Damaged connecting rod - how easy/ difficult to repair/ replace?

[paul83]

Hi All,

 

I managed to strip the thread of one of the big end bolts in a con rod... Can I repair this, or do I need to replace the rod, or the entire set?

 

The connecting rods are standard, with +0.10" big end bearings.

 

If I have to replace the rod, what do I need to consider? How do I ensure that it is the same weight/ balance as the others? And what about the bearing size? Or is this really a job for a specialist?

 

Or, do I replace the entire set?

 

Thanks,

 

Paul

[Motorsport Mickey]

No to the repair, why gamble with a repair when there are available not expensive replacement options.

 

I'm not a 6 cylinder owner so unless there are various offered original manufacturer (ie Triumph original supply) sets I'd have thought any of the TR spares suppliers could supply an odd rod at reasonable cost. You could use the missuses kitchen scales (digital) to get a weight off your original rod and then any offering over that weight (likely to be within 10 grams I'd thought) can be reduced easily by a little gentle filing/smoothing blending. The length of the rod will be identical to all the others within a couple of thou and unless being raced you'd have no problems using it as is. Might be advisable to send a photo to the suppliers of the rod to help them identify any differences which may be offered in it's original manufacture.

The little end can be replaced separately by any engineering firm easily and cheaply and the big end bearing size will be the same on all anyway (unless a 6 owner knows other wise for different cranks used).

 

Mick Richards

Edited May 3, 2016 by Motorsport Mickey

[Austin Branson]

You might try talking to Chris Wittor. I believe he has a lot of Triumph parts. Let us know how ylu get on. Austin

[Mark69]

Paul

I have a set if interested

Mark

[oldtuckunder]

 

I managed to strip the thread of one of the big end bolts in a con rod... Can I repair this, or do I need to replace the rod, or the entire set?

 

If I have to replace the rod, what do I need to consider? How do I ensure that it is the same weight/ balance as the others? And what about the bearing size? Or is this really a job for a specialist?

 

Or, do I replace the entire set?

 

The factory rods aren't balanced sets, but they are close enough for a road engine. There are lots of similar sets i.e. length, width, bearing size etc so they are all sort of interchangeable, but some have a cup around the small end oil hole, and some have a hole drilled in then at the end of one of the bolt holes to prevent hydraulic lock up when tightening the bolt.

 

Within reason any of the correct sized rods from the TR6,2000, 2500, GT6, Vitesse, Spitfire 1500 will do, and others have reported stripping engines that were working OK with a mix of rods in them.

 

However if it was me I'd try and get one of an identical style as its likely to be a closer weight to start with, and again given the choice I'd go for a heavier rod as its easier to take weight off 1, rather than off the other 5.

 

Now I was hoping that someone else would have jumped in before me and asked the awkward question. How the F..K did you do it?

 

Now it could be that a PO did the damage and in your carefull torquing of the bolt the thread just gave way?

 

But I have to ask, are the threads in the rod absolutaly clean, no oil/crud in them, did you add lubrication to the bolts (they are supposed to be torqued dry) Have you got your torque lever calibrated (I have one new one here that is off little use other than for banging in nails). Had you bought new bolts? like ARP's that aren't the correct length, Sorry but when you said that you managed to strip one of the threads is raises some serious assembly questions.

 

NB. I have a couple of spare rods, one oval and useless, but might make a good torquing exercise piece! and some good ones.

 

If you post a picture of the offending item, I can let you know if I have a spare to match, otherwise a good set from Mark might be a good bet, as if in assembling them one failed, could the same cause have damaged others.

 

Alan

[TriumphV8]

Now it could be that a PO did the damage and in your carefull torquing of the bolt the thread just gave way?

 

 

 

Just when reading it the question came up what he might have done to the other rods

and as a rod fault causes quite a big damage isnt it better to change the whole set?

 

Seems to be not necessary but the Maxspeedingrods are a nice add and not as

expensive as the Carillos. Disadvantage is they are quite tight to the engine block.

[snowric]

I found this supplier in the US when looking to rebuild my engine.

 

About £400 for a set of lightnened, balanced original rods.

 

http://www.aptfast.com/ShowItem/100093%20Triumph%206%20Cylinder%20Prep'd%20Connecting%20Rods%20OUTRIGHT.aspx

 

Sets of six come up regularly on ebay, very cheaply.

 

IN the end we fitted maxspeeding rods - which after 5000 miles have held up nicely BUT for a 40 thou bore we needed to notch the bottom of each cylinder to permit clearance.

 

With hindsight and a rev limited at 5750, I wonder now if a good set of polished and balance originals would have done just as well.

 

Snowy

[boxofbits]

No to the repair, why gamble with a repair when there are available not expensive replacement options.

 

" You could use the missuses kitchen scales (digital) to get a weight off your original rod and then any offering over that weight (likely to be within 10 grams I'd thought) can be reduced easily by a little gentle filing/smoothing blending."

 

Mick Richards

 

Yea just make sure she's not making an apple crumble or something at the same time. Doesn't always go down too well and you might find it tastes a bit oily!

 

A few months back I put a Mini clutch housing in the oven to heat it up to get the idler gear needle roller bearing out, not realising there was some batters cooking on the lower shelf. Changed the smell of the batters somewhat..

Edited May 4, 2016 by boxofbits

[paul83]

Hi All,

 

Thanks for the replies and the offers. How did I do it? I misread the brown book and set the wrong torque on the wrench - it was the second bolt I tightened, having just thought 'gosh, that seems awfully tight for a big end bolt'...

[oldtuckunder]

Hi All,

 

Thanks for the replies and the offers. How did I do it? I misread the brown book and set the wrong torque on the wrench - it was the second bolt I tightened, having just thought 'gosh, that seems awfully tight for a big end bolt'...

 

So it looks like only one scrap rod, so you have some options, a good single, or a full set. At least the scrap one will give you a style and a good enough weight to work from if you go the single route.

 

NB, don't know what others do, but when I'm doing BE bolts I work on the whole set of 6 BE at the same time, slowly coming up in torque values and checking rotation as I go just in case something for some reason goes tight, then you have a chance to investigate before doing any damage to the shell's or in your case the rod.

 

Alan

 

PS Well done for admiting it was your fault, a lot wouldn't and would have started a red herring chase for different causes!

 

PPS Take opinion from others better qualified than me about the implications on the crush effect on the shells in the rod you overtightened, they are thinner on the out side edges and are supposed to crush a little at the correct torque, I don't know what happens if you go above that .

Edited May 4, 2016 by oldtuckunder

[Motorsport Mickey]

Alan,

 

The bearing crush is limited by the fit of the bearings in the preformed big end bearing diameter formed by the torqued big end, the cap fit will not alter whatever torque is applied, it being set by it's machining tolerances on the dia.

 

Mick Richards

Edited May 4, 2016 by Motorsport Mickey

[oldtuckunder]

There you go, only have to wait twelve mins to get the answer!