, is either the oil pressure was a little low for a while.

i was going to say abuse, but ive done and seen 10k+ abuse, and not really seen damage/excessive wear like that.

 

How much of a step is that side plate wear? It's hard to tell from pictures, but sometimes those lines can look pretty bad but you can barely feel them with your finger nail.

And I can't see anything on the rotor, you need a better pic.

 

I found out the engine has about 230,000km on it. I don't know about oil pressure, the bearings don't look like they went without oil.

I haven't measure yet but they are deep enough to catch a finger nail on.

 

To me - that looks like really worn irons. Thats all.

And I can't see the removed material on the rotor either......better pic is needed there. But I certainly don't see anything out of the oridnary for an old N/A, looks like typical wear to me.

 

With that many km's on it you should expect lots of wear on the plates. A couple thousandths of an inch wouldn't be abnormal.

 

my friend pulled an engine apart once that had no front cover o ring, and thus low oil pressure. the bearings looked decent, but everything else was totally shot (1/8" of wear on the side housings!).

the bearings are relatively large, so if its just driven normally with low oil pressure, they dont really show it, and it just wears side plates and seals and stuff.

sounds like yours is just a high mile engine though

 

Now that you mention it... there was a rubber O-ring between the front cover and front plate, but the plastic spacer was absent. The O-ring was stuck to the front plate though, which means to me that it maintained a good seal. If oil was leaking from that point, the O-ring would have been loose and just fallen right out when I removed the front cover.

I'll ask the PO about the oil pressure.

 

Thats just a high mileage worn engine is all. If the rotor came in cotact with the side plates there would be deep grooves and more damage to other components. Those marks that you see are just caused by the side seals,corners seals, and oil seals going round and round millions of times and it causes wear. You have to look in a rebuild manual because I forgot the specs and measure the worn areas with a dial indicator. If you can feel the grooves with your fingernail, then they are most likely out of spec. From the pictures it looks like they are beyond specs and either need to be lapped or turned into boat anchors.