11-27-2020, 10:46 AM
I'm an open-minded guy, and have been wrong more times than I can count. That being said, can anyone think of a plausible reason why the timing chain tension would need to be released before taking clearance measurements? There are three reasons not to:
1) The intake cam could be out of its intended timing position by as many as 3-4 teeth when you turn the crank to a TDC position to take measurements. The slack on the loose side of the chain can be taken up by the intake cam being forced forward by valve springs it is holding open, resulting in slack between the cams. You can see this happen when turning over the crank by hand--the slack goes from back to front as valve springs push on rear facing intake lobes.
2) The intake cam sprocket can jump a tooth while turning the crank. If this happens, you'll be forced to remove the cams to correct the timing, even of all your valves clearances were perfect. You'd double the work for nothing.
3) Once you remove the cover bolt from the cam chain tensioner, you get to install a new washer when you replace it later. Again, if the clearances are correct, you save that step. That's a small factor compared to the others.
The chain slack does not affect the clearance measurements one iota when the cams are in the correct positions and held down by their holders, any more than a burned out headlight would. The sole function of the chain is to maintain timing between the crank and the cams. Again, one may prove this by taking measurements with and without slack. I've done several times out of curiosity and gotten the exact same result. Besides, the engine runs with no slack, so it certainly isn't hurting anything to leave it on.
The shop manual does have you releasing the tension on the chain in the cam removal section. If you follow the steps exactly as given in the valve clearance steps, you'd be releasing the tension twice.
One example of cascading shop manual errors that show up over multiple bikes (proof they copy general steps from manual to manual in order to not 'reinvent the wheel' each time):
All of the fuel injected 781cc VFRs have a vacuum activated baffle on the top of the airbox that opens and closes to optimize airflow under various running conditions. ALL of the 1998-current VFR factory shop manuals have an incorrect test procedure for that particular system. The manual says if you unplug the neutral wire switch and start the engine, the baffle will be open under some fixed rpm level (around 6,000rpms if I remember right); the default position is closed. Every VFR800 out there, including the three models I had, fail this test. Honda even got me a new ECM under warranty when I demonstrated the failure of that test to the dealer on my 2003. Later, after i tested several other local VFRs, Honda admitted the test as specified in the manual was wrong. The throttle had to be nearly full open (in addition to being in gear or neutral switch disconnected) for the baffle to open. The manuals continue to be sold with this error, even after they became aware of it in 2003. It happens. By the way, the VFR manual does not have you take tension out while making measurements. Neither do any of my cars. It's not general shop knowledge.
When installing a new chain & sprockets on my 2014, my factory manual said to remove the gear position indicator as one of the required steps. That switch was far enough away from the front sprocket that it could be left alone; there was no reason to remove it, so I didn't. The job went off perfectly.
Anyway, I'm open to logic if anyone has a reason (other than following what may be a goof in the book) for releasing the tension from the cam chain before taking measurements.
1) The intake cam could be out of its intended timing position by as many as 3-4 teeth when you turn the crank to a TDC position to take measurements. The slack on the loose side of the chain can be taken up by the intake cam being forced forward by valve springs it is holding open, resulting in slack between the cams. You can see this happen when turning over the crank by hand--the slack goes from back to front as valve springs push on rear facing intake lobes.
2) The intake cam sprocket can jump a tooth while turning the crank. If this happens, you'll be forced to remove the cams to correct the timing, even of all your valves clearances were perfect. You'd double the work for nothing.
3) Once you remove the cover bolt from the cam chain tensioner, you get to install a new washer when you replace it later. Again, if the clearances are correct, you save that step. That's a small factor compared to the others.
The chain slack does not affect the clearance measurements one iota when the cams are in the correct positions and held down by their holders, any more than a burned out headlight would. The sole function of the chain is to maintain timing between the crank and the cams. Again, one may prove this by taking measurements with and without slack. I've done several times out of curiosity and gotten the exact same result. Besides, the engine runs with no slack, so it certainly isn't hurting anything to leave it on.
The shop manual does have you releasing the tension on the chain in the cam removal section. If you follow the steps exactly as given in the valve clearance steps, you'd be releasing the tension twice.
One example of cascading shop manual errors that show up over multiple bikes (proof they copy general steps from manual to manual in order to not 'reinvent the wheel' each time):
All of the fuel injected 781cc VFRs have a vacuum activated baffle on the top of the airbox that opens and closes to optimize airflow under various running conditions. ALL of the 1998-current VFR factory shop manuals have an incorrect test procedure for that particular system. The manual says if you unplug the neutral wire switch and start the engine, the baffle will be open under some fixed rpm level (around 6,000rpms if I remember right); the default position is closed. Every VFR800 out there, including the three models I had, fail this test. Honda even got me a new ECM under warranty when I demonstrated the failure of that test to the dealer on my 2003. Later, after i tested several other local VFRs, Honda admitted the test as specified in the manual was wrong. The throttle had to be nearly full open (in addition to being in gear or neutral switch disconnected) for the baffle to open. The manuals continue to be sold with this error, even after they became aware of it in 2003. It happens. By the way, the VFR manual does not have you take tension out while making measurements. Neither do any of my cars. It's not general shop knowledge.
When installing a new chain & sprockets on my 2014, my factory manual said to remove the gear position indicator as one of the required steps. That switch was far enough away from the front sprocket that it could be left alone; there was no reason to remove it, so I didn't. The job went off perfectly.
Anyway, I'm open to logic if anyone has a reason (other than following what may be a goof in the book) for releasing the tension from the cam chain before taking measurements.