Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Doom64 on June 25, 2018, 09:34:27 PM
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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.
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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.
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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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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.
Sent from my X6pro using Tapatalk
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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.
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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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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.
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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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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?
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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.
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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
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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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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.
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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.
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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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I dyno tested it before I put the big bore kit in it.
Everything was standard apart from a shorter silencer and electronic ignition.
So is it just the big bore kit, short silencer and electronic ignition you have now?
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Yes I still have those and the head has been skimmed now that's the only difference.
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So really then it most probably is the primary chain but as none of us including yourself has got a crystal ball or x-ray vision, the only sure way to diagnose the problem is to strip the engine right down. It still may be something else but you won't know until you take the engine apart.
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Someone else done it before and said it was within spec.
I balanced the carbs again today, took it for a spin and it does seem a lot quiter than it was before, it's back to how it was with the standard kit in it thankfully.
I will probably strip it down again winter time and do the bottom end, this was the first engine work I have done and the bottom end is a bit trickier isn't it?
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Someone else done it before and said it was within spec.
I balanced the carbs again today, took it for a spin and it does seem a lot quiter than it was before, it's back to how it was with the standard kit in it thankfully.
I will probably strip it down again winter time and do the bottom end, this was the first engine work I have done and the bottom end is a bit trickier isn't it?
It's especially important with these older bikes that you learn to do the work yourself, or only entrust it to someone with plenty of experience of older Honda's. Also, as you progress with ownership, don't assume just because a part is new it can't be faulty, they can, and people spend hours chasing their own tails trying to find the problem without checking the new part is fit for purpose! Glad you got it sorted, as I said at the start of this thread, it was the most likely suspect. Enjoy riding it.
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Thanks for the help everyone, a lot of handy info. I have started doing near enough all the work to my bikes recently a lot of learning to do still. :)
About the clutch rattle I started the bike and took the oil cap off and you can hear a loud knocking from the clutch, does anyone know of anywhere you can get rubbers from apart from the ttr site?
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And for what it's worth I'm just in the process of running-in my 400/4 after a complete rebuild which included a Yoshi big bore kit, 455cc. I've just given it the first service. To cut a longer story short the engine was rather quieter with new oil in, and then got noisier as I made each service adjustment, bearing in mind that the tank was off so you can really hear things. I was somewhat perturbed by this as the primary noise was quite loud- lo and behold the final thing was to balance the carbs, and one (no2) was miles out on synchro and we now have sewing machine like rustling. So, from my experience balance is essential if you want a quiet engine, and on my ride earlier today, rather smoother.
I'll post at more length and include some piccies when time allows.
Regards,
Arfa.