Engine rattleing after complete Rebuild
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I had a DT125R engine that developed a random rattle once, turned out that the flywheel had come slightly loose and was moving on the crank.
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Every cog in the engine is meshed together permanently, except the starter cog which is designed to engage when the starter is depressed and to slip if the kick start is kept down with the engine running, or the starter stays engaged. I don’t know about dtre starters, but car ones push forward as they are energised and rotate in much the same way...
The only other thing I can think of is that some different pistons use different small end bearings. If these can be mixed up I don’t know, but only one of the above makes any sense to me if it’s only making the noise on the over ~run...
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@spookdog So I had the Flywheel cover off today and and the starter overrunning clutch seems to be ok. Also there is no play in the mainbearings and there are no oil leaks at all. I think I´ll take of the cylinder tomorrow and check the small end bearing. the noise only appears when the enginge is decelerating and not on tickover.
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@zx125 said in Engine rattleing after complete Rebuild:
@spookdog I think I´ll take of the cylinder tomorrow and check the small end bearing
I think that’s your only option
The only time I ever had a noise like that it was because my barrel & piston were badly worn. You could get a lolly stick between the two! My piston was slapping around on the overrun. I don’t think it’s that because of the rebuild. It’s just the only other thing I can think of ...
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Hello,
First of all I want to thank everybody for your constructive answers.
sadly i hadn´t had time for my project bike this summer. After I checked the piston size it was clear that the loud ratling was piston slap because the clearance between bore and piston was around 0,09-0,1 mm instead of 0,05 mm. So I got a new piston that fits the bore of my cylinder, installed it and the bike ran way smoother. But after around 200-300 km I realized a new sound coming from the left side of the Engine. I uploaded a video: https://www.youtube.com/watch?v=Qj7QRH6IZOcI hope somebody has an Idea what this ringing sound could be. sounds like a bad bearing to me but all bearings were replaced like 350 km ago and when changing the piston the big end bearing and the main crankbearings had no radial play at all. I think the sound is coming from the left side of the Engine. Also I´d like to note that the clutchbasket has some play but the sounds doesn´t seem to come from the right side of the bike. except this noise the engine runs great and it seems to have good power as far as i can tell because i have not been reving higher than 6500 rpm.
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@spookdog That´s not impossible since its my first two stroke bike and I normally drive a 600 ccm 4 cylinder which runs way smoother. I don´t realy know how to describe the sound but I think ringing wasn´t the best word to describe the sound. It is most audible to me from around 0:08-0:15 when the engine is decelerating and to me it seems to have the crank RPM if it is a rotating part so probably nothing gearbox related. But it´s good to hear that the engine sounds normal.
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@zx125 When rebuilding the engine, you must ensure that you timed it appropriately.
Whilst on a two stroke engine there are no cam shafts to time, a lot of engines still have timing marks. On these engines the timing marks denote top dead centre on the crank shaft and the balancer shaft.
These must be timed correctly otherwise you will encur excessive vibrations, and likely ringing, from your engine.
Are you confident that you reassembled the balancer shaft appropriately?
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@calum Thank you for your answer. Yes I´m confident that the balancer shaft and crank align proper acording to my repair manual. On my engine there is one mark on the cranks gear and and one on the balancer shafts gear and these are aligned correct. I think they can only be alinged in 1 position because of the keyweys and the 1:1 gear ratio but please correct me if I´m wrong here.
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@zx125 Sure, as long as the timing marks are aligned then that's fine.
The clutch basket has a rubber union connecting the primary shaft to the output shaft.
This rubber can deterioate over time. Did you notice any slack in the basket.
I'm just trying to throw ideas at you for noisy operation.
On that note, the clutch plates themselves must also be balanced. I assume this was done correct. This will also cause noise.
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@calum I realy appreciate any ideas and experiences.
The dampers in the clutch basket are worn and there is some play in it but the noise does not seem to come from the right hand side.
I have assembled the clutch according to the manual as well so this should be fine.
For me the noise seems to come from the left hand side of the bike but I am not sure if any part of the starter clutch or flywheel could make a sound similiar to the one in my video. -
@zx125 The powervavle covers have bushes on them. When they wear they rattle. And apparently can cause the engine to seize believe it or not.
So make sure the powervalve end bushes are in good condition
I think this was the video I saw on it.
https://www.youtube.com/watch?v=4Rk8a51VqBc
https://www.youtube.com/watch?v=REPjGEhrZKQ
Description:
Finally its time to make a start rebuilding the 'top end' of the Yamaha TDR250's engine. Due to a previous Power-valve to piston contact causing immediate engine seizure I performed a complete top end strip down to see what had gone wrong...
