Improving the 2005+ Montesa 4RT

This thread will document discoveries about and improvements to a 2005 Montesa-HRC 250 4RT by yours truly, motobene (by the way, that is from Italian and is pronounced moto-baynay and means "moto-good), and KrAzyOSUCowboy (I get confused as to what is in caps and what is not). My hope is KrAzy will weigh in A LOT (it's your bike). I don't want this to be a one-man show :huh as the results on-the-ground are better reported on by the rider and owner.

This first posting sets up the background in a stand-alone thread which we'll fill in later with detail as we get time. 4RT riders please contribute your opinions, experiments, and foibles. My hope is you will try some of these things and report back.

This particular 4RT was bought within this year in pampered shape with few hours. It was and remains in exceptionally good condition. The rider came off a 2006 Beta Evo 250. Reason for seeking out a 4RT was the preference for 4 stroke power characteristics. KrAzy had a positive experience test riding a Beta 300 4 stroke, but the 4RT was available and was less than half the price given the 7 model years difference.

The positives of this design are many, like the super compact 4-stroke top end, excellent build quality and reliability, very good power. I have found test riding it that is one of the best bikes regarding on-the-rear-wheel handling.

The 2005 was the first model year of the 4RT. Some details weren't as worked out as could be on the more recent model years. We don't know what a more modern 4RT feels like because there isn't one here or anywhere near here. We can't report on the overall differences between a 2005 and a 2013, or even a 2007, unfortunately.

KrAzy has toured the parts lists extensively and found very little difference across model years and some interesting facts about what parts are shared with the Honda product lineup. Suspension, valving specs, rake and trail, FI mapping and other minor details (which sum to significance) are outside the parts lists, however, and we are blind in that regard.

What we can report accurately on is the 2005 model and making it significantly better. I hope you all will find that interesting and helpful as this thread fleshes out.

Targeted Improvement Areas:

- Handling. Reducing over steer (hyper-active steering in small-radius turns).

- Clutch. Disengages and re-engages too fast, faster than the rider's brain can keep track of especially when tired. This causes rider brain 'control system ring'. Pull in clutch = fast release. Brain says, "Woa now, I gotta go!" Letting out the lever result in quick engagement and a too-strong impulse forward, causing the next over compensation. Pulse-pulse or pulse-pulse-pulse results! The clutch increases brain 'calculation burden' resulting in distraction, inaccuracies and points taken. The negative effects are more pronounced with less experienced riders.

- Suspension. Excellent hardware but out-of-date 'software' (valving specs). Too slow in 2005. Way way too slow in 2013! The rebound adjusters were quickly set at full minimum and they stayed there until recent major improvements (more on that later). Set up stock the bike feels very heavy (worse in colder weather) requiring forceful rider inputs. The slow response also hinders learning techniques.

- Power. We have had no issues with power. This bike came de-restricted and it runs very well.

Improvements don't imply the 4RT isn't unique or great. They don't imply you can't kill the competition on your 4RT. This is all about the joy of improving and the pleasure that comes from 'mo-bettah.'

You have my atttention.
It would be helpfull to know what level competition the bike is being set up for, Intermediate, Expert, etc. As well as the operating conditions, wet coastal, dry desert, high elevation etc.
By the way a 2006 Beta would be a Rev not an Evo.

I know mine is an 07 4RT and may not have the same needs as an 05 but I am on the edge of my proverbial seat...

Depending on what it takes to try some of what you are doing I may even be willing to dabble a little in trying some of the modifications. (FYI: if I decide to do so I am a bit of a procrastinator in getting things done fast, just so you know) I really should be better about that.

And thank you for all the hard work and info!

Ooh, I'm in.
I will include my improvements to my 07'.
I will work on the write-up.

We rode the modified 4RT extensively yesterday. It is transformed. I found myself wanting to ride it a lot, and that never happened before, as certain details were irritatingly imposing themselves into the center of my attention, like the slow suspension and jerky clutch.

