the best way to fight it that i have noticed is to just make sure the coolant is always fresh and mixed with distilled water, changed yearly, with good engine grounding.

my car also had a brass radiator, one less sacrificial anode and one reason why mine was so abnormal compared to all the rest of the engines i have torn down.

i'm still finishing up the porting and then i will treat the surface in a few days and get pictures after i smooth the surfaces and harden them.

 

I had something similar done in a motor of mine and ended up with a cracked spark plug hole, and it wasn't a high HP application. Dunno if they were directly related, I didn't take too good a look at the busted housing, but it's possible that this sort of mod can cause stress raisers in the material that allow cracks to begin.

 

i suppose that it may still not be enough to keep the plug holes from cracking.

how many miles did you put on the engine before pulling it apart and were they used housings or brand new? the cracking is perfectly normal but something that should be avoided if possible by any means.

 

isnt there anything that can safely coat the water jackets to prevent any build up? like how they have paint for the v-8's to help with the oil...ill check my magazine to get the name in a few

 

the best heat transfer is a raw surface, adding any coating will just reduce efficiency, aluminum has a hardened protective surface when oxidized anyways. an example of this is anodized aluminums, but the cooling system can do this on it's own however it can also continue to anodize the surface indefinitely(like submerging an aluminum part into a battery and applying voltage it will eventually disintegrate down to the base metals leaving basically an aluminum goo like jello and copper particles), as referred to in the "sacrificial anode" discussion earlier. adding a buffer may be better but also counteracts the benefits made from the modification. oxidizing the surface to start with is much better than leaving it raw and starting the anodizing process on it's own, leaving the majority of the cooling system heat transfer properties intact.

the OEM cast rotor housings already have hardened oxidized surfaces in the passages, which mazda left alone i assume because it didn't greatly negatively impact the cooling system heat transfer properties(rather it protects them), if there was no drawback i assume they could have cleaned the passages prior to the final milling stages which would have taken minimal work, the external housing surfaces have a much more raw aluminum finish which leads me to believe that they oxidized the internal passages on purpose for the reasons i mentioned.

 

The thermal conductivity of oxidized aluminum is nearly an order of magnitude less than that of plain aluminum. If the coolant passages are, in fact, oxidized, any effort to remove the oxidized surface would be hugely beneficial for the cooling of the housing.

 

perhaps that is why racing beat leaves them raw and submits them only for racing applications but my purpose is to get the most out of the modification for street driving purposes which is what most cars now are built for. also depends how much you oxidize the surface, the more black/greyed it becomes the less of the aluminum is on the surface leaving the copper behind which conducts less heat transfer than the aluminum. the stock housings aren't oxidized much and hold up for long periods of time.

perhaps later on a non customer vehicle i can play with protective coatings.

 

Used housings on a rebuild. Maybe 15k miles I forget, but a lot of them were on the track. Only one housing cracked.

Do you know what I'm talking about when I say a stress riser? I don't know how much engineering background you have...

 

Do you know what I'm talking about when I say a stress riser? I don't know how much engineering background you have...

.. stress riser? You are talking about the cracking of a chrome surface on a stamped steel insert cast into an aluminum housing where the opposite side of the aluminum would be machined for this mod....

You want to look into the expansion rates of chrome, steel and aluminum to find the forces at work with the very common spark plug hole cracking.

 

it's common in more than just those cases, many automobile heads tend to crack between the intake and exhaust valves because the heat can't be evacuated fast enough so it heats the most, in most cast iron cases this is a bad point for expansion/contraction cracks to form. in bad enough cases they would crack beyond the hardened valve seats into the passages or into the coolant jackets in even piston engines which have much cooler combustion temps. the cracks always form at a 90* angle to the apex seals on the rotor housings, sometimes some chatter is noticed if the cracks are bad enough, which i assume is what you mean by "stress risers". i still haven't seen the cracks really affect the seals too much or cause premature failures but i still don't like them present.

 

I tried to read this whole thread, but only a couple mentioned any corrosion or electrolysis.

Also, the raw aluminum immediately builds an oxide that inhibits the heat exchange, but the increased surface area is a plus. I do all of mine, because it makes me feel that I'm going the extra mile. But then none of mine are streetable.

I believe that anything you can do to better the heat dissapation is a good deal. But there are allso a load of placebos out there in the Rotary world.

EDIT: Calculon mentioned the oxidation item. If you could coat the AL with something, it would help to reduce the oxidation.

