Kasama Srimok Rotor Head for Trex600

Reviewer: Rob Turnbull
Review Date: 4th November 2008
Supplier Kasama
Manufacturer: Kasama
Unit Cost: $260

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Kasama have built up a good reputation for their high quality machined components. When I heard about the upgrade head for the Trex600, I had to find out more. Kasama then very kindly agreed to supply the head for review on this site.

The first thing you notice when you open the parcel is the outstanding finish to the component parts. Everything looks stunning and, as will become apparent through the build, the machining tolerences are very tight making the end result really very good indeed.

The head arrives in four clear strong plastic bags which are all sealed together. Each bag has the component parts sealed off from each other for protection. Obviously the head requires assembly before it can be used, and at the time this one was received no real instructions existed - however, it isn't rocket science, so the build quickly got underway.

Here's some of pictures of the head as it arrived in the clear plastic bags.

  • Bag 1Bag 1
  • Bag 2Bag 2
  • Bag 3Bag 3
  • Bag 4Bag 4

As the bags are not numbered, and seemingly spread out a little, here's a breakdown of what's in each bag looking at the top compartment of each bag and working down it.

Bag 1 contents: Fixings, damper mounts and damper rubbers, Feathering spindle, Head button (stopper), Head block

Bag 2 contents: Fixings, Blade grip levers, Blade grips

Bag 3 contents: Ball links and fixings, Washout base, Flybar carrier ends, Flybar levers, Flybar carrier (Seesaw)

Bag 4 contents: Links, Mixing arm fixing bolts, Mixing arms

Assembling the head

To assemble the head, you will need to re-use a few items from your stock Trex600 head, including the lower mixing arms attached to the washout base and the flybar and paddles. You also need to either re-use, or supply new, the missing rocket links - the supplied links all come with just one rocket link attached.

I found putting all the fixings together in a pile saved searching through each of the pockets of fixings for the item I needed. I just searched one big pile instead. Alternatively, you can just cut out the parts that you need to use as you need them through the build process.

So let's get straight into the build.

The washout base and mixing arms

Parts used:

The first thing to assemble is the washout base and the mixing arms taken off the original Trex600 head. The bolts that attach the mixing arms to the head are provided, as are the brass spacers that sit between the mixing arms and the washout base. While the opportunity presents itself, check that the ball links on the mixing arms are in good condition and change them if they look worn.

Slide an M3x14 bolt through one of the mixing arms, add the brass spacer and then threadlock the bolt into the washout base.

  • Parts used to assemble washout base and armsParts used to assemble washout base and arms
  • Fit a bolt through an arm, then the brass washerFit a bolt through an arm, then the brass washer
  • Threadlock the bolt into the washout baseThreadlock the bolt into the washout base
  • Repeat for the second arm on the other sideRepeat for the second arm on the other side

Note the orientation of the arms. The short side of the arm sits to the left of the squared off area of the washout base to which the arm attaches.

Assembling the blade grips

First, lets have a quick look at these lovely blade grips.

  • Blade grip lever mounting point (flat)Blade grip lever mounting point (flat)
  • Radial bearings surround the thrust bearing/racesRadial bearings surround the thrust bearing/races

They look great and are machined to incredible tolerences. In order to get the bearings out of the grips, you must heat the grip up - they will not pop out on their own!

Parts used in this stage of the assembly:

One 4mm bolt and one 8mm bolt are used to attach the blade grip lever to each blade grip. The longer bolt fits into the hole nearest the headblock and the shorter bolt fits nearer the blade. If you look at the threaded holes you can see the outer one is shallow than the inner one.

Push the bolts through the blade grip levers and threadlock them into the blade grips.

The short bolt goes through the narrower end of the lever. Once fitted correctly, the rounded cutout on the shallower end of the blade grip lever nicely matches up to the round inside edge of the blade grip.

  • Blade grip lever mounted to a blade gripBlade grip lever mounted to a blade grip
  • Both blade grip levers mountedBoth blade grip levers mounted

With both blade grip levers threadlocked into place, we next need to fit the upper mixing arms to the blade grip levers.

No shims or spacers are needed between the upper mixing arms and the blade grip levers, or the mounting bolts as the blade grip lever is machined with the equivalent of a spacer on it (to avoid the bearing from getting jammed) and the bolt sits on the inner race edge so that the bearing can move freely.

Fit the 14mm bolt through the upper mixing arm from the side the ball links are fitted, so the ball links are facing out when fitted to the blade grip lever. Carefully add a little threadlock (do not get any threadlock in any bearings) and then fasten the bolt securely to the blade grip bolt. Repeat the same procedure for the second blade grip.

