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Post Info TOPIC: Frightening knocking sound - bad crank bearing?


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Frightening knocking sound - bad crank bearing?
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Four days into a trip of trail and dirt road riding my TTR went from sounding a little bit off to frighteningly loud knocking sounds from somewhere low in the engine. Now that summer is winding down I have had some time to pull the engine and start to tear it down.

 

There was a lot more glitter in the oil than I was expecting. 

bedazzled my filter

 

Just as scary in the sump screen.

sump sparkles

 

I don't know if I have all the tools that I need to finish the tear down. So far I have pulled the head, cylinder and clutch. Initial findings are indeed a bad bottom end for the connecting rod. I have maybe 3mm of radial play on the bearing. I'm pretty sure that this is what caused the knock.

Here's the next problem - it looks like the piston skirt hit the cylinder wall.

piston

 

cylinder

 

This is the first time that I have gone so far inside of an engine, so I really don't know if I'm drawing the right conclusion on this one. Seems that the worse problem is the connecting rod bearing. There's also a chance that all that metal floating around in the oil has caused other damage that I haven't seen yet.

Before I go much further, I'd really like some input from you guys. If I'm looking at a new crank, re-bore and a new piston am I getting to the point where I should be looking for a replacement engine?

Anyone know if a WR450 motor would fit? :P

 

 



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Bad luck cry

Very unusual for a TTR that has had its oil level maintained correctly to lose a big end.

However, the good news is that it looks like the mesh screen and the oil filter did their job biggrin

 

There are some threads showing full engine rebuilds on the forum e.g. see here

However, make sure you have the pucca Yamaha workshop manual by your side - just in case.

Be methodical and have some boxes/container to keep the parts in safely. The best tip is to put bolts back in their respective holes after removing an item or fix them to the part that has come off with tape. Take lots of photos if in doubt about how parts are going to go back.

In terms of special tools, you need to have a good torque wrench that can accurately work with 10Nm which is what the majority of case screws etc will need to be done up to.

You will need to remove the crankshaft and take it to an engineer's shop where they will split the crank and replace the big end pin, bearing, thrust washers and conrod. They will press it all back together in line and balance it up for you. This is what the new parts look like:

Conrod_bigend_kit.jpg

 

I have not heard of anyone fitting a WR450F engine but all things are possible if you have access to cutting and welding equipment.

Any questions, just ask.

Brian



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Exeter, Devon, UK

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Oh my, you would have to link to the big bore build wouldn't you.  :)

That's very tempting. It looks like I'm going have to save some money and make some phone calls.

I've got the manual. I've been taking pictures, marking parts after I take them off and trying to keep them organized.

tear down

 

 

I'm not sure what the root cause was. I have been trying to stay on top of the oil status. I think I was going a little too long before oil changes. My manual says 600 mile intervals but I have stretched that to 1000 miles on an occasion or two. I try to top up before rides too.  She sees a lot of hard use hauling my heavy butt around on long days. I'm about 280 pounds with gear on and I've done 200 mile trail days and 350 mile road days on the TTR. Maybe oil breakdown is part of the problem?

I'm going to continue taking the motor apart to be sure all the metal shavings are cleared out, clean and service the valves too while I have it apart. Reassembly will be on the back burner while I save up for parts. I plan on having her back on the road by spring. Hopefully for less than $1000 US.



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I took the crank and the needed parts to my local machine shop today. They advised me that the cost of labor on the rebuild would make it more economical to replace the crank with a new item. He said getting the timing correct on the counterbalancer gear was part of what made them so time consuming to rebuild. He was quoting 1 1/2 hour of labor for the work. Did I get bad advice? He sounded pretty reasonable to me.

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