Lost apex seal- please comment on photos
08-03-14, 01:04 AM
#1
Lost apex seal- please comment on photos
I bought this engine from gracerx about 4 years ago. It had around 20K miles all at 10-12 psi with a streetport. My recollection was that it was rebuilt by RX7 Store with a street port.
After I got it, I found that whoever did the oil pan didn't clean the threads and so when the oil pan bolts were tightened, it cracked the bolt hole and the housing. A piece of the rear housing cracked and left a hole. What I did was to fill that hole with JB Weld and then push that piece onto the hole so that the JB Weld and the cracked piece basically are bonded to the housing. I put some grease onto the oil pan bolt and then threaded the bolt in so that it formed thread on the JB Weld.
I did this on the recommendation of a Nascar mechanic and what do you know the thing never leaked a drop of oil from the oil pan (just the turbo).
I put on an additional 35k miles, running 16-17 psi of boost with the aquamist 1s spraying 300 milliter starting at 7psi of boost. I ran Mobil 1 extended 10W-30. I used the Rotary Aviation OMP adapter to inject WalMart Tec3 2-stroke oil. I ran Idemitsu in combination for about a year but then stopped.
Recently, the engine was harder and harder to start (but it will start) after a hot shutdown. It finally lost an apex seal when one of the hose to the wastegate actuator split causing me to overboost. And fuel cut is not good when there is detonation. Apparently 300ml of water wasn't enough to prevent detonation.
Note that in total the motor had 55K from the original rebuild with mileage combined from myself and gracerx. I got this from gracerx for $1K and it was a steal.
Take a look at this picture, note the off-color where the JB weld bonded has a different color (rusty looking). It might be a reaction from the hot oil constantly on the JB weld?
After I got it, I found that whoever did the oil pan didn't clean the threads and so when the oil pan bolts were tightened, it cracked the bolt hole and the housing. A piece of the rear housing cracked and left a hole. What I did was to fill that hole with JB Weld and then push that piece onto the hole so that the JB Weld and the cracked piece basically are bonded to the housing. I put some grease onto the oil pan bolt and then threaded the bolt in so that it formed thread on the JB Weld.
I did this on the recommendation of a Nascar mechanic and what do you know the thing never leaked a drop of oil from the oil pan (just the turbo).
I put on an additional 35k miles, running 16-17 psi of boost with the aquamist 1s spraying 300 milliter starting at 7psi of boost. I ran Mobil 1 extended 10W-30. I used the Rotary Aviation OMP adapter to inject WalMart Tec3 2-stroke oil. I ran Idemitsu in combination for about a year but then stopped.
Recently, the engine was harder and harder to start (but it will start) after a hot shutdown. It finally lost an apex seal when one of the hose to the wastegate actuator split causing me to overboost. And fuel cut is not good when there is detonation. Apparently 300ml of water wasn't enough to prevent detonation.
Note that in total the motor had 55K from the original rebuild with mileage combined from myself and gracerx. I got this from gracerx for $1K and it was a steal.
Take a look at this picture, note the off-color where the JB weld bonded has a different color (rusty looking). It might be a reaction from the hot oil constantly on the JB weld?
Last edited by pomanferrari; 08-03-14 at 01:30 AM. Reason: mileage clarification
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08-03-14, 01:45 AM
#12
Full Member
OH MY! thats the uglyest *** exhaust port i have seen. I don't think this was built by anyone with a brain. I would also guess that it killed your apex seals.