  • Grips, levers and fixing boltsGrips, levers and fixing bolts
  • Add a small amount of threadlock to the boltAdd a small amount of threadlock to the bolt
  • Fasten mixing arm to blade grip leverFasten mixing arm to blade grip lever
  • Both blade grips with upper mixing arms fittedBoth blade grips with upper mixing arms fitted

Assembling the flybar seesaw and head block

Parts used in this stage of the assembly:

The seesaw is fitted to the headblock first, and then the remaining parts are fitted as you slide the flybar through the assembly.

  • Seesaw and headblock with fixing boltsSeesaw and headblock with fixing bolts

Slot the flybar seesaw into the headblock and line it up so that the centre mounting holes are positioned inline with the bearings in the side of the headblock. Add a little threadlock to the M3x7 bolts, carefully slide them through the bearings in the side of the headblock and fit them into the seesaw mounting holes. Tighten them up without overtightening, and then check that the seesaw moves completely freely in the headblock.

If you have two M3 hex drivers, tighten these two bolts together (at the same time) in order to keep the seesaw central. The bolts should be tightened down with equal strength.

  • Lightly threadlock the boltsLightly threadlock the bolts
  • Seesaw fitted to the headblock with fixing boltsSeesaw fitted to the headblock with fixing bolts

Next we fit the flybar through the head and attach the right parts to the head in the right places as we push the flybar through, as follows.

First, fit one of the red seesaw ends loosely onto the flybar with the flat edge facing the seesaw then feed the flybar into the end of the seesaw. Hold one of the mixing arms in position (noting the correct orientation of the arm to the headblock) in the seesaw and push the flybar through it. Continue pushing the flybar through the headblock and then fit the second mixing arm (again, noting the arms orientation) before pushing the flybar through and out the other side of the seesaw. Fit the other red seesaw end onto the flybar with the flat edge facing the seesaw.

  • Fit red seesaw end to flybarFit red seesaw end to flybar
  • Slide flybar through head - fit arms as you goSlide flybar through head - fit arms as you go
  • Grub screws for the red end capsGrub screws for the red end caps
  • Loosely fit grub screws in red end capsLoosely fit grub screws in red end caps

The two flybar mixing arms are locked onto the flybar using grub screws, but the flybar must be centralised in the head first.

To try and make this job a little easier, what I do is nip up one of the grub screws in one of the red ends to just lightly pinch the flybar. Then I use a vernier (or calipers) to measure the distance from the outer edge of the red end to the end of the flybar, and get both sides exactly equal before tightening both of the grub screws down onto the flybar with threadlock.

With the flybar centralised, and with no horizontal play on the flybar, we can fix the flybar mixing arms in place. When correctly fitted, they are angled down by 10 degrees and this angle is important to ensure the head works properly. There's no need to panic though as setting the angle perfectly is a simple job. First, turn one arm so that it hits the bottom stop of its available rotation, centre the arm on the flybar in the seesaw slot and then tighten the grub screw down using threadlock. Then hold the first arm firmly in place (rotated down) and rotate the other arm fully upwards and tighten the grub screw in place using threadlock. The correct angle is now set on these mixing arms - simple!

We can finish the flybar part of this assembly now by fitting the paddles, making sure that they are equidistant from the centre of the head. Knowing that the flybar is perfectly central means that you can safely measure from the outside edge of the red seesaw ends to the inside edge of the paddle and know the distances are correct.

  • Flybar fitted and arms positioned correctlyFlybar fitted and arms positioned correctly

Fitting the dampers

Parts used in this stage of the assembly:

This rotor head comes with its own damping sytem which involves rubber o-rings mounted onto a split metal collar which is then fitted into the head. The feathering spindle then slides through that collar and it's all a very close fit leaving a lovely slop free head. The rubber o-rings should be greased a little before fitting to the head.

  • O-rings and split metal collarsO-rings and split metal collars
  • Dampers greased and ready to be fittedDampers greased and ready to be fitted

Fitting them is simply a case of pushing them into the headblock with the wider end of the collar facing outwards to help prevent the damper rubbers from coming out of the head block. The outside edge of the damper holders also acts as the spacer between the headblock and the blade grips.

  • Headblock ready for dampersHeadblock ready for dampers
  • Dampers fittedDampers fitted

Fitting the feathering spindle

Parts used in this stage of the assembly:

This head uses its own completely flat 8mm feathering spindle.

The stock Align 8mm feathering spindle can't be used owing to it having a step down to 6mm where the thrust races and bearings are fitted to it inside the blade grips.

Fit a bolt through one of the special grip washers, add a small amount of loctite to the bolt and then tightly fit it into the end of the feathering spindle.