I asked KrAzy yesterday to contribute to this thread, as it is his bike. He said something to the effect that I am better at words regarding tech things, but my hope is he will get verbose or I lack some credibility as this is not my personal bike.

But I can start with a detail or two.

CLUTCH

This bike has the 2006 plates. It has the 315R master cylinder. It does not have the Mitani kit. We do not have access to the fancy ELF oil used in Europe. KrAzy reports the importer says the cost is ridiculous and not worth it.

Test conditions: High traction. About 70 degrees F (21C).

Yesterday I was surprised to find I'd get off the 4RT during test rides and find no memory of the clutch. The clutch is still a little faster engaging than a GasGas and some other bikes, but our simple mods slid the clutch behavior to inside the acceptable window, meaning outside inserting itself in the center of rider attention with hyper behaviors. I could ride the 4RT concentrating more on terrain without added calculations required to keep track of the clutch.

I'd switch back and forth to my GasGas 300 Raga and be surprised at harder clutch pull and less plush suspension (more on the suspension mods later). The 4RT is for me now flat out fun to ride!

Here are our simple fixes, launched from the base of 2006 plates and the 315R master cylinder: Removal of two of six clutch springs does wonders for this bike! (Always remove springs such that the clutch clamping force remains balanced). We did not go further yesterday to three of six clutch springs because the clutch was working well. This clutch is used in much larger displacement bikes and I think they over sprung it, especially with respect to its grabby characteristics. It would be fun to experiment with three clutch springs... just to know what that feel like and where the slipping point versus load and gears of this clutch.

The other variable was oil. We've tried a ton of different oils in the gearbox and in the master cylinder. We settled on a ~520cc of medium-heavy weight synthetic oil of brand [update: Silkolene 10W40 full synthetic]. Not sure if others would not or work better, but it worked well. In the master cylinder is some high proportion of heavier mineral oil (intestinal lubricant), yet I found it to not slow the lever return as it did on my GasGas. Perhaps what was in the slave cylinder mixed with the heavier oil and lowered its viscosity to the point it doesn't affect anything?

I found with oils and this clutch that my assumption that thicker and thicker oils will slow engagement linearly is off. Changes in viscosity are instead more non-linear in effect. KrAzy, what the that last oil in there, both type and proportion with Lucas Transmission Fixer? [Update: Lucas Tramsmission Fixer 350cc and Silkolene Extreme Gear Oil (whatever that is) 170cc].

With the heavy-heavy oil, the bike, when cold, would want to take off when snicked into first gear. We'd simply hold the front brake on. It would quickly release, and as the oil warmed it would quickly start to feel normal. But I think we found that the clutch would release FASTER with really thick oil. I believe this was because the longer-chain oil molecules would re float the plates faster. Getting rid of too fast-engagement AND too-fast of re floating is important on this bike.

Determined by experimentation: One should avoid light clutch-transmission oils or the clutch will be more grabby, particularly when the engine is hot. Very heavy oils cause a few weird effects. Better are thicker oils as the viscosity needs to be there to slow engagement, but not so heavy as to speed up float. Also, use a full synthetic for the better friction characteristics (may keep the plates from 'grabbing' quite as fast). Also, the synthetics are higher VI or viscosity index, thus have more resistance to changes in viscosity with temperature.

A problem with viscosity is almost no oil seller labels actual viscosity and viscosity index. SAE numbers are not viscosity numbers but are a rough guide to thickness. 10W40 means SAE grade 10 Winter and theoretically 40 (when hotter). It's not really accurate, however, as none of these oils thicken as much as the second number implies when hot. I have heard multi-viscosity oils are accomplished through inclusion of coiled polymer chains (plastic) that lengthen, straighten out, as temperature rises, thereby thickening the oil or compensating somewhat for thinning. When it comes to actual viscosity, short of test machines, there is not substitute for direct measurement. And easy as we are to self deceive, experimentation for confirmation or learning is king.

The sensitivity to friction characteristics and perhaps viscosity is what the fancy ELF oil may have addressed. I haven't experienced it directly. Perhaps it is both a synthetic and heavier, with friction modifiers?