AND you have oil starved. Or started to + the bearings may have been Poorly installed
The color is from a hot spot as far as I know
I maybe way off, sure someone could tell you
AND you have oil starved. Or started to + the bearings may have been Poorly installed
The color is from a hot spot as far as I know
I maybe way off, sure someone could tell you
08-03-14, 08:42 AM
#13
Racing Rotary Since 1983
iTrader: (6)
it is nice that your motor gave you a fair amount of miles. much of what i see is not particularly unusual.
pan bolt issues w re to leakage and stripped threads, especially on the aluminum front cover, are not uncommon. i did a thread on "Oil Pan Tech" in this section detailing proper installation. it does begin w re-tapping all threads.
if the threads aren't clean you won't get proper torque on the bolts (100 inch pounds). it is much easier to either twist off a bolt or strip the aluminum.
your rotor housings, as always, tell a tale. first off, you have Spark Plug Mountain (SPM)... too much retained heat around the sparkplug forces the metal to expand and the only direction is up. in addition something has to give when the mountain rises and that creates cracks.
the SPM forces your apex seal up and off the rotor housing surface. numerous bad things occur. anywhere on your housings that you have carbon your apex seal is off the housing and not, well, sealing.
apex seals are cooled by being in (ideally) constant contact w the rotor housing. they offload heat into the housing which is mostly aluminum and has coolant behind it. apex seals of course are steel and steel, no matter what kind, or seals no matter what brand grow w heat. the two primary mechanical challenges as they make their journey around the housing are SPM and the exhaust port.
if you run as cold a plug as you can more heat will vacate the plug boss area and the height of SPM will be reduced. less lifting of the apex seal.
apex seal lift is caused by SPM, the close of the exhaust port and the minor housing axis.
of course any lifting and you have communication between two rotor faces. hot gas into the intake face... evil.
the apex seal is backed by a spring and is free to move inward and outward. notice the chatter marks.
chatter lifts the seal off the housing, flattens the leading apex seal shoulder which needs to be round, destroys the flat housing surface decreasing compression and adds significant apex seal warping heat to the seal.
fortunately much of the chatter marks can be fixed w a proper diamond hone.
the exhaust port on the BREW is a work of art. it is huge, peripheral, aggressive and of significant duration. the free flowing exhaust port is one of the reasons our 80 cubic inch rotaries can make 690 flywheel hp and live.... for a while.
the port does not need to be enlarged from a flow standpoint. the last thing it needs is to be widened as your port is. widening removes crucial apex seal to rotor housing cooling.
Mazda raised the close on the FD port and any further later close will tend to pollute the incoming charge air w hot non oxygen bearing detonation inducing gas. further, Mazda did a very good job in radiusing the close so as to mitigate apex seal bouncing. someone raised your close and notice the chatter. this is the worst time to have your apex seal off the housing as the incoming charge is entering the adjoining face.
if you do raise the close, generally most limit it to 3 mm. anymore and it pollutes the incoming face. notice you have carbon for at least 2 inches! that is all going into the intake. gasoline auto-ignites around 480 F!
i suggest, don't mess w the close on the FD exhaust port.
carbon tracks tell the story both on the housings and the rotors.
carbon behind the sideseals means your sideseal to corner seal gap is too wide. it should be approx .002 on a properly built motor.
i would not re-use the rotor housings due to the widened exhaust port.
it does appear you have adequate lubrication as your housings don't look overly chromey.... i believe you need a colder plug and a better exhaust port.
the rotor looks nice thanks to AI
howard
pan bolt issues w re to leakage and stripped threads, especially on the aluminum front cover, are not uncommon. i did a thread on "Oil Pan Tech" in this section detailing proper installation. it does begin w re-tapping all threads.
if the threads aren't clean you won't get proper torque on the bolts (100 inch pounds). it is much easier to either twist off a bolt or strip the aluminum.
your rotor housings, as always, tell a tale. first off, you have Spark Plug Mountain (SPM)... too much retained heat around the sparkplug forces the metal to expand and the only direction is up. in addition something has to give when the mountain rises and that creates cracks.
the SPM forces your apex seal up and off the rotor housing surface. numerous bad things occur. anywhere on your housings that you have carbon your apex seal is off the housing and not, well, sealing.
