renesis removal/rebuild
05-17-2008, 01:40 AM
#27
kevin@rotaryresurrection
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Okay, back to the action.
Front iron mounted on engine stand.
Stat gears with pretty new main bearings...
Rotor housing w/coolant seals and dowelpin orings installed...
Drop it on...
Drop the rotor in, install apex springs.
install coolant seals, lube bearings, drop in e-shaft...
drop on intermediate iron...
Install coolant seals and dowelpin orings on rear rotorhousing...
Lube rear rotor bearing and drop rotor in, install apex springs...
Install coolant seals on rear rotorhousing...
Install rear main seal into stat gear, rear stat gear o-ring and rear stat gear into iron...
Lube rear main bearing...
Drop it on, install and torque tension bolts in sequence.
Flip it over, start on front stack. Thrust plate, thrust washers, spacer installed.
Oilpump, counterweight, OMP drivegear, thermal pellet replacement, etc. installed.
install front main seal in front cover, install front cover gasket and front cover, pulley hub, loctite and torque front hub bolt. Shortblock is now complete. Note my proprietary, baller-status black and gunmetal metallic paint scheme. :D
Flip it over, clean bottom mating surfaces one last time, install oil pickup.
Completely assembled longblock, ready to drop back in and fire up. I had this bad boy in and running approximately 2.5 hours after I took this picture.
Front iron mounted on engine stand.
Stat gears with pretty new main bearings...
Rotor housing w/coolant seals and dowelpin orings installed...
Drop it on...
Drop the rotor in, install apex springs.
install coolant seals, lube bearings, drop in e-shaft...
drop on intermediate iron...
Install coolant seals and dowelpin orings on rear rotorhousing...
Lube rear rotor bearing and drop rotor in, install apex springs...
Install coolant seals on rear rotorhousing...
Install rear main seal into stat gear, rear stat gear o-ring and rear stat gear into iron...
Lube rear main bearing...
Drop it on, install and torque tension bolts in sequence.
Flip it over, start on front stack. Thrust plate, thrust washers, spacer installed.
Oilpump, counterweight, OMP drivegear, thermal pellet replacement, etc. installed.
install front main seal in front cover, install front cover gasket and front cover, pulley hub, loctite and torque front hub bolt. Shortblock is now complete. Note my proprietary, baller-status black and gunmetal metallic paint scheme. :D
Flip it over, clean bottom mating surfaces one last time, install oil pickup.
Completely assembled longblock, ready to drop back in and fire up. I had this bad boy in and running approximately 2.5 hours after I took this picture.
05-17-2008, 03:06 AM
#31
kevin@rotaryresurrection
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None, in my opinion. But, I have never been a builder that favors lapping/surfacing of irons.
We all know of the factory hardness treatment that the iron faces receive. It keeps the irons from wearing prematurely from the side and corner seals, rotor oil seals, and in the case of the renny, the cutoff rings. It is only a few thousandths deep into the surface. Almost any lapping will remove most or all of this hardness.
I dont know how other builders run their operations, I know some of the larger operations lap housings on a semi regular basis. Maybe they are just grinding them flat, maybe they are retreating the housings for hardness after the process. I would say that the latter is the only "right" way to do it, but if it works for them, fine.
I have taken apart a few "recent rebuilds" of rotaries that were built by other shops, with documentation that they were built by them, and lapped. On these engines the customer complains of compression loss and severe smoke and oil consumption, a few thousand miles after the build.
When I tear them down (this has happened several times) I see extreme wear into the iron face...we're talking more than 1/8 of an inch. It looks like a brake rotor that someone let a bare pad backing run against. This in turn chews up the rotor side seals and costs a ton of compression, and causes smoke and oil consumption.
The ONLY time I see this is on recent rebuilds from certain shops. I can only assume that the lapping is the cause of the extreme wear, as I have NEVER seen anything remotely similar on any of the other 400+ cores I have torn down since 2001.
As far as the wear on the iron housings, it is always negligible at worst. We're talking 3-4 thousandths of step wear at 3 and 9 oclock on the face, in about a 2 inch area. There is normally no wear anywhere else on the housing, including the oil seal track. Because of this, I consider the wear to be moot, since compression and oil control will not be significantly sacrificed even when using 100k+ mile irons.