Lots of dogmatic discussion on oils, usually by 'experts.' There is no one fix. One-fixers are often ego smoke or from someone with a commercial interest. The more important thing is to try to understand why something works or doesn't. That opens up a knowledge is power situation that can get real and good results.

Hopefully our unwillingness to NOT accept the clutch as it was and our experimenting will provide other 4RT owners with better experience. Removing clutch springs is a very simple mod. The O-ring-sealed clutch cover make removal and replacement a no brainer. You can lay the bike over on its left side, remove the cover and not have oil puke out. The clutch springs and their fasteners are right there. As I suggested earlier, I'd leave the two springs out but put the fasteners back in so you don't lose them. But make sure they are not loose as the absence of springs can have them backing into the clutch cover if they are loose.

I'd do the springs mod first before change the current oil. I'd test it to fully warm, then change the oil and see what oil does after the springs are removed.

I look forward to your comments and experiments.

Did you do the spring removal, oil changes, and master cylinder change independently so you could assess the results of each?
Do you feel that less clamping force = slower engagement? If so would you attribute the slowed engagement more to the oil change or the springectomy?

FYI, I use a 315 master cylinder and Maxima 75w (extra light) synthetic gear oil, and don't notice any difference between my 2006 4Rt and any other modern Trials clutch.
Based on your posts I may try medium weight gear oil.

Read my last posting pretty fast, eh?

Yes

Yes

Springectomy

A bit of curiosity here....

What prompted the change to the 315R clutch master cylinder?

Brewtus, it appeared and was suggested by others that this was a factory change for 2008 and we were looking for the easy simple fixes first.. Seemed like a small improvement when installed, but not really sure. More fluid volume for sure but no change in bore diameter and no real geometry change at the lever makes me wonder if there is any real advantage here. On the bright side I have a spare.

When I heard about the 315R master cylinder solution, I assumed its diameter was smaller than 2005 OEM because the 4RT begs for either a smaller master cylinder or larger slave cylinder diameter to slow the clutch 'lift plate' throw rate versus the lever movement. But according to KrAzy there is no difference in diameter or the lever ratio. Both master cylinders are 9.5mm. It became a waste-of-money mod, unless I'm missing something. Are there other, truly beneficial reasons for the 315R master cylinder? Fluid volume doesn't mean much, functionally speaking.

FYI: The guy I picked up my 2007 4RT from had 3 containers of the ELF so that's what I have in my bike, for now. with the size of the containers I will be able to get 4 oil changes each (12 total) before I run out...

For what its worth I am guessing its a synthetic. It is quite interesting, its clear and almost water thin, and has one of the strangest smells. :huh When coming out of the bike it has a light murky haze to it and just pours out quick.

When riding I don't know if I would say that the engagement with the ELF is a light switch but it is fast, more on/off than my wife's 2008 TXT Pro but not crazy fast (I run Honda HP Transmission Oil 80w/85w in her bike). It could just be my perception though as I haven't had someone else ride it. Side note: considering going to the Maxima 75W Extra Light in her bike...


Clutch mater change?...
I am wondering about the clutch master and slave, I see your talking mineral oil with a 315R master... I am almost sure my 07 master/slave is using DOT... I will double check this when I get home tonight.

Interesting! The ELF is apparently light stuff and the stinky may mean friction modifiers. Given you have ELF you'd be a great test case. ELF and your six springs, then keep the ELF and so the -2 springs, then later at the oil change try the Silkolene 10W40 synthetic, then later some other oils. Be nice to know if the ELF is really doing something significant, or if it voodoo smoke. Be nice to know how no ELF and 4 springs compares.

BTW the gassers really like the ATFs. I've been using generic synthetic ATF+4 a long time. Save$.

I was on a gasser with the ATF and it was closer to my 4RT in clutch feel with the ELF, but with my wife riding the Honda HP Transmission Oil 80w/85w was much slower and with her experience being so much less than mine it has been better for her to run the non ATF.

