Author Topic: CB750 camchain rattle? how to adjust?  (Read 5310 times)

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Tnrfd

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CB750 camchain rattle? how to adjust?
« on: October 25, 2007, 06:05:18 PM »
 - My cam chain rattles quite loud. I can hear it over the other engine noises when I cruise along. Is this normal or do the chain and tensioner need attention?

I have tride to adjust it, but ain't sure i got i right..

 - How to adjust properly? the manual says TTC on cylinder #1 + 15degrees. Does this mean just piston #1 is on top (no mather if the valves are open or closed) or piston #1 on top AND both valves closed (start of the power stroke)??



Offline mkramer1121

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Re: CB750 camchain rattle? how to adjust?
« Reply #1 on: October 25, 2007, 06:09:26 PM »



Tnrfd

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Re: CB750 camchain rattle? how to adjust?
« Reply #2 on: October 25, 2007, 06:23:21 PM »
See the FAQ here:

http://www.sohc4.us/forums/index.php?topic=369.msg3328#msg3328



That helps alot, but I didn't find a definitive answer on my question about the meaning of TDCC# (regarding the position of the valves).
 
 - Thanks



Offline mkramer1121

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Re: CB750 camchain rattle? how to adjust?
« Reply #3 on: October 25, 2007, 06:30:50 PM »
Top dead center of valve 1 plus 15 degrees.  Set it to the mark, verify that both intake and exhaust rocker arms on cylinder 1 are loose, then advance it forward 15 degrees.



Tnrfd

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Re: CB750 camchain rattle? how to adjust?
« Reply #4 on: October 25, 2007, 06:35:11 PM »
Top dead center of valve 1 plus 15 degrees.  Set it to the mark, verify that both intake and exhaust rocker arms on cylinder 1 are loose, then advance it forward 15 degrees.

Thanks!



Offline dpen

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Re: CB750 camchain rattle? how to adjust?
« Reply #5 on: October 26, 2007, 04:22:40 AM »
At the risk of opening a can of worms, the easiest way to do it is the same as that recommended for a lot of cars.

Get someone to push the kickstart down gently, just so resistance is felt.

This pulls the chain in the direction of rotation & leaves any slack at the rear of the motor.

Undo the adjuster etc & you're done.



Offline UnCrash

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Re: CB750 camchain rattle? how to adjust?
« Reply #6 on: October 26, 2007, 08:02:47 AM »
When I resurrected my 750F, I found that the plunger for the cam chain tensioner was stuck inside the cylinder.  Steel against aluminum + grime...

So I took off the entire unit and cleaned it out with the aid of WD40, confirmed that the spring was working etc, then put it back and followed the procedure for adjusting it.

Taking off the bottom of the airbox made this job easier.

Good luck!
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upperlake04

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Re: CB750 camchain rattle? how to adjust?
« Reply #7 on: October 26, 2007, 09:13:56 AM »
At the risk of opening a can of worms, the easiest way to do it is the same as that recommended for a lot of cars.

Get someone to push the kickstart down gently, just so resistance is felt.

This pulls the chain in the direction of rotation & leaves any slack at the rear of the motor.

Undo the adjuster etc & you're done.

  This I can understand - can someone with a better mechanical understanding than me explain why the official method uses TDC, rockers loose,advance etc.etc?



Offline UnCrash

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Re: CB750 camchain rattle? how to adjust?
« Reply #8 on: October 26, 2007, 09:21:46 AM »
I believe (but could be wrong) that slack/tension is not even in the cam chain as it goes round and round.

This is why you have to align the engine to the most slack point (as in the instructions) then set the tensioner.  Otherwise you won't achieve ideal tension.

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Offline jtb

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Re: CB750 camchain rattle? how to adjust?
« Reply #9 on: October 26, 2007, 09:47:22 PM »
When I resurrected my 750F, I found that the plunger for the cam chain tensioner was stuck inside the cylinder.  Steel against aluminum + grime...

So I took off the entire unit and cleaned it out with the aid of WD40, confirmed that the spring was working etc, then put it back and followed the procedure for adjusting it.

Taking off the bottom of the airbox made this job easier.

