HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Feb 25, 2014, 07:03 AM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
Discussion
SkyRc SR4 Dirtbike Review & Tips

Good day all
Have 20 years experience in nitro/electric heli`s, planks, on/off road cars, boats and also have a upgraded Gpv1 which drives great, BUT I do not have any dirtbike experience.

Okay 1st off - We all know that rtr is 90% of the time not rtr.

When I opened the big box I could see both my front shocks/forks leaked all over the place. I removed them to change the o-rings with some new/descent o-rings.
The shock bodies consist of 2 tubes that screw into each other(http://www.helipal.com/sk-700002-01-...mgtpe61uvjs222) - there were no way that I could remove them from each other to eventually remove the shock internals. I tried a vice/pliers etc, could not remove them. So I installed them back on the bike and used some 40wt oil. Just by standing on the bench and compressing the forks, you could see a bit of oil coming out on each press.

The chain rubbed on the rear tyre - What I saw is that the front sprocket were installed too deep on the drive shaft - There were about 2.5-3mm shaft showing. I installed the front sprocket so that the shaft were flush with the end of the sprocket and that fixed it. The chain were also way too stiff.

With neutral steering, the servo horn were not 90 degrees to steering linkage and both spring`s tension were not the same - Quick fix.

Seems like all bolts going into metal had thread lock - Some bolts going into plastic were not tight. I replaced all grub screws as the stock grub screws WILL strip.

After 1 5300mah 30c 2s lipo I removed the rear shock - Someone at the factory thought that 2 drops of shock oil were enough for the rear shock. I cleaned it out and used 1000cps diff oil until my traxxas revo shock arrive.

Amazingly my front/rear wheels spins true and compared to video clips, my e-gyro are balanced with no vibrations, lot less noise and working great. There are a big difference between 12 000rpm which are walking speed stable and 8000rpm - I opted for 10 000rpm and will stay there for a while.

It`s a pain in the butt to remove and replace the main body. There`s a bolt going threw the rider`s ass that are difficult to remove.

I did 7 lipo`s till now and everything seems to hold up great - had a few front tumbles and wheelies - The wheelie bar will bent up 45 degrees with ease - Must think of something stronger + a airie wheel on the wheelie bar. Steering are good, but think it can be much better with a steering damper - 10% of the time I have a head wobble especially on grass. The 7 lipo`s were done on grass with some bumps and on gravel.

My awaited upgrades will be a steering damper, 6mm nylon wires and a revo rear shock. And then I must figure out if I`m going to buy a complete set replacement shocks or If someone else can recommend a complete front end from another bike???
Bking1340 is offline Find More Posts by Bking1340
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 25, 2014, 09:25 AM
Registered User
Everett, Wa
Joined Sep 2004
230 Posts
Thanks for the great review, will be watching to see your progress with the mods your doing and if you can fix the front end.
lazer is online now Find More Posts by lazer
Reply With Quote
Old Feb 25, 2014, 11:04 AM
RC Dirt Bike Action
JohnnyMc's Avatar
California central coast
Joined Feb 2010
1,673 Posts
Hi BK and welcome to rc dirt biking. For reference - here is link to another SR4 discussion too with bits of info http://www.rcgroups.com/forums/showthread.php?t=1983135 I do not personally own the bike but a few owners are poping up here and there mainly from UK or Europe.

Not sure what bore size the revo shock is but for the Atomik MM450, a 16mm 1/8 front shock (HPI Vorza buggy for reference) did absolute wonders for the bike. Every single 1/4 bike should have 16mm going forward and if they dont, designers are clueless to what the owners have figured out. I guess they are too busy copying the previous design to look ahead. Not sure what will fit in the SR4 but its worth looking into before you get a revo shock. Just measure length and width of frames to see what will fit.

