strok question
10-29-2011, 04:57 PM
#61
Three Wheelin'
I met a guy that worked on the Indy cars that Gordon Johncock drove in the early 70's that
used the 4 cyl turbo Offy engines. Several of the top teams had what appeared to be be rod failures.
Turned out that the pins were deflecting due to the high momentary forces of combustion, transfering the deflection into the rod/ bearing/ crank. Those were pure race engines with centered rods.
There is a lot of things happening at the pin end.
Why would you not want the rod to be centered and the pin well supported by the piston?
Enough things can go wrong without building in trouble.
used the 4 cyl turbo Offy engines. Several of the top teams had what appeared to be be rod failures.
Turned out that the pins were deflecting due to the high momentary forces of combustion, transfering the deflection into the rod/ bearing/ crank. Those were pure race engines with centered rods.
There is a lot of things happening at the pin end.
Why would you not want the rod to be centered and the pin well supported by the piston?
Enough things can go wrong without building in trouble.
Last edited by Jim Devine; 10-29-2011 at 05:32 PM. Reason: add
10-29-2011, 05:51 PM
#62
Rennlist Member
I met a guy that worked on the Indy cars that Gordon Johncock drove in the early 70's that
used the 4 cyl turbo Offy engines. Several of the top teams had what appeared to be be rod failures.
Turned out that the pins were deflecting due to the high momentary forces of combustion, transfering the deflection into the rod/ bearing/ crank. Those were pure race engines with centered rods.
There is a lot of things happening at the pin end.
Why would you not want the rod to be centered and the pin well supported by the piston?
Enough things can go wrong without building in trouble.
used the 4 cyl turbo Offy engines. Several of the top teams had what appeared to be be rod failures.
Turned out that the pins were deflecting due to the high momentary forces of combustion, transfering the deflection into the rod/ bearing/ crank. Those were pure race engines with centered rods.
There is a lot of things happening at the pin end.
Why would you not want the rod to be centered and the pin well supported by the piston?
Enough things can go wrong without building in trouble.
The real question is just what, if anything should be done about it. The answer is, NOTHING!!!!
Jerry Feather
10-29-2011, 05:54 PM
#63
Rennlist Member
On the other hand, what you are saying is that due to the "high momentary forces of combustion," even with EVERYTHING CENTERED there is still the possibility of rod failure. SO?????
Jerry Feather
Jerry Feather
10-29-2011, 05:58 PM
#64
Rennlist Member
Yes, obviously the piston will not be rocking like suggested, due to the tight clearances. However, there will be an unnecessary torque applied to one side of the piston, trying to rotate it side ways. This will create extra friction, which will not only reduce power but also increase wear that eventually causes failure.
Jerry Feathr
10-29-2011, 06:02 PM
#65
Rennlist Member
Come on you guys!!!! I am beginning to feel a little like Columbus, or whoever, who thought the world was round when every one else was certain it was flat.
Jerry Feathr
Jerry Feathr
10-29-2011, 06:06 PM
#66
Rennlist Member
Im also wondering..if the cylinder bored are not as rigid "in space" as they would appear..similar to pinning or posting a honda block?
Just following what I think..as a non-anything expert here, to the concept of forging into solid forms -vs- the not so solid and fixed in space 928 cylinder. (Again following what the honda people have dealt with with a similar open cylinder design in the block).
Again, total n00b here..just wonderin'..
10-29-2011, 06:55 PM
#67
Three Wheelin'
On the other plane, what we have been discussing, with any offset the piston can not rotate around anything, there will be an uneven force on the rod bearing and the bushing on the rods small end. The piston will try to rotate the wrist pin from one end to another, this alone should be obvious that there should not be any offset, its not natural for the pin trying to swap ends, that would be a big fail. It will be like trying to rotate the crank shaft from the flywheel side to the front pulley side.
And about those race engines failing, its hard to speculate what went wrong without actually inspecting the engines, like Greg has said before.
In our case Greg's argument is valid since he has actually opened a few "failed" 928 stroker motors that used the chevy offset. Its possible that some of the other builders that used chevy offset have actually modified the rods to either eliminate the offset or reduce it, maybe that's why some failed and some didn't.
One thing's for sure, Greg is the only 928 stroker builder that has come forward providing his experience.
Can you think of a reason why other builders are not coming forward to provide their experience and discuss this issue?
