[budgetrider]

Hi,
I'm starting this thread to share the mods about the Marz DOT. If you have a better fork, and wish to make fun of people riding lesser forks, please refrain from posting on this thread. Thanks.

Marzocchi DOT's are notorious for spiking. I personally didn't believe in spiking, that was until I tried a pair of DOT's on my bike. My previous fork was a 4 inch z5 with extra heavy springs set on max preload with 10wt oil. I weigh 77kgs, and basically the fork was set to be rigid until you hit something.

Marzocchi DOT's despite having 2 more inches of travel, felt harsher on stairs, drops to flat and drops to tranny than my z5 XC fork. The reason I found was the compression damping.

What I did: Change the compression damping by drilling extra holes in the pumping rod.

How: 1. Drain the oil from both stanchions, then disassemble the fork. I'm sure there's another thread somewhere on how to take apart Marzocchis, I'll add the link when I find it.

2. Clean off oil on both the pumping rods that DOT's use for damping.

 

[KleinMp99]

Marzocchi department of transportation? Great thread!!! :evil:

 

[budgetrider]

3: The pumping rod on the spring side of the fork has an extra white clip around the T-shaped head of the pumping rod. That's to keep the rod centered within the stanchion because the pumping rod on the spring side of the fork has to carry the all forces of the spring to the fork lowers.

I drilled two extra holes in this pumping rod. There are indentations all along the pumping rod. I chose to drill out the two indentations closest to the bottom holes on the pumping rod.

Why the bottom two? because I wanted to soften the compression over as much of the fork's stroke as possible. As the fork compresses the pumping rod moves up through the Marzocchi SSV (their damping valve which sits at the bottom of the stanchion - composed of the removable metal ring that fits into the bottom of the stanchion and two metal disc-ish things that slide up and down the pumping rod). So long as the holes are below the valve assembly, they will increase the flow of oil from the lowers up into the stanchion during compression.

 

[budgetrider]

If you drill extra hole in the indentations further up the pumping rod, it will soften the compression only as long as those holes are below the valve assembly. So drilling out the topmost holes would only soften compression during the initial 2-3 inches of travel. Once those holes pass above the valve assembly then they won't be contributing very much to increased oil flow from the lowers up to the stanchions.

Drilling out the top holes would be good if you wanted to keep the hard compression damping of the DOT in the bottom half of the fork's travel in order to prevent bottoming on big hits.

I don't do big drops, so I chose to drill the bottom indentations, to keep the fork soft for as much of the travel as possible.

 

[budgetrider]

The non-spring side:

With the pumping rod on this side, I drilled out the bottom two indentations, just like on the spring side. But I also drilled out the topmost two indentations as well, to make the fork extra supple in the first 2 inches of travel.

Why different on each side? I put some thought into this before I did it, and here's my reasoning. If i drilled each pumping rod exactly the same on both sides, then the change in compression as the fork moves through its travel might be very noticeable. i.e. The position of travel where the pumping rods go from 4 open compression holes in each side to two open holes in each side is exactly the same for each leg. So the change in compression damping might be quite sudden and unexpected from very soft to hard.
If you drill each leg assymetrically, you can get one leg going from soft to hard two inches into the travel, and the other leg changing from soft to hard at at 4 inches of travel.

 

[budgetrider]

Disadvantages

The more holes you drill, the faster you make the rebound.
I personally find hard rebound easier to deal with than hard compression.
I drilled 6 extra holes in total, and
the rebound on my DOT is now pretty fast. With preload set up to Marz spec for my weight, compressing the fork to 5/6 inches of travel will cause a rebound that can throw you off the back of the bike if you're leaning backwards - so good technique and staying centered on landings is important when taking my modded DOT off of drops.

The good news is that the fork is super supple over stutter bumps, making it an excellent trail fork.

 

[zane]

Shoot a Pm over to TWISTED, he's done some mods on his Drop Off Triple and likes it.

 

[budgetrider]

Finally bottomed out the modded DOT on a 5 foot to flat concrete drop. Currently the fork is at 30psi air in each stanchion with no spring. With the stock air/coil setup and 10 psi in each stanchion I found I was blowing through 4 inches of travel on 2 foot to flat drops (No good). Getting rid of the spring and running higher air made the fork more progressive, - only blows through 2.5 inches on 2 foot to flat. However the fork feels much harder in the first 2 in of travel. (Though not quite as hard as it was before drilling out the pumping rods.) I haven't tried high pressure air with 1 spring yet, I will next week.
Interestingly the rebound with air/air is slower than with coil/air, about halfway between unmodded DOT and DOT modded as above running coil/air.

