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Discussion Starter #1 (Edited)
I'm generally a lurker but this thread caught my interest. I noticed you went back to the same steel rods. Any particular reason? Wouldn't aluminum ones be lighter?
I'm curious from those in the know. I'll be needing to rebuild my engine before spring and thinking of replacing my 40 year old rods then add a big bore kit and probably a belt drive! Suggestions welcome and appreciated.
Mark
Hi Mark,
Where are you and what bike do you have?


I always use Thunder Engineering Con Rods on just about every bike I have, I am like you and do not trust 40 year old con rods.
Having said that Triumphs do not have a reputation for breaking rods, you are more likely to break the crankshaft.
Thunder Engineering con rods are superb quality and are often used competitively, I believe Alp Sungurtekin uses them along with Thunders strengthened crankcases.
Steve is a really nice and interesting guy, I have visited a couple of times and had a tour of his workshops.

http://www.thunderengineering.co.uk/

Regards
Peg.
 

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Alp uses Thunder Rods in his nitro engines, MAP steel in gas powered engines..More to do with the "cushioning" of aluminum rods in a nitro engine that actual strength...Triumph rods were strong when new..Aluminum will break at less than it's fatigue limit,more so when old, steel will not....I use R&R aluminum rods in one of my race Triumphs, the dual engine bike has MAP steel rods...On my scale a MAP steel rod is 420 grams, stock Triumph is 400-405..
 

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MAP rods in mine.

no issues so far except that i recommend not re-using the expensive ARP rod bolts. i put new ones in now at every tear down , and will only torque them once.

Don't the instructions say to torque and loosen ARP bolts 3 times using their proprietary thread lube? Likely that is part of your "torque once" procedure.
 

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Rancidpegwoman, as to your Thunder rods, would you mind telling me how much they cost what they weigh (small end), and what bolts do they use? I see another set of broken alloy rod on facebook. Sure wish i could buy a brand new set of original rods (not LFH)

Mark
 

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According to John Healy,who does know about these things, the big end out of round is the only clue you'll get of soon to happen rod failure. Other than obvious signs like severe heat caused discoloration on the small end...
 

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Discussion Starter #8
Rancidpegwoman, as to your Thunder rods, would you mind telling me how much they cost what they weigh (small end), and what bolts do they use? I see another set of broken alloy rod on facebook. Sure wish i could buy a brand new set of original rods (not LFH)

Mark
Hi Mark,
Sorry I missed this, The Thunder Engineering Con rods are not cheap allow £300-£400 depending on whether you have to pay VAT.
They are shipped with bolts, they are not a nut and bolt setup, the bolts screw directly into the con rod. I do not know the weight, I take the crankshaft/rods/pistons,etc. to Basset Down Balancing and they sort the components for smooth running. If you are changing the weight of any component, to me this is the only logical step.

Give Steve a call at Thunder he can answer your questions, he's a nice guy and very helpful. (+44 116 283 4640)

Rancidpegwoman likes alloy rods but have heard too many of those having broken (there is one on face book now with a broken cap)
I'm not wedded to alloy rods, my 900cc engine is with Carrillo rods, but alloy Thunder rods will have worked just as well.
Speedrattle and Truckedup are striving to get the last ounce of power out of their bikes and unleash it in a mile of fury, everything is on the limit of destruction. They are tuning magicians.
I however just want streetable engines that will last a reasonable amount of miles.

regards
Peg.
 

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Hi Mark,
Sorry I missed this, The Thunder Engineering Con rods are not cheap allow £300-£400 depending on whether you have to pay VAT.
They are shipped with bolts, they are not a nut and bolt setup, the bolts screw directly into the con rod. I do not know the weight, I take the crankshaft/rods/pistons,etc. to Basset Down Balancing and they sort the components for smooth running. If you are changing the weight of any component, to me this is the only logical step.

Give Steve a call at Thunder he can answer your questions, he's a nice guy and very helpful. (+44 116 283 4640)



I'm not wedded to alloy rods, my 900cc engine is with Carrillo rods, but alloy Thunder rods will have worked just as well.
Speedrattle and Truckedup are striving to get the last ounce of power out of their bikes and unleash it in a mile of fury, everything is on the limit of destruction. They are tuning magicians.
I however just want streetable engines that will last a reasonable amount of miles.

regards
Peg.
The MAP steel rod is the best bang for the buck.... Forged steel will last forever if it's stress limit is not exceeded...That is not the case for aluminum...and that's why no production vehicle uses aluminum rods(other than old Brit bikes) and no racing engine uses aluminum rods other than drag racing...There was a push in the 1930's for a British manufacturer of aluminum rods, but it never caught on...However, in a bike a properly designed aluminum rod is not necessarily prone to failure in normal use...
 

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No? Whether you use a torque wrench or measure stretch they are still "torqued" and I believe ARP has a specific procedure of torque and relax for new bolts.
they do have a recommended torque/relax procedure, which they say to use if you don't have a stretch gauge. a torque wrench requires repeated torquing and looseninng to knock the high spots off the threads that increase the friction, and therefore the force needed to stretch the bolt to a certain point within the elastic limits of the metal. once you polish thethreads you can get a toque that is proportional to stretch, rather than to stretch minus friction.

but its stretch that youre actually trying to impose, not torque.

using a stretch gauge, the pound-feet reading of the wrench is irelevant-- because you are measuring stretch directly, you don't need to use torque as a substitute for actually measuring it.

there are some exceptions. ive been told of ARP bolts that took more than reccommended torque without stretch. as i recall, the advice from ARP was to set the stretch gauge down and use a torque wrench.

there are other arguments for using a torque wrench as well, but the ARP engineers will still tell you that stretch is what you should be using.

i'll see if i can dig out the instructions. but there's this

https://arp-bolts.com/p/technical.php
 

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Not really relevant to this discussion - well maybe - many 'modern' torque settings are only the baseline setting. ie you torque to 30psi then continue for another 60 degrees [or whatever is needed] of arc using a dial torque gauge. This is supposed to provide the bolt stretch required.
 

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The rods in my LSR Triumph are USA made R&R aluminum forged billet...the ARP bolt thread directly into the rod like all high performace rods..The recomended torque is 55 ft pounds with a 5 torque down sequence on new rods.7/16 bolts..The bottom end was disassembled one, same rod bolts used at 55 ft pounds....My bike has about 25 runs down the track, two hours on the dyno and about 50 street miles...Kevin's engine turns about 500 rpm higher than mine but I don't think that's a factor..But his has more time on it and that's a factor.
I still believe Kevin's rods had a suspect bolt or one was improperly tightened...It's easy to make a mistake especially when work is stopped and started because distractions..
 

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Went to the MAP website. Found a link to their catalog (the tech tips were especially interesting), much better than searching around in a website, could be just an age thing, I suppose!

I'm convinced to move forward with steel rods, now just need to decide how much further I really want to go with this project!

Mark
 
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