Thanks everyone - the funny markings (see attached word document) are are mentioned in the Service Manual but nothing about the conrod markings.
I have asked this question on the Sandcast site. Or maybe I could ask John Wyatt?
Bryan/Hondaman - I do have access to accurate micrometers and bore gauges- problem is getting used to using them correctly, when you are an electronics engineer !! - perhaps I should just try to measure everything and try to select the correct shell colours. At least I have the crank markings on the replacement crank. They took some finding too - they were nothing like I expected - they look more like crayon marks my son used to do when he was about 4 years old!!! I will also take high res photos of the con rods and see if they reveal anything I am not seeing with the naked eye (as I think Bryan suggested in another post).
Thanks again for all of your kind help - AshD
Just got an LED light and magnifying glasses on the con rods:
Each con rod has a number of notches one notch for Con rod nearest Alternator, two notches for second conrod in etc.
Each conrod and its cap have marks on them (etched in) as follows
Q743 Cap Q743 conrod
Q776 Cap Q776 conrod
Q775 cap Q775 conrod
Q786 cap Q786 conrod
There another mark like a 7 - could this be the weight code?
This is one for your book Hondaman !!
The notches are unusual! I don't remember seeing those.
With the lots-of-touch assembly that was done to the sandcast bikes, it would not surprise me to find out that they were matching rods to positions on the crank: a big (sales) deal was being made of how smooth the bikes were at the time (like they needed any more help to sell them...). As wrenches, we were flogged to balance the carbs every time a K0 stood still in our shop. Those 4 cables sure were a nuisance for that particular feature!
The "Q" codes you've found are much like the numbers that got stamped into the matched caps on the Rocker Towers: they indicate parts that have been matched in machining. Starting in the K1 series, or maybe during the early diecast engines, the weight codes became spread over the split in the rod caps so the extra match-markings were not needed, eliminating a step in production.
The "7" you found is an early weight code: they are usually "5", "6" or "7" so they don't get confused with the bearing/journal numbers of "1", "2", "3" / "A", "B", "C". Most of those came and went, mostly 'went' in the K5 and later engines. K3 lost them for a while, too, as I remember. And, they are hard to see! As the cranks got better in casting, the rods were used to offset the variances in the flyweights instead of trying to match the weights. This is one big reason why the engines after K2 were not as smooth as the legendary "old factory" K0/K1 engines. If you don't have the markings on the crankshaft, it's not very simple to balance the rod weights with the crank!
ByranJ: there
were Katakana characters on the very early crankshafts (and rod weight codes), and in a few other places, too. They became "normal" characters pretty quickly for exported bikes, though. I have seen the pictographics on bikes that were bought in Japan, too!
Ash:
In my 'real' life (before I switch to my ketchup-and-mustard cape suit), I, too, am an Electronics Engineer: I turned Controls Engineer 25 years ago. You can do those gages! Most come with a "standard" rod (micrometers, here...) that is 1.0000", 2.0000", etc. to match the mike. That provides 2 things for you:
1. It gives you a test reference, in case the mike got dropped or something.
2. It gives you the perfect test piece to test-measure and get the "feel" of the tool.
Pratice with those rods, you'll figure it out: it's all about how much you tighten the knob on your part. You never want to tighten it so much that the mike spreads or the reading will be too big: it also can read too small then if the material is soft, like brass or aluminum.
You're a smart guy: you'll figure those out.
