only real answer is to use cap nuts.

matt

 

I hope you replace the upper left hand corner one with a stock dowel and dowel pins.  If you use those studs, you just plugged up the turbo oil supply line...



-Ted

 

Ted, the stock tension bolts do not run through the stock dowel pins.
This stud kit just replaces all of the stock tension bolts with studs the same diameter as the tension bolt holes. They do not machine any studs to fit in any non-stock position, so if these studs are installed as per the pictures shown, the stock dowels would also be installed, and the oiling system left untouched.

 

We have been making these studs for our customers race engines for a few years now and we have found it to be very strong and reliable. We also use dowelling on some engines [depending on customers budget] as building an engine with the studs takes ALOT longer to do. What we have found is that after a period of time,the end of the studs DO weep a tiny bit of coolant.
We have rectified this problem by trying different material washers etc. Overall,I have no hesitation using the studs for block strengthening as we have undergone various successful testing.

 

So when will a 20B kit be available?

 

Any word yet on the 20b kit

 

Thanks for all this info guys. I have one more question about replacing the studs. Is it better to machine the studs to fit the housings perfectly, or to machine the housings to fit larger studs?

Also, I'll put up some pics of the porting I'm doing soon. It's nothing special, just a medium/large streetport.

 

Just make sure the studs stretch the same as the OEM tension bolts.

 

Xtreme Rotarys

Pics here.
So who makes these kits, Guru? does Xtreme sell on behalf? I would think that if Guru made them then they would list it on their site but they dont? So who actually makes them??

 

Why? Stretch is a measure of bolt tension and since you're in fact completely replacing the stock tension bolts the studs are going to stretch a different amount when torqued. Since the studs are fatter I would fully expect them to stretch less than the original tension bolts when they are torqued to the same value.

 

They NEED to be able to stretch as the engine expands and contracts with heat.

For example: VW aircooled engines. VW changed the studs that held the heads to less-elastic ones. What happened was the engines started blowing head gaskets regularly. The studs would over-crush the gaskets, then when everything cooled off again, the gaskets would blow out because there wasn't any tension on them anymore. Or what would be worse, they would tear the threads out of the engine case, especially around #3 where the oil cooler was, because that's where the highest heat loading was.

Translate to rotary. The stock tension bolts are designed to work with the engine's stock temperature range, just the right amount of stretchability (I can't for the life of me remember the correct term) without losing tension when the engine cools off.

What happens when you exceed the stock temperature range and overheat? The bolts can't stretch anymore and the housings get crushed as they try to expand against the bolts. Then after the engine cools off, the tension bolts are no longer "tensioned" and the coolant O-rings blow at best, or you lose all cranking compression at worst.

So what happens if you use bolts that don't stretch as much? You might crush the housings at normal engine operating temps, or to combat that you could put less torque on the nuts when you put the engine together, meaning you're more likely to blow a coolant seal on an engine that is still cold and hasn't expanded to operating temperature yet.

One reason why I think it'd be neat to build a 2 rotor using a 20B front and front-intermediate housing. Have two sets of short tension bolts instead of one set of long spindly ones, less stretch needed per bolt set so it's less likely to blow seals when cold. The third e-shaft bearing would be a nice bonus!

 

THIS IS NOT COLDY I have hijacked his I.D. (It's dad, the one he real'ies on for knowledge, food, shelter and machining.) Thanks to all of you for the great info. You guys are right, this is no cheap job. To provide all the studs and machining would run about $800-$1100 at our normal shop rates.He(coldy) thinks this stuff is so easy! I'd hate to have one of the studs seized in a housing. My questions are, would 4140 pre-heat treat (RC28-32) and turned ground & polished be OK? Is'nt 4340 chrome moly? Does the black oxide do anything? The studs pictured look more like they were flame hardened, annealed on the ends for threading, or nitrided. Alignment & proper clearance have to be correct or numerous problems would occur.Also, streching of bolts/tie rods should probably only be done 3-4 times.

 

Just to clarify: Guru Motorsports & X-Treme Rotaries are NOT the same thing. X-Treme is a distributor for Guru products. I think this is where the confusion seems to come in. The Stud Kits are sold by X-Treme Rotaries and are not a Guru product. Both the 10mm & 12.7mm 13B versions have been extremely popular and we have now developed 12A & 20B versions. (12A is available, 20B is rolling off the "production lines" as we speak) The 10mm kit is a direct fit for the current through holes, the 12.7mm kit requires machining and is recommended for anything producing 400+hp.

We also sell kits of 5 studs, which is usually all that's required for street applications.

We machine the plates for AU$395.00. We've developed a set-up that allows us to do all plates at once, which is the only way to ensure accuracy. More & more Australian workshops are sending their plates to us to be machined this way.

 

For the 12.7MM kit, do just machine the end plates, or are the rotor housing machined also? What is the price for the 20b kit?

 

Yeah what IronMdnX said

 

You know, we keep getting into technical discussions. I went and dug this one up because I got reminded of it.

Coefficient of thermal expansion is, I think, the term that you're looking for. How much something expands under heating.

You're absolutely right about what happens if you overheat the engine when the tension bolts have a different rate of expansion than the rotor housing. The thing is, the stock Mazda ones do too. From what I recall, this is the exact cause behind the rotor housings warping after overheating. In fact, just about nothing of any decent tensile strength will have the same rate of expansion as the aluminum housings... aluminum is just too different.

