Latest Experiment…Failure!
 

Latest Experiment…Failure!
Water jacket leaking at rear rotor trailing plug. This experiment was to try to improve the cooling of the rotor housing in the area of the spark plugs to minimize heat distortion.

OK you already know the results are failure but let me tell how I got to this point. 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 thought then went to a better water pump (mazmart) and porting the rotor housing in the hot spots as shown above.

Great plans! But is where the problem started. I had just gotten some new long shank carbide burs. Boy do they cut fast. I cut a little too fast and nicked a spark plug thread causing a leak at start-up.

Any thoughts?

Barry

So your saying you cut into the backside of the spark plug thread while porting the water passage?

The car is up and running. So the experiment is continuing.

I made a temporary fix by removing the shorter Iridium BR10EIX plug and installing the two thread longer BUR9EQP and 620 Loctite.

Barry

Yes Tony, here is a picture of the prototype.

http://i287.photobucket.com/albums/l...5-2536_IMG.jpg

Notice the cuts are made through the Racing Beat type grooves and Mazda 3rd gen cooling mod.

Barry

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...5-2508_IMG.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

ive seen engines that have rotted away in the spark plug thread area, its thin!

your fix is a good one though.

Barry,
If you notice Mazda did take a step in addressing this very problem by removing aluminum around the spark plug area with their latest s6 rotor housings. Though I agree 100% that even more needs to be removed from that area to really have an effect. Every little bit counts.....

The BIG question to me is, if Carlos stated that he thought heat was the main cause NOT stress then what does he do to "bring down" the heat? Modify the housing like you? Water pump mods? Are maybe something different.... I think information like this needs to be shared with the rotary community more freely. These little engines have enough going against them for important info like this to not be more freely discussed amongst the community. So, how about it ya'll.... I know all those race prepped engines that the "big" boys build (like Mr. Lopez etc.), aren't keeping cool etc. with just hopes, dreams, duct tape and bubble gum. Come on enlighten us!?



-J

one of the most interesting reads I have seen on the forum in a long time. Please update this.

My next question is: How well can the "spark plug cooling mod" effectively remove heat? I know heat goes to cold but 210c (410F) over and over and over again is a lot of heat to remove. But I guess a little IS better than nothing.

-J

Yes -J, we neophites can only make somewhat educated guesses at what others already know through their hard-fought experiences. It would save the Rotary Community countless unwise experiments if these Gurus could enlighten us. But how can we expect them to guide us without somehow being rewarded for their knowledge and experiences?

Carlos Lopez probably tops the list with his wringing-out high-temp power, for long periods of time, on ALMS endurance racing rotaries. So his opinion is one of the most valuable, but there are many more. It would be great to learn from them.

Barry

Well the practice of slowing the pump down to stop cavitation seems counterintuitive to effective cooling. That also goes for lowering the cooling system pressure.

We need more surface area to be cooled so the fins or grooves will help.

Barry
http://i287.photobucket.com/albums/l...oling09224.jpg

Cavitation is basically caused by the blades moving too fast and creating cavities of water vapor (the water boils under the too-low pressure). So slowing the pump down reduces cavitation.

You want to INCREASE, not decrease, pressure to reduce cavitation. Decrease water pump speed or increase the pump's effective range.

Yes Peejay, but if the main reason for the cavitation is a poor impeller design, like sharp square blade leading edges it has to cavitate! A small nick on a propeller will look like a pot beginning to boil at its sharp surfaces. Notice where the cavitation starts on the pump housing. Right at the leading edge area of the pump.

http://i287.photobucket.com/albums/l...2508_IMG-1.jpg

very important thread....First important "investigative" thread ive seen in a long time. Good work and keep us updated. Thanks for helping the community!

Thanks Iceman and Mirabile,

I should add a little Quiz!

Can anyone guess how I added over 8 square inches of aluminum to help cool this critical plug area?

Barry

I used a Dremel carbide cutting tool with an aluminum spacer to limit the cut depth locked at desired height in a drill press as I moved the rotor housing around on the drill press table.

https://www.rx7club.com/attachment.p...5&d=1134124294

I run Evans NPG+ in a zero pressure system and it really helps eliminate minor leaks and its properties should alleviate the problems of lack of heat transfer at the plugs due to vapor barrier.

Also, can't detonation also cause oscillation of the rotor housing against the side housing in the area you note?

awesomeness

keep in mind that the more material that is removed there will be slower overall coolant speed through the engine. u could counter that by filling in the cooler passages. it seems to me that stock the housings flow coolant nearly equally in all areas when i think it should be modified to concentrate flow more in the areas that need it.

Beautiful job BLUE TII! But not what I was alluding to.

An extra 8.8 sq. inches beyond your great groove mod.

Barry

hhn2002, good thoughts.

We only want to remove material in order to increase flow in the critical sparkplug area.

So we revert to Mazda's original flow rate using original size pulleys, a better pump (Mazmart), and added cooling area (8.8sq. inches).

Barry

Keep in mind also that the rear rotor is seeing the discarded coolant from the front rotor with some interaction from the intermediate plate.

A loop line to this area could be beneficial.

Barry

I don't know the answer to this one. My idea of course would be to keep the temps down to deter detonation.

One thing that “J-“ said about spark plugs made me consider something about cold plugs and why we need them so badly. They are trying very hard to stay cool through heat transfer in this same super heated area and when they can’t keep cool they may cause preignition! Bad Karma as Lynn Hanover says.

Barry

ok, so how did you add 8.8 sq inches to improve cooling here???

Increasing heat transfer surface area would be something to keep in mind. As long as you have constant flowrate increasing volume does only so much. Rate of heat transfer will be gained more by the amount of surface area coolant has in contact with. Ie internal heat exchange fins, but inline with the direction of coolant flow to reduce flow losses.

Agreed, coolant being drawn from the water pump directly, then placed in between the spark plugs would do a lot to alleviate the temperature differentiation of the front and rear rotor housings around the spark plugs.