Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Lobo on October 11, 2020, 09:14:37 AM

Title: Fork oil height..
Post by: Lobo on October 11, 2020, 09:14:37 AM

Hi all,
Having to top up folk oils (K2) as a leak on one side through the cherry treated copper washer 🙁...
Rather than drain / refill, can anyone advise me the distance of oil to top of Stanchion, and whether springs in/out, fork collapsed or extended.
(SeanSD recently advised 140mm... but went on to add the below, which has kinda put me off (sorry Sean!)
Cheers,
Simon

“I’d be interested to hear what others think of this, because after replacing the springs and shocks (IKON also) the bike developed a severe head-shake at about 35-35kph if I took one hand off the bars. This quickly settled and at higher speeds it was fine. I have yet, 20,000km later, to solve this problem, so any ideas welcome. I have just rebuilt the forks completely while replacing the seals, so here’s hoping 🤞”

Title: Re: Fork oil height..
Post by: Erny on October 11, 2020, 09:35:02 AM

Check steering stem bearings if they are not loose of worn. I had this problem on my previous Honda CBF1000F, the same behavior that was getting worse and worse.
It was cause by worn bearings but the way impossible to recognize when assembled (just when I took forks off and only stem and upper top tree left, I felt that bearing movement was not smooth, it was kind jumping). Replacing bearings by tapered one totally cured problem and no more issue after for next 40.000km

Title: Re: Fork oil height..
Post by: Bryanj on October 11, 2020, 01:18:36 PM

That was never speced by Honda so its only if somebody has measured it

Title: Re: Fork oil height..
Post by: SteveD CB500K0 on October 11, 2020, 04:57:06 PM

Can you not just measure the one that doesn’t leak?


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Title: Re: Fork oil height..
Post by: K2-K6 on October 11, 2020, 07:26:49 PM

You can work it out.

Take the spring out,  push stanchion up to full compression,  then measure from top of stanchion to down to seal face,  that's the level to set as it will always cover the damper valves but not hydraulic lock against the top cap when reassembled. 

If you increase the volume from there it effectively adds more of an air spring effect to the fork particularly under max travel.

Title: Re: Fork oil height..
Post by: SeanFD on October 12, 2020, 11:14:46 AM

No worry Lobo; It more than worried me!!

I filled the forks after rebuilding with the recommended amount 230ml of ATF. This left an air gap of 232mm with the spring out and the lower leg fully compressed, as per IKON instructions. With the spring in, there was a preload of only 10mm, but I decided to run with that to see what happened.

I took it out for a ride with an Advanced Riders Group - so we were”making progress” as they say – and covered about 80 miles without a problem. Maybe a little soft at the front, but otherwise fine.

But in general I think the main thing is to have nothing sides the same, so as previously suggested, you could measure the one non-leaking side and then make it the same on the other.

Title: Re: Fork oil height..
Post by: Lobo on October 12, 2020, 12:24:15 PM

Thanks all.
Erny methinks you misread my post.
Bryan... yep, I was trying a short cut & being lazy... today I simply drained both forks and started again / added 200mL / side.
Steve - ha! I was so bloody peeved at the rejuvenated copper washer leaking that I thought, “sod it!” and pulled ‘em both / swapped to fibre washers in a pique... before thinking your idea. Doh.
K2-K6. Cheers... always up for the lateral thinking bits.
...and cheers too Sean, glad you got it sorted.