Hi, the trusty Kwak dealer listened to my complaint that the bike engine cut out when I rolled off the power.

The engine cutting out was most upsetting when filtering between cars while coming up to traffic lights. I would be hoping the lights would go green, but sometimes they did not, so I'd roll off the power... and the engine might cut dead. Pretty annoying when at that moment the lights would go green. Some times i could bump it, other times the electric start did the job. (if the valve clearances were right it would start first touch).

So after a while they gave me the bike back and said the Exhaust OH cam needed to be replaced. I don't know what else they did, I guess the valve clearance needed reset because of the new cam. But its been good since.

A couple of other things...

The chain split link needed replaced as it had stretched causing a lumpy feeling to the chain rotation around the sprockets.

I had also mistakenly swapped the spacers around when refitting the rear wheel, which caused the rear calliper brake pad to drag a bit on the rear brake disk. I had thought the calliper was ceasing a bit, but on inspection and a clean up it was fine, which perplexed me a bit, till i realised the brake disk was too far over towards the centre of the bike. Swapping the spacer around but the back into the correct alignment with the calliper.

Now the bike is running sweetly and I can thrash it into work and home again each day!

see the pics of the cam... as you'd image its hard to spot anything wrong as the failure was not catastrophic.

Ex cam - 1
Ex cam detail -2

 

Were you/they able to attribute what caused the galled cam?

 

If the cam bearing journals are galled, what does the bearing/bushing material look like in the head?
Have you ever run low on oil or dumped the bike on its side while the engine was running, starving it of oil?

Ride on
Brewster

 

Exactly. You don't usually get one without the other...head bearing surface and cam. The cam is harder that the head. I was hoping there was just a cam manufacturing issue that somehow spared the head cam bearing surfaces. I think that's doubtful from looking at the pic...looks like classic galling between cam and head cam bearing surface...but then, we didn't get to inspect the components while disassembled.

 

Yes I agree, I had wondered as to the state of the engine head end. I thought (when I was doing valve clearance checks) that the cylinder head did NOT have collets fitted, as I've seen with other bikes. To me, the cams seemed to sit directly onto machined surface of the alloy head end. I will ask the dealer what was done about wear on the cam seats. For the money I was charged I'm thinking a new cam was fitted is all. There was no mention of machining the cylinder head or fitting collets. I did ask if they had needed to grind the valve seats; they did not do that.

KLX250S9 (2010)
JKALX250SSDA02922

The bike is running well..... but for how long? Well, that is anyone's guess!

 

I have a hard time understanding how a bearing issue on the cam would make the engine run different. Maybe the valve or seat was shot or the clearance was too tight, and the cam bearing issue was found on inspection?

 

Interesting...I'd never heard insert bearings referred to as collets. Over here we call them insert bearings or plain bearings. Just different terminology and cultures.

On the cams sitting directly into the machined head, that's the most common way most OHC motorcycle engines have been done for some time. It was pretty unusual for my 1973 Kawasaki Z1-900 to have insert plain bearings. Even the original Honda CB750 just had the cams riding directly in the head. This design works great as long as lubrication and pressure is maintained.

 

I'm wondering if the fault lies in the decompressor. If that is keeping an exhaust valve open at idle it would cause stalling.

 

There are supposed to be two dowels in the cam cap. If those are not installed it will be a crap shoot to get the clearance set.

92042 is the dowel

 

Thanks. Yes the dowels are in place OK, so the cam's bearing clamps are holding the cam in position, aided by the dowels for alignment.