In my mind, I do not like the idea of spending 3-500 dollars (including shipping) for a service that may significantly decrease the life of my rebuild, when I know for a fact that I can save that 3-500 dollars, run the parts I have as-is, and be guaranteed a good running engine with minimal compromise to quality. There are several professional, individual, and armchair builders who agree with my view, and then there are those who would rather lap every iron in every engine they build. IF they can make it work, then good for them. I see no need to take the risk and spend the money.
The rotor housing chrome surface is a MUCH more important area to focus your attention and concerns, IMO. It is almost entirely responsible for the startup, and final compression that the engine will generate.
FWIW, the irons in this build had less than 1.5 thousandths of wear anywhere on the face. They were almost perfect.
We all know of the factory hardness treatment that the iron faces receive. It keeps the irons from wearing prematurely from the side and corner seals, rotor oil seals, and in the case of the renny, the cutoff rings. It is only a few thousandths deep into the surface. Almost any lapping will remove most or all of this hardness.
I dont know how other builders run their operations, I know some of the larger operations lap housings on a semi regular basis. Maybe they are just grinding them flat, maybe they are retreating the housings for hardness after the process. I would say that the latter is the only "right" way to do it, but if it works for them, fine.
I have taken apart a few "recent rebuilds" of rotaries that were built by other shops, with documentation that they were built by them, and lapped. On these engines the customer complains of compression loss and severe smoke and oil consumption, a few thousand miles after the build.
When I tear them down (this has happened several times) I see extreme wear into the iron face...we're talking more than 1/8 of an inch. It looks like a brake rotor that someone let a bare pad backing run against. This in turn chews up the rotor side seals and costs a ton of compression, and causes smoke and oil consumption.
The ONLY time I see this is on recent rebuilds from certain shops. I can only assume that the lapping is the cause of the extreme wear, as I have NEVER seen anything remotely similar on any of the other 400+ cores I have torn down since 2001.
As far as the wear on the iron housings, it is always negligible at worst. We're talking 3-4 thousandths of step wear at 3 and 9 oclock on the face, in about a 2 inch area. There is normally no wear anywhere else on the housing, including the oil seal track. Because of this, I consider the wear to be moot, since compression and oil control will not be significantly sacrificed even when using 100k+ mile irons.
In my mind, I do not like the idea of spending 3-500 dollars (including shipping) for a service that may significantly decrease the life of my rebuild, when I know for a fact that I can save that 3-500 dollars, run the parts I have as-is, and be guaranteed a good running engine with minimal compromise to quality. There are several professional, individual, and armchair builders who agree with my view, and then there are those who would rather lap every iron in every engine they build. IF they can make it work, then good for them. I see no need to take the risk and spend the money.
The rotor housing chrome surface is a MUCH more important area to focus your attention and concerns, IMO. It is almost entirely responsible for the startup, and final compression that the engine will generate.
FWIW, the irons in this build had less than 1.5 thousandths of wear anywhere on the face. They were almost perfect.
05-17-2008, 03:22 AM
#33
kevin@rotaryresurrection
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I would like to run 4-6 thousandths instead of the 12-16 that mazda seems to want to run, using the seals in the standard manner.
Last edited by RotaryResurrection; 05-17-2008 at 03:34 AM.
05-17-2008, 03:42 AM
#34
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+1 on excellent thread and documentation.
i am from NE tennessee. bout 2 hours from you, i will be home for a month in august en route to honduras. i'll have to swing by and say hello/talk shop(meaning, i hope i learn something from you
)
i am from NE tennessee. bout 2 hours from you, i will be home for a month in august en route to honduras. i'll have to swing by and say hello/talk shop(meaning, i hope i learn something from you
)
05-17-2008, 05:46 AM
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That's the best set of pics I've ever seen - thanks heaps for your efforts. How many miles would you expect the owner to get out of that particular rebuild?
TS
TS
05-17-2008, 01:31 PM
#36
kevin@rotaryresurrection
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IT's hard to say. Most of my builds leave and are not heard from again, so I have no real way to track their progress. The rx-7s tend to change hands fairly rapidly, every couple of years in some cases, so there is no way to know for sure. My best guess would be somewhere in the 50-100% of the original mileage range depending on how it is cared for and driven. Obviously, if an all-new-parts engine straight from the factory lasted X number of miles, then an engine with mostly used and some new parts is *probably* not going to equal the original mileage, unless there was some unusual or catastrophic failure of the original at low mileage.
There are also other factors that will make a rebuild less likely to last as long as the original. Here is an excerpt from my DIY rotary rebuild CD/writeup. Parts of it were written with older rx-7s in mind as you can tell, but you still get the idea.
