Mazda 3 MPS L3 Turbo build

Hi Guys,

I have a few queations regarding others experience with the MAZDA MPS 2.3 turbo L3 engine.

Firstly, mine has high ks and oil consumption is to some degree expected, however this engine consumes approx an additional 5lts oil between changes these days which i dont leave any more than about 3000k due to the state of the oil. It goes black within a few hundred km of changing. It doesn't blow smoke at idle but blows plumes of black under power. Now you say rings for sure but my compression test say good consistent compression in all four. It doesn't leak any oil still runs fine just burns shitliads oil. I have replaced the turbo as part of my elimination process. So what has your experience been with these engines as far as reliabilty in this area..?

Ive resigned myself to doing a rebuild and bought a complete engine with a big end knock for next to nothing that had done aboit 130k. I have stripped this down and the big end and main bearings are shot to shit and no.1 big end bearing was in the oil pick up. Now obviously some machaning is required to the crank however my question here is there is some distinct heat discolouation in No.1 big end cap being quite black when the other 3 are a grey colour also black discolouration around No.1 crank jounal. Q. Will this heat adversly effect the rod/cap and crank. I am not chasing big power from this engine but i would like it to run nice and be reliable..? Ive gone this way so i can keep the oil guzzler in use for the time being and do the build at my own pace. Am i playing with fire with this crank and rod..?

Going full circle, I also noticed the wear patterns in the bore on this engine were quite inconsistent and the oil that came out thia engine was black as. So is this common with these engines from factory. Its not the first MPS ive seen around with a sooty tail pipe and bumper. Sorry to babble on but would appreciate any advice/recommendation on your experiences.

Cheers

Gerard

I haven't personally had anything to do with these engines so i can't comment if there is a specific failure mode that's common. What I can say is that if the donor engine you've got has seriously damaged bearings then you may find the crank and rod aren't salvageable. You'll definitely need to grind the crank but if there is serious heat damage then the crank may also be exhibiting some degree of bend and may also show cracking around the fillet radius. Whether or not the rod can be salvaged will depend how hot it has gotten and how much wear is showing. You can have the rod journal resized but if the thing has gotten seriously hot it may affect the heat treatment of the steel. An engine machinist will be able to advise on the chances of saving the components.

With any engine that's had a bearing failure you'll also need to be ultra careful with cleaning prior to assembly to ensure that any trapped bearing material is completely removed. The oil pump may also be worn since it will have been pumping a fair amount of debris through it, and if the engine uses an oil to water heat exchanger at the base of the oil filter, this will need to be replaced.

For sure. Cleaning was a priority. I was doubtful about the rod so thanks for the second opinion. Have an experienced machine shop that ill run it by.

Cheers

Hi. I have a question regarding ring types and bearings. I am progressing with the build and have all my components back from the engine machinist.

My question is in relation to different types of rings. In the engine building course you refer to rings predominantly with a bevelled inside edge and the need to load the rings in the run in process to apply pressure behind the ring. However due to remaing with the factory pistons in my build and availability of aftermarket rings I have gone with Hastings Moly Rings (not my first choice but satisfactory for this build). To the question...

Q1.Why are some ring square edged and can therefor be installed either way up. How do these rings get addition pressure on the bores if they are only reliant on tensile spring prrssure.

Q2. The main bearings in this engine do not have a locating tang. I have not seen this before and thought it was an essential part of the bearing function. Is this common and how does the bearing not want to spin in the main bearing housing...

Cheers.

Hey Gerard, firstly I'd be inspecting the rings for a dot or mark on one side of the ring - if this is evident then this faces up. In some rings which are visually symmetrical, if there is no mark then you can install either way. Regardless of this however, the rings will still have the benefit of the combustion pressure getting behind them. there is always going to be some amount of clearance between the ring and the ring groove and this allows the combustion pressure to get behind the ring even if there is no bevel present on the ring itself.

The locating tang on a bearing shell is for exactly this purpose - Helping to locate the bearing shell during installation. Many people believe these are there to prevent the bearing shell from spinning in the journal but that is not the case. It's the crush on the bearing shells that prevents spinning and while I can't recall any engines I've built recently without locating tangs, they do exist. You just need to be a little more cautious to align them correctly during installation.

Hi Andre,

Measuring my end gaps and finding them to be considerably larger than the factory recommendation. Although they are not at the point of unusable I would appreciate your thoughts on my results against the recommended and if you believe these would lead to excessive or more than desired blow-by and oil consumption. I have used an average to simplfy.

Piston to bore Result - 0.08mm Manufact Max - 0.11mm

Top Ring Result - 0.60mm (0.0236") Man Recom - 0.14 - 0.24mm

Second Ring Result - 0.50mm (0.0196") Man Recom - 0.34 - 0.44mm

Oil ring result - 0.70mm (0.0275") Man Recom - 0.15 - 0.40mm

Manufacturers Ring Gap Max of 1.0mm

As you can see the Top ring and the Oil rings are almost double that of the recommended. Would you consider this to be to large and should I consider going to an oversize ring and file to fit or am I being a bit to fussy on a factory freshen up. I just don't want to risk excess oil consumption as this is my whole reason for this build.

Cheers Mate.

Are you rebuilding this engine with stock factory components? Are all of these components new?

Basically the workshop manual will give you recommended clearances/specifications, and then a maximum (or minimum depending on the component). If you're outside the max/min range then the part is a no-go. The ring end gaps you're measuring are larger than I'd personally like to run, although I have no doubt the engine will run and perform adequately with these gaps. It comes down to what parts you have to select from though and if you're dealing with factory parts then you may have few options.

Basically if you're buying a genuine factory ring set and your bore diameter is within spec, there's no real reason why the ring end gap would be wildly out of spec.