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Discussion Starter · #1 ·
I need an expert on this 900C Honda.. i bought this bike two weeks ago 51,000 miles
Tire Wheel Land vehicle Fuel tank Vehicle
Tire Wheel Land vehicle Fuel tank Vehicle
Tire Wheel Land vehicle Fuel tank Vehicle

the owner trailered it over three hours to my home at no charge, but he did not tell me there was a problem with the engine. The bike sat in my garage three days before starting... California rain... yes rain lol.. anyway upon starting i heard this rattle for about five seconds... three hours later re start no rattle... i recorded this cold morning start i will post the link here...so i contacted the owner and told him about the noise...Deny he did.... when he brought the bike and we started it i could only hear the clutch clatter and i knew i would have to replace the dampers... my second video shows the noise clutch basket repaired. The 900c has a primary chain and it has oil fed pressure tensioner... i checked the cam chain tension and the three bolts on the starter gear...here is the link to video
 

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Discussion Starter · #2 ·
If i re start say four hours later there is no rattle... to me it sounds like a chain slapping or gears clacking
 

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indoor video sound is not a good indication of anything, the exhaust sound and echoes over-power the ability to hear mechanical sounds.
Primary chain slap is easy to identify, with the engine not running, put it in gear and roll the bike backwards and forwards, if it rolls very far before the engine stops the rear wheel from turning in each direction, that indicates a whole bunch of backlash in your drive train somewhere.
I would start by checking the valve clearances, while it might no be the source of the mechanical noise that concerns you, it won't be a wasted effort because you can bet the valves have never been checked before. ... & I bet it has the original oil in the front forks too.
 

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Discussion Starter · #4 ·
indoor video sound is not a good indication of anything, the exhaust sound and echoes over-power the ability to hear mechanical sounds.
Primary chain slap is easy to identify, with the engine not running, put it in gear and roll the bike backwards and forwards, if it rolls very far before the engine stops the rear wheel from turning in each direction, that indicates a whole bunch of backlash in your drive train somewhere.
I would start by checking the valve clearances, while it might no be the source of the mechanical noise that concerns you, it won't be a wasted effort because you can bet the valves have never been checked before. ... & I bet it has the original oil in the front forks too.
Thanks... i was told the valves were checked last year when the owner did the chrome job on the valve cover, and said they were within specs, last owner did not have any history from the past owners, i did notice on the front frame the engine has been out before, the 900c has the transfer case and is known for backlash, i could check in gear and turn the rear wheel back and forth..... primary chain maybe and the big... But... there is no noise re starting say two hours later. Bike looks like its been taken care of.. might be a good idea to do the cold re start outside
 

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Discussion Starter · #5 ·
just done the primary chain thing rolling back and forth in gear.. i would say about half inch play back and forth... but there is backlash in the transfer case, normal for the 900c
 

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That's not much, based on that I doubt your primary drive chain is the clatter problem.

I've met a few people that can do a good job of checking valve clearances. ... just a few. Most don't even recognize what the valve clearance spec even is, and half of those don't own or read a micrometer correctly. ymmv.
... he chrome plated the aluminum rocker cover? :unsure: so I assume he copper plated it first, that sounds like a terrific expense, he must have really loved the bike.
 

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Discussion Starter · #7 ·
... the guy also plated both engine covers left and right /starter cover/cover behind rear brake lever turning into a Harley lol .... i agree about the valve clearance done several in the past shims on this model.. something to check down the road, but its not my concern at the moment..
 

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Discussion Starter · #8 ·
Re started this morning cold engine, listening to the engine i got a lot of clatter from the gearbox most was from the transfer case sub transmission warming up, bring the rpm to 1250 smoothed things out, carbs were rebuilt last year and sync was done i contacted the shop... i will record video later today to confirm my no clatter four hours later
 

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Could be primary chain tensioner as it is both sprung and a hydro tensioner on it too. The hydro tensioner bleeding down. Get bike outside and cold where it makes the noise and start it up to the noise and in gear take off very slowly and speed up, noise going away over maybe 2-4 mph says primary chain, the noise will also show up if the engine gets lugged like a takeoff where you give a bit too much clutch out but not enough throttle, they almoat always rattle for a fractional second then even new. A careful carb sync minimizes the noise to sometimes even go away.