Changing forks may cost more than trying to fix yours. Not only the forks but the triples and the axle for the wheel have to be sorted. Your options include discontinued MM450 forks which you will need all the parts found but may not be around for long. You can go ARX forks, but those dont use oil, so if you want oil filled on those then you have to do a mod like Throttlejunkie did to make them oil dampening forks. Phantom400 are similar to ARX but slightly different and need same mod. Finally the Himoto mx400 are not oil filled either so you would need to figure out a mod if you wanted oil filled for those.

Keep us posted on the mods you do. If they work out I can add them to the HOW-To's on my website.
JohnnyMc is offline Find More Posts by JohnnyMc
Reply With Quote
Old Feb 25, 2014, 11:51 AM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
I see you Johnny - Was just thinking, I must maybe order a new set of front forks (Give SkyRc a chance) and then I can assemble them myself. Because I`m itching to remove these forks again, but I know I will mess them up by trying to remove the 2 piece shock housing and that is the only option to remove the inners. If you look at this link: http://www.helipal.com/sk-700002-01-...mgtpe61uvjs222 this is only 1 fork/shock housing/barrel that screw into each other and make one shock. It seems like they glued them together - so in the meantime I`m screwed. If the new set also leaks, I will run them with 2 drops of oil, because the bike is actually handling very good.

For the rear shock, I have a 1/10 Revo, must maybe remove one of the shocks and try it on the sr4 rear end.
Bking1340 is offline Find More Posts by Bking1340
Reply With Quote
Old Feb 25, 2014, 01:14 PM
RC Dirt Bike Action
JohnnyMc's Avatar
California central coast
Joined Feb 2010
1,673 Posts
Maybe soak one end in hot water and see if it expands enough? Glad you got a shock to test free.
JohnnyMc is offline Find More Posts by JohnnyMc
Reply With Quote
Old Feb 25, 2014, 06:54 PM
Registered User
Nice
Joined Nov 2008
272 Posts
My own experience about the front fork is the inner fork brake after two lipos used on offroad track with close hard jumps.
Sometimes the bike touch the base on the jumps and hurts a lot .
I was thinking use a strong front fork without oil about Phantom 400 maybe more hard to brake because less parts inside ..
Helicoy is offline Find More Posts by Helicoy
Reply With Quote
Old Feb 25, 2014, 11:20 PM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
Okay some more bad news. I can move the front wheel about 3-4mm sideways and front to back and this comes from the shock shafts. I still have only 7 lipo`s on the bike on gravel & grass with 0 front impacts.
So it seems like I have to get a new front end - Any suggestions?

Edit: Found the problem - The lower thicker shock shaft came loose from the upper thinner shaft - Still needs to split the shock body to fix this.
Bking1340 is offline Find More Posts by Bking1340
Last edited by Bking1340; Feb 26, 2014 at 12:11 AM.
Reply With Quote
Old Feb 26, 2014, 12:20 AM
Registered User
Australia, QLD, Burua
Joined Jul 2012
2,397 Posts
Quote:
Originally Posted by Bking1340 View Post
Okay some more bad news. I can move the front wheel about 3-4mm sideways and front to back and this comes from the shock shafts. I still have only 7 lipo`s on the bike on gravel & grass with 0 front impacts.
So it seems like I have to get a new front end - Any suggestions?