-------------------------------------------------------------------------------------
I developed my build method my examining real world failures of running engines. Ever hear of someone have a legitimate blown engine from a "worn side seal"? What about "yeah, my engine stopped running because my rotorhousings had too much chrome flaking on them"? Or "yeah man, I was driving along and the car died, and my mechanic took it apart and told me I had too much step wear on the side of my iron housings"? Not likely.
Bottom line, exceptional circumstances aside, 3 things go wrong with 95% of all rotary failures: worn or broken apex seals, worn oil control rings, or leaking coolant seals. The other seals and springs wear little to none. You replace those main wear items and reuse the other stuff after close evaluation and you will have a good engine that'll last indefinitely.
As long as the original? Almost certainly not. As long as most people need it to? Almost certainly...these cars are rarely daily driven, and 5-10k/year is the average mileage. So what if you only get 50k out of the rebuild...it's still 4 or 5 solid years! So if the basic $1000-1500 rebuild gets you 50k, and you haven't sold/wrecked the car by the time you need another, you can always go for another basic build, probably get another 60k or more out of it, and STILL be under the cost of ONE "new part" rebuild. You can also do one budget build and apply the savings into mods and make far more power than you otherwise would with the "new parts" engine.
Let's look at the "will it last as long as the original" side of things. When a car is new, people pay a lot for it, they have high financing and insurance to pay. Even though the car was under warranty from the dealer, obtaining proper service could be a pain, so they would rather not tear it up. SO they treat that baby right for 3 or 4 years. Nobody modded these cars when they were new either. This means that all original engines had an easy first few years/50-100k miles, so it's not fair to ask a rebuild to compete with that. In this day and time, most all the owners are younger guys that raise hell and modify their cars. Even if a rebuild is done as good as the original, there's no way it'll last as long as the original did. Add to that that almost all rebuilds have some used part content, and of course it won't be quite as good as new.
There are also other factors that will make a rebuild less likely to last as long as the original. Here is an excerpt from my DIY rotary rebuild CD/writeup. Parts of it were written with older rx-7s in mind as you can tell, but you still get the idea.
-------------------------------------------------------------------------------------
I developed my build method my examining real world failures of running engines. Ever hear of someone have a legitimate blown engine from a "worn side seal"? What about "yeah, my engine stopped running because my rotorhousings had too much chrome flaking on them"? Or "yeah man, I was driving along and the car died, and my mechanic took it apart and told me I had too much step wear on the side of my iron housings"? Not likely.
Bottom line, exceptional circumstances aside, 3 things go wrong with 95% of all rotary failures: worn or broken apex seals, worn oil control rings, or leaking coolant seals. The other seals and springs wear little to none. You replace those main wear items and reuse the other stuff after close evaluation and you will have a good engine that'll last indefinitely.
As long as the original? Almost certainly not. As long as most people need it to? Almost certainly...these cars are rarely daily driven, and 5-10k/year is the average mileage. So what if you only get 50k out of the rebuild...it's still 4 or 5 solid years! So if the basic $1000-1500 rebuild gets you 50k, and you haven't sold/wrecked the car by the time you need another, you can always go for another basic build, probably get another 60k or more out of it, and STILL be under the cost of ONE "new part" rebuild. You can also do one budget build and apply the savings into mods and make far more power than you otherwise would with the "new parts" engine.
Let's look at the "will it last as long as the original" side of things. When a car is new, people pay a lot for it, they have high financing and insurance to pay. Even though the car was under warranty from the dealer, obtaining proper service could be a pain, so they would rather not tear it up. SO they treat that baby right for 3 or 4 years. Nobody modded these cars when they were new either. This means that all original engines had an easy first few years/50-100k miles, so it's not fair to ask a rebuild to compete with that. In this day and time, most all the owners are younger guys that raise hell and modify their cars. Even if a rebuild is done as good as the original, there's no way it'll last as long as the original did. Add to that that almost all rebuilds have some used part content, and of course it won't be quite as good as new.
05-17-2008, 02:03 PM
#37
Fantasic write-up!
Weird side question - about how much would it take to build a show/race renisis as a backup for when if mine fails?
Powdercoated housings, anodized pulleys; good high end stuff. When mine goes; I'll likely be due to an apex seal - so I might as well have a baller longblock ready to go in; and just hand off my original Renny as a core.
Weird side question - about how much would it take to build a show/race renisis as a backup for when if mine fails?
