Lazer zxr tub runner

[rob m]

After racing my Lazer zxr over the winter months for the last couple of years I have decided to treat myself to a fibre-lyte tub chassis.
I have fully dismantled cleaned oiled and greased all the parts ready for the new tub chassis and thought I would share what I have changed to compete in todays world of buggy racing, but still trying to keep the zxr's identity using period upgrades and modified items in keeping with the original car.

[rob m]

First thing is the ball diffs.
I have not felt the need to change anything over the stock kit build. The plates, balls and thrust assembly all work as they should.
I have a few spare diffs so I did take the time to match up the compression washers on each diff to keep adjustment front and rear identical to aid fine tuning trackside.
They have been stripped cleaned and rebuilt using AE lithium and black grease.

[Welshy40]

I use ceramic balls and tungsten carbide thrust and works fine without alteration

[HKS_TRD]

Look forward to seeing this build progress

James what diameter balls and thrust washers did you use, the ceramic balls I got seem to be slightly smaller than the Kyosho ones and are a loose fit in the diff pulley

[alcyon]

Guys..try super lube synthetic grease for your ball diff and thrust bearings.
i find that it works better than ae grease and seem to withstand pressures better.

[Welshy40]

Originally Posted by HKS_TRD

Look forward to seeing this build progress

James what diameter balls and thrust washers did you use, the ceramic balls I got seem to be slightly smaller than the Kyosho ones and are a loose fit in the diff pulley

I think I put the sizes I bought on the ZXR thread somewhere. Yes the big balls are fractionally smaller and just drop on rather than lock in like the original kyosho balls. I think the thrust was the same size.

[rob m]

Originally Posted by Welshy40

I use ceramic balls and tungsten carbide thrust and works fine without alteration

Its not that I need to adjust the diffs to keep them working. When i rebuild the diffs i set them to the same tension front and rear and when at the track I can tweek them to get a desired drive and steering response.
A lot of people do upgrade to ceramic diff balls and are happy with the results but i have tried them in other cars and couldn't see any advantage. I feel they are wasted on me.

[rob m]

Originally Posted by alcyon

Guys..try super lube synthetic grease for your ball diff and thrust bearings.
i find that it works better than ae grease and seem to withstand pressures better.

Alcyon if I ever run out what feels like an endless supply of AE grease i have got with new kits over the years, I will give super lube a try.

[rob m]

Next up is the shocks.

I have tried many different combinations of springs, pistons and oil weights from original kit pistons to lazer zx5 pistons, kit black springs and a variety of AE springs. below is the shock setup I find works good for me.

The shocks have had new seals and bladders fitted, self made pistons that are the same size as the originals but with 2x 1.4mm holes in the rear and 2x 1.3mm holes in the front. I have also added droop limiters to stop the drive shaft popping out of the outdrives as I use the inner hole on the rear arm, I have 3mm droop limiters in the rear and 2mm droop limiters in the front to balance the weight transfer by making front and rear droop the same amount. Shock oil I use AE and have 30wt in the rear and 40wt in the front. The springs are original kyosho option house springs and are the hard gold set front and rear.
With the rear shocks using the hard springs and having the 3mm of droop limiters I had to remove the spring stoppers to get a suitable ride height replacing with a thin spring collar and spacers.

[rob m]

One downside to the lazer is the design of the way the front shock tower is fixed onto the gearbox case. The tower is fastened to thin tabs that can break easily on impact. A way to help strengthen this is to use a tower with a cross brace over the top. In addition to this I have made two small delrin supports that fasten onto the top deck with the two 4mm screws and onto the gearbox with the two upper tower mounting screws.
They may not look fancy but they saved my gearbox case when I have snapped two carbon fibre shock towers and still the gearbox is ok, now I am on my third tower which is 4mm thick!

[Welshy40]

Yes your solution is a good idea, wish id thought of that to save on costs as i strengthend the bottom and middle upper sections of the towers, also MMS gearbox casing was used but cost a bit.

May be an idea to get the front end of the top deck done thicker based on your design as its a really good idea.

[rob m]

Originally Posted by Welshy40

May be an idea to get the front end of the top deck done thicker based on your design as its a really good idea.

