Stock Studs vs. Enlarged Studs
08-05-09, 06:15 PM
#1
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Stock Studs vs. Enlarged Studs
Stock tension bolts vs. big tension bolts (studs)
It seems alot of people are saying aftermarket studs aren't worth a ****, now.
What's up with that!
It seems alot of people are saying aftermarket studs aren't worth a ****, now.
What's up with that!
08-06-09, 05:31 PM
#5
I remember reading they had this problem in the 60s as well when trying a strong close fit stud.
I *think* it had to do with thermal cycling and the expansion rates of steel and aluminum. Maybe the beefy stud couldn't stretch enough and the tension went through the roof?
If I come across the passage again I will dig up this thread and put the quote in.
I *think* it had to do with thermal cycling and the expansion rates of steel and aluminum. Maybe the beefy stud couldn't stretch enough and the tension went through the roof?
If I come across the passage again I will dig up this thread and put the quote in.
08-07-09, 09:22 AM
#7
Studs are a backwards step from bolts? How do you figure? I'll have to go redesign our 2200 hp pumps here at work if that's the case (sarcasm).
I personally don't believe in using larger studs in place of dowel pinning. The primary loads on the studs is not the rotational stresses but merely the force of holding 5 plates together front to rear. Rotational loads are primarily absorbed by the dowel pins. Detonation forces are trying to push the faces of the rotors inwards and the housing walls outwards. No stud or dowel can help that.
I think the biggest mistake that people make is in thinking that the tension bolts, even larger ones, have a huge impact on controlling rotational twist on the housings. The stock ones being smaller than the hole they insert into aren't doing crap to help this. Larger ones that fit tightly into close tolerance bored holes do a bit better but each sharp little edge from the top of a thread is a stress point and you never want an edge to bear any loads if possible. Round or smooth surfaces are best hence the shape of the dowel pins. While there is some rotational stiffening benefit to be had from new larger tension bolts, it's still mostly controlled by the dowel pins. I design stuff like this all day at work for the oil drilling machinery and loads and their directions are very important to know.
A better option would be dowel pins that go all the way through the engine from front to rear. This reduces the loads from having 4 edges on the ends (which are relieved with a small chamfer btw) since we have 2 dowels back to back and have a total of 4 in the engine. If we could replaces these with just 2 long dowels, we'd spread this load out along the length of the pin better which would help control stresses in the end and intermediate housings. This alone could potentially save S4 housings from breaking at the dowel land locations. Better yet would be to add at least 2 more dowel pins all the way through the engine.
Let the dowels control the rotational forces. Let the tension bolts control the front to rear forces. As for the forces resisting detonation that are trying to split the engine apart in the last dimension, don't detonate! We can't strengthen this area without doing some serious modding to the housings themselves. For most street driven people that don't have 500+ hp that still have engine related strength problems, the dowel issue would take care of much of the problems.
I personally don't believe in using larger studs in place of dowel pinning. The primary loads on the studs is not the rotational stresses but merely the force of holding 5 plates together front to rear. Rotational loads are primarily absorbed by the dowel pins. Detonation forces are trying to push the faces of the rotors inwards and the housing walls outwards. No stud or dowel can help that.
I think the biggest mistake that people make is in thinking that the tension bolts, even larger ones, have a huge impact on controlling rotational twist on the housings. The stock ones being smaller than the hole they insert into aren't doing crap to help this. Larger ones that fit tightly into close tolerance bored holes do a bit better but each sharp little edge from the top of a thread is a stress point and you never want an edge to bear any loads if possible. Round or smooth surfaces are best hence the shape of the dowel pins. While there is some rotational stiffening benefit to be had from new larger tension bolts, it's still mostly controlled by the dowel pins. I design stuff like this all day at work for the oil drilling machinery and loads and their directions are very important to know.
A better option would be dowel pins that go all the way through the engine from front to rear. This reduces the loads from having 4 edges on the ends (which are relieved with a small chamfer btw) since we have 2 dowels back to back and have a total of 4 in the engine. If we could replaces these with just 2 long dowels, we'd spread this load out along the length of the pin better which would help control stresses in the end and intermediate housings. This alone could potentially save S4 housings from breaking at the dowel land locations. Better yet would be to add at least 2 more dowel pins all the way through the engine.
Let the dowels control the rotational forces. Let the tension bolts control the front to rear forces. As for the forces resisting detonation that are trying to split the engine apart in the last dimension, don't detonate! We can't strengthen this area without doing some serious modding to the housings themselves. For most street driven people that don't have 500+ hp that still have engine related strength problems, the dowel issue would take care of much of the problems.
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08-07-09, 11:40 AM
#8
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I have a question.
Doing a little reading, it seems you can't use a stock flywheel for the large studs or stock sized studs. Is this correct?