Powdercoated housings, anodized pulleys; good high end stuff. When mine goes; I'll likely be due to an apex seal - so I might as well have a baller longblock ready to go in; and just hand off my original Renny as a core.
05-17-2008, 03:03 PM
#38
kevin@rotaryresurrection
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Well, I dont know about other rebuilders, but I don't sell any outright, or have any pre-built. I do buy cores as they present themselves, but I don't have enough spare stuff to put together a whole engine most of the time. And even if I did, the whole "core exchange" thing never worked out well for me when I tried it. I either got back boat anchors as cores, or had trouble getting people to return them at all. This placed an extra burden on me to continually hunt down more useable core parts, and I had to adjust pricing to cover the junk parts that were coming back in. I was sending out blocks with 10 major reuseable parts, and getting back cores with 4-6 reuseable parts, and those parts aren't free. But, I can't charge the customer for the parts until I see inside the core, but by that time it was already too late anyway.
Instead I decided to do everything based on the customer's exact core instead of doing any exchanging. This leads to longer turnaround but a fairer and easier overall procedure. You have a good core? Your price stays low, and you get to keep all your original parts. You have a boat anchor core? You are held responsible for it's condition with the price of replacement parts. If something comes off of my shelf, it gets paid for right then, no guesswork about what core parts are going to come in on exchange, and no need to raise prices to average in for some people's junk cores.
What would need to happen, for me at least, is for you to obtain your own core and send it to me. IF you want some mods done to the longblock stuff, then you'd need to buy and send in all that stuff too, if the engine you bought doesn't come as one. With exception to internals, any parts you want installed (pulleys, water pump, thermostat, etc.) would need to be purchased by you and sent in for me to assemble.
If you want powdercoating I do offer that service, but not ceramic coating or anodizing, polishing or anything along those lines.
So assuming you sent me a longblock, and I am to tear it down, rebuild it, and reassemble all the longblock accessories again for you, you'd be in the $1500 range if everything in the core were reuseable and it just needed seals/springs. IF the core were like this one and needed bearings, etc. then the price could go up a few hundred.
Powdercoating prices depend on what is getting done. ONly bare metal parts can be coated. The UIM for instance cannot be powdercoated. IF you want something complex like a lower intake manifold, or an alternator coated, they have to be completely disassembled and all the electrical and moving internal parts left out, and the case gets coated. It's really all this disassembly/prep/reassembly that costs when doing powdercoating, the actual act of blasting and coating the parts is not bad at all. To do a few pullies, an alternator case, etc. is 50-100 bucks, if I am doing a whole motor's worth of brackets and manifolds, cost goes up around $250-400 depending on how much stuff. There is not that much on a renesis that can be done, really. Lower intake, alternator, a few brackets, pullies, that's about it, the rest is plastic. I guess you could do the front cover/waterpump housing too.
I have done a set of rotor housings in powdercoat before and they looked awesome when they were done. But after they ran in an engine for several months and hundreds of heat cycles, they looked worse. Aluminum tends to outgas a lot. During the coating process I try to preheat large aluminum parts for at least half an hour to outgas as much as possible before applying the coating and curing. This works well for manifolds and stuff that don't get too hot. BUt the rotorhousings appear to have outgassed after the engine was built, causing lots of small bubbles under the coating. Painted housings don't do this, so I am guessing that the paint allows the outgassing to "breathe" without disturbing the paint too much, so it looks better for longer.
Bottom line, I can powdercoat rotor housings, but I would not really go around recommending it to people based on what I've seen. Front covers and iron housings seem to do fine...the iron doesnt outgas much, and the aluminum front cover doesn't see as much sustained heat as the rotorhousings.
Just for ***** and giggles, here are some pics of powdercoated parts I have done.
My engine bay in my FC, though I have since redone my alternator in black and red:
Instead I decided to do everything based on the customer's exact core instead of doing any exchanging. This leads to longer turnaround but a fairer and easier overall procedure. You have a good core? Your price stays low, and you get to keep all your original parts. You have a boat anchor core? You are held responsible for it's condition with the price of replacement parts. If something comes off of my shelf, it gets paid for right then, no guesswork about what core parts are going to come in on exchange, and no need to raise prices to average in for some people's junk cores.
What would need to happen, for me at least, is for you to obtain your own core and send it to me. IF you want some mods done to the longblock stuff, then you'd need to buy and send in all that stuff too, if the engine you bought doesn't come as one. With exception to internals, any parts you want installed (pulleys, water pump, thermostat, etc.) would need to be purchased by you and sent in for me to assemble.