Slide the feathering spindle through a blade grip starting from the blade side (not the head block side).

  • Headblock ready for dampersFeathering spindle and fixings
  • Bolt through special grip washer and threadlockedBolt through special grip washer and threadlocked
  • Bolt fitted to one end of the feathering spindleBolt fitted to one end of the feathering spindle
  • Feathering spindle fitted through one blade gripFeathering spindle fitted through one blade grip

The metal damper sleeves also act as the spacer that you would normally fit between the headblock and blade grips so an extra one is not needed here.

Push the feathering spindle through the dampers in the headblock and fit the second blade grip to it on the other side. Fit the second bolt through the special grip washer and add a small amount of threadlock to it before carefully fitting it into the end of the feathering spindle (inside the blade grip) and then tightening it up.

Be careful when fitting this second bolt as you do not want to get threadlock into the bearings inside the grips.

You will need to use two hex drivers, one in each bolt in the ends of the feathering spindle, to tighten them up. Make sure there is no lateral play along the feathering spindle once completed - i.e. the blade grips cannot move, at all, along the feathering spindle. Zero play.

  • Use two hex drivers to tighten both bolts upUse two hex drivers to tighten both bolts up
  • Blade grips and feathering spindle fittedBlade grips and feathering spindle fitted

The head button

Parts used in this stage of the assembly:

Fit the bolt through the red head button, add threadlock and fix to the top of the head block. Take note that the underside of the headbutton is rounded so that it fits flush onto the top of the round head block.

  • Head button and boltHead button and bolt
  • Head button fittedHead button fitted

The red flashes on this head make it look even better that it would have without them. I guess it's a personal thing but I find them to be a very nice touch.

Fitting the extended double ball links

The final part of the mechanical build of this head, prior to setting up the rod links, is to fit the extended double ball links to the flybar seesaw.

These can be fitted in one of two positions which will affect how responsive the head is in flight. The hole furthest away from the main shaft allows for a more stable setup, while the hole closest to the main shaft will make it more aggressive. I fitted this one on the aggressive setup option.

The short double links are connected from the inner ball of each extended double ball link to the short side of the upper mixing arms.

  • Extended double ball links on flybar seesawExtended double ball links on flybar seesaw
  • The double linksThe double links
  • Ball and link fittedBall and link fitted
  • Ball and link fitted (closeup)Ball and link fitted (closeup)

Fit the main shaft

Loosely fit the two pinch bolts to the base of the head block ready for fitting to the main shaft.

  • Loosely fit the pinch boltsLoosely fit the pinch bolts
  • Completed head assembly (excluding rod links)Completed head assembly (excluding rod links)

Fit the head assembly onto the main shaft, slot the jesus bolt through the centre of the head block and main shaft and tighten into the thread inside the head block (there is no nut to fit), then tighten up the pinch bolts on both sides of the head equally. Do these bolts in small stages on either side so they tighten down the same amount on both sides of the main shaft.

Fit the washout assembly

Slide the washout assembly onto the main shaft ensuring the longer side of the washout base is closest to the swashplate. Fit the swashplate below the washout base and then clip the radius arms onto the swashplate.

The whole assembly can then be fitted to the helicopter.

  • Washout base fitted and radius arms connectedWashout base fitted and radius arms connected
  • Head assembly on the heliHead assembly on the heli

Make up the rod links

Next comes the rod link assembly and fitting. The head assembly comes with half made up rod links, and the missing rocket links are taken from the existing links on the original head assembly, or preferably use new ones if you have them.

I made up these links to the following lengths:

Your link lengths may vary slightly.

  • Rod links to be made upRod links to be made up
  • Links made upLinks made up
  • Links fitted to the headLinks fitted to the head
  • Links fitted to the headLinks fitted to the head

The three links that connect the bell cranks up to the swashplate will also need adjustment. I set mine to have a gap between rocket links of 29.5mm which was a full 8 turns shorter on each rod. Again, link lengths will vary and can also be affected by swashplate choice.

  • Swash links adjusted and reconnectedSwash links adjusted and reconnected

Fit the main rotor blades

The blade grips take a standard 12mm root blade without the need for spacers, and the bolt and nut are supplied with the head assembly. There is a cutout into which the nut will sit once the bolt is tightened down - make sure the nut is seated correctly when tightening the bolts.

The supplied nuts were too big to fit the supplied blade grip bolt so I used the original nuts instead.

  • Blade grip bolts and nyloc nutsBlade grip bolts and nyloc nuts
  • Supplied (top) and original (bottom) nyloc nutsSupplied (top) and original (bottom) nyloc nuts
  • Blades fitted to the head assemblyBlades fitted to the head assembly

Add lubrication to the blade grip thrust bearings

The blade grips have a tiny hole in the top of each grip which is there to allow you to lubricate the thrust bearings inside the blade grips.