Edit: Found the problem - The lower thicker shock shaft came loose from the upper thinner shaft - Still needs to split the shock body to fix this.
Maybe try some heat from a cigarette lighter. Too much heat may damage the seals and bushings so don't go overboard.
chktm is offline Find More Posts by chktm
RCG Plus Member
Old Feb 26, 2014, 05:45 AM
Registered User
Australia, QLD, Burua
Joined Jul 2012
2,397 Posts
Quote:
Originally Posted by Helicoy View Post
My own experience about the front fork is the inner fork brake after two lipos used on offroad track with close hard jumps.
Sometimes the bike touch the base on the jumps and hurts a lot .
I was thinking use a strong front fork without oil about Phantom 400 maybe more hard to brake because less parts inside ..
The Phantom or ARX forks should fit I'd say and you've always got the option to make your own oil forks with these as TJ did.
chktm is offline Find More Posts by chktm
RCG Plus Member
Old Feb 26, 2014, 06:08 AM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
Got the 2 shock bodies removed from each other with a lot of sweat - really seems like they used ca. Have rebuild the shocks and so far no oil leaks. The problem was that some stupid idiot at the SkyRc factory thought that one o-ring will be enough - I replaced them with 2 pure silicon o-rings on each fork.
Bking1340 is offline Find More Posts by Bking1340
Reply With Quote
Old Feb 26, 2014, 12:05 PM
RC Dirt Bike Action
JohnnyMc's Avatar
California central coast
Joined Feb 2010
1,673 Posts
Wow, you were able to use another brand oring. For future reference you got info on size or link to where you got them in case owners can shop for them locally?
JohnnyMc is offline Find More Posts by JohnnyMc
Reply With Quote
Old Feb 26, 2014, 12:10 PM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
Okay after 4 lipo`s - still no leaks on my front shocks, but I have a question. I have mounted both front forks without springs to check for binding and the shocks are smooth. When I install the springs it`s still smooth, but takes a lot of effort to compress. For example, when I press on the front body post in front of the rider, the back shock bottoms out before the front shocks start to move. While driving on small bumpy grass terrain, I can not really see the front shocks working, only the rear shock.
So it seems like the springs are way too stiff.
Any way around this?
Maybe cut a certain length of 1 or both springs?
Bking1340 is offline Find More Posts by Bking1340
Reply With Quote
Old Feb 26, 2014, 12:14 PM
Registered User
Bking1340's Avatar
South Africa
Joined Jan 2010
458 Posts
Quote:
Originally Posted by JohnnyMc View Post
Wow, you were able to use another brand oring. For future reference you got info on size or link to where you got them in case owners can shop for them locally?
I bought them from my local hobby shop - It`s seems like the tamiya 1/10th scale aluminum shocks o-ring`s, but the package came with other shock parts as well and were a bit pricey. Don`t know if you can get them separate, but here are the tamiya part #53574
Bking1340 is offline Find More Posts by Bking1340
Reply With Quote
Old Feb 26, 2014, 02:03 PM
Registered User
Everett, Wa
Joined Sep 2004
230 Posts
Do you have to much oil in the forks, Do the oppositte. remove all the oil and check with just the springs.
lazer is online now Find More Posts by lazer
Reply With Quote
Old Feb 26, 2014, 06:32 PM
Registered User
Australia, QLD, Burua
Joined Jul 2012
2,397 Posts
Quote:
Originally Posted by Bking1340 View Post
Okay after 4 lipo`s - still no leaks on my front shocks, but I have a question. I have mounted both front forks without springs to check for binding and the shocks are smooth. When I install the springs it`s still smooth, but takes a lot of effort to compress. For example, when I press on the front body post in front of the rider, the back shock bottoms out before the front shocks start to move. While driving on small bumpy grass terrain, I can not really see the front shocks working, only the rear shock.
So it seems like the springs are way too stiff.
Any way around this?
Maybe cut a certain length of 1 or both springs?
MM springs fit in the forks and are quite a bit softer, maybe worth trying.
chktm is offline Find More Posts by chktm
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion 1/4 Dirtbike steering damper Bking1340 Motorcycles 43 Mar 15, 2014 06:38 AM
Video SkyRC SR4 Super Rider 1/4 RC Dirty Bike ray2006 Car Talk 0 Sep 09, 2012 09:08 AM
Discussion SkyRC Super Rider SR4 Crossbike Gartenzwerg Motorcycles 27 Aug 03, 2012 02:04 AM
Build Log SKYRC F14 Tomcat Build Log/Review with Flight Video! J.E. Johnson Foamy EDFs 283 Feb 27, 2011 09:17 PM