Stan Stephens on how to make Indian-bought RD barrels work!
New genuine parts for your classic are getting harder to find, so many parts are now not available. Owners and restorers have to turn to pattern parts of which some are useless but many are of fairly good quality and let’s face it if there is no alternative they can save the day! These pattern parts come from a variety of places, some are made in Japan and are usually exactly the same as genuine parts. For years many pattern parts were made in Taiwan and their quality was dreadful but nowadays the quality has greatly improved. China has now taken Taiwan’s previous mantle in this... Recently when trying to source a set of pre-war girder forks for my Brooklands Special I found new copies of old British BSA, Norton and Ariel forks available and being made in India. As a last resort I ordered some; they were rubbish but when I thought about it at least I had a set of girder forks! This is when you have to look at things a little differently. I had the basis of a set of forks and with some fairly simple remachining they were quite acceptable. As you know, engines are my trade so most of my contact with pattern parts has been with engine parts. You can buy pattern indicators or footrest rubbers and they can be poor but usable. Engine parts, however, have to be right. Recently a customer brought in a pair of new Yamaha RD350 barrels and pistons, made in India! The customer, who wasn’t a mechanic or an engineer, said would I machine the ports the same as in the original Yamaha barrels because even he could see the ports were all over the place. The Indian barrels looked great but everything I measured was badly wrong. The ports didn’t match the liners and were all different heights and widths but the worst part was that the pistons would not go in the bores. The customer assured me that if you pushed them hard enough they would go in. I told you he wasn’t a mechanic! Thinking back to the Indian forks, here was a set of new barrels for a 45-year-old bike; where else would you get them? Again, some machining would put them right and another classic would be saved. No doubt there are or will be other ‘Made in India’ barrels for sale in future so the work I had to do on these RD350 barrels will give CMM readers a few clues on what to look out for. The piston kits were good quality Japanese Mitaka. The problem was the cylinder bores: they measured 63.90mm but the pistons measured 63.97mm. The pistons were 0.07mm larger than the bores. The clearance needed to be 0.05mm so the bores were 0.12mm too tight. To bore out such a small amount on a boring bar everything would have to be perfect in setting it up. My boring bar is very accurate but if you can imagine boring an approximately 100mm long liner it would only have to be the tiniest bit out at the bottom to completely miss one side at the top. The cylinder barrel sits on the boring bar the same way it would do on the crankcases so the bore has to be at a right-angle to the cases, which also means the bore has to be at exactly a right-angle to the bottom gasket face of the barrel. I checked and the gasket face was not square to the bore, not by a lot but enough that the bore cutter would have missed by the time it came to the top of the bore. The amount that it was out would not have mattered if I was doing a rebore but to take out such a small amount it had to be put right. I put the barrel onto the lathe
and centralised the bore in the chuck and skimmed the minimum amount off the barrel and then took the same amount off the other side. It was then time to bore the barrels. As the boring bar goes through the barrel you can hear the continuous sound of the cutter boring its way through. I held my breath, hoping that it did not become the intermittent sound it would make if it was missing one side. All was okay and when I checked the clearance that was as it should be. Another bad point of the barrels was that the ports had not been chamfered but I would do that after porting them. The customer had supplied a porting map diagram for a standard RD350 which he had downloaded for me to machine the ports to. Luckily all the ports in the barrels were too low and/or too narrow so it was a matter of porting them to the correct dimensions, I say luckily because you can’t put metal back on. Here’s a tip. When faced with ports in the barrel not matching the ports in the liner, don’t just match one to the other as quite often they don’t match but you don’t know which is right and which is wrong, the barrel or the liner! Frustrating! With the ports now correct I chamfered the ports and honed the bores. The customer now had a set of new barrels and pistons which were ready to go.
This picture shows the piston tight in the bore.
At last the transfers are finished!
Now we’re skimming the bottoms of the barrels.
The barrel mounted on the boring bore.
The barrel now has the correct clearance.
The exhaust port mismatch between barrel and liner is seen here!
This is the finished exhaust port. You do have to do some graft here!
My goodness! Everything is wrong!