To lubricate the thrust bearings, you will need a suitable lubricant and applicator. I purchased some Tri-Flow Oil with Teflon which comes with a thin tube to be used as an applicator, and it fits perfectly into the hole in the blade grip.

I was liberal with the application of the lubricant as you cannot see how much has gone into the grip. I kept squeezing the bottle until it was dripping out of the grip, then figured that might be plenty!

Add lubricant to both blade grips.

  • Lubricating the thrust bearings in the blade gripsLubricating the thrust bearings in the blade grips

As the lubricant is oil rather than grease, it will be worth reapplying a small amount regularly to ensure continued smooth operation.

The final thing to do is to check your pitch setup and make any final rod link adjustments ready to go and fly. I have tried to include my final rod link lengths through this article to hopefully help save some time but your links may vary so make sure you check them and get them set correctly.

Flight review

I fitted Stubz paddles with the flybar weights right next to the paddles for flight testing.

One of the first things I noticed was that the cyclics feel maybe half as fast again over the stock head and more precise when fitted with the same paddles and weights.

Coming from the original Trex 600 head assembly, the Kasama head is a definite improvement. The original head on my Trex 600 had a minor phase issue which was noticeable in straight flips (it doesn't flip perfectly straight). This does not happen with the Kasama head, it flips dead straight. Rolls are also fast, in keeping with the strong cyclics. The pitch feels very responsive but I think it's hard to find much difference between this and the stock head here as both are very good.

For any type of flying, and specifically 3D flying, accuracy is the key. You want the helicopter to go where you tell it, when you tell it, without veering off in some random direction - and the Kasama head certainly performs well in this area - it's very accurate. Flying precise manoeuvres feels more locked in and large loops (for example) track straight all the way around as they should. A more extreme example of accuracy is a tumbling loop, which will stay on track through the whole manoeuvre. It's an absolute pleasure to fly!

The stock head can be made more precise and responsive with swashplate, washout base and mixing arm upgrades that will cost less than this head assembly, but the bling factor of the Kasama head, along with the accuracy and precision it brings to manoeuvres really helps to sway the argument. Obviously looks are subjective but visually I think it stomps all over the stock head.

The supplied dampers are 80 durometer which I find a bit soft for long term hard 3D flight so a harder 90 durometer damper would be desirable to help maintain accuracy and responsiveness in flight. That said, the 80 durometer dampers lasted significantly longer than the Align 80 durometer dampers in the stock head setup.

All in all, I find the combination of the Trex 600 helicopter and the Kasama head with the Quick UK swashplate fitted to be very good indeed.

Pros and Cons

Helps to make the helicopter fly very accurately
Well engineered and sturdy head assembly
Good price for a complete metal head assembly
Easy to assemble
Looks great
Jesus bolt and two pinch bolts to solidly attach the head to the main shaft
Dampers are of a low durometer for long term 3D - stronger (90 durometer) would be better
Non-standard feathering spindle - not interchangeable with the standard Trex600 part


The first version of the headblock had an issue with the main shaft sitting a little bit too high inside the block, which would potentially foul the flybar seesaw. Certainly, on the bench this is what you could see happening, but having flown that version myself, I found the seesaw never actually hit the top of the mast. Some people suggested chamfering the top 3mm of the main shaft to approximately 30 degrees to resolve the issue - but I never had any issues flying this setup without chamfering the main shaft.

The newer version of the head block does not have this issue - you can fit the stock main shaft without any modification as the bolt hole has been moved down by approximately 3mm. Again, I didn't modify mine in the original block anyway and had no issues in flight.

There is less play between the washout base and the guide pins than on the stock Trex head, which really helps make the helicopter fly very accurately.

Bearings on the moving parts of the head help to keep everything silky smooth and free. It would be nice to have this head assembly come supplied with lower mixing arms, as I'm not keen on the screw that the stock Align arms use to connect the Radius arms to them. I would like to see the bolt and bearings style of fixings as per the upgrade arms available from Align. Obviously, re-using a couple of parts makes sense in order to keep costs down.

I currently know of one UK supplier, which is Zip RC, that stocks this head.

Having had my helicopter fail in flight, which was nothing to do with the head assembly (it was a regulator wire issue), I can assure you the head is solidly made. My crash saw the heli land inverted on the rotor head but caused minimal damage to the helicopter generally, and only bent the feathering spindle on the head. Good quality metal components have been used here.

Having flown this head for over 80 flights so far, I find it a fantastic piece of kit and have no problem recommending it as an upgrade if you are looking to replace the stock head assembly.