6G Celicas Forums

there is also a good post in the GT4OC called "Why you should NEVER fit an Lightweight Alloy Crank Pulley"
Documented with lots of after effects including pictures of internal damage.

http://www.gt4oc.net/forums/viewtopic.php?...amp;hilit=pully

I’ve been saying this for countless years to my customers not to fit the alloy crank pulleys in replacement of the standard Damper Pulley. Toyota did this for a reason and I’ve seen countless failures of the crank and quite a few with my own 2 eyes but up till now I have not recorded a failure, just did the repair as instructed. Well I had a customer come to me with a knocking coming from the bottom end of his GT4 ST205, the knocking sounded very much like a bigend rattle so I advised that if this was caught early enough we could drop the sump and as long as the crank was in perfect condition and the journal measurements came within specs and a plasti-guage final check we could get away with re-shelling the conrods, which basically means fitting new bearings with the crank in-situ and just bolt it all back up. If done correctly this is a perfectly adequate repair and will give many years of trouble free motoring. Conrod bearings will wear because of a few reasons, Age and power is the main one which is the conditions that give the most successful repair of this nature. The other is foreign material or metal entering the bearing or lack of oil, these will typically damage the crank which requires a bottom end partial rebuild.

Upon inspection of this car I noticed it had an alloy crank pulley fitted (pictured below)





The sump was dropped and the bearings were inspected, #1,2,4 were all in perfect condition. #3 was in a terrible state, extensive wear and a deep grove down to the base metal of the bearing. This was the cause of the knocking. The crank was inspected and seemed in good condition but found a small lump on the top of the journal which you could just feel with your finger tip, at the time it was facing the top of the engine so I was feeling blind. Believing at first to be a part of the bearing stuck to the surface I rotated the crank to give a better view but found this damage instead. There was a fine Hairline crack which ran almost 3/4 the way around the bearing journal of the crank, and in one part the surface had pushed upwards creating that small lump felt earlier, and the cause of the deep grove created in the bearing. Damage pictured below







The job was completed with a new set of bearing throughout, a replacement crank that was rebalanced, journals polished for clearance and rebuilt. The alloy pulley was also replaced with a factory item and the customer collected his car, Which had an initial fire-up and running-in by my to set the bearings and 300miles of normal driving before replacing the oil and going back to normal full boost operations.

The car this happened to only modification was an exhaust system; boost was even standard so power wouldn’t have exceeded 260bhp at the most. Yet the crank had failed. To put this into perspective we’ve done drag cars running over 900bhp with standard cranks without a single failure or even bend. Some models for testing were also extremely machined to remove any metal we could for revablity, they were machined like pieces of paper and at still exceeding 900bhp still not a failure. All these were fitted with the standard damper pulley. Yet this example failed at 260bhp with a pulley that could control the harmonics which had lead to its premature failure.

The reason behind the failure was Harmonic Resonance Failure. Without getting to in-depth I’ll keep the explanation simple but there are a few good examples for the technical minds amongst us on wikipedia.
http://en.wikipedia.org/wiki/Resonance
http://en.wikipedia.org/wiki/Harmonic_oscillator

Basically everything in the universe vibrates, whether it is the human body, sheet of metal, or in this case a crank. This is called its structural resonance frequency. Now this frequency is best expressed as a wave, with its peaks and troughs. And if you can generate an additional wave with the matching frequency (so the peaks and troughs match) the amplitude of that wave will grow, or the item will vibrate with more force, it’ll keeps growing until it structurally fails on a molecular level. To put this into everyday context you need to picture a swing with a fat man on it and your trying to push the swing with your little finger, Normally this isn’t going to happen but if you can get the swing started adding the small amount of force at the correct period, just at the peak of the swing you can over time make the swing oscillate higher and higher. This swing is the oscillation frequency and at the top of each swing is the peaks of the wave form and the base of the swing would be expressed as its trough. Now if you continued to keep adding this small force at the top of each swing the arc would eventually get higher and higher until either the swing broke or the fat man fell off, this would be the expression of the structural resonance failure. To stop this you need a simple damper that will effect outside frequencies (in our case the engine) or crank rotation from matching the frequency of the crank resonance. Going back to our fat man on the swing the damper would be effectively stopping the outside force, (you with your little finger) pushing on the swing at the correct time, for example before the swing meets its peak point, This would do nothing to aid the swing and certainly wouldn’t add force the its momentum making it arc higher and higher.

This is what the Toyota standard Harmonic Damper Pulley does, it removes harmonic resonance from the crank and additional frequencies causing the failures were seeing above.

For curiosity purposes I went all over the crank looking for more hairline cracks and found another around #2 journal leading into the counterweight but it was only very small, around 1cm in length but if left unattended would have grown like #3. So to see how far the resonance damage had gone I caused a controlled failure of the crank by putting in it a press until it snapped on the cracked areas. The pictures of this can be seen below. If you analyze the pictures you will see there are 2 different types of metal texture. The shinier, almost polished appearance is the damaged caused by the resonance; this is a failure on the molecular level and as you can see it quite extensive in #3 and starting to spread inwards on #2 just being visible on the outside edge. The other type is a more harsh texture, this was good metal until the press finished it off, this is typical of a pressure break where the cast material of the crank has basically shattered and all this was caused by me so ignore that. But it does show the 2 different types of damage, and how close this celiac came to complete destruction, where instead of a hairline crack and a rattley bearing the crank would have snapped pushing the rods out the side of the block casing and the entire engine unit would have been a total write-off.

Before people jump the gun and say “well I’ve got one and running 400bhp for years” this isn’t a situation where it’s a loaded gun at your head, where you fire you will die. It’s a situation where failures can/normally happen eventually, ranging from a matter of weeks to years, and from standard power up to 1000bhp. It’s a device which doesn’t address the base foundation of structural physics where the original Toyota unit does.

I hope this has enlightened people to the dangers of fitting an item like this, yes you will save around half the weight of the stock pulley but this really doesn’t add up to any noticeable gains in performance or revability and all its doing it radically effecting the longevity of the engine.











Tim

Sorry Tigs.
Taken from the GT4OC:

Feel a bit sick... My forged fresh built engines knocked since about 500 miles into the break in. Put it down to the solid engine mounts Think i know why all of a sudden! I used ACL race series bearings throughout, would this help save the bottom end or would you guys think its game over? When i say knock, it s a gentle one at tickover, oils been changed every 100 miles or so and i also slick 50'd it after break in. Its never been above 4k since i built her (still mapping her). I'm also running high lift cams so its been harder to notice as they are more "tap happy". Gonna fit the OEM pulley this week n hopefully it should improve... Think I need a beer : $