10-29-2011, 07:51 PM
#68
Rennlist Member
The wrist pin is round, in this plane it is normal for the piston to lightly rock (rotate around the pin) side to side. That force is transferred to the crank shafts rotation. The force will not try to bend anything, since the assembly was meant to rotate in that direction.
On the other plane, what we have been discussing, with any offset the piston can not rotate around anything, there will be an uneven force on the rod bearing and the bushing on the rods small end. The piston will try to rotate the wrist pin from one end to another, this alone should be obvious that there should not be any offset, its not natural for the pin trying to swap ends, that would be a big fail. It will be like trying to rotate the crank shaft from the flywheel side to the front pulley side.
And about those race engines failing, its hard to speculate what went wrong without actually inspecting the engines, like Greg has said before.
In our case Greg's argument is valid since he has actually opened a few "failed" 928 stroker motors that used the chevy offset. Its possible that some of the other builders that used chevy offset have actually modified the rods to either eliminate the offset or reduce it, maybe that's why some failed and some didn't.
One thing's for sure, Greg is the only 928 stroker builder that has come forward providing his experience.
Can you think of a reason why other builders are not coming forward to provide their experience and discuss this issue?
On the other plane, what we have been discussing, with any offset the piston can not rotate around anything, there will be an uneven force on the rod bearing and the bushing on the rods small end. The piston will try to rotate the wrist pin from one end to another, this alone should be obvious that there should not be any offset, its not natural for the pin trying to swap ends, that would be a big fail. It will be like trying to rotate the crank shaft from the flywheel side to the front pulley side.
And about those race engines failing, its hard to speculate what went wrong without actually inspecting the engines, like Greg has said before.
In our case Greg's argument is valid since he has actually opened a few "failed" 928 stroker motors that used the chevy offset. Its possible that some of the other builders that used chevy offset have actually modified the rods to either eliminate the offset or reduce it, maybe that's why some failed and some didn't.
One thing's for sure, Greg is the only 928 stroker builder that has come forward providing his experience.
Can you think of a reason why other builders are not coming forward to provide their experience and discuss this issue?
10-29-2011, 10:42 PM
#69
Drifting
ROTFLMAO.
Not to get into this to much, but I know that piston slap is real and that is why as Greg said most piston wrist pins are off centered to minimize the slap.
Also it should not be rocket science that if the rods do not hang down perfectly square on the crank journals, that beyatch is going to come apart and stick that rod out the side.
So what am I missing as I have only scanned this thread.
I was looking for the HP vs Tq war.
10-29-2011, 10:52 PM
#70
Former Vendor
Jerry, I'm sorry you don't understand the problem. If you ever build an engine....you will.
10-29-2011, 11:01 PM
#71
The problem forming here is that when you have a somewhat complex (its not complex , really, though) and abstract mechanic conversation, and it takes place in a public forum like this, everyone can "contribute" - and I suppose rightfully so. The PROBLEM here, however, is that when you allow everyone to contribute, as we must, you can't avoid the inevitable "monkey in the courthouse" sort of situation. Someone who is so purposefully ignorant and who fundamentally misunderstands even the most simple concepts, yet takes others comments as some form of false-positive on the righteousness of his "opinion" - and therefore is almost a "self-propelled" problem.
The more the conversation moves forward, and the more people simply avoid making any direct statements like "You are incorrect and fundamentally misunderstand the most simple physical forces and leverages in an IC engine" - the more it gets completely destroyed (the technical conversation) with complete nonsense perpetuated by the one who is completely wrong in the first place.
What I am "concerned" about in these instances is that there are "silent" contributors who subscribe to these threads, read them, and possibly could take away COMPLETELY erroneous information from said "monkeys" and could even spread that info to other places.
So I am going to try this once. And only once - as really, if it continues, I will only have two choices after putting out the correct info just once - I will either attempt to ignore the thread, or come back and start calling people immature yet funny names - like douche nozzle. But I am not calling anyone that name at this point, so this post should not be removed.
To think that the forces involved in an explosion inside of a combustion chamber, which is intended to forcefully push down on a piston which is only suspended in the cylinder laterally by very thin steel but spring-tensioned piston rings, and is suspended in the cylinder vertically by a steel member (called the rod) which rides while operating ON A LAYER OF HYDRAULICALLY pressurized liquid, are negligible, is laughable, completely misinformed, and speaks to the true purposeful ignorance that can breed very serious and expensive mistakes even in the most-simple life operations.