 

[budgetrider]

Update: To try and prevent bottoming, I added oil to each stanchion so the levels when the fork is fully compressed was 50mm (top of stanchion to oil). Thus when the fork is fully compressed there's a pocket of air about 38-40 mm tall between the oil and topcap. At full extension the air pocket is about 5x bigger 190mm - so at bottoming the air pressure is 5x higher than the air presure at full extension. I inflated each leg to 25psi and bottoming on 5ft to flat was cured. BUT the high oil height made the damping all hard again - not as hard as the spiking before drilling out the pumping rods, but no longer pillow soft like before.

Conclusion: As long as you don't do 5+feet drops to flat concrete 50/50 or nose first like I was doing, drilling out the rods is a good mod. Otherwise, you need HSCV to prevent bottom outs on flat landings (or just put up with spiking)

 

[budgetrider]

Travel upgrade: I've read on this forum that DOT's are the same as 2004 JrT's minus the QR 20. Does anyone know if the stanchion lengths are the same?

cause if so, upping the travel on the DOT from 150 to 170 is as simple as removing two spacers from the damping rod and converting to air.

 

[allsk8sno]

why don't you just measure the stanctions and see how much bushing overlap there is
seems pretty simple

 

[budgetrider]

Will measure next time I take the fork apart, till then...

 

[budgetrider]

without taking the ofrk apart, my guess isthat 04 jrt's have the same stanchion length as DOT's because when the fork bottoms the stanch has to hit the bottom out bumper athe bottom of the lowers, and since the jrt lowers are interchangable with dot lowers (correct me if i'm wrong but i read it somewhere) the bottom out bumpers must be the same height. Which means the jtr's are getting 170mm travel by decreasing overlap b/w the stanch and the lowers, not by having longer stanchions

 

[BRacing]

Fantastic information, and good research and innovation. Even though I don't own a DOT, I think what you're lookin into is very good! Keep us updated!

-Brad

 

[budgetrider]

Thanks

 

[Dirtbike]

The only difference is internals dropouts, and topcaps (i think the jr has coil preload, and DOT has nothing)

EDIT: Alright. I just checked the Zokey site and the differences are that the JR.T has adjustable coil preload on both legs. The DOT only has air preload on both legs. The DOT only has a coil on the left leg and air in the right. Both forks use Marzocchi's forged Magnesium casting. The JR.T has the 20mm and the DOT has QR. They both use the same stanchions and crowns. Marzocchi makes almost all of their stuff compatible, so if you wanted, you could get different internals to upgrade the damping. Heck, you could get HSCV cartridges for it.

 

[fattyfat1]

i did something completely different to mine. i took my dot apart, drained all oil, and looked at what i had. with some help from bike shop buddy, we measured the alluminium spacer plus the spacer that was almost an inch long. we then cut two pieces of pvc pipe (1" diameter) and tapped them gently in place. we then put springs in both sides! yes both sides! filled up fork with 15 wt. oil and only ran 4psi. air pressure! don't forget to cut a thin piece of pipe for spring stop in side that didnt come with spring! my drop off feels like a super t pro, plus i have 6.75 inches of travel instead of 6 inches!

 

[WV Hippy]

Excellent discussion! Anyone have any information on interchange of the internals between forks? I've thought about getting a slightly used Jr T converting it to 150mm and using the internals out of my Z1. Maybe even convert the left side internals to SL. I'd ride it on the front of my Heckler. Any thoughts?

Also thought of converting my DJ1 to SL internals...help lighten up the 100mm pig.

 

[budgetrider]

I think the internals are all pretty interchangable as long as the stanchion diameter is the same.

 

[budgetrider]

So I was gapping this brook today, and I cased my front wheel hard on the far bank on some rocks, but the DOT soaked it up and I didn't go over the bars. The fork didn't feel like it bottomed, but I looked at the stanchions and there was an oil ring mark well past the minimum crown height sticker 155mm up the stanchion. So I did a few more jumps and then I rode home and measured how far up the stanchions the sliders went to leave that oil mark. 160mm!!! That means that the 2004 DOT has only 5mm less positive travel than the 2003 Super T (which says its 170mm but if you measure from the seal to lower crown it's only 165mm)

btw. my modded DOT only compresses about 5 inches on 5 foot drops to flat landed nose first. (gives you some idea how hard I cased on the far bank)

 

[DROP]

so your saying that dots are convirtable to 7" of travel cool