Yamaha XT350 Engine Knock

[LanaTheGreat]

My Yamaha XT350 is in daily use. I use it to go to work and back, but since last week I started to observe that the engine has a knocking sound, getting faster as the engine accelerates. When decelerating the sound seems to get less. It is quite embarrasing, especially when people stare at me thinking I am riding a piece of junk. I replaced the piston and cylinder not too long ago, so I doubt if it is a piston slap. Any advice is highly appreciated.

[TUG]

sounds like its time for a bearing change, is it a 2 stroke? if so it sounds like the big end bearing wants to quit and retire, meaning you need a new one to replace its job.


____________________
Haz ER-5, innit!

[LanaTheGreat]

The bike has a 4-stroke engine.

[TUG]

could still be a bearing possibly, did u cnage the rings with the piston and run it in propperly?
____________________
Haz ER-5, innit!

[LanaTheGreat]

I replaced the cylinder, piston and rings (the engine is standard size now). I also run in the engine as prescribed in the manual and had no trouble. I also forgot to mention, the noise seems to get worse when the engine is hot.

[Robby]

So the knock is in time with the engine, and sounds worse when the engine is under load.

Sounds like a big end is going to me.

I remember your thread when you sorted the top end - it sounds like the engine in your bike has been run for an extended period with no servicing whatsoever, and now its comprehensively knackered.

A decent replacement engine would be the best way forward. You could fix this problem, but there's a fair chance that another problem will surface soon afterwards, like a gearbox bearing giving up.

[TUG]

so looks like i was on the right track, i'd check/replace your big end bearings when possible.
____________________
Haz ER-5, innit!

[LanaTheGreat]

So big-ends it is. The replacement engine option seems like a VERY expensive option. Where do I look for a replacement engine, and what will it cost?

[TUG]

i wouldnt opt for a replacement unless you know 100% of a trust worthy friend its in top nick, just get the big ends and put em in so u know that its not gunna scrap in the next 100 miles.
____________________
Haz ER-5, innit!

[LanaTheGreat]

Thanks for all the help. When I do the big-ends, will there be anything else that will have to be done?

[TUG]

good old fashioned oil change and filter change, take it easy again, let em run in for smoother use, also, try not to touch em so much try not to polish em or anything just better for em to be clean and untouched.


____________________
Haz ER-5, innit!

[LanaTheGreat]

No polishing of the crank necessary? I remember the gudgeon pin having a bit of play when I replaced the piston too. I was wondering if it would be necessary to replace it too, and also the con-rod. Jeez this is going to empty my pocket.

[TUG]

hmmm never thought about that, i'd give it a quick google, or search on this forum regarding engine rebuilds, i dont remember being told to polish the crank when rebuilding, but i'd get someone who knows there stuff to give you a second opinion.
____________________
Haz ER-5, innit!

[LanaTheGreat]

Thanks for the trouble. I was just wondering, as I am not really a mechanic. It never hurts to learn

[TUG]

neither am i, did a course for certificates but finding it hard to get an aprentaship, i was told about changing the big end shells, but i just cant remember about polishing the crank, but like i said, someone on here is bound to know.
____________________
Haz ER-5, innit!

[sickpup]

[TUG]

ye its allwed to move side to side on the pin isnt it? not up or down or anything other than run along the pin?
____________________
Haz ER-5, innit!

[sickpup]

[TUG]

will do that when i get round to doing my fzr might overhaul the engine in winter. thanks again for another tip sick.
____________________
Haz ER-5, innit!

[LanaTheGreat]

I'll probably rip the engine apart tonight, luckily I have the workshop manual for it, and have a look at what is causing the racket. I hope I will be able to identify the problem though, it is a big job for me to work on an engine. I guess I shouldn't ride the bike now before I do more damage. There goes my primary means of transport...
I guess it will stand for a month or two.

[TUG]

tbh with you if you can make it a prioty then it will take a couple of days but with time goin on other things will take longer, its not a huge job as your not rebuilding a bike, now thats huge lol, a bike mech could fix it in 5-7 hours, but your following a guide so will take you 12-24 hours, maybe less than that but then again it depends on how much time you really want to have taken away in a day to go towards fixing it.
____________________
Haz ER-5, innit!

[Robby]

Replacement engines are best found on ebay. Ideally you would want a crashed bike with a good engine, that way you would be able to hear it run as well.

But as other have said, gudgeon pin sounds likely, I'm quite surprised you didn't replace it when you did the top end. If you are fitting a new gudgeon pin you should fit a new small end bearing as well, these are cheap, and new circlips to locate the gudgeon pin in the piston.

[LanaTheGreat]

I stripped the engine last night. The gudgeon pin fits snugly into the piston, but has a fair amount of play inside the small end of the con-rod. What I also saw is that the con-rod has a lot of play from side to side at the bottom end, and when I jerk it up and down there is quite some play, and I bet it is a combination of the two that is causing the knocking sound. I guess I will have to get a new con-rod too, as it seems to be excessively worn. Will I need any bearings? Any advice?

[Robby]

This is why I recommended a replacement engine. This one has signicant wear in bits that you don't expect to wear out until mega miles.

The up and down play in the conrod is your big end bearing, some side to side play is allowed, but up and down play isn't.

So its a new big end, new small end, and new gudeon pin for you, along with new gaskets.

[LanaTheGreat]

Replacement engine will cost too much for me I'm afraid. I do have a full gasket set handy at the moment so that is not a problem.