Good luck!

ditto.  Take the adjuster off and clean it.  Takes 15 minutes and well worth it.
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Offline HondaMan

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Re: CB750 camchain rattle? how to adjust?
« Reply #10 on: October 26, 2007, 10:24:11 PM »
First question above: "What is TDCC?" That's "Top Dead Center, Compression" stroke. The camchain should be set when cylinder #1 is 15 degrees past TDCC or #4 is passing TDC WHILE THE INTAKE VALVE IS STARTING TO OPEN, stopping in that forward direction at the "corner" of the spark advancer: that's the 15 degrees point. This geometry sets all the tension to the front side of the chain at the highest mechanical load point on the chain. Don't let the crank back off from here: release the tensioner's bolt, make sure the plunger moved inward (you can give it a tap with a small screwdriver and hammer to help), then tighten the little bolt and nut.
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Tnrfd

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Re: CB750 camchain rattle? how to adjust?
« Reply #11 on: October 27, 2007, 07:20:13 AM »
Thanks for all the replies. Now i'm 100% certain how it's done. The bike soon goes in the garage for the winter so i have plenty of time to adjust and clean the camchain and tensioner.



Offline Ekimyar

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Re: CB750 camchain rattle? how to adjust?
« Reply #12 on: June 05, 2011, 01:09:48 PM »
At the risk of opening a can of worms, the easiest way to do it is the same as that recommended for a lot of cars.

Get someone to push the kickstart down gently, just so resistance is felt.

This pulls the chain in the direction of rotation & leaves any slack at the rear of the motor.

Undo the adjuster etc & you're done.

If I tension the cam chain using the kickstart method, do I need to turn the engine to Nr 1 TDCC?



Offline MCRider

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Re: CB750 camchain rattle? how to adjust?
« Reply #13 on: June 05, 2011, 01:21:14 PM »
At the risk of opening a can of worms, the easiest way to do it is the same as that recommended for a lot of cars.

Get someone to push the kickstart down gently, just so resistance is felt.

This pulls the chain in the direction of rotation & leaves any slack at the rear of the motor.

Undo the adjuster etc & you're done.

If I tension the cam chain using the kickstart method, do I need to turn the engine to Nr 1 TDCC?
While this sounds reasonable, I submit it will not absolutely result in a properly tensioned chain. If you loosen the tension bolt, then put a small screwdriver in the back of the tensioner you'll hit the end of the tensioner push bar. Now while you turn the engine over using the kickstart or the ignition nut, you'll feel the tensioner push bar go in and out A LOT. Some places have the slack on the back row, others have the slack on the front row. Depending on how the valve springs are pushing on the cam.  Just because you are attempting to roll the engine forward does not guarantee slack in the back. If you just tighten the tensioner down at some random point, you could be locking all the slack in the front and it will be LOUD, or something in between.

This may be a characterisitic of the SOHC vs the car, but that's the way it works.

 So the only way to be absoutelly sure you have ALL the slack at the optimum position is to use the #1 TDCC method +15°. And if you do, you'll be happy with the quiet sewing machine quality of the chain sound.
« Last Edit: June 05, 2011, 01:23:58 PM by MCRider »
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
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Offline Ekimyar

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Re: CB750 camchain rattle? how to adjust?
« Reply #14 on: June 05, 2011, 02:23:36 PM »
Ahhhhhh.... Ok, that makes sense. Thank you!

For other bikes, I've seen it recommended to stick something through the spark plug hole in nr 1 cylinder to determine TDCC- is there another, smarter way for The CB750?

And thanks for the help- I'm just not smart on this bike yet. Downloaded the manual today, going to start my homework now!

(1978 CB750F)



Offline MCRider

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Re: CB750 camchain rattle? how to adjust?
« Reply #15 on: June 05, 2011, 02:27:15 PM »
Ahhhhhh.... Ok, that makes sense. Thank you!

For other bikes, I've seen it recommended to stick something through the spark plug hole in nr 1 cylinder to determine TDCC- is there another, smarter way for The CB750?

And thanks for the help- I'm just not smart on this bike yet. Downloaded the manual today, going to start my homework now!

(1978 CB750F)
Remove the #1 intake valve tappet cover. Turn the engine forward and watch the tappet. It goes down, then starts back up. When it reaches the top of its travel, you will be very near TDCC. Continue forward to TDCC+15.
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
Youth and Talent are no match for Age and Treachery.

 

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