Nobody even the shops ever adjust shim type valves as much as they should. That engine well known for the valves tightening up from recession to close up and then they burn, how most of them die. Set valves shooting for .005" and the setting job will last 100% longer and engine runs better. Disregard what the service manual says.
 

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Nobody even the shops ever adjust shim type valves as much as they should. That engine well known for the valves tightening up from recession to close up and then they burn, how most of them die. Set valves shooting for .005" and the setting job will last 100% longer and engine runs better. Disregard what the service manual says.
Man, I wish I'd known that 35 years ago. I burned valves not once but twice on my '81 CB900C. I shimmed them according to the Clymer manual.
 

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The problem is in the OEM clearances on the cam caps, they can be up to .008" but the valve clearance is only .003", yet they can burn valves at .002" because what you get even checking them 50 times is not accurate because the cams move around in the caps to vary the numbers you get measuring. If you check carefully enough you WILL find the numbers are inconsistent at setting and resetting and you will never get the same value twice in a row. Why you go up to .005", fully .002" of any number you get there is fake and needs to be tossed to get a real number that works long term in the real world.

I burned 5 valves on my brand new 750 in just over 3000 miles. Then I did the job myself and found out why. After that the normal valve setting time of every 4000 miles I extended to 15000 with no problems other than the valves WILL sink after a while anyway as they are utter crummy quality parts.

Honda knew there was a problem there and changed the cam marks for setting the valves but it did nothing to solve the problem at all.
 

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Tuning a motor starts with proper valve clearances . As all adjustments after are 'built' on that .
 

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Wife gone and I can turn the noise up. The first vid has the engine not starting up on all four cylinders, listen and the rattle happens when the engine starts up lopsided and only shuts up at 4.00 seconds into vid (watch the timer) when the deeper noise of apparently a more powerful cylinder suddenly kicks in. Engine way out of tune, any engine can rattle like that. The second vid the engine starts up with the predominant cylinder running instantly and why there is no rattle. You are way out of carb sync or wildly varying power contribution by cylinders due to tune or age, 50K being a lot and usually pretty worn by then. Compression test will tell the tale. Listen close to second vid, you have one cylinder (pair?) louder and deeper and the strong even one(s), likely with more butterfly opening and the others are filling in at times seeming in tune but I hear irregular hitsand misfire there, they are not equal in ignition to the one main one you hear.

The mark of incompetent bike owner, drive it while WAY off tune until it dies, not smart enough to fix it. The PO denial confirms it, people like that tend to lie at the drop of a hat, it goes in lockstep with lack of mechanical ability. Somebody has some work cut out there.
 

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Discussion Starter · #15 ·
Good info thanks...carbs were rebuilt and sync done last year.... new plugs...its time to check the valve adjustment/cam chain tensioners.... idles great normal temp/cold blooded until then... plenty smooth power
 

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If you run compression then carbs wide open and all plugs out doing it. Looking for 170 psi as the standard there.
 

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!70 would be nice in a perfect world , but with your mileage 150 is more likely and fine for all intents .
 

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It's a 4 cylinder engine, first thing I would be looking for is the compression to be the same on all cylinders.
 

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Discussion Starter · #19 ·
I decided to pull the valve cover and check the chain tension... middle chain under the cross over plate seemed i little loose not much, but i could lift it up with my finger and tap the plate could this be my rat a tat noise... anyway i turned the crank with the two domed nuts loose on the back of the head ..got that sorted both chains tight and the tensioners are holding ok no soft springs.. all the valves are within specs except for #2 exhaust they are .001 clearance.. so i need the tool to get the shims out... amazon..
 

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improvise
I bet shims are magnetic.
What does Honda say the valve clearance and tolerance is on that engine?

Best way to check for wear on any chain is to lay it along side a length of new chain.
 
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