Power band flat between 3k to 4k after valve clearance adjustment.

[Loren Moto]

Hello fellow S10 owners. I have a 2015 ES. I've put 40k miles on it and the bike has always run great. I recently did the valve clearances. Three of the exhausts were off so I adjusted to proper clearance. I'm pretty meticulous when I come to working on my bikes and am pretty sure I did everything right. I took my time and double checked as I went. On test riding the bike, I noticed the power band goes a little flat between 3k and 4k RPM. This is during hard acceleration. It is not major, but it is noticeable, and it wasn't happening prior to the clearance adjustments.

Timing shouuld be spot on based on the paint pen markings I made on the cams and chain prior to disassembly. With that said, I did not have the electrical panel off to view the actual cam markings. Timing? Throttle bodies? I love to get some feedback before I go back in and have to deal with that darn valve cover gasket again...

Thanks.

 

[OldRider]

Did you make sure it didn't jump a tooth on the crank sprocket? Did you back off the cam chain tensioner and release it after it was put back on?

 

[~TABASCO~]

Once you adjusted the valves, and you had the cams back installed, did you go back and "check the valve clearance" again to double check your work ?

BTW- you can see the cam sprocket horizontal (to the case) hash marks by peeking in from the back corner (intake) and the front corner with out having to tear open that whole side... Just take out the 3-4 screws holding that panel on so you can pull it back off the frame a hair.....

You know your bike.... If you can feel it, I would maybe suggest double checking a few things... Cam sprocket timing, double check valve clearance. Ive certainly seen and helped a few folks that had all the very best intentions and something ended up a little 'off'........

 

[Loren Moto]

I lined up the "K" with the split in the case and made sure the marks on my cam sprockets matched up with the marks on the cam chain.

Did you make sure it didn't jump a tooth on the crank sprocket? Did you back off the cam chain tensioner and release it after it was put back on?

I lined up the "K" with the case split and made sure the paint marks on the cams lined up with the paint marks on the chain, so I think I'm good in that respect. Yes, I did release the chain tensioner.

 

[Loren Moto]

Once you adjusted the valves, and you had the cams back installed, did you go back and "check the valve clearance" again to double check your work ?

BTW- you can see the cam sprocket horizontal (to the case) hash marks by peeking in from the back corner (intake) and the front corner with out having to tear open that whole side... Just take out the 3-4 screws holding that panel on so you can pull it back off the frame a hair.....

You know your bike.... If you can feel it, I would maybe suggest double checking a few things... Cam sprocket timing, double check valve clearance. Ive certainly seen and helped a few folks that had all the very best intentions and something ended up a little 'off'........

Yes, I did recheck the clearances and verified they are now withing spec. Thanks for the tip on the pulling the panel back to check the hash marks. Looks like I'm going back in to check everything. I have one of my other bikes up on my lift now so I'll finish that and then get the S10 back on the lift. I'll update once I get to that point. Thanks for the input.

 

[OldRider]

I lined up the "K" with the split in the case and made sure the marks on my cam sprockets matched up with the marks on the cam chain.

I lined up the "K" with the case split and made sure the paint marks on the cams lined up with the paint marks on the chain, so I think I'm good in that respect. Yes, I did release the chain tensioner.

Lining up your marks on the cams and chain is good as long as the chain didn't slip on the crank sprocket. You need to make sure that the cams are lined up with the cylinder head while the K mark is lined up. In other words, you could zip tie the chain to the cam sprockets, take the tension off the cam chain and move the chain around the crank sprocket a tooth or two while the K marks stays lined up.

 

[Jlq1969]

Perhaps, the cam timings are correct….Perhaps “before” you did not notice any flattening between 3k and 4k rpm, the acceleration was more linear, but “less”….now, with the valves in range, you feel that flattening, but maybe the acceleration is greater.
In those images downloaded from the internet (who knows if they are real or not)… “apparently”, the test rollers feel the same as you between the 3k and 4k rpm

 

[Loren Moto]

Lining up your marks on the cams and chain is good as long as the chain didn't slip on the crank sprocket. You need to make sure that the cams are lined up with the cylinder head while the K mark is lined up. In other words, you could zip tie the chain to the cam sprockets, take the tension off the cam chain and move the chain around the crank sprocket a tooth or two while the K marks stays lined up.

Ah, I see where you are going. Thanks for the input. Like I said, time to open her back up and pull back the electrical panel so I can see the actual timing marks. I have a feeling this is what happened. I'll post an update when I get to it, probably next week, after I'm done with my KTM.

 

[Loren Moto]

Perhaps, the cam timings are correct….Perhaps “before” you did not notice any flattening between 3k and 4k rpm, the acceleration was more linear, but “less”….now, with the valves in range, you feel that flattening, but maybe the acceleration is greater.
In those images downloaded from the internet (who knows if they are real or not)… “apparently”, the test rollers feel the same as you between the 3k and 4k rpm
View attachment 110273

Wow, that graphs looks like exactly what I'm feeling....as best I can tell anyway. Thank you for posting this...I find it very interesting.

 

[Jlq1969]

Wow, that graphs looks like exactly what I'm feeling....as best I can tell anyway. Thank you for posting this...I find it very interesting.

If you read carefully what Hulkss comments about how the hand accelerator behaves vs. the butterflies controlled by the ecu... or at what point the oxygen sensors stop controlling the mixture and the injection system becomes a open system... you will understand better what you feel….you are feeling the change in the injection management system...from close system to open system, between 3K and 4K rpm

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