If you want powdercoating I do offer that service, but not ceramic coating or anodizing, polishing or anything along those lines.
So assuming you sent me a longblock, and I am to tear it down, rebuild it, and reassemble all the longblock accessories again for you, you'd be in the $1500 range if everything in the core were reuseable and it just needed seals/springs. IF the core were like this one and needed bearings, etc. then the price could go up a few hundred.
Powdercoating prices depend on what is getting done. ONly bare metal parts can be coated. The UIM for instance cannot be powdercoated. IF you want something complex like a lower intake manifold, or an alternator coated, they have to be completely disassembled and all the electrical and moving internal parts left out, and the case gets coated. It's really all this disassembly/prep/reassembly that costs when doing powdercoating, the actual act of blasting and coating the parts is not bad at all. To do a few pullies, an alternator case, etc. is 50-100 bucks, if I am doing a whole motor's worth of brackets and manifolds, cost goes up around $250-400 depending on how much stuff. There is not that much on a renesis that can be done, really. Lower intake, alternator, a few brackets, pullies, that's about it, the rest is plastic. I guess you could do the front cover/waterpump housing too.
I have done a set of rotor housings in powdercoat before and they looked awesome when they were done. But after they ran in an engine for several months and hundreds of heat cycles, they looked worse. Aluminum tends to outgas a lot. During the coating process I try to preheat large aluminum parts for at least half an hour to outgas as much as possible before applying the coating and curing. This works well for manifolds and stuff that don't get too hot. BUt the rotorhousings appear to have outgassed after the engine was built, causing lots of small bubbles under the coating. Painted housings don't do this, so I am guessing that the paint allows the outgassing to "breathe" without disturbing the paint too much, so it looks better for longer.
Bottom line, I can powdercoat rotor housings, but I would not really go around recommending it to people based on what I've seen. Front covers and iron housings seem to do fine...the iron doesnt outgas much, and the aluminum front cover doesn't see as much sustained heat as the rotorhousings.
Just for ***** and giggles, here are some pics of powdercoated parts I have done.
My engine bay in my FC, though I have since redone my alternator in black and red:
Last edited by RotaryResurrection; 05-17-2008 at 03:12 PM.
05-17-2008, 03:11 PM
#39
Interesting; thanks for the info - seems like it still might be worth it when I get back to the States.
Shipping from HI to CONUS is just too much $$$ to make it worth it; but I would love to get a nice fully dressed show ready engine to go into my car when/if my current one goes or I just want to swap them and rebuild my current Renny.
Too bad about powdercoating the housings; that would look cool. I guess just some good high temp paint would be the way to go.
Shipping from HI to CONUS is just too much $$$ to make it worth it; but I would love to get a nice fully dressed show ready engine to go into my car when/if my current one goes or I just want to swap them and rebuild my current Renny.
Too bad about powdercoating the housings; that would look cool. I guess just some good high temp paint would be the way to go.
05-17-2008, 11:33 PM
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In your picture titled...
"Intake/compression area of the housing, looks good, no chatter, light wear."
I can see marks on the surface that do look a bit like the chatter marks I have seen in books on the rotary engine's development. You can clearly see what appear to be ripples on the surface of the metal. Are these the beginning of chatter marks (a problem I thought had been totally eliminated), or something else?
Cheers
TS
"Intake/compression area of the housing, looks good, no chatter, light wear."
I can see marks on the surface that do look a bit like the chatter marks I have seen in books on the rotary engine's development. You can clearly see what appear to be ripples on the surface of the metal. Are these the beginning of chatter marks (a problem I thought had been totally eliminated), or something else?
Cheers
TS
05-18-2008, 12:45 AM
#43
kevin@rotaryresurrection
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Maybe I should have said "no significant chatter". All rotor housings will have a very minor amount of chatter as shown there. It is insignificant, though. The chatter talked about as "the devil's teeth" in books and documents about early rotary development challenges, are much more severe, and look like you took a grinding wheel to the housing in 1/4 inch increments.
05-19-2008, 05:52 PM
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These types of posts are starting to scare me more and more. My engine only has 14000 on it now so I feel I still have some hope. I am going to move to 10W-40 oil and go to 3000 mile changes rather than 5000 like I was doing.
Also I am hoping the updated 2009 water pump fits our cars if not I am going to buy the aftermarket one I have seen others using.
Also I am hoping the updated 2009 water pump fits our cars if not I am going to buy the aftermarket one I have seen others using.
