nigelog

couldn't see any 21" rim, ta anyway

Front wheel chrome is rough on my C15 trials and I have been looking for alternatives, forks are B44 clamp type at bottom of fork leg did any japanese/ european manufacturers ever use a 40 spoke alloy rim in 21" that I could change to I can find a lot of alternatives in 36 hole, and have toyed with the idea of lacing the 40 hole drum to a 36 hole rim, but sourcing the odd length spokes may be a problem any pointers appreciated

holes drilled through primary side crankcase act as a weir keeping a level in the primary casing for the chain to pick up - the excess crosses back through the two holes into the lower crankcase and returns to the sump / oil feed pick as per normal - all this system does is reroutes it out to the prmary case and back in again so you are working off the one reservoir of oil. The primary case oil therefore is always topped up and always clean and filtered oil.

Hi Davetom I forgot to add that what was not mentioned by Rupert Ratio but I did (I spent so much time looking at the engine during rebuild the idea grew on me) - when you look down the crankcase mouth there is a ledge on both halves of the crankcase just below the barrel lip. On the timing side it is drilled to feed oil to the timing pinion bush. I drilled the primary side the same giving me a a feed that exits just above the primary gear and chain. I ran the engine yesterday with the primary case off as I wanted to check the clutch before replacing the cover and the spray of oil onto the chain and gear is better than I hoped for. I couldnt see the benefit of just leaving out the primary oil seal and hoping for the best. So my oil seal is in place and feed comes pressurised from the crank downstroke. I may have pictures somewhere - if I find i'll post bottom pic shows ledge on timing side - repeated for primary side to provide feed shown - no discernable ill effects

Davetom i did the weir type conversion on mine leaving the two ports tapped in case I needed to blank off again. I have experienced no problems with this method and have had less hassle with primary wear and clutch slip. Just do it as it says in the book

Hi Mcman I was unable to source them during my rebuild and being so small near impossible to measure. They are a tight fit and you possibly would get away with the old ones and a dab of silicone.

Hi mcman if what you are saying is that are the tube for the swingarm pivot and the lower frame cross support parellel to each other then yes they should look in line across the width of the bike- height wise I'll check later

Try talon gears they might go down to 15 teeth

Standard set up for the B40 would have been as mentioned earlier 52T clutchwheel- 23 front sprocket and 70 link duplex chain The trails dropped it to 52T - 18 and a 68 link duplex chain The b44/50 with more grunt went the other way and had 52T - 28 and a 72 link chain At the moment I am machining a compromise front sprocket of 26 teeth for road use as the 23 still low and limited. I think then I will be at the limits of the adjustment of the 72 link chain which fits the 28. As pat says with chain available for 20 or so it pays to replace it. I have a stator and rotor that look as if the chain snap at some stage broke either the crankpin or the gearshaft on the primary side.

Hi Charlie, heres a pic of the assembled pieces, interested by the "top hat" idea. Does mean more work on the outer though.

Charlie, needle roller definately the way to go. Worked out fine. Full story Http://rebuildbsac15.blogspot.com

Removed and sold elsewhere, price would have been interesting though

Hi all, Charlie I finally got my bearing from Alpha and they machined it (ground) to my tolerance which was good of them and very reasonable. I am sticking with my 23mm US bearing so as it matches the shim I made. I also got the 20mm bearing from Alpha to compare it so if you havent bought yours yet I'll swap it for a C15 metal clutch plate (I'm missing 1) and an Amal carb fibre spacer(mine is too small vertically and does not cover the seal all around). Re-assembly starting tomorrow. I also went with the crankcase breathing by drilling 2 x 3/8 holes but I tapped them so that if it does not work out I can block them without separating the crankcases. I also replicated the oil catch (used for the inner timing cam bearing) on the other side of the case to feed extra oil into the primary case. I'll see how I get on. Can be viewed at Http://rebuildbsac15.blogspot.com

Hi there all, West Cork is definately trials heaven but not many organised events as far as I can tell. Vinnie you'll have to get them nearer to us down here (keep me informed if u can). Bike was targeted to be finished Feb but a delay with a bearing set it back. I have it now and will start rebuild tomorrow. There is a good chance I will pre 65 trial it as I found I have a set of drive gears of the appropriate size which can be swapped over in a few hours. Looking forward to getting it finished.

Seasons greetings to you all and thanks for the assistance/advice over the last year. Rgds Nigel

I am not so familiar with 4 stroke crankcase compression but surely there is a limit to the amount of airflow provided. Why go to all the trouble of creating a timed/ported breather on the timing side whena hole drilled through the casing would have sufficed or even left the timing gear shaft hollow. The brain cells seem to remember crankcase pressure was required in piston ported 2 strokes to provide the transfer of fuel air. I would be interested to know what influence crankcase pressure or the lack of it has on a 4 stroke

Hi Lads on the subject of engine breathing - might as well think of that while I wait for the bearing - I have been toying with the idea mentioned in Ruperts book re:B50 breathing with 2 x 10mm holes drilled from the drive side into the lower crankase. These holes are supposed to be drilled at a height which will act as a weir and hold "engine oil" in the primary case. The primary gear and the engine would therefore share an oil supply. I like the idea of a single oil level to monitor but I have been unable to find out any more details or get sight of a B50 casing to have a look. I think it may provide "too much" breathing for the engine but I would be interested in anyones input. Rgds Nigel

Hi Dave did the same jod on mine and it was not rough. I will check dimensions and get back to you to see if you can avoid an oversize bush. Ta Nigel

I thought long and hard about that and decided against it for the drive side bearing and removed both to provide continuous oil feed. Could have left the outermost but was concerned about crankcase pressure. The sleeve gear bearing I did leave the outermost to help the oilseal keep the muck out. When I stripped engine there was 1/4 inch of what could only be described as MUD in the sump well. I have allowed for gearbox pressure by venting the filler cap with a .8mm hole drilled to vent at the side of the bolt and not the top.

Hi Charlie Alpha sell the bearing @

I have had a disaster with an experimental bearing I had intended for use on a C15. I wanted to replace the timing bush with something more robust and opted to machine the inner and outer bearing components to fit a needle roller. It was with the assistance of this forum that I managed to get the bearing over from the US. Everything was fine until the machinist took about 8thou too much off of the outer bearing case (and for some reason shortened it to the same width as the bearing) making it unuseable. All the other components, inner sleeve, bearing and thrust washers are perfect. I can only find complete items with the sleeve bush in place at

Hi mcman my bike is not dedicated trials but previous owner for some reason chose B25 piston and compression ratio landed at 8.75:1 Useful link here for calculating Visit Puma Tech

Hi Beardy sizes used to be available a b and c at different thicknesses. It is probably as easy to gather what shims will fit and try various combinations of them. Ta Nigel

Hi distance of drive gear from crank bearing (and hence the timing gear from the seal)is controlled by a spacer behind the gear which can be replaced by smaller/larger to allow alignment of the timing chain on the drive sprocket and clutch drum. This spacer provides the surface which the oil seal runs on. If the two cogs are not in line, which can be measured with the edge of a steel ruler, and the drive gear too close to engine a larger spacer is needed. If they are in line and the chain is still rubbing you may have to correct the end float of the mainshaft to bring the clutch out further and then match up the drive gear. I am not 100% if the B40 mainshaft has a nut on the timing side to stop end float, but if it has not then the thrust washer in the middle of the shaft will need replacing. Hope this helps