Trans mounted clutch... TRX90

Instead of the button screws that hold the plate on for the oil spinner, I took the plate, and added a angled recess to it and then put flush bolts in there. I also ground off a lot of the lip that goes around it for clearance. That lip adds some regidity, but it doesn't need it...there's no pressure on that thing. So if you need clearance, you can cut that down quite a bit.

As for your throw...there's more than one way to deal with that. You can find a thicker bearing, you can replace the throwout cage entirely and replace with a Honda Nice version (bigger and thicker bearing), you can machine a 2-3mm ring and put it in before the bearing.

I think when I built my poor man's nice, I ended up using a honda nice cage and bearing instead of the stock trx90 one. I also once busted a honda nice one and replaced it with a TRX90 one and had the same issue with throw. I eventually replaced the cage with the Nice one.

I made up a pusher out of a 5/16" bolt, just to try the, nearly 5mm, head thickness. I think it's too much. Seems to change the leverage of the clutch arm. I'm now thinking 3mm thickness, or close, would be about right. The pusher that came with it might be ok actually.

My cover is powder coated...I think..? How can I tell for sure?? Try blasting it??
Anyway, it's flaking off everywhere I touch it with the screws, kickshaft, etc. What's the best way to get rid of powder coat from a clutch cover?? Cook it off in a oven?? How hot does it have to be, and for how long, to cook it completely. So I can blast it clean and paint it?? It's powdered right down into the dipstick hole, kickshaft hole, etc. And...it's a poor finish to boot.
It'll have to go before this cover goes on for the last time.

OOps...this post in progress.

I opened it back up and swapped the kickshaft. I put the dratv TRX90 kickshaft kit in. The doc gives some instruction on how it should be installed, but it was kinda weird and unclear to me.
http://dratv.com/tradkistas.html

It comes with 2 different thrust washers. A 17mm and a 20mm. In my opinion, the 17mm needs to go on to the shaft, on top of the spiral cut gear, before you put the right side case back on. This is similar to how the CT70 setup is. The washer protects the engine case from the spiral gear, and holds the shaft in place. Then the right case goes on. Then the spring and retainer. Then the snap ring. (Dratv didn't include a snap ring in the kit.)

The doc shows the 20mm washer going in UNDER the return spring. I don't think that's right, or necessary. It's just too big and sloppy in there, and not needed.

This is a nice part IMO, just leave the bigger washer out, and order a new snap ring.

The first pic is of the old shaft Thai I took out.

Whatever the finish on the cover is, this stuff takes it off in short order.

Easy peasy.

My new paint doesn't look too good either tho. But hopefully it won't flake off.

Well I've gone a couple more rounds with this engine. I have it all together, kinda.

I put the needle bearing into the clutch cover...the one that the shift shaft rides in. But when the cover was bolted down, the shift lever was binding, and wouldn't "return". Turns out the shift shaft was a little bent, so I had to replace it. Works great now, but, it has about 3.5mm of side to side play...about ⅛". A little too much I think. So I plan to pop the cover back off and put a washer or two on the end of the shaft, which should correct it easily...holding the shaft toward the left side...where it needs to be. While I'm in there I decided I should swap in 2 heavy duty springs into the clutch. 2 of 4...fatcaaat recommended that to me a while back.

I think that should do it. Just need a bike to put it into for a test run...maybe my 93ct or zb50.
I put the Honda monkey bike stator in it, that I modified to match the ZB or 93 stator plug. Hopefully that will work great and make this motor easy to pop into different bikes.

I also bought another TRX90 engine from eBay. Will be a while before I get it tho. All I really needed was the left side cover and pull start bits...but the motor was cheap, and has those parts on it...in, hopefully decent, shape. I want to be able to swap the pull start on and off...or leave it on I spose. Just don't think I can use the kicker on a 3 wheeler.

I hope to have a 3 wheeler to run this engine in eventually.



I didn't find the race cam until a little while ago. So I'll need to install that now.

I also need to paint the stator cover.

Then...it will be all together...done.

So far so good with the manual clutch kit. Hope to see how it actually works pretty quick. Right now, I'm still sayin it's a bargain for 100 bucks.

C'mon spring :--)

I will also have to find a foot peg setup to get out past the giant sized engine covers...this clutch cover...and a pull start on the left. The pegs will need to be around 9 feet wide. lol

I'm thinking aftermarket ATC70 footbar...maybe with a kickstand bracket added...or maybe when it's mounted on a motorcycle, I can just lean it over on the superwide footpeg

I see you used the trx90 stator and flywheel. Before you do anything, you need to validate the TDC and cam timing. The trx90 flywheel is stamped in a different spot for timing because the timing cover is different. If you used that mark, you will definitely be off on your static cam timing! When I did this, I went ahead and made a new mark on the flywheel once it was in the correct position.

fatcaaat said:

I see you used the trx90 stator and flywheel. Before you do anything, you need to validate the TDC and cam timing. The trx90 flywheel is stamped in a different spot for timing because the timing cover is different. If you used that mark, you will definitely be off on your static cam timing! When I did this, I went ahead and made a new mark on the flywheel once it was in the correct position.

