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Cooling System Mods
Some thoughts on improving the cooling of the rotor housing in the area of the spark plugs to minimize heat distortion.
Let’s go back to my previous engine failure. Whenever an engine is disassembled I do a failure analysis (an old habit of mine from working on helicopter turbine engines for a large oil company) and attempt to determine the Root Cause. Sounds so simple but like they say,” the devil is in the details”. So first we have the broken apex seal. The very common type failure with the apex seal chip imbedded in the rear rotor and it gouging the housing. Next we have the cracks at the spark plug holes and lifting of the apex seals in that area. http://i287.photobucket.com/albums/l...5-2523_IMG.jpg Add to that chafing of the side plates to rotor housing interface that same spark plug area. http://i287.photobucket.com/albums/l...5-2527_IMG.jpg At this point we have two contingents drawing different conclusions. One thinks we should secure the area better with dowels and or studs. The other group thinks better cooling of the area is appropriate. I started looking for 3 studs to reinforce that area. In my search for studs and reamers I contacted Carlos Lopez. He changed my direction. Carlos thought that creep was a symptom but not the root cause. The problem was high heat and low water flow in that area. He mentioned that the 3rd gen pump was one of the poorest designs. Kenichi Yamamoto's book shows the temps around the plug area. http://i287.photobucket.com/albums/l...usingtemps.jpg My thoughts then went to 1-A better water pump (Mazmart) and, 2- Porting the rotor housing in the hot spots as shown above. Barry |
This heat problem also leads to cracks around the spark plugs when someone takes the revs too high on a cold engine. Just a side note... :D
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^^very good point BUT Mazda improved on the old rotary designs to minimize this damage in the newer (80's+) rotaries. It IS still possible though.
How would you "port" the housing to improve on the hot spots? I am not able to visualize the modification. |
Basically you make grooves in the water jacket area around the spark plugs to increase surface area for water to get to.
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sounds reasonable, is this common practice (i haven't advanced to internal work so I dunno)?
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"Another problem Toyo Kogyo experienced that had been seen at NSU was the formation of cracks in the rotor housing around the sparkplug holes. It was determined that they were a result of "thermal shock" or sudden thermal loads placed on the housing when it was taken from a relatively cool temperature and sharply accelerated to 7,000rpm in all gears on a road test. By developing a test bed procedure that could consistently reproduce these conditions, engineers could then do systematic studies on cooling system improvements and their effect at relieving thermal loads. Tests were showing that on cars driven hard immediately after startup, the temperature of the inner wall of the rotor housing reached 450*F within one minute of startup. This abuse consistently produced cracks in the housing around the sparkplug opening after 4000 cycles.
Improvements in the cooling system brought the maximum temperatures of the rotor housing trochodial wall to below 410*F. But the final improvement was the redesign of the housing itself. The bosses for the tension bolts which held the engine together were relieved from the inner wall of the housing, thereby relieving part of the mechanical restrictions on the part that gets the hottest. Repeated testing after this improvement produced no more cracks in the housing." So this was back in the 70s. They've made the improvements on the engine since then to further reduce this problem. You lost an apex seal in the rear housing and I'm under the impression that the rear rotors tend to blow due to heat/preignition (cooling problems you're addressing) but it sounds like you may have also over-boosted and caused the sidehousing damage? :dunno: Are you monitoring exhaust temps? Are you going to do the cooling mod and the pump at the same time of will you try the pump first and see if the damage occurs again? How did you lose the motor (under boost/load)? What are your mods? Do you have close up pics of the sparkplug holes? It's cool that you're documenting and finding things like this. Thanks. |
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http://i287.photobucket.com/albums/l...oling09224.jpg |
The stock 3rd gen water pump with its square leading edges causes cavitation. Notice the damage is at the leading edge area of the housing.
http://i287.photobucket.com/albums/l...2508_IMG-1.jpg An early attempt at getting the stock pump to not cavitate by contouring the leading edge. http://i287.photobucket.com/albums/l...3-2399_IMG.jpg |
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Barry |
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Very Interesting, Barry |
I actually did two housing mods. The first was to enlarge the passages in the hottest areas next to the sparkplugs as shown in Yamamoto's housing temp diagram.
