R80/7 Front Suspension Sag

[jackonz]

Just wondering what amount of sag I should be getting on my 1978 R80/7 on the front forks, I j=know I should get some when it comes off the centre stand and a bit more when I get on it but am getting hardly anything.

The forks are not binding at all checked it all out during the rebuild and all fine, any sugestions.

[Rob Frankham]

Too much fork oil causing a hydraulic lock???

Rob

[barryh]

Laden sag should be approx. 1/3rd of fork full travel and having hardly any isn't right. Could be excessive stiction, are the forks free to move and do they bounce back to almost the same position. A zip tie around the stanchion is a good indicator to record movement.

Could be someone put excessively strong springs in while ignoring the need for an appropriate amount of sag.

[PAS]

Is the bike new to you? Perhaps it has extra pre-load added to the forks.

[jackonz]

Too much fork oil causing a hydraulic lock???

Rob

Well no I measured the correct amount as per the manual when I re assembled the forks, my thinking now is the oil I have used may be too heavy, but finding the correct grade is an issue here in NZ as we just don't get the selection options.

Besides I have a new more serious issue that following a ride yesterday the rear main seal is leaking, not a huge amount bet its there and this is after replacing the seal on the rebuild.

[jackonz]

Is the bike new to you? Perhaps it has extra pre-load added to the forks.

Good question, yes I was given the bike just on 2 years ago and have not long had it on the road following a re commission, that also involved rebuilding the forks, they do have large plastic spacers above the springs and these are shown in the parts list but I have no idea if they are the correct length.

[jackonz]

Laden sag should be approx. 1/3rd of fork full travel and having hardly any isn't right. Could be excessive stiction, are the forks free to move and do they bounce back to almost the same position. A zip tie around the stanchion is a good indicator to record movement.

Could be someone put excessively strong springs in while ignoring the need for an appropriate amount of sag.

Hi Barry, forks are not sticking been through that, am wondering is it's one of 3 issues, first too heavy oil, incorrect springs, incorrect length spacers on top of the springs, I can change the oil but doubt it will change the sag, so am left with the springs or pre load spacers that may be too long.

[barryh]

i don't think thick oil would cause lack of sag unless it was treacle.

If this is a previous owners doing, you might be suffering from the syndrome that the universal cure for all fork ailments is to put in stronger springs or preload them, however misguided that can sometimes be.

I can't remember where this came from so I can't credit it, but it was a good source. It might help you identify what you have once you get them out. If all else fails it's possible to calculate the spring rates from the spring dimensions and that could then be compared to stock springs. If it comes to that I can do the calculation for you.

Fork springsPNG.PNG (35.12 KiB) Viewed 940 times

[melville]

Sag is all on the spring and the preload. Oil (all other things equal) only changes how long (time) it takes to get to the sag.

One note--if the oil level is too high, the air space above the oil becomes a highly progressive spring. See if loosening the caps at the top of the fork legs gets you a different sag result. Don't bounce on it with the caps loose as the fork legs will spray some oil out.

[jackonz]

i don't think thick oil would cause lack of sag unless it was treacle.

If this is a previous owners doing, you might be suffering from the syndrome that the universal cure for all fork ailments is to put in stronger springs or preload them, however misguided that can sometimes be.

I can't remember where this came from so I can't credit it, but it was a good source. It might help you identify what you have once you get them out. If all else fails it's possible to calculate the spring rates from the spring dimensions and that could then be compared to stock springs. If it comes to that I can do the calculation for you.


Fork springsPNG.PNG

Hi Barry, thanks I am thinking more in line with you and need to look at the springs themselves as being the issue and maybe the preload, I have no springs to compare them with and if am going to replace them maybe there is better option to go along with the standard damper rods, any suggestions please. Note NZ roads are very bumpy even Henry Cole commented on how bumpy the roads are here, my F800gs with its suspension glides over them.
As for the packers on the top of the springs anyone know what length these should be?

As for the previous owner he is in Yorkshire and regretfully in poor health and memory not what it was, he did have a lot done to the bike in the UK and on it's travels on it's way to NZ, happily he kept a lot of the paperwork so am going to wade through it and see if there is anything in there relating to work on the forks, I did look briefly through them but nothing I can remember that rang alarm bells.

Still it will keep me busy