apex seals are cooled by being in (ideally) constant contact w the rotor housing. they offload heat into the housing which is mostly aluminum and has coolant behind it. apex seals of course are steel and steel, no matter what kind, or seals no matter what brand grow w heat. the two primary mechanical challenges as they make their journey around the housing are SPM and the exhaust port.
if you run as cold a plug as you can more heat will vacate the plug boss area and the height of SPM will be reduced. less lifting of the apex seal.
apex seal lift is caused by SPM, the close of the exhaust port and the minor housing axis.
of course any lifting and you have communication between two rotor faces. hot gas into the intake face... evil.
the apex seal is backed by a spring and is free to move inward and outward. notice the chatter marks.
chatter lifts the seal off the housing, flattens the leading apex seal shoulder which needs to be round, destroys the flat housing surface decreasing compression and adds significant apex seal warping heat to the seal.
fortunately much of the chatter marks can be fixed w a proper diamond hone.
the exhaust port on the BREW is a work of art. it is huge, peripheral, aggressive and of significant duration. the free flowing exhaust port is one of the reasons our 80 cubic inch rotaries can make 690 flywheel hp and live.... for a while.
the port does not need to be enlarged from a flow standpoint. the last thing it needs is to be widened as your port is. widening removes crucial apex seal to rotor housing cooling.
Mazda raised the close on the FD port and any further later close will tend to pollute the incoming charge air w hot non oxygen bearing detonation inducing gas. further, Mazda did a very good job in radiusing the close so as to mitigate apex seal bouncing. someone raised your close and notice the chatter. this is the worst time to have your apex seal off the housing as the incoming charge is entering the adjoining face.
if you do raise the close, generally most limit it to 3 mm. anymore and it pollutes the incoming face. notice you have carbon for at least 2 inches! that is all going into the intake. gasoline auto-ignites around 480 F!
i suggest, don't mess w the close on the FD exhaust port.
carbon tracks tell the story both on the housings and the rotors.
carbon behind the sideseals means your sideseal to corner seal gap is too wide. it should be approx .002 on a properly built motor.
i would not re-use the rotor housings due to the widened exhaust port.
it does appear you have adequate lubrication as your housings don't look overly chromey.... i believe you need a colder plug and a better exhaust port.
the rotor looks nice thanks to AI
howard
Last edited by Howard Coleman; 08-04-14 at 02:30 PM.
08-03-14, 11:06 AM
#14
it is nice that your motor gave you a fair amount of miles. much of what i see is not particularly unusual.
i suggest, don't mess w the close on the FD exhaust port.
carbon tracks tell the story both on the housings and the rotors.
carbon behind the sideseals means your sideseal to corner seal gap is too wide. it should be approx .002 on a properly built motor.
i would not re-use the rotor housings due to the widened exhaust port.
it does appear you have adequate lubrication as your housings don't look overly chromey.... i believe you need a colder plug and a better exhaust port.
the rotor looks nice thanks to AI
howard
i suggest, don't mess w the close on the FD exhaust port.
carbon tracks tell the story both on the housings and the rotors.
carbon behind the sideseals means your sideseal to corner seal gap is too wide. it should be approx .002 on a properly built motor.
i would not re-use the rotor housings due to the widened exhaust port.
it does appear you have adequate lubrication as your housings don't look overly chromey.... i believe you need a colder plug and a better exhaust port.
the rotor looks nice thanks to AI
howard
The engine dynoed at 310 rwhp at 11 psi when it was in gracerx car. Despite all the shortcomings in the porting and side seal clearance, it ran for at least 8 years ...
08-03-14, 10:41 PM
#15
Bearings are also done. What spark plugs were you running? I didn't see it mentioned. As Howard stated, too hot of a plug will expand the metal around the plugs causing the cracking. The exhaust port doesn't look to have much of a bevel if any at all, which leads to the skipping marks on the rotor housings. Over time the apex seals will lose radius from crashing into the sharp edge of the port as it closes, and can break a seal eventually.
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