Commando con-rod bolts.

Mmmm.. reminds me of 2002 when I blew my engine which had newish rod bolts intalled. They had done 3000 miles, were in genuinepackaging from a known dealer. I of course could not prove that the wrecked cases, rod and piston, costly Maney barrels and bent frame were in any way due to faulty manufacture. I still have the parts and the one bolt I found clearly shows staining from a crack that had developed earlier. The break was just belowthe point where the bolt is waisted and the others evidenced machining scores which in Paul Dunstall's notes is an area that should be polished. I ended up with used cases, 850 look alike 750 boredbarrels, pistons and new rods/ managed to save the crank. FWIW the bolts on the new rods were perfectly smooth where the original 'new' replacements had a coarse tool spiral.

http://i424.photobucket.com/albums/pp322/keith1069/IMG_0265-1.jpg

Con rod bolts are available in at least two qualities. I have always sold the genuine Andover Norton ones (just under 1000 pieces in the last 20 years), and have yet to have a problem with them. I have been selling and using them for over 30 years now. We use them in racing engines and road engines; in neither have they ever caused a problem.

There is at least one wholesaler in the UK who now sells con rod bolts, supposedly for Nortons, cheaper than what Andover Norton pays for the unfinished forging(!). These pattern con rod bolts are not made from a forging, and the threads are cut rather than rolled. I know, I bought one just for inspection purposes. Don't tell me they aren't sold by certain "Norton specialists", as otherwise this item was not made for that wholesaler presumably in the Far East and offered for sale by him.

The difference is obvious if you put the two items- the genuine 06-6486 from Andover Norton, and the offending pirate item- side by side; not even the general dimensions are correct. However, if a layman throws the old bolts out and then puts the new ones in I doubt he/she will notice the difference.

I am sure that the "specialists" selling these pirate parts will make sure they put only the genuine con rod bolts in engines or bikes they rebuild and have to give a warranty for........

Previously wrote:

Recent topic of conversation at the Braemar rally was con-rod bolts. I spoke to four Commando owners who had all experienced recent bolt breakagesunder normal road use.All bolts were new i.e not new old stock,obtained from reputable dealers andI have no doubtof all four owners ability to assemble an engine.

I have no idea who is selling junk bolts. I certainly dont suspect Andover of such.

I alsohave the John Hudson video on Norton engine rebuild and have watched it several times and one of the points he made was that he never replaced the bolts ona rebuild or had any fail even in the racing engines. Correct me if i am wrong please?

it's a wonderful video for any that have not had the chance to view, full of information and colorful commentary. what a great man and credit to Norton.

he showed how to examine and correctly fit the reuseable bolts which he consider possibly better than what was being produced at that time.

regards,

steven phelps,

currently assembling my 850 with the old bolts, thanks John

I used to sell a lot of Commando spares and once when I was at the Shenstone factory there was mention of one well known dealer having his own labels printed.

Previously wrote:

Previously wrote:

Mmmm.. reminds me of 2002 when I blew my engine which had newish rod bolts intalled. They had done 3000 miles, were in genuinepackaging from a known dealer. I of course could not prove that the wrecked cases, rod and piston, costly Maney barrels and bent frame were in any way due to faulty manufacture. I still have the parts and the one bolt I found clearly shows staining from a crack that had developed earlier. The break was just belowthe point where the bolt is waisted and the others evidenced machining scores which in Paul Dunstall's notes is an area that should be polished. I ended up with used cases, 850 look alike 750 boredbarrels, pistons and new rods/ managed to save the crank. FWIW the bolts on the new rods were perfectly smooth where the original 'new' replacements had a coarse tool spiral.

http://i424.photobucket.com/albums/pp322/keith1069/IMG_0265-1.jpg

Mine too had machine tool marks on the 'waisted' part of the bolt and broke at one of these points. Similar break to your photo too, part of the surface showedcrystalline structure suggesting a tensile fracture, other part of the surface showed evidence of shear.These bolts had done 15,000 miles from brand spanking new.

Interesting stuff. For sure I knew I had torqued these properly (22ft/lbs though some recommend 25) Look at the other bolt which despite being whipped around, breaking the cases and whacked by the crank is hardly bent. Check the steel cap, almost straightened out!

http://i424.photobucket.com/albums/pp322/keith1069/IMG_0263-1.jpg

http://i424.photobucket.com/albums/pp322/keith1069/IMG_0263-1.jpg

Makes you wonder why the bolts are waisted at all. The only reason I can think of is to allow the cap to align itself with the journal without being influenced by the close fit of the bolt. I dont think the torque is an issue, The bolts would have been turned on a lathe including the waisted portion then the accurate diameters ground, probably on a centreless grinding machine. It would have been expensive to grind the waisted portion so you rely on the quality of the tool sharpener (and how many had been done on that tool). High tensile steel, if that is what it is? having had the head forged? will not be an easy steel to turn and leave a good finish. Probably done on a capstan in batches of 500+ If you need to change your bolts, you might as well go for a machined Carillo type rod and change the lot for the peace of mind. If you know your bolts and rods are proven, just change the nuts. Bear in mind, as Simon has found, after market rods and bolts may not clear the bottom of the crankcases without some work. ie relieveing the crankcases and chamfering the nuts. Maybe these bolts should be called wasted.