Its as if the concept of clearances and the fact that almost the entire assembly rides on a cushion of oil - the only barrier between metal pieces - the absence of which would allow metal-to-metal contact if there are undue twisting and rocking forces - is completely lost or purposefully ignored.
Even more clearly, I can tell (as can many others) that this misunderstanding also shows that there is no hands-on experience in building an engine - of any type of IC engine - in any way, shape or form. Because if that experience had been had - the understanding of how the piston (and its required clearances) is held in the bore would exist. This understanding clearly does NOT exist for "some".
Lastly - the combustion process is a violent, nominally uneven event that happens (on a molecular level) differently EVERY time. Therefore ALL mechanic connections and clearances need to be repeatable and acceptable - with no unevenness on the underside of the "lever" that is receiving these forces.
As Greg explained - once formed as an idea - it is so simple to understand. My opinion is that either the misinterpretation and suggestion that greg and Carrillo are incorrect is a Joke, or we are truly dealing with someone who should be kept away from the sharp knives.
The more the conversation moves forward, and the more people simply avoid making any direct statements like "You are incorrect and fundamentally misunderstand the most simple physical forces and leverages in an IC engine" - the more it gets completely destroyed (the technical conversation) with complete nonsense perpetuated by the one who is completely wrong in the first place.
What I am "concerned" about in these instances is that there are "silent" contributors who subscribe to these threads, read them, and possibly could take away COMPLETELY erroneous information from said "monkeys" and could even spread that info to other places.
So I am going to try this once. And only once - as really, if it continues, I will only have two choices after putting out the correct info just once - I will either attempt to ignore the thread, or come back and start calling people immature yet funny names - like douche nozzle. But I am not calling anyone that name at this point, so this post should not be removed.
To think that the forces involved in an explosion inside of a combustion chamber, which is intended to forcefully push down on a piston which is only suspended in the cylinder laterally by very thin steel but spring-tensioned piston rings, and is suspended in the cylinder vertically by a steel member (called the rod) which rides while operating ON A LAYER OF HYDRAULICALLY pressurized liquid, are negligible, is laughable, completely misinformed, and speaks to the true purposeful ignorance that can breed very serious and expensive mistakes even in the most-simple life operations.
Its as if the concept of clearances and the fact that almost the entire assembly rides on a cushion of oil - the only barrier between metal pieces - the absence of which would allow metal-to-metal contact if there are undue twisting and rocking forces - is completely lost or purposefully ignored.
Even more clearly, I can tell (as can many others) that this misunderstanding also shows that there is no hands-on experience in building an engine - of any type of IC engine - in any way, shape or form. Because if that experience had been had - the understanding of how the piston (and its required clearances) is held in the bore would exist. This understanding clearly does NOT exist for "some".
Lastly - the combustion process is a violent, nominally uneven event that happens (on a molecular level) differently EVERY time. Therefore ALL mechanic connections and clearances need to be repeatable and acceptable - with no unevenness on the underside of the "lever" that is receiving these forces.
As Greg explained - once formed as an idea - it is so simple to understand. My opinion is that either the misinterpretation and suggestion that greg and Carrillo are incorrect is a Joke, or we are truly dealing with someone who should be kept away from the sharp knives.
Last edited by BC; 10-30-2011 at 01:41 AM. Reason: editing of word usage.
10-30-2011, 09:54 AM
#72
Rennlist Member
If the wrist pin can be .050 inches offset in one direction there is absolutely no reason the the rod cannot be offset by at least that much in the other plane. Simple as that. So long as the clearances needed are met, and the pistons provided by Porashe have sufficient clearance between the pin bosses, there is not any problem with the offset.
If the lack of centering were such a big deal or any big or little deal at all then why is it not a problem for the center of thrust to be offset now in and on the rod bearing journal as with the Carillo offset rod?
The fact is that there are probably very many ways to deal with the fact that the stroker cranks made to use Chevy rods have rod journals that do not line up centrally with the cylinder bore. The offset has to go somewhere.
Why don't you post some pictures or a decent analysis of the situation rather than trying to justify your position(s) with what sounds a lot like "techno garble" off of Star Trec?"
