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Looks like I need new con rods for my 1970 T120 engine rebuilds. I see new ones for sale at the Bonneville Shop and MAP cycle. They're pretty expensive and I'm wondering if there is a source of used rods that have been inspected and reconditioned for a lower cost.

I'm hesitant to buy used rods on eBay because of what I've learned here while evaluating the rods that came out of my engines. People seem to be buying them though.

Anyone know of a good source for used rods?
 

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Thunder engineering in the UK manufacture new rods. Try them for a quote.
 

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Looks like I need new con rods for my 1970 T120 engine rebuilds. I see new ones for sale at the Bonneville Shop and MAP cycle. They're pretty expensive and I'm wondering if there is a source of used rods that have been inspected and reconditioned for a lower cost.

I'm hesitant to buy used rods on eBay because of what I've learned here while evaluating the rods that came out of my engines. People seem to be buying them though.

Anyone know of a good source for used rods?
I put a set of Thunder engineering rods in my 70 T120R when the engine was rebuilt 3 years ago. Thought they were reasonably priced at the time.
Probably an overkill, as I don't regularly venture up to 7000 rpm, but when I do, I know it is not going to let go.
I would never buy used rods as you don't know their history. Do you really want to take that risk with a freshly rebuilt engine on your first venture up the rev range?
 

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you already have used rods. why buy two more from someone else?

buy new ones and sell your used rods on eBay.
 

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It looks like Carrillo is still in business?
 

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If the big end is actally round wthin a half a thousands, if the rod is not discolored from heat and the small end measures ok..It should be safe use in a stock street bike not ridden like a racer...Otherwie do as said above..
 

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What is meant by this: "Whilst every care is taken to ensure these conrods are a direct replacement for required and in some cases it may be necessary to chamfer the big end bolts."

Why is chamfering required?
 

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Hi MWL9110, I looked at rods on eBay. That's a crap shoot with very poor odds!! At swap meet & cycle salvage, I looked at about 100 pairs of rods. They were all junk. Scrap metal really.

The guys at Rabers suggested steel rods vibrate more than normal rods even with dynamic crank balancing.

So it was basically no choice but new rods. Taking rod scale to shop for checking non matched rods, I found they were all over the place, even 10-15g different. The crank was getting dynamic balanced, but I was afraid they'd have to take too much off rods. So we ordered "matched set" LF Harris. The matched set weighed in at .1g. Basically spot on. Sadly the first set was dropped in the factory & had dent/gouge on the beam. 3 week wait for another set which was good. Was not expecting to speed $390 for new rod set, but that's the cost of ownership as they say. Proved $$ well spent in the end. You certainly want to quality control rods when you get them. Assume nothing on new parts. Each must be carefully inspected.

The new Harris rods have a beefier big end transition to shaft. Slightly beefier at small end. Heavier overall, but the heavy is mostly in big end so that's rotating mass compensated for in the balancing. Comes with new rod bolts installed with plain nuts holding them. Lock nuts were finger tight on ends of bolts. I'm scared of things backing off. I used loctite blue 243 on lock nuts during final assembly. I used torque wrench. I couldn't get repeatable readings with bolt stretch. Rods cleared cams, cylinder base etc. just fine. Didn't need to grind or modify anything. Used bolts & lock nuts that came with rods.

The motor was as shaker before, very uncomfortable at 65-70mph. Would burn you skin from vibration. Had .020 over pistons, looked like original Triumph. 7g different left to right. Original rods about 7g different left to right. Both heavies on same side. In the end after balancing the motor is dead smooth at 3800. Uncanny smooth. At 65-70 very acceptable, but you'll never get a Triumph twin smooth as we'd like. Shop took a lot of metal off the right pork chop on crank. I don't have advise of balance factor. We use 68%. I'd probably go higher percent next time.

You want to fit cleaned sludge trap to crank before balance. Don't stake plug yet. Remove trap after balance & reclean everything. Our balancer shop is a good place, but with grinding etc. there was like 4-5 specs of metal in oil way to journal. That would have damaged inserts. After cleaning crank again, I staked plug. I always use sealant on plug threads & look at the oil drilling below plug. Do the math. Don't allow plug to even partially block oilway.

I found weighing LF Harris, Emgo pistons, they were very close 1-2g or less. Several sets. The OD of pistons were very close as well. .0002". I don't know who makes these, but the quality control was amazing on the examples I checked. Piston pins fit pistons tightly cold. Heating pistons hot, but not yet spit boiling, the pins slid in nicely. I used heat gun.

