Yamaha RD250 ticking noise?

[iranana]

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!

[kneescraper]

Kind of sounds like it might have a worn cylinder, perhaps its scored alittle. If you get the engine real warm, hotter than operating temp does the engine start to labour and doesnt want to rev out cleanly? Piston slap can some times be heard easier if you let the bike idle then open the throttle to alittle over half, if there is piston slap you will hear the sound then....sometimes.

My kind of thought is perhaps its been seized before, by getting the engine real hot the piston expands and if its been seized before the piston will pick up on the scoring marks and the revs will die down as the engine trys to keep running...if that makes sense.

Ticking sound can also be a leaking exhaust manifold, you might not beable to fuel the exhaust fumes leaking but they can make that type of sound.

Also gudgeon pins can make a ticking sound, esp' at low revs. I have seem motors that have had a big end rebuilt because the old gudgeon had seized to the piston and when installing the new piston they mechanic has just honed out the con-rod to allow the new gudgeon to slide though...this isnt to much of an issue unless your talking high-spec motors....

I would pop the top of the motor and check the cylinder, check the piston for float/ play and then go from there.

[FJRider]

Use a short piece of hose as a stethascope to find WHERE in the engine the noise is coming from.

[kneescraper]

Use a short piece of hose as a stethascope to find WHERE in the engine the noise is coming from.

This methods a good idea but noise travels....even more so in a two stroke so keep that in mind.

[FJRider]

This methods a good idea but noise travels....even more so in a two stroke so keep that in mind.

At idle it wont travel far. Surprisingly accurate actually.

Not that many bits inside a Two stroke ...

[kneescraper]

Two strokes make more exhaust noise (which can travel quite far because of the vibrations etc) then most four strokes...In most standard engine/ exhaust situations.

Im not saying not to use the tube....I use a simular thing at times but its better he/she knows that noise can travel quite abit.

[iranana]

Hey guys thanks for the replies! Gives me more to contemplate when I take it apart and start looking for the problem...When I use a screwdriver against my ear and place it at points on the engine, the noise is loudest in the exhaust region. The performance of the bike suggests that it's in pretty good shape, it pulls pretty hard and the front gets rather light once you hit the powerband, but I haven't really tried pushing it or riding it for long to get it really hot as I don't want to make things worse if there is indeed something amiss. It blows a good deal of smoke though, so it's going to need a good wring out down the motorway to clear its throat when I'm confident it'll be fine to do so. I'll pop the head off next weekend and I think I'll start a thread somewhere to document the restoration/rebuild process. I'm sure the cause of the noise will make itself pretty evident once I get inside the machine. It hasn't been registered/wof'd since 1988, so it'll be great fun to get it back up in tip top shape and running well

[FJRider]

...When I use a screwdriver against my ear and place it at points on the engine, the noise is loudest in the exhaust region.

It sounds like one of the rings is catching the exhaust port.

Whip the head off and have a look ... not a biggie on a two-stroke.

[Akzle]

I'll pop the head off next weekend and I think I'll start a thread somewhere to document the restoration/rebuild process. I'm sure the cause of the noise will make itself pretty evident once I get inside the machine. It hasn't been registered/wof'd since 1988, so it'll be great fun to get it back up in tip top shape and running well

top shit bro.