In the meantime I will continue to play with knives and I will continue to say it is round while you all are saying flat.
Jerry Feather
If the lack of centering were such a big deal or any big or little deal at all then why is it not a problem for the center of thrust to be offset now in and on the rod bearing journal as with the Carillo offset rod?
The fact is that there are probably very many ways to deal with the fact that the stroker cranks made to use Chevy rods have rod journals that do not line up centrally with the cylinder bore. The offset has to go somewhere.
Why don't you post some pictures or a decent analysis of the situation rather than trying to justify your position(s) with what sounds a lot like "techno garble" off of Star Trec?"
In the meantime I will continue to play with knives and I will continue to say it is round while you all are saying flat.
Jerry Feather
10-30-2011, 10:30 AM
#73
Rennlist Member
BC, it is not an "explosion" as such, and that only comes about when you have detonation issues. It is a controlled burn.
Later, you corrected yourself you said "The combustion process is a violent, NORMALLY UNEVEN EVENT that happens differenty every time." (Emphasis added). If that is taken literally I think it completely cancels your whole argument. If it is in fact uneven and therefore applies forces on the top of the piston unevenly there is no way to say that the rod end has to be exactly in the center (which it never is anyway) because it will only occasionally, if ever, be in the center of the force.
That is why there are such things there called cylinder walls, piston skirts, oil film, wrist pins and beefy connecting rod ends and shafts, to allow for and direct the "uneven" forces to the crank shaft and to do so by cancelling any tendency for the piston to rock in either plane or to cancel any tendency for the connecting rod to bend.
Jerry Feather
Later, you corrected yourself you said "The combustion process is a violent, NORMALLY UNEVEN EVENT that happens differenty every time." (Emphasis added). If that is taken literally I think it completely cancels your whole argument. If it is in fact uneven and therefore applies forces on the top of the piston unevenly there is no way to say that the rod end has to be exactly in the center (which it never is anyway) because it will only occasionally, if ever, be in the center of the force.
That is why there are such things there called cylinder walls, piston skirts, oil film, wrist pins and beefy connecting rod ends and shafts, to allow for and direct the "uneven" forces to the crank shaft and to do so by cancelling any tendency for the piston to rock in either plane or to cancel any tendency for the connecting rod to bend.
Jerry Feather
10-30-2011, 10:43 AM
#74
928 Collector
Rennlist Member
Rennlist Member
Is Marc dictating, or are you copying and pasting his responses?
BC, it is not an "explosion" as such, and that only comes about when you have detonation issues. It is a controlled burn.
Later, you corrected yourself you said "The combustion process is a violent, NORMALLY UNEVEN EVENT that happens differenty every time." (Emphasis added). If that is taken literally I think it completely cancels your whole argument. If it is in fact uneven and therefore applies forces on the top of the piston unevenly there is no way to say that the rod end has to be exactly in the center (which it never is anyway) because it will only occasionally, if ever, be in the center of the force.
That is why there are such things there called cylinder walls, piston skirts, oil film, wrist pins and beefy connecting rod ends and shafts, to allow for and direct the "uneven" forces to the crank shaft and to do so by cancelling any tendency for the piston to rock in either plane or to cancel any tendency for the connecting rod to bend.
Jerry Feather
Later, you corrected yourself you said "The combustion process is a violent, NORMALLY UNEVEN EVENT that happens differenty every time." (Emphasis added). If that is taken literally I think it completely cancels your whole argument. If it is in fact uneven and therefore applies forces on the top of the piston unevenly there is no way to say that the rod end has to be exactly in the center (which it never is anyway) because it will only occasionally, if ever, be in the center of the force.
That is why there are such things there called cylinder walls, piston skirts, oil film, wrist pins and beefy connecting rod ends and shafts, to allow for and direct the "uneven" forces to the crank shaft and to do so by cancelling any tendency for the piston to rock in either plane or to cancel any tendency for the connecting rod to bend.
Jerry Feather
10-30-2011, 02:20 PM
#75
Like Greg said - assembly your engine anyway you want. Nobody will
Give a care when it becomes scrap- more so because you are so purposely ignorant about proven issues.
And clearly - its because you already spent the money - and want to justify this combination's use.
Give a care when it becomes scrap- more so because you are so purposely ignorant about proven issues.
And clearly - its because you already spent the money - and want to justify this combination's use.