On New Years day, motor will have covered 10k miles in 3 years. Several 300 mile days, from 32f to 110f. I'd use the Harris rods again.
Don
 

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It would help if you said what these instructions were from! The likes of T140 rods, and I’m sure others, hit the inside of pre-unit cases, for example. I would never chamfer rod bolts, I grind out the cases to suit. Not sure I’d trust anyone giving that advice. I have a stash of the late 650 rods, they are thicker around the small end, but as Don says, it is a lottery buying.
 

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It would help if you said what these instructions were from! The likes of T140 rods, and I’m sure others, hit the inside of pre-unit cases, for example. I would never chamfer rod bolts, I grind out the cases to suit. Not sure I’d trust anyone giving that advice. I have a stash of the late 650 rods, they are thicker around the small end, but as Don says, it is a lottery buying.
See above re: Thunder Engineering Rods.

What would be the advantage of these custom rods over factory rods?
 

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It would help if you said what these instructions were from! The likes of T140 rods, and I’m sure others, hit the inside of pre-unit cases, for example. I would never chamfer rod bolts, I grind out the cases to suit. Not sure I’d trust anyone giving that advice. I have a stash of the late 650 rods, they are thicker around the small end, but as Don says, it is a lottery buying.
What part of the bolt would one be chamfering, the end of the bolt because it is too long? Is the risk that it could create a hairline fracture in the bolt that could cause the bolt to splinter and the con-rod fail?
 

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See above re: Thunder Engineering Rods.

What would be the advantage of these custom rods over factory rods?
there are no more new factory rods, unless you can find NOS.

having said that, i wouldn't hesitate to use NOS rods in a street bike that didn't get hot rodded too much. but i don't think you'll find any.

but old rods are simply old. aluminum has a limit on how many stress ccyles it will endure before it fails. with a used rod, you don't know how far along the rod is - how many times was it redlined? how often did it endure severe detonation? you just don't know.

because its the fatigue that makes the aluminum rod fail, i don't know how that could be reconditioned out. the rods could be polished, resized, new bushings installed, and given new bolts and nuts. it will be pretty, but the metal won't have changed. you could probably have the rod heattreated to relax any inner stresses, but i don't know how you could eliminate micro-cracking unless you re-forged the piece.

thunder engineering is a welknown company that makes cases for triumph record holding land speed bikes. while i use MAP rods in my rebuilds, i wouldn't turn up my nose at anything from thunder.
 

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there are no more new factory rods, unless you can find NOS.

having said that, i wouldn't hesitate to use NOS rods in a street bike that didn't get hot rodded too much. but i don't think you'll find any.

but old rods are simply old. aluminum has a limit on how many stress ccyles it will endure before it fails. with a used rod, you don't know how far along the rod is - how many times was it redlined? how often did it endure severe detonation? you just don't know.

because its the fatigue that makes the aluminum rod fail, i don't know how that could be reconditioned out. the rods could be polished, resized, new bushings installed, and given new bolts and nuts. it will be pretty, but the metal won't have changed. you could probably have the rod heattreated to relax any inner stresses, but i don't know how you could eliminate micro-cracking unless you re-forged the piece.

thunder engineering is a welknown company that makes cases for triumph record holding land speed bikes. while i use MAP rods in my rebuilds, i wouldn't turn up my nose at anything from thunder.
Instead of factory, I should have said OEM, but I am not even sure that is applicable or accurate. I have rods that I purchased 40 years ago from a Triumph reseller in SF (Munroe Motors). I would assume the quality of the product from an authorized reseller would be decent? The engine was never fully assembled and hence the rods never used and during the various moves I always made sure the rods were protected.

My crankshaft was balanced ahead of installation of rods and and crankcase. I have some doubts now about my torque settings and plan to pull the engine apart again to 1) re-torque big ends, 2) polish crank case and 3) anything else that I might have left out.

It sounds like for some, balancing con rods is a necessary move for smoother engine operation (frankly I never thought of that, it never occurred to me that two con rods would not have identical weight properties). Oddly, Thunder con rods advises against the use of Loctite.
 

