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Author Topic: Sound advice please!  (Read 3045 times)

Offline Ryan Stecken

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Re: Sound advice please!
« Reply #30 on: Jun 22, 2017, 14:23:49 »
Hope this get sorted out man...the bike looks amazing!

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Offline teazer

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Re: Sound advice please!
« Reply #31 on: Jun 22, 2017, 17:49:37 »
I would be really wary of sending it back where it came from unless you are there when the head comes off.  I agree with others that you need to turn the motor over slowly while someone more experienced listens and watches to see when the parts are clicking.

Offline quadracer351

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Re: Sound advice please!
« Reply #32 on: Jun 30, 2017, 20:20:27 »
The mechanic came over my house for two days and we worked on the bike here. First day he was hoping it was just a valve clearance issue which didn't seem to be the case. Next visit we pulled the motor and took the valve cover off and went through it better checking the clearances. They were good but a tiny bit on the loose side so we made them a little bit tighter. While everything was off he was able to replicate the noise with the exhaust tappets of cylinder 2 and 3. There is still a tapping sound but not as bad when turning the motor over by hand with kick starter. Everything else on top, the cam, timing, chain, guides all looked good and put together properly. Maybe it's just the sound of two parts from two different motors breaking in? No other issues were seen or found at all. The cam is getting plenty of oil, the Pistons all look like there fine and free of any debris, scratches or other markings out of the ordinary.

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« Last Edit: Jun 30, 2017, 21:13:09 by quadracer351 »

Offline quadracer351

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Re: Sound advice please!
« Reply #33 on: Jul 03, 2017, 13:59:27 »
Still at a lost. As I said in my previous post everything up top looked fine but that tapping is still very much there. Any other ideas?



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« Last Edit: Jul 03, 2017, 14:01:48 by quadracer351 »

Offline irk miller

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Re: Sound advice please!
« Reply #34 on: Jul 03, 2017, 14:03:12 »
There is nothing you can say to me, or show me, that would convince me that it is okay to run it with that noise.  That's violent metal on metal contact.  It can't end well.

Offline quadracer351

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Re: Sound advice please!
« Reply #35 on: Jul 03, 2017, 14:32:22 »
There is nothing you can say to me, or show me, that would convince me that it is okay to run it with that noise.  That's violent metal on metal contact.  It can't end well.
Of course not. If I thought I could ride it I would throw the few remaining parts on and take it out. However it hasn't been rolled more than 10 ft away from my garage yet. I'm just at a lost with the top end. Starting to think about what it could be lower down. I just watched a video where an r6 had the same exact sound and was it's connecting rod. But while my motor was apart the rods were checked for play. Here's the video of the r6




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Offline irk miller

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Re: Sound advice please!
« Reply #36 on: Jul 03, 2017, 14:35:18 »
Your CB750 doesn't have connecting rods.  In the description of your time with the mechanic, you don't say anything about removing the head.  You say you just removed the rocker cover.  Did the head stay on?  I think the head needs to be removed to really see what's going on with the 3 and 4 cylinders and their corresponding valves. I'm still leaning towards a possible issue with the valve guide.  I hope there's not contact with the piston crown and a valve.

Offline irk miller

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Re: Sound advice please!
« Reply #37 on: Jul 03, 2017, 14:41:45 »
Something else I would do is to remove all the plugs, so you're not fighting against compression, and rotate the motor in 5 - 10° increments.  Check valve clearance every time, making sure there aren't any major gaps in valve clearance along the way.  That could indicate a mismatched cam profile or a concentric cam.

Offline irk miller

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Re: Sound advice please!
« Reply #38 on: Jul 03, 2017, 14:56:29 »
Another thing to double-check (I don't think any good shop would make this mistake) is that the valve timing is being done correctly.  When you rotate the motor to TDC on cylinder one (T 1-4 mark), you adjust the 1/3 intake valve and the 1/2 exhaust valves.  Not the intake and corresponding exhaust.  Then rotate one revolution to the (T 1-4 mark) and adjust 2/4 intake and 3/4 exhaust.  The CB750 SOHC is a wasted spark system.

Offline quadracer351

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Re: Sound advice please!
« Reply #39 on: Jul 03, 2017, 15:11:52 »
Your CB750 doesn't have connecting rods.  In the description of your time with the mechanic, you don't say anything about removing the head.  You say you just removed the rocker cover.  Did the head stay on?  I think the head needs to be removed to really see what's going on with the 3 and 4 cylinders and their corresponding valves. I'm still leaning towards a possible issue with the valve guide.  I hope there's not contact with the piston crown and a valve.
sorry but you can you please explain? Might be a stupid question or maybe I worded my last post wrong but the motor doesn't have connecting rods? The only thing that came off last he was over was the cam cover. He went through all the valves, checking clearance and making sure the timing was good which it was (I should of taken pics) while that was open he was able to move tappets for cylinders 2 and 3 and both of those the exhaust side had a slightly louder tap then the others which we thought with higher rpms would be the sound. He adjusted both of those to be slightly tighter and we put the motor back in. He had to run before I got everything set up again and had it running. Called him about it yesterday he said he'll come by and give it another listen and probably end up having works engineering in Brooklyn who originally did the motor come and get the bike and figure it out in shop

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