drop in performance after valve adjustment

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

hi, I adjusted the valves of my Ninja 300. all the exhaust were too tight, so I changed the shims by as much as 0.10mm to be in spec. Afterwards, I had a loss in the top end of about 10mph (from 115 to 105). Now, I think 115 is more than what normally users report as the top speed of a Ninja 300, so probably it was as high because of the tight valves.

it is my understanding that tight exhaust valves increase performance because of the increased overlap between in and ex valves.

I also noticed the engine runs some rpm higher at the top end, compared to before, when sitting at top speed in the highway.

The only other reason I could think of is that I misplaced the cam chain by 1 roller. I did count the number of rollers between the two cam sprockets, and it corresponds to the manual value, so I am sure that the tension between the two cams is correct. But, the chain might have moved with respect to the engine bottom sprocket (not sure how it's called).
Now, I don't think the chain moved, and I think it's just the valves, but I'd like to know if my thought on the valves and performance is right.

I did align the marks of both cams at TDC, but those rollers are small, not sure I can tell the difference of just 1 roller as the TDC mark is pretty large.
thanks!

Fisty · Super Spammer Joined: 11 Apr 2007 Karma :

So your question is what?
____________________
Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

Paddy Blake · World Chat Champion Joined: 29 Jun 2006 Karma :

I think you are imagining things tbh.

Shims at the right setting when cold are close to no gap when hot.
So tight shim gap when cold would lead to valves not closing all the
way with reduced performance and maybe pitted valve seat.

RhynoCZ · Super Spammer Joined: 09 Mar 2012 Karma :

What forced you to check the valve clearances?
____________________
'87 Honda XBR 500, ~~'96 Kawasaki ZX7R P1~~, ~~'90 Honda CB-1~~, ~~'88 Kawasaki GPz550~~, ~~MZ 150 ETZ~~
~~'95 Mercedes-Benz w202 C200 CGI~~, '98 Mercedes-Benz w210 E200 Kompressor

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

this is not a direct question it's more trying to understand how the engine works and the reason for the drop in speed. I was hoping somebody who has a lot of experience with valves would know.
I am not imagining the drop in speed, it's definitely there, although it's not a big deal as I don't usually go 115mph on the freeway.

I check my valves around each 7.5k as per manual, to avoid damage for example like Paddy Blake said, which can develop if you don't adjust the valves for a long time.

I did read that racers like to keep the exhaust valves tight. it has to do with that time during which both the ex and in valves are open, which is the overlap. the amount of overlap affects performance. so, tight shim ex valves have increased overlap, I believe, as the ex valves are open for longer.

cb1rocket · World Chat Champion Joined: 30 Jan 2010 Karma :

Could be Down to the fact that as you have made the clearances bigger, the valves don't open as much as they used to. I wouldn't worry about it
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

garth · World Chat Champion Joined: 15 Dec 2004 Karma :

How can it 'run higher revs' at the top end but go slower?

Sure you were in top gear? Laughing

____________________
You ain't a has been if you never was

monkeybiker · World Chat Champion Joined: 23 Sep 2014 Karma :

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

well it seems that at least somebody agrees that it could be either the change in valve clearance, or an accidental change in the drive sprocket by 1 roller, which is what I thought.

my rear tire is new, and hopefully nothing is spinning or slipping.

and yes I am sure I am in 6th gear, if I'm not, it can rev up to the limiter at 90-mph, it's not something that escapes your notice, the limiter kicking in. if there's a small drop in performance, it makes sense that, to reach the same high speed, the engine has to be at a higher rpm - to move the bike at a given speed you need X work. less work production per cycle, the higher number of cycles you need to produce X work, hence a higher rpm at the same high speed.

thanks everybody

monkeybiker · World Chat Champion Joined: 23 Sep 2014 Karma :

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

pdg · World Chat Champion Joined: 15 Sep 2012 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

Ah thanks. it is clear now. see, I was looking at the engine as a black box delivering energy, something I generally do as a physicist - making approximations (I have a PhD in physics from Cambridge).

However, I was blind in not realizing that there is a simple, continuous mechanical link: with the same gear and drive sprocket, a certain rpm in the engine corresponds to a certain rpm in the wheel - hence a certain speed.

Nexus Icon · World Chat Champion Joined: 26 Aug 2010 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

Nexus Icon · World Chat Champion Joined: 26 Aug 2010 Karma :

Musketeer · World Chat Champion Joined: 27 Jun 2011 Karma :

Regarding the valve clearances, increasing gaps between cam lobes and tappets reduces the distance and time by which the valves open. So yes, within spec higher gaps will likely slightly reduce power compared to the being on the tighter side of spec. But not by the margin you describe. Are you sure the gaps are just not too big?

As for the REV to SPEED ratio if you gear ratio / sprockets remain the same it wouldn't change.
____________________
Current Bike: Yamaha XSR900 Previous bikes: Honda CBR1000RR Fireblade, Kawasaki ZX-6R Ninja, Aprilia RS125 2-stroke

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

Our future monarch chose St Andrews, is all I'm saying on that.

On your valves, how confident are you that you measured them correctly? Would it be unfair to suggest that you may have gone in there looking for trouble, and therefore found it?

At this point, I'd suggest that getting a second opinion might be useful.

Or try some science. It works, bitches. Have you got or can you obtain a compression tester?
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

MaybeGuy · Super Spammer Joined: 12 Mar 2007 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

RidingBear · Derestricted Danger Joined: 24 Feb 2015 Karma :

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

Humanities and humanity are worthless, but at least Oxford and St Andrews alumni use capitals at the start of their sentences. Tut Tut

Compression testing is a lot quicker than whipping the head off and fiddling with shims. Whatever happened to scientific method? Crying or Very sad

Tweaking aside, unless you're putting in stellar mileages, I'd be wondering why your valves keep tightening up. Bikes can and do go tens of thousands of miles without needing adjusted once, let alone twice.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

wr6133 · World Chat Champion Joined: 31 Dec 2013 Karma :

Ignoring valves briefly isn't 115 Mph total all out, voodoo in your favour speed on those 300 twins? If so "losing" 10 Mph is probably down to other factors. My 400 IL4 can just pass 130 if the stars align correctly and I do the correct form of human sacrifice prior to riding but on days where it only makes 115 I don't worry about it.