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If, you're not sure buy new. When they arrive spend some time checking them. My rods came from Harris, the weights written on the box were within a gram or two but it seems they weigh them with both the temporary and the lock nuts fitted. They then omitted said lock nuts from one rod. Come fitting time neither big end was finish machined to the correct size, one was just a gnats cock the other would not even fit over the journal. Both were re machined locally since Covid had just hit and I was not about to send them back to the UK. As it turned out the weight difference between the two rods turned out to be the same as the originals although he new ones were heavier. The bike still vibrates enough to ensure the young lady on pillion should arrive ready to go.
 

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Hi
I think it useful to think of the con rods as a wear part.
Alloy rods have a useable lifetime of fatigue and time, it certainly wasn’t originally set at 50 years.
If you had the bike from new and know the full lifetime history that was easy on rpm, then maybe there is a argument for re-using (a thin argument) the original rods.
Maybe if they passed a magnaflux check and were peened and polished, you could argue that they were ok for re-use, but I’m not convinced.

Having said this, the crankshaft is still a weaker component than the rods at high RPM.

I always buy Thunder Engineering Rods.
These are my reasons:
Race and road proven.
The guy who designed them, who sources the materials, who machines them and controls quality, is the guy you pay- full traceability.
I have never had anything wrong in many purchases, perfect every time, this is one of the few component sources where I don’t feel That I need to be my own quality control department.
If I pick up the phone or visit, I talk to the main man, not some intermediary, a PR dept., Salesman, etc.
——————————————————————————————————————————————
If you change the rods, it is a good idea to have the crankshaft rebalanced, dynamically if possible.
Dynamic balancing is good idea even if you don’t change the rods.

Regards
Peg
 
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Instead of factory, I should have said OEM, but I am not even sure that is applicable or accurate. I have rods that I purchased 40 years ago from a Triumph reseller in SF (Munroe Motors). I would assume the quality of the product from an authorized reseller would be decent? The engine was never fully assembled and hence the rods never used and during the various moves I always made sure the rods were protected.

My crankshaft was balanced ahead of installation of rods and and crankcase. I have some doubts now about my torque settings and plan to pull the engine apart again to 1) re-torque big ends, 2) polish crank case and 3) anything else that I might have left out.

It sounds like for some, balancing con rods is a necessary move for smoother engine operation (frankly I never thought of that, it never occurred to me that two con rods would not have identical weight properties). Oddly, Thunder con rods advises against the use of Loctite.
I did have a quick look at the Thunder Engineering instructions, and they do indeed talk about chamfering the bolts! As the bolts go in from the bottom of the caps into the rods themselves, that could work, but it makes far more sense (if a bit more fiddle) to "ease" the crankcases. Usually, this would mean taking a little off the camshaft bush housing on the drive side, T140 rods need some extra off the case as well. That said, I just built an early pre-unit race engine with Lightning rods, and they cleared fine. I spoke with Steve at Thunder Engineering, and the chamfer bit comes from the Commando application, where there apparently is an oil gallery that can be breached if modifying the cases.
Any crank balancer should be checking that the conrods are the same weight anyway, measured at both the big ends and small ends, it's not enough that the overall weight of the rods are the same. As the Lightning rods are CNC machined they will be as near as dammit identical, its actually a shame hiding them inside an engine!
The later, stronger OEM rods do not have a casting number on the alloy near the bottom of the rod, I only have late rods, but I'll measure the thickness below the big end eye if anyone wants!
HTH
****.
 

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Instead of factory, I should have said OEM, but I am not even sure that is applicable or accurate. I have rods that I purchased 40 years ago from a Triumph reseller in SF (Munroe Motors). I would assume the quality of the product from an authorized reseller would be decent? The engine was never fully assembled and hence the rods never used and during the various moves I always made sure the rods were protected.
if they were good quality then, they should be as-new now. but the original quality issue is problematic. the only aftermarket aluminum rod people i remember from back in the 70s and 80s was JRC.

My crankshaft was balanced ahead of installation of rods and and crankcase. I have some doubts now about my torque settings and plan to pull the engine apart again to 1) re-torque big ends, 2) polish crank case and 3) anything else that I might have left out.
lol

i have no brains left these days. when i do something critical in a motor like torquing the rods, i mark each bolt with a paint pen and then photograph the process as i go. the last machine i assembled i couldn't for the life of me recall whether i correctly torqued one bolt. so i took th emotor down again and checked. it was fine, but now i record the progress as i go to save myself stress
 
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