iranana
15th February 2013, 11:06
Hey people, I just got my hands on a 1978 Yamaha RD 250E for restoration and before I pull the thing to bits I have a few questions... First off, the right cylinder of the engine makes a 'ticking' noise at low RPM/idle - when you increase RPM to above 2,500 the ticking gets quieter and by 3,000 it seems to disappear entirely. It's not a knock or a thudding noise or anything, just a light tick, very similar to the sound the valves on a four stroke make.
Now, from my understanding, piston slap is usually an irregular sound - is this correct? I initially thought it could be that one of the little end bearings/gudgeon is worn but this now seems unlikely seeing as the sound disappears. I'd expect a little end noise to be consistent and get louder as the engine is put under load, am I correct in thinking this? The fellow I'm buying it off doesn't know what the noise is either, but he's suggested that it could be an ignition timing issue; perhaps from a build up of carbon on the pistons as they're probably pretty dirty by now... He also suggested that it could be the stainless steel reed valves opening and closing, but the noise doesn't seem to come from that area.
He's unsure if it's ever been rebuilt (probably hasn't) and it's done 47,000 kms (pretty high for a two smoker!). The bike runs wonderfully though, starts first kick without much effort and still has plenty of power, especially once you hit the power band. It's probably due for a re-bore and a rebuild anyway.
Does anyone have any suggestions on what the issue at hand might be, or does anyone have any experience with two smokers making odd noises like this? I think it's less likely to be a bearing/gudgeon knock based on the regular nature of the sound at low RPM and the absence of it at mid-high RPM. Perhaps the carburettor that feeds the right cylinder isn't delivering the right fuel/air ratio? I think I'll whip off the head next weekend and see what the deal is with the pistons/cylinders. In the meantime, I thought I'd ask around to see if anyone can shed some light on this :) Thanks!
Now, from my understanding, piston slap is usually an irregular sound - is this correct? I initially thought it could be that one of the little end bearings/gudgeon is worn but this now seems unlikely seeing as the sound disappears. I'd expect a little end noise to be consistent and get louder as the engine is put under load, am I correct in thinking this? The fellow I'm buying it off doesn't know what the noise is either, but he's suggested that it could be an ignition timing issue; perhaps from a build up of carbon on the pistons as they're probably pretty dirty by now... He also suggested that it could be the stainless steel reed valves opening and closing, but the noise doesn't seem to come from that area.
He's unsure if it's ever been rebuilt (probably hasn't) and it's done 47,000 kms (pretty high for a two smoker!). The bike runs wonderfully though, starts first kick without much effort and still has plenty of power, especially once you hit the power band. It's probably due for a re-bore and a rebuild anyway.
Does anyone have any suggestions on what the issue at hand might be, or does anyone have any experience with two smokers making odd noises like this? I think it's less likely to be a bearing/gudgeon knock based on the regular nature of the sound at low RPM and the absence of it at mid-high RPM. Perhaps the carburettor that feeds the right cylinder isn't delivering the right fuel/air ratio? I think I'll whip off the head next weekend and see what the deal is with the pistons/cylinders. In the meantime, I thought I'd ask around to see if anyone can shed some light on this :) Thanks!