But use caution! I cut through on the lower side of the Trailing plug. A bad combination of new carbide burs and being too large. 1/4" long shaft would probably be best. http://i287.photobucket.com/albums/l...2536_IMG-1.jpg |
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so the info about the cooling is cited from:
"Toyo Kogyo's Research and Development on Major Rotary Engine Problems" SAE transactions. Paper #700079 for SAE meeting of January 1970. |
Im doing the water jacket mod. Will post pics tomorrow.
Im doing a crappy job BTW. Doing it by hand its quite hard.... it does the job anyways, even if it does not look pretty |
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Another place to look is the flashing left over on the irons from the mold. I go through and clean all of the excess metal off to smooth out the flow.
Dan |
Just for the record:
to do this properly you gotta have great pulse ... or a CNC machine up your ass :D |
On my next set of housings I am going to try a wood router and carbide bit. Routers have great height adjustments.
Barry |
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So I think the cracking has to be just high heat from poor cooling in that area. The housing with the cracks didn't have the 3rd gen housing cooling mods, but both housings were lifting in the spark plug area. Notice the carbon stains to the side of the hole. http://i287.photobucket.com/albums/l...5-2523_IMG.jpg I have a theory that this lifting of the apex seal and jamming of the triangle tip is what breaks the seal in some cases without detonation being present. I found one unbroken but cracked apex seal. It was cracking from the bottom! I visualized them breaking from the top. Barry |
I am thinking that we need to increase the temperature in the carbon stained areas and drop the temp at the plug so I am going to try this.
The slotted spoke will concentrate the cooling conduction effect to the plug boss but not to the housing. Maybe added grooving perpendicular to water flow would also help. Barry http://i287.photobucket.com/albums/l...6-2659_IMG.jpg |
damn, i see what you did. So, how safe is it to remove so much of that metal? What boost do you normally see?
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Normally 14 but up to 20 psi. I checked out a 16X and a rx8 housing for the latest cooling mods. They are similar. But they remove most of the fin that could be used to cool the plug bore.
Barry http://i287.photobucket.com/albums/l...Rx8Housing.jpg |
Very Interesting Barry! I would love to see the results of this mod. Maybe we could get one of the CNC guys to program this in and mass cut the housing... I also like the idea of parallel groves vs. the perpendicular grooves I've seen before.
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Doing some housing mods for a current rebuild. Just setting up a bit to do the common jacket mod.
I was thinking about the fin idea......whats the thoughts on basically standing some AL sheets in the paths around the plugs? I'm thinking if they're sized properly the sandwiching of the engine oculd hold them in.....? Not entirely sure though, I certainly don't want the twisting around and clogging up a vein. |
My best guess would be to oven braze two aluminum fins into slots cut into the main existing fin. Radiator type solder may work.
Barry |
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I dont like the parallel grooves. by observation, coolant flow is horizontal and those grooves seem like a great place to trap air. which would be counter productive to cooling. i would much rather see the parallel grooving. |
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Barry |
can't wait to see the results fellas.
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This weekend im going to the wrecker and ill see if i can grab some garbaged ones to use as an example. |
1 Attachment(s)
Attached a pic of one of the housings I did for my recent (and first entirely solo) rebuild.
I just did the common jacket mod, nothing super special. The only other thing I did thats neat is welded up the EGR holes in the exhaust sleeves and groudn them smooth. Take a good look at a housing next time you get the chance and take note of all the cavities that would be filled with (at WOT +1600F) HOT exhaust gas and soaking into the coolant as a result. Don't know how effective that mod will be, but I'm giving it a shot nonetheless. On the rebuild I'll do on the keg I'm swapping this one for, I plan to do similar jacket grooves (done with a dremel engraver bit on the drill press, nothing too special...) but with my newly found thin and LONG end mill I will add a piece of 1/8" AL to either side of the plug bore on a diagonal. I'll be cutting out a piece from center of the "divider/support" between the dowel bores and then notching the inside and outside edges to provide support for the piece. It will be a minor interferance fit and the sandwiching of the engine will also prevent it from uprooting afterwards. Keep the discussion/thoughts going :) |
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I wonder if you could fuse the 1/8" AL to the "divider/support" for better heat transfer? Barry |
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