Click to expand...

Thanks for the heads up fatcaaat. I had seen where you posted about the trx90 flywheel before. I actually used a xr70 flywheel as I built this engine, but I've now switched to the TRX flywheel.

One thing I've learned from building these motors, the keyway in the crankshaft points directly at the timing mark on the head when it's turned to TDC. So with NO flywheel on, you can get the crank turned close, just by eyeballing the keyway.
Just before installing the head, I usually pull the cam chain to a point and spin the crank to point the keyway right toward the point in the cam chain. Then i put that chain link on the O on the cam gear.
Also when the cam timing is at TDC, the cam, and crank, will turn back and forth easily about 100-150 degrees...easily enough that you can spin the crank without needing the flywheel on to do it. If the cam timing is on the wrong stroke..."waste stroke"??... the cam and crank will only spin a few degrees each way before it hits a cam lobe. Then you'll know it's on the wrong stroke...for setting valve lash etc, even if you cant see the cam gear.

So, when you are at TDC, on the correct stroke, the cam gear will line up the O on the timing mark on the head, AND the keyway on the crank will also be pointing at that same timing mark, AND the crank will spin back and forth easily... then you know all is well.

(I know YOU don't need a lesson fatcaaat. I was just sharing some info.)

My motor IS ready to mount and test now, but I still haven't brought a bike home to mount it into. I might bring one home from storage tomorrow or Tuesday. I bought a hardened bolt and made a new clutch pusher gadget that I like a little better. I installed that pusher. I added a single washer on to the end of the shift shaft while I was in there...that fixed the excessive side to side play in the S shaft. I decided NOT to mess with swapping in HD clutch springs yet...until I see how everything is workin as is. I DID swap in the DRATV Z40 cam. I did a little grinding inside of the stator cover and then painted it up...ready to rock.

I'm gonna try running this engine in my 93 CT70, with a VM20, and a improvised exhaust. Hopefully I have a throttle cable that'll work.

I forgot to get a picture of my new clutch pusher piece before I installed it. But this is the bolt, and the dims I used. I just cut it for length, sanded off the sharp spots, and polished it up a little...easy peasy. I pictured the original pusher and it's dims too.

I just have to finish cleaning the innards, then my pullstarter setup is ready to reassemble too...all cleaned and painted. I also need to stop at the bolt store to buy some push-on washer/retainer clip gadgets, to replace the ones I had to destroy to remove from the back side of the plastic (HONDA) cover.
I want to measure and weigh this engine with the pullstart installed, without the pullstart and the regular 12v stator cover, and then measure and weigh a regular CT70 engine...for comparison and...to log the info.

I'm trying to debate finding another TRX90 engine or to sell the worked TB V2 head i have here. Got any extra trx90 engines laying around?

Actually I do. Check post #899 here.
I may have just a lower end too if that's all you need.
https://lilhonda.com/index.php?threads/too-much-crap.15030/page-45

Here's some info.

The trx90 engine with the pullstart installed measures
16.75" long
12.5" wide 41lb 12oz dry weight

trx90 with typical 12v stator cover (No pullstarter)
16.75 L
10.875 W
40 lb dry

SL70 with stock covers...4 speed engine
16.5 L
10 W
36lb 14oz dry (including some dirt and sludge)

Z50 with stock covers...3 speed engine
16.5 L
10 W
36lb 6oz dry (including dirt)


No carbs or levers on these motors

Last Sunday I started my engine for the first time. I had it mounted up in my ratty 93 CT70 with the clutch lever mounted, improvised exhaust, and a Mikuni VM20 carb.
It started right up pretty easily, but I had forgotten to put the sealing bolt in at the cam chain tensioner...useless hole.
I plugged up that hole and then warmed the bike up well. My clutch seemed to be working as intended. But when the motor was all warmed up, it started to smoke. I started to get a drip of oil from the exhaust to head connection, and I could see the motor was blowing oil out thru the muffler. I've seen this before when I had a problem with the head casting...sucking oil into the combustion chamber and blowing out smoke and unburned oil. So that was what was in my mind. I started to wonder if I had forgotten to put valve seals on, or if I reused the old seals. I was also thinking about the rubber seals that go into the head gasket, or maybe I put a ring upside-down.
I waited to see if it would clear up, but it seemed to be getting worse. I started getting nervous and I shut it down.
The next day I pulled the head, and cylinder. About that time I realized that I never torqued the head studs properly. I only torqued to 100 inch pounds because I didnt know the correct torque for trx90 studs. Then I forgot to look it up before I fired the engine.
But I didn't see any sign that oil was being sucked in around the head gasket. No sign of oil coming in thru the intake. No problem with the rings...they were clocked and installed correctly. The valve seals were there, but I couldn't tell if they were new, and it has been a LONG time since I built the head, maybe a year...so I couldn't remember if they were new.
I ordered a couple new head gaskets, and a stack of new valve seals. I didn't find a obvious problem.

