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  • RCS rebuild

    Attached a pic of the sorry state of the Silverstone I've started rebuilding. I think the oily-rag or rebuild question is easily answered in this case. Thus far I have managed to get the gearbox together, repaired the tank, made a plug for a new GRP seat and am looking at the rusty remains of three crankshafts. I hope to be able to post updated images as progress is made.
    Attached Files

  • #2
    Simon Bateman can sort out the cranks by machining for a needle roller conversion. Usually rusted on the bearing surface by being left unused with Castrol R as the lubricant.
    Dogsbody

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    • #3
      It is a bonus that it came with the later CC gearbox, first fitted to the RDS. I see there are the remains of the bracing tube still attached to the upper rear motor mount that had to be removed to make space for the later gearbox. My Silverstone also has this as evidence it started life as an RCS frame.

      As for the crankshafts, I can see no difference between the Alpha cranks used in the Challenger and those used in the Silverstones so, if the shafts are beyond salvaging, that is an alternative that might be more readily available. I would also endorse DBs recommendation to use one of the needle roller small end rods if you intend to race the bike.

      Stan

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      • #4
        Thanks for the input. I think I'll be OK crankshaft wise, following a conversation with a Silverstone rider at Donington last weekend I should be able to regrind the shafts and use oversize rollers. I last rode the bike in 1979 and would like to get it back to as close to as it was then as possible and then work from there. The main challenges will be in the frame and pistons. Although I have two frame loops the subframe is in very poor shape on one (not visible in the pic) and is completely missing from the other. I have one new piston, but I think the dykes rings are pretty much unobtainable now, so I'll switch to a thin ring piston. Does anyone have experience running the cast pistons sold by Greeves Motorcycles with a single ring? The original bike had good provenance, ex Alastair Kirkaldy, Dave Street and Peter Pinion and I rode it for seven years in Bemsee, Southern Sixty Seven and Bantam Club meetings before life got in the way.

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        • #5
          I didn't know there were single ring pistons even available for the Silverstone. Since the supply of Hepolite, dyke ring pistons dried up I have been using the re-manufactured pistons that use the 1mm thick CR250 rings (2),originally the cast version but more recently the forged ones sourced by Simon and now sold be Villiers Services (I have been racing mine continuously since 1982 so have gone through a lot of pistons).

          I have read that single rings only work if the rpm are up in the 10,000 range and that, at the 7,500-8,000 used on the Silverstone, 2 rings are needed to prevent blow by. My Yamaha TD2B falls flat on its face below 8,000 and makes power to 11,000 and that uses single ring pistons. I do run standard Greeves porting on the Silverstone so maybe, with extensive porting, the power band can be moved up so that a single ring would be effective but I doubt it would ever be much over 8,500-9,000 if the crank is up to it as the pistons are quite heavy.

          BTW what size is your original piston as I might have a pair of rings.

          Stan

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          • #6
            Thanks for the advice. It sounds like I should be fitting the two ring piston, they're probably at least as good as the original dykes in terms of ring configuration. Thanks again.

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            • #7
              Running a single ring is fine in a racing engine it makes no difference as long as it's in good condition... But the best piston available is the forged one Nametab used to sell. Ideally I'd use one of their rods with the 16 mm needle roller small end as the standard 1/2" gudgeon pin is ridiculously undersized. I assume villiers services now sell them?

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              • #8
                Thanks very much for the info, I'll be taking your advice and getting a new rod with a needle roller conversion. You're right about the standard gudgeon pin, back in the 70s when I was racing I changed the pin every third meeting to avoid failure. The one time I ran it at a fourth meeting the pin let go and grenaded the engine. Not only were they small in diameter, but I thought they were hopelessly made, with big steps in the middle where they had been bored from either end causing stress.

                Do you have to change the piston clearance at all when going from a cast to a forged piston?

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                • #9
                  I went with .004" clearance for the forged piston when I had my damaged cylinder resleeved here in Canada last winter.

                  This past weekend was our last event of this year so time for a strip down, but the bike ran trouble free for the 4 race weekends even though the only running-in the piston/bore got was a few gentle practice laps totaling about 40 miles before racing it in anger.

                  I would be interested in Will's opinion on this clearance though.

                  Stan

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                  • #10
                    Regarding Will's comment about the 16 mm pins, all the pistons, both cast and forged, that I have bought from Simon and more recently from VS have had 1/2" pins as they are listed as drop in replacements for the Villiers engines, whether running bush or needle roller small end.

                    The Alpha needle roller rods that I have been using also have a 1/2" bore inside the crowded rollers to suit this pin size. Are there pistons and rods available with 16 mm pins?

                    I am not sure now what the pin bore diameter of the original Hepolite pistons were but over the years I have received pins with pistons with bores of .312"' .272" and .236", and those are only the ones I have laying around. All the pistons I have received lately have the .236" straight through bore, so the thickest walls.

                    I have never had a pin break in my 34 years of racing my Silverstone but one of the needle roller rods broke where the stem meets the big end boss at the last race of 2015, taking out the crankcases and cylinder sleeve. I worked out that the rod had about 1,100 race miles on it but the big end clearance was still fine, as was the piston pin bearing (I run Castrol R at a 20:1 mix). After corresponding with Alpha, not as a complaint but as information, they asked me to return the rod to them for analysis. Max told me the heat treatment of the 2 ends were OK and he reckoned the rod had torn and not snapped, although I am not sure what the difference is. The fracture line was about halfway across the rod section from, I think, the back edge, one half having a polished appearance the other half granular. There didn't appear to be any stress raiser at the point the rod started to crack but it was hard to tell after the damage when motor locked instantly. Max put it down to a couple of partial seizures I had had the previous year that started the failure, but on both occasions I felt it tightening up and pulled in the clutch and by the time I had pulled the cylinder in the paddock the piston was free and only required a gentle clean up and the aluminum removed from the bore, so they weren't violent seizures. The thing that does concern me, if that is all it took to propagate the failure, is that reconditioned rods are available and how does one know the previous history? This was a new rod as it was the first needle roller rod I had used and, even if the rod is still in one piece, I will always replace them with a new rod.

                    Anyway, I put in another needle roller rod for this year and it has run fine. I will be checking it very carefully though when I strip the motor over the winter.

                    Stan

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                    • #11
                      Simon used to do a rod and piston with a 16 mm pin. Nto nought one for a couple of seasons though. It's a much more robust setup and you can run closer squish.

                      I run about 4 thou piston clearance as well.

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                      • #12
                        Thanks again for the info. One of my regrets is that somewhere along the line I lost the notebook I had with all the info I'd built up over the ten years I was riding the Silverstone. I had it in my mind that I was running about 4 thou clearance, but needed to check. Funnily enough I still have the notebook which Alistair Kirkcaldy and Dave Street put together in the 1960s which has some useful information.

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