andy.t Posted October 11, 2011 Report Share Posted October 11, 2011 Could somebody confirm something for me please. A chap told me something about a Beamish 250cc barrel having a sleeve that could be pushed out to enable it to take a 325cc piston. The way I understood it was the sleeve came out and the bigger piston went in, not a re sleeve as in you need to take a smaller sleeve completely out and fit a larger one. Cheers for any replies. Quote Link to comment Share on other sites More sharing options...
woody Posted October 11, 2011 Report Share Posted October 11, 2011 All of the black engines were made as 325cc, it was cast into the bottom of the barrel on the ignition side but ground off on the 250 as yes, the 250 was a sleeved down version. I doubt it was done that way though. I think it was a new liner. There was also something different about the exhaust port between the two but I can't remember what it was now. The 250 had a bigger weight on the clutch OR it was a mod to lighten the weight to get the 250 to pick up quicker - probably the latter. The combustion chamber was different in the 250 head as well I think. All these are outline points, the actual details I've forgotten. The 325 is a very torquey motor, I had one and loved it. Best way to make the 250 perform better, if that is what you are after, is to lighten the weight of the clutch flywheel and maybe ignition side too? A lot cheaper than converting back to 325. Quote Link to comment Share on other sites More sharing options...
turps Posted October 12, 2011 Report Share Posted October 12, 2011 The black engine that I have has two grubscrews at the bottom of the barrel. Take these out and press the smaller liner out and hey presto you have a 325 barrel. Don't know about any other differences but I believe that the pistons are quite hard to come by. Quote Link to comment Share on other sites More sharing options...
b40rt Posted October 12, 2011 Report Share Posted October 12, 2011 The black engine that I have has two grubscrews at the bottom of the barrel. Take these out and press the smaller liner out and hey presto you have a 325 barrel. Don't know about any other differences but I believe that the pistons are quite hard to come by. I thought you told me you took out the two grub screws & it turned into an SWM which is going to appear this weekend ? Quote Link to comment Share on other sites More sharing options...
woody Posted October 12, 2011 Report Share Posted October 12, 2011 The black engine that I have has two grubscrews at the bottom of the barrel. Take these out and press the smaller liner out and hey presto you have a 325 barrel. Don't know about any other differences but I believe that the pistons are quite hard to come by. Never knew that. I think Nigel Birkett may have standard size 325 pistons as generally it is the oversizes that have disappeared over the years. Quote Link to comment Share on other sites More sharing options...
beamish owners club Posted October 13, 2011 Report Share Posted October 13, 2011 The manual shows no difference in flywheel between 325 and 250 and no weighting on the clutch side like the Bultaco. As Woody says, all black engine models left Japan as a 325. To make it a 250, it was sleeved as you know but also the pilot jet was changed from 20 to 27.5 and the head was skimmed and the squish band altered. This weekend I will be taking the top off my converted 250 as it blew a head gasket on it's first outing despite putting in a thicker base gasket to try to reduce the compression ratio! The 325 has a compresion ratio of 7.5:1 and the 250 6.7:1. If you just use the 250 head on your convertion you end up with a compression ratio of more than 8.7:1 - mine snapped the kickstart at that ratio. I have a borrowed 325 head and I will photograph and measure both and put the findings on my website. I have heard of a guy who is supposed to be having some new 325 heads cast and I will keep all informed on that via my website too if it comes to fruition. Quote Link to comment Share on other sites More sharing options...
02-apr Posted October 17, 2011 Report Share Posted October 17, 2011 I seem to recall that the 325 had a small hole drilled near the exhaust port, possibly to reduce compression for starting, the pressure when running effectively closing the hole. I remember Motorcycle Mechanics, of all publications, tested the beast and the published torque curve was incredible. Max torque seemed to be not much above tickover and tailed off from there. They were certainly a real "bottom end" bike which is probably why some favoured them for the then current style of riding an outfit. Quote Link to comment Share on other sites More sharing options...
beamish owners club Posted October 18, 2011 Report Share Posted October 18, 2011 I have the head and barrel off mine at the moment so I will tkae a good look and put some photos on the Beamish website if you are correct. I know one mod was to put a 1mm hole in the piston under the bottom ring by the exhaust port to aid lubrication but hadn't heard of a hole in the barrel. I have the 325 engine in my outfit and it sure does pull 24 stone with a chair on it no problems right from tick over! Quote Link to comment Share on other sites More sharing options...
beamish owners club Posted October 21, 2011 Report Share Posted October 21, 2011 I inspected my barrel and there is no small hole in or near the exhaust port. East of starting would be a decompression valve in the head but Suzuki didn't leave space to fit one easily. I was told (by Graham Beamish) that the head was skimmed for the conversion from 325 to 250 but had never actually seen both heads side by side to compare them; I now have a photo on my website of both heads. I had taken the head off a friend's 325 to compare it with mine but the looked identical - I now know that he also has a 250 head on his 325! Having a 250 head on a 325 gives a compression ratio of nearly 9:1 which would be fine for a MX bike but is a bit fiery for trials. I have had some conversion plates laser cut to compensate for this and to bring the compression ratio back to standard. Quote Link to comment Share on other sites More sharing options...
beamish owners club Posted November 7, 2011 Report Share Posted November 7, 2011 I have now had some coversion plates laser cut to correct the compression ratio if you have a 250 head on your 325 or have taken the liner out of your 250 and want to be able to start it without snapping the kickstart! Quote Link to comment Share on other sites More sharing options...
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