Strange noise. Is it normal?

If it's broken or just needs tweaked

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cajun
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Strange noise. Is it normal?

Postby cajun » Sun Mar 12, 2006 5:07 pm

I have a 85 cb650 nighthawk with 32,000 miles. Runs like a dream. After it gets warmed up I hear a rattle noise under the valve cover. Its only when I am at 2,000-3,000 rpms. Its the loudest when I am letting off the gas. I have the valve cover off and dont see any metal to metal contact or any loose bolts. The timing chain has tension on it but it might not be enough. I dont hear the noise until the bike is warmed up. If I park it and crank it up after 10 minutes I dont hear the noise for a few minutes. It is only under 3,000 rpms and not at idle. Its very strange to me. Any ideas how to check the tension allowed without taking out the cams and tensioner? Any help would be great. Thanks

ok I measured the chain slack up and down between the 2 cams. I pushed down on the chain to get the most possible out of the chain. Its 1/2 inch freeplay. If I turn over the motor a few times and check the tension it is maybe an 1/8 maybe.

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Volker_P
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Re: Strange noise. Is it normal?

Postby Volker_P » Mon Mar 13, 2006 2:27 am

If it does not have a hydraulic chain tensioner nor hydraulic tappets (please report if it should have), probably your cam chain is worn. However then when you turn further, the chain play should again increase and not stay at 1/8" (which I would think should be a good value, but I have no experience with the DOHC CB650).
Chain rattle might be normal to some extend so I would not worry until someone tells you you should or it sounds really ugly metallic.

cajun
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Postby cajun » Mon Mar 13, 2006 8:49 am

It has hydraulic tappets and a spring tensioner. When I turn the engine over it has alot of tension. I dont see any metal to metal anywhere, and it only does it between 3,000-1,500 then stops at idle. I wasnt to worried about the noise until a buddy told me it sounds bad. I just dont want to tear the chain out and venture into alot of engine work.

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Volker_P
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Re: Strange noise. Is it normal?

Postby Volker_P » Mon Mar 13, 2006 9:33 am

Interesting to hear about hydraulic tappets. CBX750 had them as far as I remember. Did all 650 Nighthawk years have them?

Whatever, hydraulic tappets explain the whole thing perfectly: As long as the oil is cold, everything is fine. When it is warm, viscosity is lower and pressure goes down so your oil pump seems to need at least 3000 rpm to maintain it. Could be a dirty oil filter, worn oil pump, partly blocked oil pump suction filter screen (my favorite), damages seals of the oil pump suction filter screen, too low oil viscosity or the cylinder head gets too hot (aftermarket exhaust?/ lean mixture?). Loud hydraulic tappets are to some extend nothing to worry about until someone who really knows this engine tells you it should be perfectly silent. A hint for something becoming slowly wrong would be that your oil pressure light comes up early when idling at hot engine.
If anything is to be done at all, I would think it is related to the oil circuit and not to the chain or its tensioner.

cajun
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Postby cajun » Mon Mar 13, 2006 11:56 am

Ok if the pump needs 3,000 rpms why does it not dod it at idle? Thats the one I cant figure out lol. Well I just changed the oil 2 days ago to try and find a cheap fix for the problem. I changed the filter and filled the bike with belray 20-50. This is what the book calls for but maybe I can go lighter. Maybe 10-30? Maybe clean out the oil circuit that is around the cams? Obviously its not something normal and the bike has 32,000 on it. I know its high for a bike. I am guessing maybe the oil pump like you said. I can fix anything on a car but this is the first bike I ever had that needed some lovin. I am up to fixin any problem I ever have, so I know its just a matter of time before its figured out. I am def rulling out chain because theres no indication of rubbing or slapping like it sounds. I know the oil is good and clean, even under the valve cover its all nice and clean with oil on everything. The oil even wipes off the cam with no hint of black at all. Just clean belray oil everywhere. LOL I am sorry to sound stupid sometimes but I really dont want to tear this engine down any further. I prob could but I have other projects still going on in my garage and just dont have any room for another engine swap or rebuild. Anyways thanks for your help, I will post if I figure it out. Until then if you think of anything I am able to check thats not digging deep, let me know. Thanks alot

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Volker_P
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Re: Strange noise. Is it normal?

Postby Volker_P » Tue Mar 14, 2006 1:45 am

The mileage should be no problem. I would get the oil pressure specification from the manual (e.g. 4bar at 3000rpm) and measure with a manometer at the oil switch thread (attention, there are sevaral similar but not identical threads around this size!) with the engine hot. If this is not possible check the clearance of the oil pump rotor. If this is allright, I would not see it critical, but just avoid to ride below 3000rpm.
As already mentioned, I am not sure how much this sound is normal. My SOHC (60tmls) is also not really quiet, but it was not much better when I got it with 20tmls 14 years ago.


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