Also, can a stock flexplate be used with studs?
Doing a little reading, it seems you can't use a stock flywheel for the large studs or stock sized studs. Is this correct?
Also, can a stock flexplate be used with studs?
08-07-09, 01:22 PM
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sheeeesh.....
08-08-09, 10:01 AM
#15
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Pretty sure rotarygod knows a thing or two about rotary engines, I tend to read his posts pretty closely
08-10-09, 08:38 AM
#16
I just looked back at what I typed and I need to correct something. I spoke of the enlarged studs from the standpoint that they were threaded their entire length. Obviously that's not the case. That's what I get for typing that at work while having a threaded rod in front of me! If an enlarged tension bolt had to be machined to fit and if it touches the housings all the way through like a dowel pin does, then yes it will absorb much of the rotational loads that the dowel pins do. That doesn't mean that I wouldn't still rather have them take only 1 directional load while the dowels take another as opposed to multiple directional loads.
08-12-09, 03:16 PM
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i think stud will have advantages if you plan to boost over 30psi.
I have no choice to use the large stud 4 pcs on my 13B-RE because that is the only easy solution to prevent the stock dowel front housing to crack again.
No problem on Clearance between stud with my os giken twin plate
Large stud kit are 1/2" = 12.7mm ,
I send to machine shop to press drill milling , drilled the housing with 1/2" drill bit and the stud cant line up straight , so redrill using 13mm bit and they fit in.
I have no choice to use the large stud 4 pcs on my 13B-RE because that is the only easy solution to prevent the stock dowel front housing to crack again.
No problem on Clearance between stud with my os giken twin plate
Large stud kit are 1/2" = 12.7mm ,
I send to machine shop to press drill milling , drilled the housing with 1/2" drill bit and the stud cant line up straight , so redrill using 13mm bit and they fit in.
08-12-09, 04:40 PM
#18
Im just going to say something.
Everything i have seen in this thread is SIMPLY A THEORY.
It should do this and would do that etc. That kind of info is great when no one has actually tried it.
But like i mentioned in the other thread.
We had an engine that produced just over 1000bhp and with the stud kit, we cracked countless plates. And they would crack from stud whole to the next.
Nothing would actually happen to the studs but plates were dead.
We binned that engine and dowelled it. And the engine has not cracked a plate since. USING FACTORY MAZDA Bolts.
The reason i think some of the theories that are coming such rotorygods one, is because everyone is looking at the problem in the wrong way. By studding the engine you have moved the problem from one area to another.
And if dowelling is done incorrectly you will do the same thing.
Using small CNCed dowells and put in the right place(i.e not anywere near the oil filter or the spark plug whole) will stop alot of plates cracking from what i have seen.
You have taken alot of twist out of the engine by adding dowells in the correct area, but you have not made the engine weaker around the spark plug area. I know it might sound alittle confusing but after trying a few different combos, the above seems to work best.
Another problem with the stud kit that i have found, is cracking on the front plate around the thread area. Simply too big. Not to mention the poor sealing on the back.
As for the guy above who has machined his engine to 13mm to fit a 12.7mm stud. Do you realise you have .3mm between stud and housing? What have you achieved by using studs other then removing a whole lot of material from your engine and make it twice as likely to crack now?
When you dowell an engine, youll get no more then .02-.03mm of clearence. Its a tight fit if done right.
I hope thats a more indepth post. After typing the same thing 100 times gets abit frustrating.
If you think im wrong. Get your engine to produce 700rwhp + and se what happens.
Everything i have seen in this thread is SIMPLY A THEORY.
It should do this and would do that etc. That kind of info is great when no one has actually tried it.
But like i mentioned in the other thread.
We had an engine that produced just over 1000bhp and with the stud kit, we cracked countless plates. And they would crack from stud whole to the next.
Nothing would actually happen to the studs but plates were dead.
We binned that engine and dowelled it. And the engine has not cracked a plate since. USING FACTORY MAZDA Bolts.
The reason i think some of the theories that are coming such rotorygods one, is because everyone is looking at the problem in the wrong way. By studding the engine you have moved the problem from one area to another.
And if dowelling is done incorrectly you will do the same thing.
Using small CNCed dowells and put in the right place(i.e not anywere near the oil filter or the spark plug whole) will stop alot of plates cracking from what i have seen.
You have taken alot of twist out of the engine by adding dowells in the correct area, but you have not made the engine weaker around the spark plug area. I know it might sound alittle confusing but after trying a few different combos, the above seems to work best.
Another problem with the stud kit that i have found, is cracking on the front plate around the thread area. Simply too big. Not to mention the poor sealing on the back.
