BSA had breakage problems with that small journal crank your rods went with. Their cure at the time was to roll harden the radii. They then went to a larger journal. I'm wondering how good of an idea a smaller journal crank really is?
Im wondering if the correct rods are not available for the crank in question?
You can spend a lot of money bodging other parts to fit a something else.. If its done right then it can work, but if its being done in a way that "saves money" then your more likely to end up with a crankcase with a newly installed breather window.
I totally disagree, i am one of the blokes who puts a limited worth on these old clunkers and therefore
will use what's available to sort them out. It doesn't mean bodging stuff but different people have different
points of view. Many race motors are prepared using stuff from different makers, does that make them
all bodge ups? Blokes have used different cranks and rods in different cases for donkey's years with
very successful results both on the track and on the road. It's one of the attractions of running these old crates.
Haven't you just put an A10 crank into an A65 Allan? Using aftermarket rods etc?
Sorry Nick, probably not my best choice of words and no offence meant.
My thoughts we could the poster no find the correct rods for the bike? There are a lot of people who buy parts for tuppence and quite literally bodge them together, resizing the rod big ends to a new size altogether is what crossed my mind.
A lot of late A10 parts have similar/identical dimensions to those used on the A65, so using A10 rods with A70 pistons on an A65 crank would work, as would B44 pistons on A65 rods on an A10 crank in A65 crank cases also work. But with all those things the key dimensions are the same, it just takes someone with better engineering skills than mine to do all the measurements and machining. Clever things have been done with Norton cranks too but a lot of this is outside my skill set.
There’s nothing wrong with aftermarket parts. I always use aftermarket rods, whether from MAP or Thunder engineering (both good rod makers)
But as I said earlier, there are people like yourself, Mark Parker and others that can cross match parts from other brands and models and make something bloody fantastic. There are others that create a time bomb from a similar selection of parts and probably waste more money doing it.
As this topic is asking about Triumph Rods, it might be worth the OP contacting thunder engineering. He’s a big triumph guy and will likely make the OP what ever he wants if the dimensions are not standard. If the crank has been ground too far then it’ll probably be worth looking for a new crank.
When I bought the A10 rods from Thunder for my long rod A65, (and this rings true with HillBilly’s comment above, I asked Steve for some 6.5” rods, the A10 rods were a fraction smaller and I ended up settling for those because I figured I could shave that few thou off the barrel instead.
I’m also one who has a good collection of spares with the intention of turning 90% of them into something a bit unique. I think a 90° 500cc twin carb will be fun!