Rattle / bottom end rumble

[Hugh Jarse]

EC300 - 07.

Hi all,

I've had my main bearings replaced less than 30hrs ago and the rumble noise came back recently... After riding it on some green lanes I'm almost certain they've gone again. Really annoying bottom end sound at low RPM, huge vibrations through the pegs (to the point of pins and needles when foot placed on them).

Does anyone know why this could have happened so soon after having them done / what else could give these symptoms?

Top end is in great condition.

It's not chain slap.

Not header pipe rattle.

Power valve is fine.

Definitely bottom end. Definitely rumbling rattle noise.

Doesn't appear to have dampened the power.

Oil same as I've been using for years. And running 40:1 on 2 stroke.

Only used for green laning and enduro but not using the 300cc to anywhere near it's potential.

Cheers in advance.

 

[Zman]

Double check that all of your engine bolts and swing arm bolt are tight.

 

[Hugh Jarse]

Double check that all of your engine bolts and swing arm bolt are tight.

I get that this would cause vibration and lots of it... The rumble noise though?

 

[(F5)]

Geez, 3 of us in a row with 07 300 crank issues.
Only had 11 years on it.
Bit of a swine only 30 hrs since last though. . .

Hopefully the crankpin wasn't a bit loose when last pushed together. That happened to me when someone a bit careless pushed my crank together. I got it tried again and had to spot weld the crankpin to get it to hold. Desperate but better than a new crank.

 

[risk74]

Geez, 3 of us in a row with 07 300 crank issues.
Only had 11 years on it.
Bit of a swine only 30 hrs since last though. . .

Hopefully the crankpin wasn't a bit loose when last pushed together. That happened to me when someone a bit careless pushed my crank together. I got it tried again and had to spot weld the crankpin to get it to hold. Desperate but better than a new crank.

Yeah, tell me about it. Here in the US we get raped nearly $800 USD on a new crank when Motocrosscenter sells them for $400. Even with international shipping it would be way cheaper.

 

[Neil E.]

Lots of ways to have bearing trouble. Whoever assembles the engine can make mistakes. Excess force on the bearings can mark the races. Assembling with barely warm cases can prevent the bearings from sliding in and thus oveload them. Cold assembly can also pinch the crank. Engines that use a compressible center case gasket can also have trouble when the gasket is crushed.

A variety of different bearings have been used. Some even had sealed bearings. If you don't remove the seals from those bearings, your premix oil can't get to them. All parts need to be kept clean. If the bike was drowned, all traces of dirt have to be removed prior to assembly.

The engine needs to go back to the shop that did a poor job, or taken to someone who knows what they are doing.

 

[PEB]

I have two used cranks for sale. Perfect to purchase and send off to the rebuilder.