As for the guy above who has machined his engine to 13mm to fit a 12.7mm stud. Do you realise you have .3mm between stud and housing? What have you achieved by using studs other then removing a whole lot of material from your engine and make it twice as likely to crack now?
When you dowell an engine, youll get no more then .02-.03mm of clearence. Its a tight fit if done right.
I hope thats a more indepth post. After typing the same thing 100 times gets abit frustrating.
If you think im wrong. Get your engine to produce 700rwhp + and se what happens.
08-14-09, 11:04 AM
#19
Theory? If you don't understand it, don't use the generic default excuse that it must be some mystical theory that no one knows how to figure out. I'm not spouting theory. It's all engineering fact. I design stuff like this all day except I have to account for up to 2200 hp (currently) and torque numbers well over 20,000 ft lbs. Theory doesn't work here. I HAVE to know this stuff! The rotary engine isn't some magical little creation that physics don't apply to either. Calculations based on material chosen, thickness, and a host of other things tell you pretty much exactly what is needed. This also tells you your safety factor. It's not difficult and with a little effort it should be possible to figure out roughly how much load in each direction the engine can take before fatiguing and ultimately failing. Even light loads will cause an engine to fatigue and weaken over time. When calculating strength and design life, one important thing to look at is are we designing this around stresses needed before complete material failure or are we looking at material fatigue to a certain level over a certain amount of time? It's all engineering but definitely not just some mystical theory. Like anything else it just needs to be learned and understood and I've found that even many of the best engine builders out there really don't know this stuff. I've always wondered how you can truly improve something when you can't explain why it was engineered that way? One of the great mysteries I guess.
All you can do is spread loads out. If you are pushing enough force into something though you'll break it. We can theoretically use tension bolts that can't be broken. We can theoretically add 10 dowels made of unobtainium to an engine. However we can't easily strength the housings themselves. At some point you'll hit a power level where there is so much force being exerted on the engine that the housings themselves will fail leaving all of our nice strong parts that we added as the sole surviving pieces. You need to figure out how clearances come into play. You need to know how each material properties interact with each other. How much do rotor housings expand with temperature compared to cast iron end housings? At what rate? Do you know how your clearances will change with temperature? Here's an example. When people clearance their seals when building an engine, those numbers are worthless when it's running! It's all different and it's not always a constant.
Going by what othes say works without any proof is typically the norm anymore. This happens alot with engine builders. They strengthen the engine based on what they know to be right by dowelling and using stronger tension bolts. They use "unbreakable" apex seals. Then they boost it to a million psi and still break the engine and claim that "in theory it was good". Nope. You need to understand the whole picture. Different loads require different techniques. People do things a certain way because they've "always done it that way". My response to that is typically "just because you've always done it wrong doesn't make it right today". Then this gets passed on to others who do it a certain way because so and so does it that way.
My point to this is that there are many people that build engines because others use certain techniques yet may of them don't really know what they are doing. They just know certain things are better but can't explain why. When they can't explain it, they claim it's some "theory" that no one knows when the reality is that someone does. They just don't.
Incidentally ever wonder why a diesel engine is so overbuilt compared to a gasoline of the same or lesser power? It has nothing to do with compression ignition as many think it does and everything to do with torque produced. Case in point, an F1 engine that revs to 19000 rpm, makes 800 hp, and has a small light aluminum block. Small torque though which means small twisting forces and hence less required strength in certain areas. The key is in understanding your loads, how much you have, and in what direction that are being applied. Just using stronger apex seals, tension bolts, and dowels doesn't mean you strengthened the engine everywhere. In reality all of these combined have done nothing for added strength in at least one dimension!
All you can do is spread loads out. If you are pushing enough force into something though you'll break it. We can theoretically use tension bolts that can't be broken. We can theoretically add 10 dowels made of unobtainium to an engine. However we can't easily strength the housings themselves. At some point you'll hit a power level where there is so much force being exerted on the engine that the housings themselves will fail leaving all of our nice strong parts that we added as the sole surviving pieces. You need to figure out how clearances come into play. You need to know how each material properties interact with each other. How much do rotor housings expand with temperature compared to cast iron end housings? At what rate? Do you know how your clearances will change with temperature? Here's an example. When people clearance their seals when building an engine, those numbers are worthless when it's running! It's all different and it's not always a constant.
Going by what othes say works without any proof is typically the norm anymore. This happens alot with engine builders. They strengthen the engine based on what they know to be right by dowelling and using stronger tension bolts. They use "unbreakable" apex seals. Then they boost it to a million psi and still break the engine and claim that "in theory it was good". Nope. You need to understand the whole picture. Different loads require different techniques. People do things a certain way because they've "always done it that way". My response to that is typically "just because you've always done it wrong doesn't make it right today". Then this gets passed on to others who do it a certain way because so and so does it that way.