05-19-2008, 06:24 PM
#46
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great work from someone who truly enjoys the product made overseas.i am very pleased to know that you took the time to answer questions i did not need to ask.
again great work and hats off to you!thank you.(i'm still learning about my rx8 after four years of ownership)
again great work and hats off to you!thank you.(i'm still learning about my rx8 after four years of ownership)
05-19-2008, 06:30 PM
#47
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All I can say is that I have always, and will always use at least 10-40 or 20-50 in all my rotaries, and have never had issues on engines making as much as 450rwhp. Other armchair engineers may debate back and forth about the merits of the thin versus thick oil, but this is what I have found to work for me and it is what I recommend. I'm not saying I know more than mazda or engineers about the situation, but I would suggest that they had a side motivation to recommend such an inadequate grade of oil for anyone except those in very cold climates...such as emisions or efficiency concerns.
If I get an opportunity to speak to the guy again I will inquire about his oil habits, but he has already paid and taken the car back home 4-5 hours away so I doubt I will talk to him again.
If I get an opportunity to speak to the guy again I will inquire about his oil habits, but he has already paid and taken the car back home 4-5 hours away so I doubt I will talk to him again.
05-19-2008, 06:36 PM
#48
Also I am hoping the updated 2009 water pump fits our cars if not I am going to buy the aftermarket one I have seen others using.
05-19-2008, 10:01 PM
#49
ok RR --looking good. I run a pettit s.c build and it is sorted out pretty good. I still have a core engine--blown #1 that took out the housing AND rotor(deep gouge all the way to the seals edge)--blew a corner and then apex of course. My "good" housing from number #2 has the usual things present, lead sparkplug cracks, some chatter marks and the two mysterious grooves above the trailing sp hole.
Big mystery to me is on one rotor the leading exhaust port edge is 42 cm from the trailing edge of the intake port and on the other housing it is 44. I have a 6 port engine by the way. Ok whats up with that?
?s--is there any work on the exhaust sleeves---any exhaust sleeve insert available? Can you close the gap between the edge of that exhaust sleeve and the housing? Can you get the exhaust port coated and the gap in the lead plug area coated and put a better bevel on it? Or am I chasing fleas?
On tear down my exhaust ports were occluded approx 10% on my 50K engine.
Good write up and pics--appreciate it---i am in ga.
olddragger
Big mystery to me is on one rotor the leading exhaust port edge is 42 cm from the trailing edge of the intake port and on the other housing it is 44. I have a 6 port engine by the way. Ok whats up with that?
?s--is there any work on the exhaust sleeves---any exhaust sleeve insert available? Can you close the gap between the edge of that exhaust sleeve and the housing? Can you get the exhaust port coated and the gap in the lead plug area coated and put a better bevel on it? Or am I chasing fleas?
On tear down my exhaust ports were occluded approx 10% on my 50K engine.
Good write up and pics--appreciate it---i am in ga.
olddragger
05-22-2008, 01:14 AM
#50
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?s--is there any work on the exhaust sleeves---any exhaust sleeve insert available? Can you close the gap between the edge of that exhaust sleeve and the housing?
Can you get the exhaust port coated and the gap in the lead plug area coated and put a better bevel on it? Or am I chasing fleas?
On tear down my exhaust ports were occluded approx 10% on my 50K engine.
Good write up and pics--appreciate it---i am in ga.
olddragger
On tear down my exhaust ports were occluded approx 10% on my 50K engine.
Good write up and pics--appreciate it---i am in ga.
olddragger
You could bevel the plug holes more as they meet the chrome surface, but you would lose a bit more compression as a result. That is the reason that the trailing plughole has a smaller orifice on the chrome surface, to minimize compression loss/blow-around as the seal sweeps over it. The same would go for enlarging the leading plughole orifice, to a lesser extent. I have never heard of anyone doing this, but if these setups continue to reveal a major problem with cracking it may be something I might try to make a part of my builds to relieve stress there. I think that would be more along the lines of putting a band aid on a bullet wound though, I'd rather find a way to prevent the heat that is leading to the cracking.
Some builders sell a "coolant port modification" that supposedly helps bring down localized hot spot temps. I know how to do it, but it seems fairly time consuming for a minimal gain. Perhaps that is something I might give a shot as well once I get to building renesis' on the regular. Right now I have only torn down a few cores and can't make solid generalizations yet. What I know from previous generations of rotary, comes from tearing down 3-400 cores, so I know exactly what is and is not common. It will take a while to get to that point on the renny.