Author Topic: Cb400f primary chain noise after big bore kit install  (Read 2273 times)

Offline Doom64

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Cb400f primary chain noise after big bore kit install
« on: June 25, 2018, 09:34:27 PM »
Hello, I have just put a 466cc big bore kit in about 500 miles ago, the primary chain seems to be a lot noisier now for some reason.
When the standard pistons were in it it could tick over at 1200rpm and there would be a slight knock but nothing really loud, but now with the 466cc kit in when it ticks over at 1200rpm there Is a very loud clunking sound and when you bring it up to 1800rpm it quietens but you can still hear it.
Pretty sure it is the primary because when you put it in gear on the center stand and put the back break on it goes quite.
I have not touched the bottom end the only thing I did was take the sump off and wiggle the primary and the sprocket.
I have balanced the carbs but there was a couple of kinks in the hoses, so I will get some new ones and do it again.(although I used the same set when it had standard pistons and it was fine)
Does anyone have any idea as to why it would suddenly go loud when I haven't even done anything else apart from change the pistons?
Thanks in advance.

Online TrickyMicky

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Re: Cb400f primary chain noise after big bore kit install
« Reply #1 on: June 26, 2018, 11:50:57 AM »
Hi, I'm no expert having never ventured any lower than the cylinder barrel, but bear in mind that even when it's in gear with clutch disengaged and brake applied, the primary chain is still moving. I think I would start with the easier task first and have another go at the carbs. Be lucky.

Offline hairygit

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Re: Cb400f primary chain noise after big bore kit install
« Reply #2 on: June 26, 2018, 12:13:03 PM »
At 500 miles it's not really properly run in yet. If you balanced the carbs before fitting the big bore kit, or done them staright after fitting it, they will almost certainly be a major factor in the noise you are getting. What worked for the original barrels will probably be way out on an engine that's still running in, and balancing carbs before the new pistons are run in properly will also have been a waste of effort. I'd keep using it until it's done at least 1000 miles and you are happy to ride it a full throttle, then try balancing the carbs again (After doing all other service items first, (tappets, timing, camchain, oil and filter change, and correct oil level) as what was okay on the original pistons which were matched to the bores, or what seemed okay with the (Tight) new pistons will almost certainly be different to how it needs to be when properly run in. 
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Offline hairygit

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Re: Cb400f primary chain noise after big bore kit install
« Reply #3 on: June 26, 2018, 01:15:48 PM »
Also might be the damping rubbers on the clutch basket not the primary chain, quite common to hear of those starting to go after so long. There was someone who could supply new rubbers for the basket but not heard of them for a bit.
That crossed my mind, and I recall it was TTR400 the member that had some made. But I discounted that probability as all he did was fit the big bore, left the bottom end untouched.

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Offline Doom64

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Re: Cb400f primary chain noise after big bore kit install
« Reply #4 on: June 26, 2018, 07:47:44 PM »
Thanks for the replies some handy info there.
I balanced the carbs again today it quietened a bit but is still noisy, I will wait until I do 1000 miles until I set it all up again as mentioned.
You can hear the rattle from both sides but it is louder on the left side.
The standard pistons and rings where put in new about a year ago, just wanted a bit more power so I put the 466 in.
Does anybody know where else sells the damping rubbers or other rubbers that fit?
When will it be safe to start giving it some harder acceleration? Kept it under 6000rpm for the first 250ish miles and slowly started increasing revs. now done 550ish miles. 
Thanks.
« Last Edit: June 26, 2018, 07:52:45 PM by Doom64 »

Offline Nurse Julie

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Re: Cb400f primary chain noise after big bore kit install
« Reply #5 on: June 26, 2018, 08:54:50 PM »
By 500 miles (after oil / filter change, tappets adjusted etc) I was riding my CB400/4 rebuilt engine 'normally' ie, full throttle, high revs. Mine had new pistons / rings / rebore / head skim /primary and cam chain. + a load of other machine work. But, I didn't have any suspicious noises from the engine.
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Offline Doom64

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Re: Cb400f primary chain noise after big bore kit install
« Reply #6 on: June 28, 2018, 09:51:41 PM »
Julie how long have you had your 400? Has it been reliable with the big bore with lots o revs?
Will riding it with this rattle do it any damage? It is quite when riding it's just at idle it's noisy.