My point to this is that there are many people that build engines because others use certain techniques yet may of them don't really know what they are doing. They just know certain things are better but can't explain why. When they can't explain it, they claim it's some "theory" that no one knows when the reality is that someone does. They just don't.
Incidentally ever wonder why a diesel engine is so overbuilt compared to a gasoline of the same or lesser power? It has nothing to do with compression ignition as many think it does and everything to do with torque produced. Case in point, an F1 engine that revs to 19000 rpm, makes 800 hp, and has a small light aluminum block. Small torque though which means small twisting forces and hence less required strength in certain areas. The key is in understanding your loads, how much you have, and in what direction that are being applied. Just using stronger apex seals, tension bolts, and dowels doesn't mean you strengthened the engine everywhere. In reality all of these combined have done nothing for added strength in at least one dimension!
08-14-09, 07:57 PM
#21
The Wankel Engine
1971
Jan P Norbye
chapter 11 "Toyo Kogyo" (Mazda parent company)
page 272
"Thermal fatigue, as a result of alternate heating and cooling of a given area, was also a problem in early Mazda engines and caused cracking at stress concentration points around the spark plug holes. These cracks, in extreme cases, penetrated to the water jacket. The first approach of the Toyo Kogyo engineers was to improve the cooling to cope with the most critical condition- rapid acceleration of a cold engine. In winder the combustion chamber walls could suddenly rise from a low ambient temperature to 450 deg F. This was the reason for adopting the most modern type of bottom-opening thermostat: one that continuously controlled bypass flow as well as flow through the radiator. A further cause of the cracking trouble was lack of flexibility in the trochoidal walls and conduction of heat from it to the cold end housings through the bolts holding them together. Improved flexibility and reduced heat transfer were simultaneously achieved by separating the side-bolt bosses from the trochoidal wall, and housings made in this way proved completely resistant to thermal fatigue.
-----------------------------------
OK, got it? Thermal stress is causing the cracking.
Remember, between Mercedes, Curtis Wright and Mazda technologies we think of as new or cutting edge like aluminum rotors, ceramic apex seals, direct injection, ceramet wear coatings, side exhaust ports, combo ports, "stud kits", etc were all evaluated in the 50s and 60s...
1971
Jan P Norbye
chapter 11 "Toyo Kogyo" (Mazda parent company)
page 272
"Thermal fatigue, as a result of alternate heating and cooling of a given area, was also a problem in early Mazda engines and caused cracking at stress concentration points around the spark plug holes. These cracks, in extreme cases, penetrated to the water jacket. The first approach of the Toyo Kogyo engineers was to improve the cooling to cope with the most critical condition- rapid acceleration of a cold engine. In winder the combustion chamber walls could suddenly rise from a low ambient temperature to 450 deg F. This was the reason for adopting the most modern type of bottom-opening thermostat: one that continuously controlled bypass flow as well as flow through the radiator. A further cause of the cracking trouble was lack of flexibility in the trochoidal walls and conduction of heat from it to the cold end housings through the bolts holding them together. Improved flexibility and reduced heat transfer were simultaneously achieved by separating the side-bolt bosses from the trochoidal wall, and housings made in this way proved completely resistant to thermal fatigue.
-----------------------------------
OK, got it? Thermal stress is causing the cracking.
Remember, between Mercedes, Curtis Wright and Mazda technologies we think of as new or cutting edge like aluminum rotors, ceramic apex seals, direct injection, ceramet wear coatings, side exhaust ports, combo ports, "stud kits", etc were all evaluated in the 50s and 60s...
08-14-09, 10:55 PM
#22
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I agree with RX72C. Its been my experience that the studs weaken the engine, not strengthen it. Adding dowels, on the other hand, will help you indeed.
08-15-09, 01:09 AM
#23
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Using small CNCed dowells and put in the right place(i.e not anywere near the oil filter or the spark plug whole) will stop alot of plates cracking from what i have seen.
Just another theory... one of these days I will actually getting around to drawing up the irons and doing an FEA. I had the extra dowels in my motor center ground down to 13mm, but have not yet been able to push the motor enough to test them out.
rx72c, could you share any info on the sizes and locations of the dowels you have seen used?
08-15-09, 01:48 AM
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i will answer all your doubts with this i usually dont get technical lol i have tried both and the studs are a 1000% better if u do them right first of all the machining is the most important thing the amount of clearance u leave will determine if the studs work or if u have just purchased them for nothing. i have a cnc program for the stud kit and all i will say is it worked so well that my cranking compression went up many of you wont believe it but i have no reason to lie the short dowels however will work to a point but do weaken the motor. i ran them for 10 years before i made the change and wont ever go back. with the studs not only do you have more clamping force put you have made everything one unit that is unable to twist expand or stretch. good luck to all
abel
abel