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Discussion Starter #1
Hi.
My mechanic says my connecting rods are a bit like chewed dog bones from something previously coming apart and banging them up.
He has ok'd me to ride the bike around but not to push it too hard - ie. stay below 6k rpms.

I will eventually have the rods replaced...but curious, have any of you ever run with dinged rods before and what are your experiences?

thanks!
 

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if they can't be polished out, I'd replace asap as the damage if one goes could be terminal.

Not just to the engine
 

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Discussion Starter #3
Probably is the best way to go.
I've been looking for a NOS set or a set in good condition...
other than ebay, can you recommend any good sources?
thanks!
 

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Yeah defentily don't use the rods dude like it was sad if it doesn't polish out trash them or hang them on the wall as lessons learned. If the rods come apart you will have bigger issues the broken rods a huge dissappointment if the numbers match on the bike if you break the case and or trash the heads is just isn't worth. It is like my brothers dirtbike he broke a valve trashed head and the piston and convincing him to replace the timing chain and the valves with good aftermarkets wasn't cheap but worth it in the long run for serviceability and not having to do the same job twice.
 

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All old aluminium conrods are getting a bit suspect these days.They weren't meant to last forever.They were meant to last about 500 miles at 7000 rpm on a 650/750 twin;maybe 500 miles at 8000 rpm on a 500.
A steel rod can last forever if the stress is low enough.An aluminium rod will eventually break at any stress level.

Never re-fit rods that have nicks,scratches or other stress-risers.Always polish the scratch marks out (even 180 grit emery paper will do,if the polish marks run vertically up the rod).Even then,it's a good idea to do crack-testing.

Triumph TR 25 rods will fit and work OK,if you can find NOS or low-mileage rods.
 

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I know Carillo doesn't list them for the 500 Triumph but has anyone ever gone through their specs to see if they make a rod that would fit? I can't believe they list them for Norton, BSA and Matchless but not 500 Triumphs.

Mutt
 

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Carillo steel rods are heavy enough to break cranks on Triumph twins.Crank failure is more common than rod failure.
It always pays to crack-test the crank.
 

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My guess would be your dinged rods are from mishandling by someone that was inside the enjoy before you got it. Could even be that they installed used rods for some reason and they were beat up when they got them.

The dings can come from many sources, depending on where the rod has been over the years (swap meet boxes, etc.). But I would think the most common cause would be letting them fall against the mouth of the crank case with the jugs off. Puts a nice v-notch in the rod and will put mutiple notches in it if you turn the crank and let them flop around.

I had a few in my rods when I pulled my '66 engine apart and they all polished out.

Mr Pete, correct me if I am wrong. But if he goes to steel rods, he's going to need to rebalance the crank with all the new parts. That expense alone justifies checking the crank for cracks.

regards,
Rob
 

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Going back many years, my mate Mal had a 5TA 'cafe racer' which he thrashed mercielssly trying to keep up with me on my A10 'cafe racer'!

After about 18 months he had some reason to take the top end off. He found that one of the conrods (both steel originals) has several large holes drilled through it. So he took the rest of the engine apart. The holes were at least 3/8" diameter and had obviously bee drilled by an amateur. The odd thing was that, when Mal weighed the rods, the one with the holes was still heavier by several grams. He looked for a set of good rods, couldn't find any within the couple of weeks before he ran out of patience, so put it all back together how it came apart. He rode it for about another year, then sold it. I kept seeing it every now and then for a couple of years after that...
 

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Discussion Starter #13
So JohnA are you saying that the rods seemed to have stayed together?
From the history of this bike I know that the previous owner rode with banged up rods the entire time he had it. My mechanic was his mechanic which is how the bike finally made it to me. The previous owner didnt want to spend the time and money to replace them and rode around with them in that condition for years...
I dont want them coming apart now....and I want to be able to ride the bike to its potential - which i cant fearing they may come apart...
 

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Depends on the material. Red dye, Zyglo, Magna-flux. Just take it to someone that knows what they are doing and they will do it for you. If you have friends in the airplane industry or racing industry, they can probably get it done for you on the side.

If you looking in yellow pages under "Laboratories - Testing" and look for non-destructive testing services. If you call them describe the crank, they can give you a price or at least an estimate over the phone.

regards,
Rob
 

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So JohnA are you saying that the rods seemed to have stayed together?
From the history of this bike I know that the previous owner rode with banged up rods the entire time he had it. My mechanic was his mechanic which is how the bike finally made it to me. The previous owner didnt want to spend the time and money to replace them and rode around with them in that condition for years...
I dont want them coming apart now....and I want to be able to ride the bike to its potential - which i cant fearing they may come apart...
Well yes, that badly and very excessively drilled conrod stayed together for several years of pretty hard riding - no idea how long it had been like it before Mal bought the bike.

However, I'm only reporting this out of interest - there's no way its worth the risk of running questionable rods in an old Triumph engine today. Back then (late 70s) you could buy a complete 5TA engine for well under 50 quid, so maybe it wasn't quite such a daft risk to take. And maybe it, as well as the experience with your bike, shows that conrods (at least on the 500s) are a lot more resilient than normally given credit for. But why take risks when the consequences can be so serious?
 

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mr petes scaremongering bout alloy rods should not convince to try steel rods,they cannot be balanced to an acceptable factor.Std rods are hell strong for capacity of engine and have never heard of one failing of its own accord, interrupted oil supply being the main culprit in causing rod failure and a rod made of steel aint gona prevent that. Find a good replacement pair and have them checked for out of round bigend, straightness,etc. resizing if necessary but very unlikely they will need it,the rods in my daytona have done 90000 hard miles and according to reconditioner they were still perfectly round ,bit of a polish and back in they went.
 

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I'm not advising anyone to fit Carillo steel rods.The're heavy enough to break the crank if you use serious rpm.
Some successful engine builders have a way to fix aluminium rods that are out of round more than 0.001" at the big-end eye.They cut the rods in half with a hacksaw,so they won't break inside anyone's engine.They would never dare re-size the rods.

The big-end and small-end eyes should be parallel within 0.002" over an 8" distance.

If everything measures up OK,you still need to polish out any scratches running across the rod.If it passes a crack-test after that,it should be OK.
You can do a crack-test by soaking the rod in hot kerosene for some time.Then wipe the rod dry and cover it with talcum powder.The powder will stick to any cracks,where the kerosene has penetrated.There is also a dye-penetrant test.

I'd always crack-test a crank by magna-flux.If it passes,it's worthwhile getting it TUFTRIDED,so it's less likely to ever break.

On a '72 model (or any other 500 built after June '69),the rod bolt torque is approximately 22 ft-lbs.A higher figure in manuals applies to earlier 26 tpi bolts.It's always better to measure elastic stretch on the bolts,up to 0.004",rather than rely on a torque wrench.
 
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