I figure as she gets better and comes up in class she will be ok with changing out to something else, however it is a little thick when cold and I think the Maxima 75W Extra Light would be just a little less fluid pull one first start.

Tell then she gets what is working for her, want to keep her feeling confident on the bike...

I used to own a Suzuki RG500. The clutches on them are less than stellar. As soon as you started to build the motor, you had to be pretty careful with the clutch. The other issue was it was a close ratio box and first was REALLY high..... Don't worry, I have a point.

We would take the clutch hub and drill a bunch of holes in the trough where the plates would run. This did a few things, smoothed out the action and kept the clutch much more clean from contaminants. Clutch life was much better with these mods. Not that we have a durability issue, but it may help with smoothing out the action.

Maybe something to try.....



Like this but smaller holes.

'Bene, I see you revised the orig post and further commented on the heavy mineral oil in the clutch master. When I changed the fluid I did a complete change, back bleed from the slave up. If there was any dilution in the slave, it was minimal.

You got me there. Individuality in bikes matters. Gotta match the oil to the application. I had to add some 20W50 motor oil to my ATF+4 recently when I put thinner oil in my clutch master cylinder to slow down the clutch.

CSP make clutch hubs for Sherco and Beta with improved fluid flow along those lines.

It's just a trifling detail, but I'm not sure you can do a full exchange through the bleeder.

When I rebuilt my Gasser, I popped the 'top-hat' piston off (the slave piston) to inspect the o-ring and see what they were made of (Buna-N). I noticed the bleeder, so it won't get knocked off, is well uphill of the slave cylinder and the single passage leading to it. I discovered it could be quite hard to bleed the slave without filling the top hat and pushing it on.

The 4RT may be the same way, as in having only one hole down there. It's possible the casting bulge in the upper left view of page 4-39 of the 2005 manual is a bleeder passage on top of a second passage to the brake line. You can see the bleeder is offset from the brake line, so maybe HRC does have 2 holes to the slave.

No way to know without pulling the cover and looking very carefully. If it's like the GasGas Pro, you cannot do a full exchange by pushing fluid into the bleeder, or even flowing down. It'll take a bit of riding to blend the trapped oil into the newer oil. And that's no big deal. You sure don't want to be messing with the slave on the HRC, as it has a pressed-in thrust bearing.

When I did my GasGas I did a 100% exchange to the thicker mineral oil by filling the top hat with oil then pushing it on until the oil was solid up to the brake line and bleeder. The lever was gluey feeling. Since you did not do a 100% exchange, your mineral oil probably blended out in viscosity to something in between the thick and thin stuff. I put in the Redline Like Water, and now have a mix of heavy mineral oil and the very thin ester-based suspension fluid.

Laser, that CSP clutch assembly is just beautiful! Are you thinking of improved oil flow because of the holes through the outer basket?

As for the holes through the inner basket like your Suzuki, mud, Ron Lee says he was doing that on his Beta... the one with the really nice clutch. For oil to flow through the basket out through the released plates, the basket itself has to have passages into it from the back or front.

The GasGas clutch gets oil flow through the outside or front, through the gaps in the 10 triangle plates that rocker the lift plate against the basket and Bellvile washer. It's a pretty good flow-through design - or so it seems. There may be a tendency to fling most of the oil out, or it could work like a pump.

On the typical coil-spring clutch, the inner hub front and back is pretty covered over by the 'lift' plate, clutch plates, and outer basket. Unless there are oil passages into this space when assembled, the oil flow issue might be one of perception is reality as the clutch is spinning fast. Oiling may be primary external and by splash.

The 4RT has a pretty covered over clutch. At least it looks that way from the manual photos. When spinning fast, the oiling might be simply whatever thin films get in there, and that's how it is intended to work.

I wish we could see a video of a clutch working dynamically in its oil bath. Funny, there are a gazillion of them of them, yet the number of humans on earth that have ever directly observed the oiling could probably be counted on one hand.