Can carbon fibre be made different thickness' ?
Easier then my design for people to do is have a top deck thats longer at the front so it butts up to the gearbox tabs and then have two rectangles of 4mm carbon or plastic that also butts up to the gearbox tabs with a hole for the 4mm screws to clamp it onto the top deck and then drill a pilot hole on assembly for the top shock tower mounting screws to tie it all together, thats if you can screw into the grain of carbon fibre?......or maybe just having the carbon or plastic rectangles on top of a normal length top deck butting up to the gearbox tabs would be good enough.

[Welshy40]

You have given me the idea so will try in a month or two but is possible to make a thicker front section surrounding the holes

[rob m]

I wanted to try anti roll bars on my lazer set ups, but found the original ones hard to come by and very expensive to buy.
I had a team associated b44 roll bar set that I no longer had a use for so decided to have a go at re-bending them to suit the lazer and then on to make some clamps from a broken carbon fibre shock tower. For the drop links I have used two pairs of front and camber links from my zxr.

[rob m]

With using modern brushless systems in the lazer and racing indoors I noticed that the motor was hot after a race, and that's with using a heatsink motor plate. I have made an alloy rear bulkhead to replace the plastic item to help with the cooling of the motor. I have kept it identical to the original to keep it looking as it should but made the openings in the middle slightly bigger to allow more air flow to the motor. Just needs anodising black before fitting.

[rob m]

After getting the assembly of the diffs and shocks out of the way its time to get the fun bits started with . First up is the rear gearbox.
On previous gearbox builds I have played around with different lengths of bushes between the pulleys on the layshaft to reduce the amount of float, but now have decided to leave it as the manual as the float will help the belts to move under load and reduce the stress and wear.
The slipper system works as it should using the wave washers so all I have done is upgraded the pads to team associated sc10 high torque pads. Once I have set the slipper and with racing on the same track types I never play around with it so I then add a spot of thread lock to keep the lock nut in place.
With running lipo and a brushless system I thought it would be idea to have belt tensioners to prevent any belt jump on the pulleys causing damage or melting them as they are hard to find and can be expensive.
The front belt tensioner is adjustable and its been made from alloy plate and 8mm bar, The rear tensioner again is adjustable and made from alloy rectangle bar and carbon fibre. I have also added a 10mm wheel bearing over the top of the rear pulley and by putting a bush in the wheel bearing to make the I/d 3mm, then cutting a section of the gearbox out I was able to fasten the bearing in place using the screw that ties the gearbox together. One last thing I decided to do was make an inspection slot so I can easily see the condition and check the tension of the rear belt.

[rob m]

All the carbon fibre parts have been made by fibre-lyte. The tub chassis is a reproduction of the original tub chassis upgrade but I decided to remove the battery slots and change the cut out for the servo saver into a 1mm deep pocket, I felt it was best to have the chassis without big slots and holes. I also had the cut out for the removal of the motor replicated on the spur gear side to save me from dremmeling a hole to access the motor mounting screw, I think it looks more pleasing to the eye being symmetrical and if the chassis has any flex it will be more even from left to right with the same cut out each side.
The top deck is a copy from the original but with two notches cut in to allow for the bridge wires for the lipo saddle packs.
The rear shock tower is a copy from an original mk2 tower, but the front shock tower is one I designed myself as I wanted the nose of the bodyshell to easily fit through the front without having to cut it off.
The lipo trays are of a simple design as I didn't want to draw any attention to them. The straps are like the original lazer zx items.

[rob m]

Next up is the assembled upper chassis.
I have replaced the kit unicrank set with the 39655 special blue unicrank set as its a lot more ridged and used ball bearings instead of the kit bushes. The ackerman plate is from a lazer zx.

[Welshy40]

Originally Posted by rob m

With using modern brushless systems in the lazer and racing indoors I noticed that the motor was hot after a race, and that's with using a heatsink motor plate. I have made an alloy rear bulkhead to replace the plastic item to help with the cooling of the motor. I have kept it identical to the original to keep it looking as it should but made the openings in the middle slightly bigger to allow more air flow to the motor. Just needs anodising black before fitting.

I had mine made with the rear top deck mounts raised by 3mm as that way my 5600 lipo saddles fit underneath. Looks good. Also like your belt tension design, seems similar to my design and should do the job well.

[HKS_TRD]

Is that alloy bulkhead a one-off or can you have more made?