Basicially, I'm just guessing that the stock tension bolts are about the same alloy as the stud kit.

 

Elasticity was the term i was looking for. How much the material can "stretch".

The concept I am trying to describe... it takes a certain amount of force to stretch the bolts. If you go to larger diameter bolts, it will take more force for a given amount or stretch.

Now, yes the aluminum does expand faster than steel. That why, at, say, 270 degrees (rough guess), the amount of force needed to stretch the bolts is greater than the strength of the housings, and the housings crush instead. If you have larger diameter bolts/studs, they won't stretch as much for a given load, so the temperature at which the bolts' strength overcomes the aluminum is lower. How much lower i can't say, without more information. But Mazda used small bolts for a *reason*.

The fact that running a rotary hot will crush the housings, and running heavy load on a cold rotary can blow combustion gases past the coolant seals, says to me that the stock tension bolts aren't elastic *enough*. It's compounded by the fact that the same bolts hold both rotors together, which is why the "2 rotor 20B" is a pet idea of mine.

 

Ahhh... I get what you're saying now. Modulus of elasticity, or Young's modulus, for reference... sorry, I was misinterpreting your argument.

Lemme think about this and run some numbers, and maybe ask my materials professor for input. I think you might have a point... my gut feeling says that you're incorrect, but maybe it's just telling me I need to give it food (har har, stupid joke) My view is that mechanical stretching of the bolts is a much less important factor than stretching from thermal expansion, for reference.

I suspect that Mazda used smaller diameter bolts for other reasons, but again, that's just speculation. On checking the site that sells the studs, they *do* sell a set that's normal diameter though.

Your idea of using two sets of half-length tension bolts should work from a point of view of mechanical stress, off the top of my head. Personally, I dislike the idea of using the 20B housings though, given their added size... but then again, I tend to look at a lot of things as problems to be fixed through custom fabrication of parts.

Again, lemme run some numbers.

 

For the sake of everyone who's bought the stud set, I hope I'm wrong. But... let's just say I want to see some numbers.

There'd be enough custom fabrication in making a 2 rotor 20B, no? I mean, besides the manifolds, and rear tension bolts, you'd need a new E-shaft, and...

Hold on a tic. 20B have larger diameter tension bolts, right? Rear only or front also? Argh, monkey wrench in my plans...

 

Yup. Steel bolts will be about same temp as the surrounding metal/alum. The housing stack height includes mabe 1/3-1/2 high expansion rate aluminum, so bolt load will increase with temp. Most of the difference in growth will be more bolt stretch, and a little housing compression. Stiff/large bolts will have more load change with temp.

At some limiting hot temp, either the aluminum housing crushes/yields inelastically, or, more likely, the studs stretch beyond their elastic range. When things cool, some of the initial preload will be lost if either part yields without elastic recovery.

Larger studs, for same preload force, would be torqued slightly higher (proportional to dia), but would be at lower stress. At that same hot temp, bolts will be at a higher force level, causing more housing compression and thus a little less extra bolt stretch with temp. Net hot stress for the big bolts will be less at the prior limiting temp, since installed stress was lower, and added stress due to temp was less. If bolt yielding was the limit before, then a higher temp can be taken before yielding the big studs. If alum hsg yield was the limiting factor, then things got worse with big bolts.

Normally a single bolt is better than 2 shorties. Stretch length is lost in the center housing, which makes the tension studs act stiffer, with more load change vs temp. I think the 3 and 4 rotor designs likely used dual studs to make assembly easier.

 

That statment to right and wrong
Yes there is a direct replacement size (10mm IIRC) that requires no machining to the holes as described above that keeps the std dowels. There is also a 12.7mm set that requires the engine bolt holes to be radial reamed. The studs are then and exact fit to the holes.

The nuts are a taper fit and the rear plate has the holes retapered to suit as part of the machine work.
The Kits have been in 100's of engines now, there are no dramas or bad side effects of fitting them.

After using these things once you wont want to use the std mazda bolts again, they are just mass produced junk! You really feel the difference when you have the torque wrench on them. The studs feel like a nice tight fastening and the factory bolts feel like there just twisting as you tighten them.

Another thing to mention is that you don't have to go with the full 16 studs, Several motors here in Aus are just running 5 Studs acting as extra more efficent dowels as well as the benifits of the studs not stretching.
The amount you need really depends on what you have planned for the engine.

All the info is on the xtreme rotaries website

 

I guess no one is going to answer our question. How much is the 20B kit?

 

I finished doing all the studding. Put in the engine, tried to start it, and it didn't work. I pulled out the plugs to unflood it, and coolant poured out the rear rotor housing. So I pulled the engine back out thinking I just pinched an inner coolant seal, but nope, wasn't pinched at all. I need to closely examine each housing now, because while reaming out the holes to 1/2", it must have broken through somewhere that would allow it to leak into the housing. Anyone know where it usually breaks through at, and what is the best way to fix it? For now, I'll be putting in my other engine, basically identical to this one except it's using stock tension bolts. So I'll have time to figure out what went wrong with the studding and how to fix it.

 

ones close to the spark plug holes or the exhaust ports are the only places.

matt