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This is my first time rebuilding a rotary, and it's been very interesting taking everything apart. I decided to rebuild the engine after some coolant seals bit the dust. Its an S4 turbo II that was rebuilt about 10 years ago, and has driven about 40k miles since then. I don't know enough about it to determine whether any bits are swapped from other series or years, but the reason for the original rebuild was at least one broken apex seal.
Anyhow, the engine was losing coolant for about 6 months with increasing severity as I drove it at least every other day about 100 miles/day. When it sat for any longer period, I drained the coolant and spun the engine over with some oil poured down the intake to try to prevent rusting. The engine was otherwise running well until the day I pulled it from the car - good compression, easy to start, no overheating or anything. It only lost oil pressure once when an oil cooler line popped getting on the highway a few years prior to the coolant seal issue - I noticed the lack of oil pressure right away, killed the engine and coasted to the shoulder. After replacing the cooler line and changing the oil, the engine ran like new. I was hoping that this rebuild would be simple - just replace the o-rings and button it back up, but the front rotor bearing looked bad enough to give me pause...
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The rear rotor looks fantastic, with no spots where the babbitt has worn through, although there was one line where it was slightly rougher than elsewhere. This may have been from when the car was sitting for about a year between draining all the fluids and getting around to pulling the engine?
There was less than 0.06 mm clearance between the e-shaft and rear rotor bearing (that was the smallest feeler gauge I had), and there was about 0.09 mm of clearance for the front rotor. Too much?
All the main bearing surfaces look ok, with some patches of rub-through but nothing that looked too concerning.
Last edited by toplessFC3Sman; 05-09-17 at 08:28 AM.
Lapping in new bearings takes a while. They are also tricky to remove and install unless you have the proper tools. Feeler gauge isn't necessarily a desired method of measurement. I prefer tubular inside micrometers or a telescoping gauge, but the FSM shows a dial bore gauge which is good for measuring variation. Both a dial bore gauge and tubular mic should be calibrated to the same standard as the micrometer used to measure the bearing, or calibrated to that mic.
According to the FSM, your bearing is very near the high limit of being in tolerance, but since you used IMO a questionable method of measurement, I can't say what your clearance actually is. If it were my engine, I'd either measure it properly and decide from there, or if you can't afford to measure/replace the bearing properly, just say "screw it" and run a heavier, high-quality synthetic oil.
Hopefully the pics are resolved now. I guess something was messed up with the previous google album that they were added to... even though it was "shared", it really wasnt.
I guess I'm leaning towards replacement, but now seems to be the time to invest in a better set of measurement tools.
05-08-17, 07:25 PM
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