Connecting Rods

[Nick Webster]

I have at last got around to rebuilding an engine that I bought as part of an abandoned restoration project. Accompanied by an approriate bill, the engine was supposed to have been a professional rebuild, but regretfully poured out water even before starting, which broke the spirit of the previous owner who thought it must be a cracked head and enough was enough.

It did not take me long to determine that the gasket support tubes had been left out. One or two other details led me to decide that really, the engine should be stripped and rebuilt from scratch. Faults were many but one of the most basic was the rear crank oil seal in back to front!

To the point of my post. The connecting rods had also been identified for position by putting a hack saw cut across them, setting up stress risers and in my view making them too risky to use. At last! A chance to search through all the old rods I had been keeping while wondering why I hung on to all these old bits. Mindful of the various learned articles that have been printed over the years (particularly on this forum) I made a bee line for rods with a "ropework" pattern on them. Turned out there are two sizes of ropework pattern and it occurs on both narrow and wide notch connecting rods AND both notched and step type. I turned up a nice set of narrow notch rods without the rope pattern. Looking at these I wondered what it was that makes the ropework ones the more favoured rod? The only apparent difference is in the "crook" of the rod where the bolt passes through, the webs of non ropework rod go all the way across the bolt housing into the bottom of the rod, ending at the join. I have attached a picture. Frankly, the continuation of the web all the way into the bottom of the casting looks if anything slightly better than the other. I realise that boken rods are not near the top of the list of Javelin engine failures but I still cannot help but wonder why one rod is considered better than the other?

Nick

[David Kemp]

Welcome to the confusion, when I started my Jupiter engine rebuild I thought having a Staffordshire knot was all you needed. Turns out the best rods have a beefier shoulder by the bolts. Please look at my post on my Jupiter restoration & you will see the difference.
I am using the serrated caps you show, as I only have 3 of the best rods.

[Srenner]

Lots of benefit to getting all your rods properly prepared. All should be the same weight within a few grams. Lots of youtube vids on this. If you go full crazy on them, you can polish all the external rough casting along the beam and the ends to remove stress risers. Then torque them to spec, have the big ends properly sized, check the small end for proper clearance on the gudgeon (wrist) pin, Have them straightened and shot peened. Even if you do nothing else, shot peening will increase the strength and lessen one coming apart. Be sure to bin the old Jowett rod bolts and get new ones. Might need to clearance the top of the bolts to clear the opposite throw.

[Nick Webster]

David, I have searched through your posting on Jupiter restoration and cannot find your reference to the connecting rods. Perhaps I am looking in the wrong place. Could you provide a link?

Scott, Thanks for your input. Just as a first pass I started weighing my various rods and was surprised to find that in general they were only a couple of grams different in total weight which seems amazing given the variation that I have seen quoted for more modern cars. I have yet to weigh them end for end though that will come.

Nick

[David Kemp]

My apology I never posted it in my restoration I emailed it to local Jowett club members.
Rod A is the latest con rod with a heavier shoulder. B is the common type.