Offline Nurse Julie

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Re: Cb400f primary chain noise after big bore kit install
« Reply #7 on: June 28, 2018, 10:01:44 PM »
My CB400/4 hasn't got a big bore kit fitted, just .50 oversize pistons. I have no rattles at idle or flat out but if I did, I would want to investigate sooner rather than later. These engines usually sound sweet and are not generally known as rattlers.
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Offline Doom64

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Re: Cb400f primary chain noise after big bore kit install
« Reply #8 on: June 29, 2018, 12:38:21 AM »
When you first started the bike after the rebuild did it have any rattles?
When the revs drop the rattle gets worse does this point to the primary chain?
I would of replaced the primary chain while it was apart but because it was quiter before the rebuild I thought it was OK, wasn't expecting it to go loud.
Would the higher compression make a rattle louder or would it make no difference?

Offline Nurse Julie

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Re: Cb400f primary chain noise after big bore kit install
« Reply #9 on: June 29, 2018, 08:12:30 AM »
When you first started the bike after the rebuild did it have any rattles?
When the revs drop the rattle gets worse does this point to the primary chain?
I would of replaced the primary chain while it was apart but because it was quiter before the rebuild I thought it was OK, wasn't expecting it to go loud.
Would the higher compression make a rattle louder or would it make no difference?

Nope, first start up after rebuild it didn't have any rattles at all. My old primary chain had about 5k life left in it but only had a very minimal chain rattle at low revs. No idea if higher compression would make the chain rattle louder but logic tells me it shouldn't make a difference.
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
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Offline ka-ja

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Re: Cb400f primary chain noise after big bore kit install
« Reply #10 on: June 29, 2018, 09:13:47 AM »
The 460 yoshi kit did not alter the "sound" of my motor, but a yoshi camshaft certainly increases camchain wear rate even with a heavy duty cam chain
nice bike,nothing in the bank

Offline Nurse Julie

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Re: Cb400f primary chain noise after big bore kit install
« Reply #11 on: June 29, 2018, 01:52:04 PM »
When you first started the bike after the rebuild did it have any rattles?
When the revs drop the rattle gets worse does this point to the primary chain?
I would of replaced the primary chain while it was apart but because it was quiter before the rebuild I thought it was OK, wasn't expecting it to go loud.
Would the higher compression make a rattle louder or would it make no difference?

Nope, first start up after rebuild it didn't have any rattles at all. My old primary chain had about 5k life left in it but only had a very minimal chain rattle at low revs. No idea if higher compression would make the chain rattle louder but logic tells me it shouldn't make a difference.

Hard to equate your engine with his though Julie, yours was a full engine apart strip with all the chains etc replaced IIRC, his has reused all the chains and that's where most if not all of the noise comes from.
Higher compression shouldn't alter the engine BUT if the engine wasn't running well on the old bores then fixing that problem would mean the engine balance would change, so carbs etc would be out, causing more noise as it's now unbalanced.
Yes Ken, that's why it's difficult for me to give Doom a definitive answer to all his questions. Everything inside my engine was new so I would have been most pissed off if I had any rattles of any type from anywhere.
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Offline Doom64

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Re: Cb400f primary chain noise after big bore kit install
« Reply #12 on: June 29, 2018, 05:34:05 PM »
Oddjob, released the cam bolt when? I adjusted the cam chain after the kit was put in and the adjuster bolt was free.
When the new standard pistons were put in the cam chain and tensioner was replaced, also when I put it on the dyno it made 30hp at the rear wheel so it was running decent when it was standard.

Offline Nurse Julie

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Re: Cb400f primary chain noise after big bore kit install
« Reply #13 on: June 29, 2018, 05:57:16 PM »
Out of interest, what other mods have you done to the bike to make you want it dyno tested? Pods, different jets or anything like that. I still think it's the primary chain though.
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
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Offline Doom64

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Re: Cb400f primary chain noise after big bore kit install
« Reply #14 on: June 29, 2018, 06:20:50 PM »
I dyno tested it before I put the big bore kit in it.
Everything was standard apart from a shorter silencer and electronic ignition.

 

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