Cooling System Mods

[Barry Bordes]

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.




Add to that chafing of the side plates to rotor housing interface that same spark plug area.




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.







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

[My5ABaby]

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...

[Barry Bordes]

Originally Posted by My5ABaby

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...

I never load the engine cold. I wait for 80˚C before boosting and always use at least a 2 minute cool-down before shutting down (a habit from working on turbine engines which is their requirement).

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.



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

[Phoenix7]

^^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.

[jgrewe]

Basically you make grooves in the water jacket area around the spark plugs to increase surface area for water to get to.

[Barry Bordes]

Originally Posted by phoenix7

^^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.

Originally Posted by jgrewe

Basically you make grooves in the water jacket area around the spark plugs to increase surface area for water to get to.

Most people do the Racing Beat fin mod around the sparkplug area. This is a big help. It adds surface area and flow turbulence.

[Phoenix7]

sounds reasonable, is this common practice (i haven't advanced to internal work so I dunno)?

[blwnrtr93]

Originally Posted by phoenix7

sounds reasonable, is this common practice (i haven't advanced to internal work so I dunno)?

From what I've seen of water jacket ports they are essentially tiers, to increase the surface area, thereby increasing the heat-sinking capabilities.

[Phoenix7]

"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?

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.

[My5ABaby]

Originally Posted by phoenix7

So this was back in the 70s. They've made the improvements on the engine since then to further reduce this problem.

Is there any documentation on that? Regardless, it likely still a sizable issue. This is why I get annoyed when people do cold burnouts and stuff. They're just asking for screwed up housings...

[Barry Bordes]

Originally Posted by phoenix7

"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."

Phoenix7, I would love to read this early research. Even though it is non turbo in its scope.

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?
Actually my rear housing was a RE type which didn't have the latest 3rd gen cooling mod, which contributed to the failure I'm sure.

Are you monitoring exhaust temps?
Yes, front and rear.

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?
Both

How did you lose the motor (under boost/load)?
Merging into 70mph traffic.

What are your mods?
RE 13B, ITO large street port, TO4S, HKS cast divided, 50/50 AI

Do you have close up pics of the sparkplug holes?
Yes, but they are not the best.

It's cool that you're documenting and finding things like this. Thanks.

I will put pictures soon. Thank you for your input.
Barry

[Barry Bordes]

Originally Posted by phoenix7

"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."

Phoenix7, do you have pictures of how "The bosses for the tension bolts which held the engine together were relieved from the inner wall of the housing". Were they severed completely? The housing wall just floated? For how far?

Very Interesting, Barry

[Phoenix7]

Originally Posted by Barry Bordes

Phoenix7, do you have pictures of how "The bosses for the tension bolts which held the engine together were relieved from the inner wall of the housing". Were they severed completely? The housing wall just floated? For how far?

Very Interesting, Barry

No pics at this moment. I'll look and see if I can find the info when I get home. That excerpt came from the most recent book on the rotary egine (released 2007 or 2008) and this section's source was an SAE paper from 30 years ago. I'll let you know which one (in case you can access the SAE papers) in a bit.

Originally Posted by Barry Bordes

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.

I see! thanks, good stuff.

[Barry Bordes]

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.




An early attempt at getting the stock pump to not cavitate by contouring the leading edge.

[Barry Bordes]

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.