GD

 

What I mean by stress risers is imperfections (such as machining marks) in the surface of a material, which can lead to cracks. Stress is at its greatest concentration at the surface of a part, so any scratch, sharp angle, etc is going to be stressed and can lead to the formation of a crack. Once the crack starts the amount of material at the spot is reduced, and the next time it is stressed it can crack more, etc...

 

Exactly, but have you ever seen a housing crack on the backside of the spark plug hole in the aluminum?

 

never myself, just the chrome face. i have seen a number of housings that electrolysis-ized through into the spark plug hole and exhaust port jacket. aluminum doesn't have a tendency to crack unless bent more than a 90* angle regardless of heat/contraction exchanges. cast irons/steel/chrome will crack when heated and cooled too rapidly in succession at weak points(imperfections in the surface, think of pouring hot water on a windshield with a tiny rock chip and think of the plug holes as that rock chip) aluminum will just laugh at you or melt/shatter if it gets hot/cold enough(cold usually not being an issue..).

i can think that the porting helps keep the surface cooler but i can also think that it also cools the surface more rapidly once the combustion heat is removed(engine off with some coolant still cycling through the system slowly). it may still effectively cool the surface too rapidly and not be beneficial to help from keeping the plug holes from cracking. but it should still be beneficial for keeping internal combustion temps lower and reduce the chance of hot spots inside the combustion chamber. basically plug hole cracking seems to be inevitable based on theory and feedback, there may be a cure for that issue but the question is, is it necessary? i haven't seen much ill effect from plug hole cracking so far even in high horsepower applications, although i don't like the thought of the exposed cracked edges being possible hot spots in the chamber.

 

Karack,
Consider increasing the flow on #5 below with a little porting. Mimic the factory racing housing water passeges.
Barry

 

How did your rerouted coolant experiment work?

Playing with 10v Audi coolant bleed modifications, I've been thinking of rerouting some coolant from the water pump outlet (engine inlet) directly to the spark plug area.

 

i did notice that the lower spark plug passage was a bit restrictive.

 

mazda has been doing that for years in some of their race cars. they inject coolant smack bang right into that area.

also, look into how the rx8 rotor housings are modified in that area.



vs this

 

interesting ideas concerning more modifications at internal cooling, keep em coming!

too bad i've been slacking off at getting these rotor housings all finished in a timely manner but it will be soon.

 

The way I machine the water jacket housings is fast, simple and cheap.

I clamp a piece of plywood to my drill press to move the housing around on and use a dremel bit (with a spacer floating on the shaft to control cut depth) as a mill bit.

I change the depth control nuts on the drill press around so that it is locked at a certain depth, make the cut, then set the depth deeper for the next cut (which is easy to gauge using the depth rule).

 

it's crazy that i came across this now because i was working on a set of rotor housings last night and thought about starting a similar thread both to see if i could get a discussion started and to see if people with better experiences would chime in on techniques.

this is my second time doing it on an engine, however, i never got to test it. my first set of housings are still sitting in my garage right now and i have no idea exactly when i'll get to use them. the housings i'm working on right now should be in an assembled engine within the next 3 to 4 weeks.

not being at home to work in my own garage right makes me think my first job was done better than my current attempt, but i did my best with what i had to work with.

see? this is one of the things i was curious about. 30 hours per set? taking into account that you probably have a deeper technical understanding (metallurgy, physcial chemistry, etc.), i'm tempted to think that i'm doing something wrong. all in all, it took me about 5 hours to do a set of housings - tops! also, that number included a few breaks here and there.

 

as one of the handful of guys aound here that i respect (and admire) their work, i'm just curious ... how fast is fast?

 

Blue TII, Can you post a pic of your gigarig setup with a iron on the press. Me very curious

 

i'm just curious ... how fast is fast?

I did my first set of housings in an afternoon. Probably same as you- about 5 hours.

My second set went a little faster mainly because I wasn't so paranoid something was going to go wrong.

Blue TII, Can you post a pic of your gigarig setup with a iron on the press. Me very curious

Its just as simple (rigged?) as you are thinking. Drillpress, sheet of plywood, rotor housing, dremel bit... safety glasses!

 

i had thought about something similar but i figured it would be almost as difficult to get a bit in there without breaking something or stab myself in the eye with flying shrapnel. i may have to give it a try and see how it goes though with something similar to save my arms some cramping.

the motor has been back together for a few months and is just about finished with break in(almost 1k miles), seems to be doing a little better temp wise than before but i won't know until mid summer when it will reach it's peak temp wise and on the dyno pushing 20+psi. i did all the faces inside the ports however, making it slightly more difficult to maneuver inside those ports, i figure it will help the effect if it is uniforum throughout but it also turned into much more work than i bargained for and was cursing by the end of it.