Engine rattle ?

[Racerboy832]

What causes the typical engine rattle in the 250r's? The noise would scare most people off if they weren' familiar with the model. I have done a ton of searches and most agree it is normal. I figured since there are diehard 250r guys on here someone must know.

[C-LEIGH RACING]

Thats hard to say, ol 250R engines got a lot of things inside that can knock & ting.
One noise I have heard from alot of 250R engines over the years, a knock or tap around the top end area.
What I beleave it to be, over a long use time or being ran at high rpms, I think the small end of the rod elongates just a bit & you end up with extra clearance from top to bottom. That extra clearance allows the bearing & wrist pin room to move up & down more than its suppost to & you have a knock.
It wouldnt have to be much clearance to cause this to happen.
I have heard this noise even on a fresh rebuilt engine that the crank was replaced useing a new OEM crank.
Then there were engines rebuilt useing the OEM crank, the engine was just as quiet.
I guess you can get good parts & bad parts as well even though they are new in the box.

Food just for thought, when a con rod is machined, are each & every one machined by the same person, & the tools that are used to machine them, are each & every one those identical.
The last process is honning the inside surface ( race area ) of the big & little ends to the proper ID, what if the operator turns their head to talk to some one & the hone machine strokes the bore two or three times more than it suppost to.
Mind you this is splitting hairs, but it can happen & most people & engine builders never even think about it, its a new part in the box so its ok to just install it.
Neil

[kiesta00]

My engine seems to have a lot of vibration lately when revved in neutral and also has an additional whirring noise when coming down from revving...any thoughts?

[86 Quad R]

good info neil. most every 2 stroke cycle engine i've ever heard, whether it be a fresh build or not made the rattling sound. the ole blaster is the worst.

keist, you may want to inspect the counter balancer and see what sort of slack may be in the bearings. also check the cranks main bearings on each end.

[C-LEIGH RACING]

Originally posted by kiesta00
My engine seems to have a lot of vibration lately when revved in neutral and also has an additional whirring noise when coming down from revving...any thoughts?

A vibration after its been ran a good while could be any part inside the engine that rotates.
Items you would notice more would be, the counter balancer bearings going bad, the crank getting out of true, & a imbalance in the clutch.
Touching of gears while rotating could give you the whirring noise or the balancer bearings early on going bad.

Crank being out of true, that can come from many times of dropping the clutch like in drag racing. The crank will slip on the big end rod pin & cause the crank to be off centered, then it wobbles.
When that happens you get vibration & a whirring noise.

How the crank halfs are made, weighted more on one side & the balancer shaft, it can only be weighted right for one certian piston, rod, combination.
Say like if the engine balancing was built for the set up of a 66mm stock piston & rod & the engine ran like it was mounted in a rubber box showing no vibs, any size piston over the 66mm the whole rotating mass would be at a imbalance to a point & get worse as the bore sizes increase, & it realy does.

I've noticed over the years that a bore size of around a 68mm, say the 265s seam to be the smootest running engines & quietest, any below or above & you have the vibs.

The more power you try to extract from an engine the more vibs & noise you will encounter.
Neil

[christophere251]

piston slap could be to blame@! when the cylinder gets worn the piston has slack in between the cylinder and the skirt cause slap at the bottom of the stroke! Plus it 2 stroke! its supposed to be loud!

[Trx250rider86]

right before my crank bearings went i heard a rattling sound near the top end area. I havnt got the motor back yet so i dont know if thats what it was but prolly is, makes sense right lol

[TheFontMaster]

Originally posted by Trx250rider86
right before my crank bearings went i heard a rattling sound near the top end area. I havnt got the motor back yet so i dont know if thats what it was but prolly is, makes sense right lol


Thats kinda what my motor did. Part of the crank berrings went, and got up in the top end. Pitted the piston, and the dome.

[kiesta00]

Yeah i'm kinda worried about it, I haven't ridden the bike since i've noticed that vibration so I shouldn't have messed anything up too bad...I'm boring my cyl soon and having it ported so I'll have my engine guy check that stuff out too just so its not a ticking time bomb lol