SOHC.co.uk Forums > CB350/400
Cb400f clutch basket damper rubbers
McCabe-Thiele (Ted):
--- Quote from: amx1992 on November 20, 2020, 10:20:10 PM ---Intresting, it seems viton would be the way to go, but to soft to be machined. I think these teflon ones will act more like the acetal ones ttr made, not much give, but might hold up better.
--- End quote ---
Nice looking adaption - I'm surprised DS or CMS haven't found a suitable replacement part.
AshimotoK0:
Years ago I had the dampers inside the CB750 primary drive analysed at Hul Uni. to determine what they are made from.
It turned out they are made of nitrile rubber but it is compounded with extra additives to give superior oil resistance to swelling and hardening at high temperatures than 'standard' nitrile rubber. I got the sample from a NOS CB750 part that had had the rubbers swapped for a racing setup. I used to work with the guy who owns this company linked below and he could definitey compound and mould the correct rubber as we used to make rubber parts for the automotive industry, at the P.L.C. we both worked for but not sure about tooling costs. Last time I spoke to him he was restoring a Gold Wing so he talks our language.
https://www.yell.com/biz/antivibe-hull-ltd-hull-2761000/
Following my analysis of the part, I this I found that a deidicated CB750 club in Germany was re-manufacturing them but only selling to club members.
cliff7:
The CB400F appears to have 3 cush drives, clutch, primary gear and rear hub. Does making one with less give in it have any disadvantages? Replacing the dual mass flywheel on a car with a solid one often works but I have also heard of increased vibration and even crankshaft failure. Be interesting to see the outcome of the Teflon ones as I think mine need replacing.
McCabe-Thiele (Ted):
--- Quote from: amx1992 on November 20, 2020, 10:20:10 PM ---Intresting, it seems viton would be the way to go, but to soft to be machined. I think these teflon ones will act more like the acetal ones ttr made, not much give, but might hold up better.
--- End quote ---
If your Teflon ones work there is a business opportunity here !
K2-K6:
--- Quote from: cliff7 on November 21, 2020, 01:17:52 PM ---The CB400F appears to have 3 cush drives, clutch, primary gear and rear hub. Does making one with less give in it have any disadvantages? Replacing the dual mass flywheel on a car with a solid one often works but I have also heard of increased vibration and even crankshaft failure. Be interesting to see the outcome of the Teflon ones as I think mine need replacing.
--- End quote ---
Yes to the question of disadvantages. All of these system components are specifically developed and included to control, mitigate or reduce the unwanted forces inherent within the working design of the engine and transmission in getting disparate frequencies to not cause breakage and improve lifing of individual components.
The dual mass flywheel is an interesting (valid in this thread context as some of the measures are easily discussed) comparison as it incorporates more than one method. Originally responding to diesel engines as they became more prevalent in refined passenger cars.
With a four cylinder diesel originally having a heavy flywheel to absorb slow pulse vibrations at low crank speed, the need to lighten the flywheel effects and speed up engine response to better match petrol motors asked for reduced mass, but then they shake like hell, making it very harsh at tickover.
The dual mass allows one part of the flywheel to spin independently of the other over a controlled maximum angle and restrained by springs. This lets one piece oscillate with the crank pulses while not transferring the peak to pass into the transmission. At low speeds the two are operating close to their optimum absorption characteristics, hence the crankshaft is pulsing with big frequencies but you don't get to feel it. Like have suspension within your drive line.
As the crankshaft speeds up the frequency doesn't have the peaks and troughs at such high amplitude so the two parts become much more in synchronisation, but the springs in the flywheel will still cushion the drive especially if you abruptly shut the throttle as a diesel has pretty severe closed throttle deceleration. It's all part of how refined current diesels feel and you could see that by not allowing this movement to happen then the peaks of the frequencies are just rattled through the component set to it's detriment.
There's little telltale signs of how effective it is too. With many diesel engines running one way clutches on the alternator as letting the crankshaft oscillations free the ancillary drive also pulses at this rate. The alternator pulley then lets the speed up part of crank pulse (firing event) accelerate the alternator spindle, but as the crankshaft pulse slows the alternator can over run the belt drive and not clatter it.
As injection development has improved both timing and accuracy, this need is getting less with low speed pulses significantly reduced when no load is being used. Which is why they sound much better nowadays in any size diesel engines. This has a parity with how we set idle circuits on these Honda engines too, it illuminates how critical and useful the adjustments are on the carb sets in use.
This is all happening in our engines, but less seen. Which is why the various cush drives are incorporated.
The cush drives within the Honda engine are primarily to mitigate pulse peaks imposed on the primary drive chain in my view. Its a very clever drive system but with very very simple bearing properties in the structure. They are also susceptible to vibration peaks which can dramatically shorten their life, making the absorption curve of the rubber components vital to their function.
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