Parts arrived Thursday, I put the engine back together today and back into the bike. I torqued the studs to 10 foot pounds/120 inch pounds, fatcaaat's recommended number. Fired it up, started smoking again, same as last time. I warmed it up to 40C, then re-torqued the studs and let it cool back down. Fired it up, about 50C, still smokin, I took it for a ride, short. About 10 minutes was plenty for me on a 40 degree day. Clutch setup is cool. Works great, kinda. It's slipping, occasionally, in a way that's different than what I normally see with the crank mounted clutches. More about that later I guess...I'm gonna ride it a bit more and see how it acts, if it gets better or worse.

BUT, the smoke was cleared up quite a bit by the time my ride ended. Maybe the rings just need to seat?? Never had one smoke like that because of new piston/rings. But I now think that the smoke will cure itself. We'll see I guess.

Soo, I've done it again. Build a motor, run it, take it back apart and...do something, then put it back together again. Seems to be...just the way I do it. This will be a very cool motor, once I get it right.
I'll post up a video to show how the clutch setup works once I get a few more rides in. It will idle in gear, you can take off in first using the centrifugal clutch, but it's a manual clutch otherwise. It would be a great setup for a beginner, to learn how to use a clutch, when to shift, etc.

I"m going to be replicating this style of clutch on the TRX90 i'll be building. I think eventually, I'm going to attempt a custom slipper, but for now, this is probably what I'm going to do.

fatcaaat said:

I"m going to be replicating this style of clutch on the TRX90 i'll be building. I think eventually, I'm going to attempt a custom slipper, but for now, this is probably what I'm going to do.

Click to expand...

Are you going to use the same side cover that I did fatcaaat?? Or do you have something else in mind?
I would certainly recommend it. I didn't put new discs in my clutch, and I didn't use any HD springs either. In my very short ride, my clutch would begin to slip, at odd times. Just during gradual acceleration in any gear...almost cruising, the rpms would rise...clutch slipping. Kinda strange to me...maybe that's how this type of clutch does it when it slips..?

But I'm getting a small oil leak from the kicker seal. It's a new seal, but it went into the cover a little too easily when I installed it. That may be a flaw with this cover. I stripped the paint out of that hole and blasted it clean. Then I didn't allow any of MY paint to go in there. Maybe I should have painted in there...might have helped a little.

I'll order up new clutch discs, then if it continues to slip I will install them, plus a couple of hd springs, and replace the seal, using a little sealant on the new one. All of this, AFTER my smoke clears up. I'm optimistic now that it IS beginning to clear up.

High temps around here are still way low for minibiking and such. But I'll be doing some short rides here and there. We'll see how it acts for a while. I'm thinking I'll need those new clutch fibers.

Another short, cold ride today. No change. Motor smoked badly, and started smoking very quickly after startup. Didn't clear up much at all while it warmed up. It made me think that oil may have seeped into the combustion chamber after I shut the engine off last time. I now have the cylinder studs torqued to about 11.5 foot pounds :-!

Rode it for about 10 minutes. Clutch slips, and I can MAKE it slip if I try.
After my ride, the smoke had cleared up quite a bit again. I let it sit and idle for a while to see if it would start smoking worse, at low rpm's...no change tho.

I ordered new fibers for the clutch today...Vesrah, from dratv...hope those are good. I also ordered some new, taller, cap nuts for the cylinder studs...thinkin maybe the short ones I have may be bottoming out on the studs..?
I'm runnin out of cures for my smoking problem...maybe the rings? Maybe a misplaced rubber oil seal in the head gasket?..twice? Maybe a crack, or other defect in the head casting?? I should have probably bought a set of new piston rings too...for 25 xtra beans...start fresh with the rings.
IDK...when I pull the top end AGAIN, I'll be looking at every single thing that I suspect COULD possibly be causing my smoke issue, VERY closely.
Any ideas??

I'll be pulling the engine out of the bike. Look for a problem that's allowing oil to be sucked or pumped into the combustion chamber. New discs in the clutch. 2 new heavy duty springs in the clutch. I'm gonna cut 1mm off of the shank of my homemade clutch pusher. Pull the rings off and check the ring gaps. Hone the cylinder and put everything back together with new cap nuts on the studs. I'll make ABSOLUTELY sure, that the round rubber seals are correct in the head gasket.
Address the leaky kicker seal.

Kicker can be fixed with a little sealant no need for a new one there. Unless the cylinder is oval i dobt think rings are the issue. Im voting forheadhasket. I know everyone says put them on dry but I always put some copper spray on them. I bet oil found a path from the light torque and now you are stuck.