Fork compression damping question

[KermitLeFrog]

Hi People, I'm beginning to put a few miles on the fella. I'm replacing a few bits and doing some general maintenance. My question is regarding the fork compression damping adjusters. It's a 98 model. The front is a bit of a bugger on bumpy roads. It feels far too harsh. I know it could be too much oil or general stiction but I'm going to try the compression adjustment first. They are currently 1/2 a turn back from fully in. The manual gives no indication of the range of adjustment. Is it one turn? Is it 20 turns? I have no idea. Does it make any difference?

I don't want to screw things way out without knowing how far I can go.

Tia,
Ian

[nt1980]

I had my standard forks set about the same might be worth sending them of to get rogered which would make a big difference

[8541Hawk]

First you are dealing with rebound not compression with stock forks as there is no external compression adjustment.

With that, if the internals are stock and you are not a twig, you will never get the forks to work correctly without a rework (springs and shim stacks).

[tony.mon]

You can't adjust it "too far" because if you don't like the feel after you've made an adjustment it's a simple matter to just set it back to where you where.
Try a trun out and see what it feels like, if it's better, tray another; if you don't like it try only half a turn more.

But you will notice a difference using 7.5 weight oil and a 130 air gap, using good quality oil.
If you don't get success then try a Hyperpro or other spring kit, or, if you want, just give it to a suspension expert as suggested.

[KermitLeFrog]

Thanks for the replies guys. I didn't realise it was rebound adjustment. I'll check things out and have a fiddle. See if notice any difference.
Cheers
Ian

[Cadbury64]

Having rebuilt my forks with new seals, bushes and oil recently, I am familiar with the workings of the VTR forks. The adjusting screw on top of the fork cap moves a long shaft down the inside of the damper rod and on the end of that shaft there is a needle valve. As you wind the adjuster counterclockwise the needle is lifted off its seat. The needle valve controls the flow of oil through a bypass orifice in the rebound valve. If you have the needle wound fully in (so it just seats fully) all the oil has to pass through the shim stack. Once you begin to back the needle valve out, more flow happens through the bypass, which reduces the damping force generated. With a tapered needle most of the change in flow happens within the first two turns back from full in. I suspect you can probably wind the needle out to 3.5 turns before it stops.

I tend to set the dampers on my bikes to a minimum setting, enough to prevent the pogo-ing sensation and maintain a feeling of control, whereas if you go too hard the fork can't extend quickly enough to keep the tyre in contact with the road and you get harshness. Exactly where you end up with your settings will be a bit individual and depend on the spring setting and also the oil viscosity. I run mine two turns out at present, with the spring preload full wound in and running 10W oil.

The other aspect of suspension harshness is the compression damping and that is fixed on the VTR. If you search on this forum you can read where people have modified the compression damping by drilling a 1mm hole through the wall of the damper cartridge just above the compression valve. This is creating an additional bypass for the compression valve shims and would take out some additional harshness, but might also lead to excess dive unless you also had decent springs in place. The HMAS valve bodies that Honda has used in the VTR have very small ports for oil flow so the ultimate solution IMHO is to replace these with a higher flow valve body.

[KermitLeFrog]

Super. Thanks for the reply. Very helpful. I know the range I can play around with now (and what it's doing). I'll let you know the results.
Kind regards
Ian

[KermitLeFrog]

2 turns out made a big difference. Now the back end feels worse than the front.

The rear shock is stock and there are adjusting screws at the bottom. Do they do anything? If so, what?

TIA
Ian

ps. Will check the forks asap. Confused with the manual though. It looks like the top of the fork damping adjuster body (FDAB) screws into the fork cap. I presume you can unscrew the fork cap and then unscrew the FDAB from the cap?

[Cadbury64]

The screw in the bottom of the shock is a rebound adjuster; screwed in is maximum. Be warned that due to their location these can seize, so don't force it.

The fork caps unscrew off the fork legs then you can extend the cap up to access the locknut that connects to the damper rod. Once that's undone you can remove the cap with the needle valve still attached, be warned its about 600mm long. Not sure that you'd need or want to dismantle the needle from the cap.

When you reassemble the cap onto the damper rod you need to set the cap height carefully so the needle seats correctly. I wind in the rebound screw so the top of the screw is flush with the top of the cap. Then screw the cap onto the damper rod until the needle just bottoms out. Now hold the cap still, back the needle out one turn, then set the locknut to secure the cap.


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[KermitLeFrog]

That's really helpful. Thank you.

Got my paddock stands today so now I can actually DO some stuff.

[Cadbury64]

Hey Ian, how's the suspension tweaking going?

My advice is to carry a screwdriver with you so you can have a play with the rebound damping adjusters when you are out riding. Find a nice bumpy bendy section that you can go back and forth over, and experiment.

The other setting to adjust is the sag, ie how much of the suspension travel you are using just supporting you and your bike at a standstill. You should aim to use about 1/4 of the available travel, and this is where the spring preload adjusters come into play.

Cheers, Terry

[KermitLeFrog]

Hi Terry, I've been into other things recently. The 2 turns out seemed to make a difference but I've been carrying out essential maintenance as a priority. Simple things like an oil change were stymied by my inability to get the oil filter off. Just now got back from a local shop who used a steel strap clamp. My nylon strap clamp was having none of it. I suspect the filter hasn't moved for years. It's a 17 yo bike and the guy I bought it off had done less than 100 miles in two years. Other bad news was that the tyres are fairly new but came with 20psi front and 27 psi rear.

I thought the chain looked rather horrible but when I got the C/S cover off and cleaned away decades of junk and put some oil on it it seems OK for a few miles yet.

I've only managed 250 miles over the last 10 days but since it started snowing last night and I've just had another flurry this morning fettling has taken precedence over riding. Plus I need to do some work every now and then. I'll keep you up to date though. Thanks for the interest.

Kind regards
Ian

ps. Ridiculous question but I have to ask it. I've been trying to track down a very old friend of mine who should be living in NZ. Ran a bike shop in Perth many decades ago. Name of Byron Wallis. Age probably mid sixties.... I suppose you never know!

[Cadbury64]

Hi Ian

Never heard of Byron Wallis, but a quick Google suggests there may be someone with that name in/near Waimate in the South Island. Listed as Wallis FB in the White Pages.

For the filter I bought a tool that looks like a giant socket that fits over the flats on the outside of the filter and can be driven with a 3/8" drive, makes filters very easy to deal with and fits a lots of standard Honda filters.

Cheers
Terry