Ranzo

Found this when I took my half bridge motor apart. Anyone have an Idea of possible causes?



I have seen something similar posted on the forum but cannot find it for the life of me.

Lynn E. Hanover

The center of the apex seal has overheated and bowed out. This allows blowby at the outer ends. The bow in the center is touching around the plug hole that is machined below the level of the chrome.



Or, the plug heat range is too high for the engine power being extracted. Or, plugs installed with no gasket and have pushed the metal around the plug hole out too far.



Or, the engine ran without an air filter.



EGTs too high. Not enough apex seal lube. Housing worn out. (they appear to be scrap) Too much RPM for steel seals. Water and, or, oil temps out of control.



Or, a combination of any or all of the above.



Lynn E. Hanover

Ranzo

The Apex seals look ok but plug range might be too high. Using ngk 9's. Engine was ran without an air filter.



Using Premix but these housings were used but looked decent. Water and Oil Temps were fine.





So air filter needs to be installed, and maybe should move to a #10 plug and possibly bump up the premix a bit.



Could be possible that the engine needed a bit more timing? It was as low at 4-5 deg in the full boost area.

Lynn E. Hanover

I don't know anything about boosted engines specifically, but, in general, In an NA engine as the revs go up, the cylinder filling goes down, due to intake open times getting shorter. So, the effective compression ratio goes down as the revs go up. So, the NA engine can stand lots of advance. Say 25 to 27 degrees for up to 10,000 RPM. In the boosted engine, the compression ratio gose up with the RPM, because the inlet pressure goes up.



The higher compression ratio needs far less advance. Perhaps even zero and 7 after if you run a split.

A builder familier with boosted engines needs to answer that.



Lynn E. Hanover

Maxt

Mazda seals are bowed out when new, when they warp, they warp inward.

Thats an extreme case, I have seen similar, the rotor seal slot was to sloppy to retain pressure to press the 3mm seal against the housing enough to contain combustion pressure. Measure your seal slots and seals. In the Sae's they say thats where seal pressure and seal movement is most important, when it goes over the housing "bump". As seal weight increase or rpm increases, its also the housing area that loses contact first.

On a boosted motor the inlet pressure only goes up to the wasteagate point, and motor VE falls off after maximum torque just like an n/a engine.

Ranzo

Ok this engine was usng RA classics and was running fine. Looking at the seals I cannot see any bowing in them at all. Are you saying that the engine in the pics is an exteme case?



I was a little worried but the black stuff wiped of easily with just a shop towel.

Lynn E. Hanover

I was told to check steel seals by holding them wear edge to wear edge, to show up any bowing, I have never used metal seals, so I have no data on them. I have built stock engines with them and never had one come back. The only garantee I can give is that I don't know.



For carbon or ceramic seals the face to face thing works fine. Never had any two that were not striaght.



If by RA you mean Tracy Crooks seals, they are for aircraft use with new rotor housings. Although they are very strong and have stood up to over boost and detonation in street engines, they are designed to function up to 7,500 RPM max, for take off, and cruise at a cool lean setting and 6,500 RPM, with cool oil and water.



I suspect (but do not know) that the strength comes from heat treating the entire seal. The stock seals may be a bit softer and have just the wear surface hardened with an electron beam. The stock seals work really well so long as the boost is at stock levels. For NA engines the very best seals are the carbon race seals. The rotor housings look better on each rebuild. For boosted engines above stock numbers the best and most painfull choice is the factory race ceramics, or one of the aftermarket ceramic seal sets. Some come, with corner pieces that reduce the installation time. Ceramic seals against new housings produce very nearly no wear, so long as a fully functional air filter is used.



http://members.shaw.ca/nrsrotorsports/index.html



Lynn E. Hanover

Maxt

I should have known that from the wear lines in the housings.. Why did you take the motor apart?

Measure all the seal thicknesses compare to stock number, and check for variances. Check the rotor slots for wear(v-groove shape from top to bottom).. on the trailing edge of the seal check for sharp edge.

Put them thin edge to thin edge and hold them up to a light source, you should see light at the ends, but none in the middle.light in the middle, they are done like dinner.

Ranzo

yeah I was waiting for this question. Once before while tuning I had a mishap with the vac. line to the FPR come off causing a lean condition and it cracked the rear housing by the dowel pin/oil filter area (you know the place) Repaired the housing and reinforced the entire area with weld. Replaced the seals with the RA ones at that time and have been running the car for more tuning and at two events since then. It has been running strong with no obvious problems but it developed a small oil leak between the rear iron and rotor housing, no big deal, I put some rags there so it would not drip on the track but it got worse and was bother me.



I thought perhaps the O ring did not seal right or had gotten twisted etc during assembly and was showing its ugly face or perhaps after welding the surface was not perfect and was causing the leak so decided to teardown and inspect/repair/replace whatever.



I will inspect the seals tomorrow and let you know what I find out.

Ranzo

Inspected the seals and could not find any sort of deformation on them at all. Gonna go back together with it and see what it does in the long run now.



Thanks for the help