virtual fishbone
virtual fishbone
(OP)
this ought to be fun for some out there -
What environmental/application factors can contribute to increased alternating stress in connecting rod bolts, while running in the engine?
- impending piston siezure, leading to increased tension
- engine overspeed giving higher tension
- rod large end lateral deformation due to _x_ leading to bending
- etc...
What environmental/application factors can contribute to increased alternating stress in connecting rod bolts, while running in the engine?
- impending piston siezure, leading to increased tension
- engine overspeed giving higher tension
- rod large end lateral deformation due to _x_ leading to bending
- etc...





RE: virtual fishbone
.. improper setup, terminal wear, or outright failure of the engine's main thrust bearing, allowing thrust loads to be applied to the conrod(s).
Mike Halloran
Pembroke Pines, FL, USA
RE: virtual fishbone
how about detonation... it's hard to picture how, but do you think that could lead to big end deformation?
RE: virtual fishbone
RE: virtual fishbone
Bore spacing, at least on the production engine would seem a stretch...A 'one off', perhaps.
Detonation usually leads to other failures first in a properly designed engine...However, I have had the bearing shells torn up by det a couple times. Perhaps left to it's ultimate conclusion, a rod bolt failure would be possible.
Most of my rod bolt failures have been the result of over-revs and or too long in service....too many races on that engine, etc.
Rod
RE: virtual fishbone
RE: virtual fishbone
Regards
Pat
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RE: virtual fishbone
EVERY TIME, yes, each and every time I've had a rod separate, had a pin pull out or a rod bolt break, it has been when I lifted to shift or at the end of a long straight. Trailing throttle problem, for sure!
Rod
RE: virtual fishbone
RE: virtual fishbone
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
www.sixstroke.com
RE: virtual fishbone
Engine detonation is also right as it will beat a rod brg. into submistion..it wasnt that many years ago methanol and nitro burning engines we tuned by the rod brgs.....yes before data recorders....and even today with all the recorders i still read my brgs....
How said rod bolt is tourqed and is it done by strecth guage or just a tourge wrench thats 25 years old....strech gauge is the only true way of doing it corectly IMOP..This also is the biggest reason of bolt failure from decel because the rod bolt has been streched to far from over tourqe...i think ARP gives there specs at 75% of bolt capacity....Ktech are a good bolt and i like A-1 out of all of them...
Johnny
RE: virtual fishbone
There are a huge number of engines that run the entire life of the engine with rod bolts tightened by a good accurate torque wrench used correctly. That is also how most main cap bolts and head bolts are installed as there is no place to measure stretch.
I agree stretch is a better method, but it is only really necessary if the bolts are marginal.
Poor workmanship or poor tools can result in a failure by either method.
Regards
Pat
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RE: virtual fishbone
PJGD
RE: virtual fishbone
Just like all the tourqe to yeild head bolts...but we are talking rod BOLTS....
Do you think Hendrick engine builders use a strech or a wrench on the rods?Any major nascar team...?
My aluminum rods are a cap bolts and I have no choice...I take great care in how i do them and what extentions add to the equation and the sockets as well....this may seem anal but my engines come down after every weekend and sometimes at the track so I have alot more to look at as I measure them on a service schedual that i maintain...
I have done many motors over many years also,I am just adding to what causes or can and the proper way which if you ask any rod manufacture is to use strecth because of the variables with wrenches...
RE: virtual fishbone
Hydraulic tensioning is common for large engine head bolts - the bolt is stretched hydraulically to a desired amount of stretch, and a nut is gently (as w/fingers) tightened, then hydraulic tension is removed. This is even done in the field on these engines.
RE: virtual fishbone
Typically, I check the stretch on several rod bolts in a set and then use the tq determined by those cks as a final setting for assembly...USING MY TQ WRENCH! I see nothing good coming from ME cking the stretch and YOU doing the assembly with another tq wrench.
Isaac--- In the field, using bolt stretch to set final tq is pretty common. Handy little gadget...labor saving device, and assembly is a breeze...especially when the bolts are ~2" dia. Even at that, the stretch is determined in the "lab" and all we get in the field is the pressure settings on the gauge of the Porta-Power.
Rod
RE: virtual fishbone
The critical point is that bolt torque is not important. The desired outcome is a particular amount of stretch (which gives you a particular joint preload). The torque required to achieve that stretch can vary wildly for a given set of geometry based on differences in lubrication, surface condition, cleanliness, etc., even between repeated installations of the same hardware.
Yes, the required force (and therefor pressure) is determined in advance when the joint is designed. Luckily the hydraulic piston diameter doesn't change much over time.
There's a nifty tool which uses an embedded chip on each bolt head to make before and after length measurements.